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THICKNESS SWELLING BEHAVIOUR OF ORIENTED STRAND BOARD
Wei Chang
A thab siibmittd in mnformity nith the rcpiurements For the degree of Master of Science in Forcshy
Graduate Department of Forestry University of Toronto
O Copyright by Wei Chang 1999
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ABSTRACT
Thickocs, Sweiîing Behavioor of Oriented Sbrnd Board (OSB)
Master of Science in Fonshy 1999
Wei Chang
Faculty of Fomtry
University of Toronto
The thickness swelling, spring-back, and swelling stresses of Onented Strand Board
were studied for cornmerciai hot-pressed and experimental stem-injection pressed
panels. Samples fiom the panel centre and edge were divided into top, core, and bottom
layers. One panel was subjected to pst-manufaturing heat treatment and similarly
analysed. Both type of panels showed a Eshaped behaviour where density and swelling
behaviour in the surface layers was greatest. However, for stem-injection pressed
panels, thickness swell and swelling stress varied linearly from bottom to top.
Sampling location showed no effect on swelling behaviour. Swelling stresses in both
samples were similar. Swelling was positively correlated to density in hot pressed
samples and not correlated in steam-injection pressed samples. Stem-injection pressed
samples have higher density, and lower swelling valws dien hot pressed samples.
Considerable reduction in sweiîing in oriented strandboard was achieved by pst-
manuf-g heat treatment. The effdveness of the treatment was tirnedependent.
ii
ACKNOWLEDGEMENTS
Deep gratitude is extended to Professor John Balatinecz for his constructive guidance
and financial support throughout this research. Mr. Shaing Law and Dr. Ernst Hsu are
to be thanked for their encouragement and advice for making this dissertation possible.
A sincere thanks is offered to Professor P.A. Cooper, D.N. Roy and S. Kant for
providing assistance. 1 would also like to thank the Faculty of Forestry, University of
Toronto for awarding me the Rosamond M. Gillies Fellowship. Mr. John McCarron is
accorded special thanks for preparing sarnples. Special thanks to companies for
providing materials in this study. Mr. Feroz Kazi, MT. Warren Mabee. and Mr. Levi
Waldron, are to be thanked for the preparation of the review and final drafts ofthe
dissertation. Great recognition address to rny persona1 cheer-leading team: Mr. Gary
L m , Ms. Fatima Correia, and Ms. Amrit Bhuie.
To my family and my fiancée, Michael A. Okincha, thanks for putting up with me!
iii
TABLE OF CONTENTS
. . ABSTRACT ............................ ........... ............................................................................... il .. ACKNOWLEDGEMENTS ... ....................................... ................................................... 111
TABLE OF CONTENTS .......-....... ....... ..... ...... .... ...................................................... iv
LIST OF TABLES .......................................................................................................... ix
LIST OF FIGURES ................................. ......................................................................... xi ... LIST OF APPENDICES ............................................................ xi11
GLOSSARY OF TERMS AS USED IN THIS THE3IS ......................................... . xiv
1 . INTRODUCTION .................................................................................................. 1
.................................................... . .. . ....*.*..*............. 2 LITERATURE REVIE W .., .... .. -4
2.1 Mechanisrns of Swelling ......................... .. ............................................................ 4 2.1.1 Types of Swelling ............................. .. ......................................................... 4
2.1.2 Restraints to Swelling .................... .... .. ..... ................................................. 5
2.1.2.1 Adhesive ................... .. ..................................................................... 5
2.1.2.2 Within fibre ......................... .,, ................................................................ 5
2.1.3 Compression-hduced Swelling ..................... ....... ..................................... 6 2.2 Sources of Stress and Stress Release .............. ., .................. .................... 6
2.3 The Characteristics ofOSB anâ Swelling .............. .. .................................. 7
2.3.1 Strength Properties ..................................... ... .......................................... 7
2.3.2 Densification and Panel Density Distribution .......... .... ........ .................. 7 ............................ 2.3.3 Compressive Deformation of Fibres ....................... ... 8
............................................. 2.3.4 Stored Potentid Energy ............................. 9
2.3.5 Vanations within the Panel ............... .........,............ ........................a...4..... 9
................................................... ........... 2.4 Factors Intluencing OSB Swelling .. 1 0
...................... 2.4.1 Service Conditions .... .................................................. 10
2.4.2 Nature of Raw Material .......... ........................................ ............... IO 2.4.2.1 W d .................................................................................................... 10
2.4.2.2 Strand geometry .................................................................................... 1 1 2.4.2.3 Strand quality ...................................................................................... 12
.... 2.4.2.4 Resin Content .. ............. .. ............... ........... 12
..... .....*....... 2.4.3 Plasticisation .. .. ..... ......... .................................................... 12
................ 2.4.3.1 Moisture Content ...... ... .... ... ............. .. 13
2.5 The Pressing Operation .................... ....... ................................................. 13
2.5.1 Controllable Pressing Variables ........... ,... ...................................... 14
. ...*...*...*.................*..........*.... . ..............*.... 2 .5 1 1 Heat Transfer Modes ..... 14
2.5.1.2 Pressing Tempera- .......................................... .......................... 15
2.5.1.3 Press Closing T h e ............................................................................... 15
.................................... ................... 2.5.1.4 Consolidation Pressure ......... ...... 15
.............................. ................... 2.5.2 Conventional Pressing Technology .... 16
............................................................... 2.5.3 Hot Pressing .................................. 16
2.5.3.1 Internai Temperature ..................... ... ........................................... 16
2.5.3.2 Internai Vapour Pressure ................................................................ 17
............................................................................. 2.5.3.3 Interna1 Compaction 18
........................................................... 2.5.4 Stem Injection Pressing ................... 18
......................................................................... 2.5.4.1 Intemal Temperan~e 19
...................................................................... 2.5.4.2 Intemal Vapour Pressure 19
.................................. 2.6 Dimensional Stabilisation Methods ............................ 20
............................................................................................. 2.6.1 Heat Treatment 20 . .............................................................................. 2.6.2 Stem and Heat Futahon 20
........................................................... 2.6.3 Po&-Mmuf8ctUringHeatTreatment 2 1
............................................................................................................. 2.7 Summary 21
.............................................................................................. 2.8 Problem Defhition 23
3.1 Justification of ExperiwntaI Variables .................... ..................................... ... 25
3.2 Objectives of Part 1 .............................................................................................. 26
3.3 Objectives of Part 2 ................... ... .................................................................. 27
3.4 Objectives of Part 3 ........................... .................. .............................................. 27
.................................. 4 . PART 1: THICKNESS SWELLING AND SPRING-BACK 28
4.1 Materialsand Methods ....................................................................................... 28
4.1.1 Specirnen Preparation ................................. .................................................. 28
................................................. 4.1.2 24Hour Water Soak ............................. . 3 1
....................... ......................... 4.1.3 24-HOM Oven Drying ......................... 1
...... ....... 4.2 Resuits .. ..................... ...................................................................... 31
4.3 Discussion ................... .. ... ..... .... .... .... ... . 35
4.3.1 Density Profile ............................................................................................. 35
.................................................. 4.3.2 Density, Thichess Swell and Spring Back 36
4.3.3 Mole Sample Cornparison ........................ ............... .............................. 36
4.3.4 Cornparison By Layer ................... ...... ........................................................ 37
4.3.5 Cornparison of Centre Region to Edge Region (KP samples ody) .............. 37
...... 4.3.6 Comlation between Density and Thickness Swelling and Spring Back 38
4.4 Anelysis of Correlation Coefficient and Variance ............................................... 43
5 . PART 2: SWELLING STRESS OF OSB ................................................ ... ............. 46
.... ......................... 5.1 Materiais and Methods .. .........................................o..t.......... 4 6
5.2 Resuits .................................................. ......................................a.............. 48
5.3 Discussion ................... ............. ..................... ........ ........ ................................... 50
............................................... 5.3.1 Mole Sample Cornparkm .......... ....... 50
5.3.2 Conprison of Layers .................................................................................. 5 0
5.3.3 Cornparison of Centre to Edge region of panel HP sample only .................. 50
...... 5.3.4 Comlation between Deasity and Thicbess Swelling and Spring Back 50
5.3.5 Swelling Stress The Profile ......................................................................... 52
...... 5.3.6 Ra&@ S ystem of Thiclcness Swell, Spring Back and Swelling Stress 54
............................................... 5.4 Analysis of Cornletion Coefficient and Variance 56
6 . PART 3: POST-MANUFACmG =AT TREATMENT ............................... 58
......................................................... 6.1 Materials and Methods ............ ................ 58
6.2 Results ........ .. ...................................................................................................... 3 9
6.3 Discussion ..... ....... .................... ......... i.. ..... .......................... 61
6.3.1 Layer Thickness swell ............................................................................... 61
6.3.2 Layer S p ~ g Back ........................................................................................ 62
.............................................. 6.3.3 Layer Swelling Stnss .................. .... .. ..... 6 2
6.3 . 4 Cornparison of layered TS. SB. and SS to whole sample ...... - ..................... 62
............................................... 6.4 Analysis of Comlation Coefficient and Variance 63
7 . SUMMARY OF RESULTS ............... .......................................... .................... 65
7.1 J-Shapeà Disîribution ........ .......... ...................................................................... 66 7.1.1 Layer Density Distribution ..................................................................... .. 66
7.1.2 Layer to Layer Swelihg Behaviour ........................................... ........ ........... 66 ................... 7.2 Comlation to Density ......................... .................................... 66
.*........... ........*......*.....*.. 7.3 Edge to Centre: Edge grrater than Centre .... 6 7
7.4 Individuai Layer Behaviour Reiative to Whole Panel ......................................... 67
7.5 HP vs . SIP SweUing Behaviour ............................................................................ 68
........................................................... 7.6 PMHT: Treatment Red- TS and SB 6 8
8 . GENERAL DISCUSSION .................................................................................... 69
8.1 Variations in Experimentai Data ................................................................... 69
8.1.1 Flake Distribution ................... .... .................................................... 69
8.12 Difference inSwelling StnssofOSBvs . Sotid Wood ................................. 71
8.2 Factors and Interactions ....... ........................................................................... 72
8.2.1 Dynamics of Steam Flow .............................................................................. 72
8.2.2 Resin Migration and Bond Sûength .............................................................. 73
8.2.3 Out-~f-Fress Spring-bk .............................................................................. 74
8.2.4 CeU Waii Fracture and Caul Serem EEm ................................................. 7 4
8 1 5 Void Volume Effect ................................................................................. 75
vii
. . . 8.2.6 Plastic~sation and Li@ Flow ............... ... ................................................... 77
8.2.7 Matrix Changes and Li& Flow .................................... ........... .................. 78
......................................................................... 8.3 Exphnation of SIP Performance 79
8.3.1 Lower Compaction Pressure ......................................................................... 79 8.3.2 Reduced Press Closing Time ............................... .. ................................. 79 8.3.3 Effect of Maximum Aminable Core Temperature ...................................... 79
8.3.4 Effects of Steam Duration ......................................................................... 80
..................................................................... 8.3.5 Effects of Sample Panel Size 8 0
8.4 Post-Manufàcturing Heat Treatment .......................................................... 8 1
8.4.1 Colour Changes ................... .......... .............................................................. 82
8.4.2 Local Variation ...................... .... ............................................................ 83
8.4.3 Dependence on Treaûnent Duration ........................................................... -84
8.4.4 EMC Reduction ............................................................................................ 84
8.4.5 Hygroscopicity Reduction and Hemicelluiose Degradation ....... .......... ........ 85
..................................................................................... 8.4.5.1 Hygmscopicity 85
8.4.5.2 Hemicellulose Degradation ....................................... ............................ 85
8.4.6 Increases in Crystallinity and Acidity ................. .. ................................... 8 5
.......................... 8.4.7 Incrrased Resin Setîing ............... ................................*....... 86
...................................................... ....................... 8.4.8 Stress Redistribution ........ 86
............................................................ ....................................... 9 . CONCLUSIONS ... 88
CITED ...................*......... .................. . . 9 1
LIST OF TABLES
Table 1 . OSB Panel layer densities ................... ..............................................e...... 32
Table 2 . Thickness swelling experimental results ............... ......... ................................... 32
......... Table 3 . Average swelling behaviour of four manufacturer's hot-pressed panels 33
Table 4 . Spring-back experimental results ....................................... ............................... 33
Table 5 . Average swelling behaviour of steam-injection pressed panels ........................ 34
Table 6 . Correlation coefficient between density and thickness sweiling by layer ........ 39
Table 7 . Comlation coefficient between density and spring-back by layer ................... 39
Tabk 8 . Comlation coefficient between thickness swelling and spring-back by layer . 39
Table 9 . Swelling Stnss measurements .......................................................................... 49
Table 10 . Correlation between density and swelling stress by layer ................. ....... 51
Table I I . Rank of panel manufachirem by thickness swelling .............................. 55
Tabk 12 . Rank of panel manufacturers by spring-back ............... .................................. SS
Table 13 . Rank of panel manufiturers by swelling stress ............................................. 56
Table 14 . Post heat ûeatment thickness swell data ......................................................... 59
Table 15 . Post heat treatment spring-back âata ...................... ......................................... 60
. ......................*...*.......*........*...........**. Table 16 Post heat treatment swelling stress data 60
............. . Table 17 Post heat treatment thichess swell data (comsponds to Table 14.). 62
.................... . Table 18 Post heat treatment spring-back data(cofze~~~nds to Table 15.) 63
Table 19. Post heat treatment swellhg stress &ta (corresponds to Table 16.) ............... 63
Table 20. Summary Table .......................................,...... . .... . .... e...........................e.. .... ..-AS
LIST OF FIGURES
..................................................... . ..*........ Figure 1 Sample preparation and location .. 29
. ........ .................................... Figure 2 niickness swelhg b y layer and manufacturer .... 34
Figure 3 . Spring-back by layer and manufacturer ....... .... ......................................... 35
. Figure 4 Density profile by layer and manufacturer .............. ............ ............................ 36
Figure 5 . niickness swelling vs . density for hot-pressed panels .................................... 40
Figure 6 . Thicloicss swelling vs . density for steam-injection-pressed panels ................. 41
Figure 7 . Spring-back vs . density for hot-presseâ panels .......................................... ...... 42
Figure 8 . Spiing-back vs . density in SIP panels ............... ..... ................................... 43
Figure 9 . Swelling stress measwement apparatus .......................................................... 47
. Fi- 10 Typical graph of thickness displacement vs . pressing force ...................... 48
. .................................................... Figure 11 Swelling Stress by layer and manufacturer 49
Figure 12 . Density vs . Swelling Stress in Hot Pressed Panels ........................m............... 51
. . Figure 13 Density vs Swelling Stress in Steam-Injection Pressed P d s .................... 52
Figure 14 . Swelling pressure tirne profile ....................................................................... 53
. ......................................... Figure 15 Post heat treamient effect on thickness sweli 59
.................................................... . Figure 16 Post heat treatrnent effects on spring-back 60
. .....................*.......*...*..........*.*..........*...... Figure 17 Post heaî treaûnent swelling stress 61
.......................................... . . Figure 18 Daisity vs panel location (hm: Lu et al, 1998) 71
Figure 19 . Factors Interactions .......... .. .............. ... Figure 20 . PMHT Factors and interactions .......................... ............................*....... 82
......................................... Figure 2 1 . OSB colour changes with PMHT exposure time -83
LIST OF APPENDICES
Appench A . Data From Expeiiment Part 1 ............................... ..................................... 95
Appendix B . Data From Experiment Part 2 ........................................................ 1 14
Appendix C . Data From Expriment Part 3 ............. .............. ...... ....... .................... 1 20
Appendix D . Sbtisticai Analysis ................. ...... ................................................... 129
GLOSSARY OF TERMS AS USED IN THIS THESIS
Anisotropic: The condition in a material in which the magnitude of a property is not
the same in dl directions.
Cellulose: A long chah carbohyàrate having the general formula (Cd4io05)n found
in uni&. It is the principal structural component of wood.
Dimmsional Stability: Resistance to swelling or shrinkage upon adsorption (or
desorption) of water.
Hemicellulose: One of the constituents of wood, consisting of a group of carbohydrate-
based polymers which bear some structural resemblance to cellulose.
Functioaally, part of the hemicellulose may be assigned to the
fhmewodc and the rest to the matrix.
Hygroexpansion: moistute induced swelling.
Hygmscopic: The property of a material which enables it to atûact moisture from the
air.
Lignin: The na- cementing and rigidifjing material forming a metnx in the
ce11 wail and between cells to hold them together to form various
anatomid s t ~ c m s in plants. Chemicdly, it is an irregular amorphous
polyrner of substituted propylphenol groups.
Ordiotropic: In material science, a speciai kiml of anisotropy which &ses when the
structure has three orthogonal planes of symmetry.
OSB: ûriented Strand Board. A composite panel formed by top, core and
bottom layers of oriented strands, arrangeci in perpendicdar to adjacent
layers.
Permeability: Characteristic describing fluid flow in a solid under a total pressure
gradient.
Spring Back (SB): It is a consequence of the release of compressive stresses induced
during mat consolidation and the permanent destruction of certain
adhesive bonds. Such expansion is ineversible through W n g .
Strand: Wood element similar to a piece of veneer, except much smaller in
dimension.
Swelling Stress (SS): the stress exerted by a wood composite panel normal to its
sudiace, as it attempts to swell due to moi- exposure. In this study,
the panel samples were placed between press platens, which
mechanically prevents the samples h m changing dimensions in the
vertical direction, so that the swelling stress could be measured.
Thickness Swell (TS): represents the hygroscopic expansion of oriented strandboard in
response to moisture exposure.
1. INTRODUCTION
Chiented Strand Board (OSB) is an engineered mat-fonned board designed for diverse
applications. It is pertidarly popuiar in light âame construction whae it holds a
signifiant market share. Its structural characteristics and lower manufacturing cost have
coaûibuted to OSB surpassing plywood in popularity and this is refiected in its rapid
expansion over the past decade. Canadian OSB production gnw 20.4% over 1997, reaching
a total capacity of 5.66~ 106 m3 (Forest Pducts h u a l Market Review, 1997). More than
87% of Canadian OSB is exported mainly to United States. By way of cornparison, the 6 3 6 3 United Staîes produced 8.41 x 10 m for the same year but consumed 12.9~ 10 m ,53%
5 3 more than its annual production. Ewopean production for 1997 reached 8.Ox 10 m , only
14% of Canadian production. Canada clearly plays a dominant d e in the global OSB
market. Unfortunately, the total market for OSB is constrain4 by ceRain technical
@ormance limitations. The most significant limitations of OSB are its low tolerance to
moisaire and high tendency for excessive thickness swelling.
Al1 OSB panels swell in thickness when exposed to moisaire. OSB cm swell f?om 2û% to
400/r when i m m d in water for 24 hours (water scdc test). Swelling can be as high as
500/, to 6û?A when panels are exposed to more vigotous tests (two hour boiling followed by
one hou cold water soak). In cornpaison, plywood sweLIs only 10"/o to 25% under the same
conditions. As OSB absorbs water and swells, its mength and stitniess decrease
dtamatidly. Panel failure can occur as Strand separation (delamination), flaring of panel
edges, transient warping or structural warping. Limitations in panel performance or
strudural failures can be thought of as an additional cost to the OSB industry. This cost
counters the ultimate purpose of minimishg enagy coasymption, marimising output or
increasing in raw material recovery. Roughly $100 million in capital cost is inaund per
OSB mill. Such a high eost of production wmbined with poor thickness sweliing behaviour
emphasises the importance of studying swelling behaviour of OSB. lmproving the @ty
of OSB wilî ensure its market competitiveness.
Moisture arposure-iaduced thickness swelling in OSB is atüibuteti to two mecbanisms: the
hygroscopicity and the accompmying sweliing of w d fibres, and spring-back.
1
Hygroscopicity represents the aawal afhity of wood substance for water. Spring-back is
the mechanical release of compressive stresses incurred during the pressing stage of panel
mamifbcturng. Hygroscopicity is an inherent characteristic of wood and cm not be totally
eliminrited without chemical modification. Sp~g-back is proportional to the amount of
residual compressive stresses retained in OSB as a consequence of the high pressun exerted
by the press platen when cowlidating the panel.
Conventionai OSB manufacturing uses the hot-pressing process. Production using steam-
injection pressing is in the experimental stages. Mat consolidation and resin cwing
aicompass cornplex interactions and phase changes during board making. Such intefactions
include compression pressure, intemal temperature (heat tramfer), intemal gas pressure, and
chemical mictions. W n g pressing, a transient environmental condition is formed between
the surfaces and the a r e of the panel. The coasequence of these interactions ekct the rate
and degree of adhesive aire (bond quality) and also the vertical density distribution. This, in
turn, influences physical and mechanical properties of the product including swelling
behaviour. Studies have indicated that thichiess swelling is positively comlated with board
density. The denser surfaces may account for the excessive thickness sweliing of OSB and
result in a substantial increase in total thickness sweK
This thesis presents my nsearch on the swelling behaviour of OSB. By relating the levels of
thichss swelling, spring-ba& and swelling stress to panel density and process variables, I
hope to explain such behaviour. In this shidy, the thicbiess swelling, spring-back, and
sweiling stress of four commercially produced hot-pressed OSB panels and one
experimental stem-injection presseci panel were rneasured and analysad. The panel samples
were sectioned into two density zones: the two surfàce layers and the core layer. The layer
somples were atposed to a water soak test that gave maximum swelling in a short time (24
hours). This was considerd to be a reliable index to characterise the thickmss behaviour of
structural panels. The purpose of layer separation was to reveaî the individuai layer swefiing
propaties and the eHécts of each layer on o v d swelling of the panel. The laya sweliing
khaviour testhg used an innovative technique which was less time consumin8 and mon
efficient t h aeditiod methods. Once the sample panel data were anaiysed, a singie panel
was selected for exposure to a dimensional stabilisation procas, namely pst-manuf'acturiag
heat tnrtment. The effects of this proass on the thickness swelling, spring-bwk, and
swelbg stress of the panel's different density zones was measwed and disaisseci. The
d t s of these experhents are presented and disaissed in this report.
This miew is divided into five sections. The first three sections address sweiling and the
characteristics of OSB. Specindly addressed are the basic mechaMsms of swelling, the
relevant properties of OSB and fàcton that influence OSB swelling. The latter two sections
consider OSB manufactwing technology. These sections discuss the state of mat pressing
technology and various pst-manifacniriag dimensional stabilisation techniques. The key
elements of the resiew are highlighted in a summary section. Fiaally, a definition of the
experirnental problem is presented.
SwelJing «ui be divided into two types: reversible and irreversible. Usualiy both types of
swelling oc- simuit~neously. The proportion ofeach type displayed by a particular OSB
panel is detennhed by the panel manufachiring process.
Wood exhibits an affinity for water and is sufficiently plastic to physically expand during
adsorptioa (Stamm, 1964). Reversiible sweiling occurs when wood adsorbs water and fonns
a solid solution. Wood can be retwned to its original dimensions by removhg the excess
moisaire. The proportion of totai swelling tbat is reversible in OSB is les then that of
unprocessed (solid) wood. The amount of revasible swelling is directly related to the
w d ' s hygroscopicity, or affinity for water. The high temperature drying and application of
elevated press temperatures during OSB proâuction reduces Strand hygroscopicity somewhat
(Hsu et ai, 1989). The dryuig process reduces the equilibrium moisture content (EMC) by as
much as 3% compared to airdried wood. Thus, OSB has a lower affinity for water than raw
wood, and it exhibiîs less m n i b l e swelling as a rmlt.
High pressures are useû to cornpress and densify the OSB mat during the pressing stage.
Cornpressing the mat to a high compaction ratio stores potaitiai energy in the panel. This
easr~y is later released during moime acposure as imversible sp~g-back (Hai, 1989).
OSB may swell sevaal times more than nanual wooâ because of this dditional energy
imparted during pressing.
Ineversible sweUing in OSB is attributed to the release ofcompressive stresses and the
rupture of adhesive bonds. The removal of excess moisture d a s not r e m the panel to its
original thickness. S p h g badc is thus irreversible. The proportion of Urevenible swelling
in OSB is s e v d times -ter than in naturai wood and amiributes signincantly to total
overall thickness swell.
2.1.2 Rcstnints to Sweüing
2-1.2.1 Adhesive
Small samples of uncompresseci wood are fia to me11 and SM reversibly and stress-ftee
in response to the moisture content of their environment. In cornparison, wood composites
have interna1 restraining farces that resist swelling and stirinkage. These forces are
produceci by min bonds formed during the extreme heat and pressure of manufacturing.
Haygreen (1980) explained that the dimensional changes of composite wood are attributable
to three factors: (1) the degree of remaint to swelling posed by adjacent layers, (2) the
degree of compression induced during panel manufacturing, and (3) the effects of adhesives
and other additives. These &ors combined determine the strengh of interna1 bonds.
Furthemore, spring-back results when these intemal bonds %l. Both the degrees of
bonding and spriag-back are proportional to the amount of compressive force introduad.
2.1.2.2 Within fibre
Wood fibres are comprised of the primary wall enveloped in lignin to fonn the middle
lamella and three cumponents of the secondary wdl, the St, S2 and Sa layers (Ye and
Sundstrom, 1997). Roughly 80-95% of the ceIl wall consists of the S2 laya which provides
ngidity and stifniess. The fibril angle ofthe S2 layer govems the mechanical properties of
the fibre including strength, elastic moduluq and swelling and shrinlage. When flake layers
are arrangeci perpendinilar to one another, they are mechanically resaained fkom swelling to
a certain degree. Roweil and Youngs (1980), indicated that swefling of wood in radial and
tangentid direction can be 30 to 100 times pater than in the longmidinaî direction, which
contributes significantly to thickness sweIl. The Si and S3 Iayas contnhte to the
dimensionai stability of wood by constricting the S2 layer, hence, preventing baüooning of
the fibre during swefling. The warty layer uui influence the amount and rate of moisain
diffusion. #en wood is compresseci beyond its proportional limit, this consniahg
structure may be desiroyed.
SweUing (reversible or irreversibi) is produced by the release of swelling stress. Sweîling is
impossible without such release. Skaar, (1988) Wlicated that when wood is restrained âom
swelling, it exerts a tomter-stress in the direction of restraint. Stamm, (1964) indicated that
the maximum swelhg pressure cannot exceed the material's compressive men@ peqendicular to the grain. ûtherwise intemal rupture would redt. Compressed wood can
withstend greater compressive forces t h uncompressed wood. Thenfore, wmpressed
wood is also capable of exating swelling stress greatly in excess of uncompressed wood.
Stamm, (1964) examined the swelling pressure ofpre-cumpressed yellow birch. He
compressai solid birch without adhesive to a specific gravity (SG) of 1.42, which resulted in
a vimially void-free condition. The sampies were confined laterdy during his expairnem.
Over a 270 &y vapour exposure, swelling pressures of 68 MPa (10,000 psi) were recorded.
By extrapolation, Stamm estimated a sample with a SG of 1 A6 would produce 82.72 MPa
(12,ûûû psi). Such a bigh prcssure release gives wood the ability to damage materials that
are much stronger tban itselc including rock.
2.2 Sources of Stnss and Stress Release
Surface layers of OSB dry in the pressing operation. This causes moisaire movement from
the d a c e zones to the core zona of the panei, as well as the outer d layers to the centre
cefi layers of individual strands. This can iaduce stress into the panel in many ways. Stress
gradients are caused by the unequai shrinkage potential of the c d wall layers and
hydrostatic tension within the c d cavities. Second, various wood tissues exhibit Merences
in shrinlrage potential. Thirâ, the rate of moisnin migration dong and aaou the grain is not
d o m (Pansiin, 1980), forming a gradient. The summation of these fwors act as source
of stress, which has the potenfial for fiihire release. When exposed to wata, subsequent ceii
waii layen start to sweU, unequal swelling potential and hyârostatic tension produce
swelîing stresses. The swe11ing differential of various tissues, moisture gradients, and the
unequai mes of rnoishin movement results in swelling stress ofdifferent magnitudes witbin
the same sample.
2.3 The Characteristics of OSB and Swelüng
The strength of OSB is greatly compromised during swellhg. The effects of hygroscopic
swell on strength reâuction was examineci by various researchers. Wu and Suchsland (1997)
studied how the modulus of elasticity (MOE) and modulus of rupture (MOR) of OSB are
affecteci by MC and thickness swelling. Their findings indicated that for an inmase in MC
of 4 to 24% with the subsequent thickness inaease, MOE and MOR were reduced in the
parallel direction by 72% to 83% and in the perpendicular direction by 58% to 67%. This
indicates that fibre expansion alone produces a signifiant reduction in strength.
Geimer (1993) studied the impact of spring-back on internai bond strength (IB). His results
indicaîed that both adhesive bonding and the orientation of wafas strongly affected panel
spring-back and the IB men&. Intanal bonds in OSB are f o d by randomly distributeci
min droplets cnating nodal joints rather than by continuous adhesive coatiag8 This
scatterd arrangement effectively permits expansion and spring-back. Furthemore, the
orientation of wafers infiuences spring-back wafer orientation determineci the probable sue
and density of adhesive bonds which in turn detemines the panels ability to resist sweUing
forces.
Bolton and Humphrey (1988) stated that a mattress of flakes experiences ciramatic changes
in deiisity during pressing The rnattress entering a press may have less than half of the
density of the solid wood used to make ihe fiakes. The fiaal product may have nearly twice
the density of solid w d .
Suchsland (1%2) introduceô that wood composite panels exhibit a threeâiiensional
density distribution. This distribution is formed diaiag mat wnsolidation as a r d t of the
interactions between temperanire9 mass tnuisfa, and compaction pressure. The vertical
density distribution of h o t - p r d OSB shows great clBeremes between the surfaces and
the con QCu and Wmistorfer, 1995). Generally, the panel SUffhces are much denser than the
con Iayer. In contmt, steam-injection pressed OSB exhibits a more homogmeous density
profile (Ho and Viden, 19%). This means that highly densified layers store more potenhi
for swelling than the core. Whai water enters the board the dense wfhce layers swell more
than the core. The resulting shear forces between layers can be significant enough to
overcome the bonding strength of the adhesive. Mamination occurs, aeating more
oppominities for watex access. If the differences betwan swfhce and cora densities were
more homogeaeous, it would be possible to reduce the mecbanid forces imposeû by
adjacent layers when the board is swelling. Stearn-injection pressed OSB produces panels
that exhibit less density differential than tracütional hot-pressed panels. This more uniform
daisity distribution should diminish swelling potentiai (Ho and Vinden, 19%). It is possible
that these panels exhibit les thickness swelling, spring-back and swelling stress compared
to hot-pressed OSB. No iitersture has explored these three variables combined.
2.3.3 Compm8ive Deformition of Fibns
When wood fibre bundles are subjected to compression, they colieaively resist deformation.
As the compression pressure increass such resistive forces persevere until a plastic state is
reached. The ce11 walls then collapse. Void volume decreases as pressure increases
ahhough it does not dissppear completely. Mataki (1996) studied the internai structure of
fibreboard and examined void volume under various pressing conditions. 'Rme mges of
pressure w m used: k s s thari 30 kg/cm3, between 30 and 50 kg/cm3 and p a t e r than 60
k@cm3. At las than 30 kg/cm3, the pressure primdy produced void volume reduction.
Void volume was inverseiy related to pressure. At 30 to 50 kg/cm3, cell lumen closed and
inter-strand contact increased. The increase in inter-strand contact producecl a npid increase
in bonding area. When the pressure e x c d 60 kglcm3, compressive deformeton of the
fibre reached an upper M t and panel densification was miinly though intemal ce11 ûactm
and coîiapse. The compressive pressure used during conventionai mat coasoiidation is
detennined mainiy by the panel tsrget thickness. The signincance of mat consolidation
pressure is discussed in greater detaii in m ion 2.5.1 -4.
The mechanical storage of force in the layers of OSB is in some ways analogous to a
compressed helical spring (Fitzgeral& 1967). Hdical springs are Eequently used in
machine design to absorb forces exerted by loads. Fitzgerald (1967) explained that the
torsional action of a spring causes deflection. The total defîection of the panel is the
cumulative defiection of many individual "coils". Ahhwgh the deformation forces of OSB
are not torsional, an analogy can still be drawn. As each flake absorbs energy exerted by the
press, the compressive force and the final thickness is the accumulation of individuai flake
deformation. When a helical spring is compressed, d s near the Surface (near the load) are
compressed more than the centre coils. This is similar to the deformation of the different
OSB iayers, where Surface layers are more compressed than centre layers. The potential
aiergy stored in OSB panels during consolidation is released later during sp~g-back.
2.3.5 Variations witbin the Panel
OS% is an orthotropic system mygreen, 1982). However, each laminate layw experiences
various degrees of interaction. This results in heterogeneous internai stress distribution.
Kamke and Casqr (1989) concluded that press closing time and MC wntrols the mat
temperature and gas pressure distribution at the surfiice and con layers of OSB. However,
tempaature md pressure changes non-uniformly fiom the edge to the centre layas of the
mat. This resuhs in diffaent compressive modulus histories across the horizontai and
vertical direction, which also results in a density gradient of the panel. The anisotropic
nature of wood fibres combined with savice MC 0uctuations to bnng about fibre expansion
and contraction which imposes uneven shear and tensile stress on the panel, and particularly
on the adhesive. Unfortunately, the varying laye propeities generally compücate the
analysis of mechanical properties of laminates.
In addition to the compressive modulus history, the hygroscopicity of wood fibre also varies
with its position in the mattress. Sekino and h l ' s (1996) atpaiments evaluated the changes
in hygroscopicity of particles within the mat. They explained that hygroscopicity may diffa
between the d a c e and core layas and between th centre and edges of the p d . TMr
results agreecl with ICamke and Casey's report thaî this is a resuit of ternpetatutc and vapour
pressure variation matecl within the mat. Sekino and Inl(1996) also pointed out that an
EMC reduction was found closely related to the maximum temperature reached during
pressing. The EMC of the hot-prased particles ranged form 73% to 93% of those non hot-
presseû particles. Sudise particle EMC was reduced more than the wre m p l e at the same
press conditions because the s d e reactied a higher maximum temperature than the core.
2.4 Factors Idluencing OSB Swelling
Three main categories of f8ctors influence the sweliing behaviour of OSB: the savice
condition, the nature of the raw materiaf, and fàctocs in the rnanufbng process. The
dominant rnanuf8Ctllfing process factors aie strand geometry, strand puaiity, min content,
plasticisation effects, and moisture content. The effects of pressing temperature, press
closing tirne, and consolidation pressure on swelling are discussed in section 2.5.1.
2.4.1 Service Conditions
OSB &ce conditions play an important d e in the longevity of OSB panels. OSB contains
roughly 8% to 12% moishire at a construction site (SBA, 1998). Flared panel edges can
occur if panels an left uncovered during construction. Such damage causes considerable
&en@ reductioa (Wu and Suchsland, 1997). Proper installation is dso vital. Typical
indoor dative humidity fluchiates âom 15% to as high as 8CT/o over the course of a year
(Haygreen, 1982). The correspondhg equilibrium moisture content ofwood is 2% to 16%.
Such moisture cycling is more tbsn sufficient to tri- changes in the panel, both i n t d y ,
as bond stressing, and externaily, as delamination.
2.4.2 Nature of Raw Mattrial
2.4.2.1 Wood
Aspen is the most cornmon wood species used in flake and OSB production. Aspen
heartwood is greyish-white to light greyish browa in colour, wMe the sapwood is slightiy
lighter. However, the wfow differences are not very evîdent betweefl the two zones,
making them difficult to Merentiate. Aspai is diffuse-porous and exhibits a graduai
transition ftom urlywood to h e w d . Its pores are smail and ovai shaped, amnged in
isolation or radiaily aligned in groups of two to seven. The rays are homogeneous and
usuaiiy a single a l 1 wide. Aspen density ranges fmm roughly 550 kg/m3 in green condition
and 350 kg/m3 when dned to 12% MC (Summitt and Suer, 1980). The rigidity of glued
joints increases with wood density (Wood Handbook, 1980). Compared to other hardwoods
aspen is low in mass, displays low mechaaical strength, moderate stiffness, low resistance to
shock, and high shrinkage tendencies.
Chemicaily, aspen consias of 53% cellulose, 3 1% hemiallulose and 16% lignin (Haygreen,
1982). It is the arnorphous regions in microfibrils that contribute to the majority ofthe
thickness swell. Howeva, changes in the fibre position and the nature of hernicellulose by
the efficient utilisation of heat and moisture plays an important role in conveying stability
(Hilliq 1984). A partial hydrolysis of hemicellulose can increase wood compressibility and
thus reduces the tendency for stresses to be built-up in pressai composites (Ho and Vinden,
1996).
15 2 The radial permeability of wood (lu m ) is much lowa than in the longitudinal direction 12 2 14 2 (1U m to 1U rn ) (SB4 1998). Wood is a hygroscopic matenal. That is, it has a naturd
afhity for wata, and always contains a certain amount of water. Bdow the fibre saturation
point, changes in moisture content will induce hygroscopic fibre swelling and hence,
dimensionai instability. This effect is one of the major mechanisms in OSB swelling.
2.4.2.2 Strand geometry
Currmt OSB manufactunng techniques use wood sbands up ta 108rnm (4W) long by
25.4mm (1") wide. Longer, mhtemipteû wood fibres exhibit greater strength. This is also
true of straaâs. Long, large strands are prefand in OSB manufacturjng for îheir supaiar
strengîh. Howewx, larga strands produce mats with greater eâge pawability. Increased
permeability allows steam to escape easily, reducing the stem pressure available for
convective heating ofthe core. R e d u d resin curing in the core resuits. This efféct is mon
pronound with long press closing times (Kamke and Casey, 1988). Idquate resin
airing leads to weaker inter-stmnd bonds. P a x curing also reâuces the panel's ability to
resist i n t d forces released during moisture-indud swelling.
2.4.2.3 Strand q d t y
Aspen is classified as a species that bonds easily. Howeva, the performance of adhesive
bonded joints is governeci by nature of the Sllffàce quality of the wood. Surnice quality
impacts the bonding process and joint strength (Wood Handbook 1980). Smooth strand
sudàces tend to aihance bonding. Any damage or SUrfhce roughness has adverse effects on
bond strength. AU otha things being e q d , low strand bond strength inaeased thickness
swelling tendencies.
2,4.2.4 Resin Content
Boading in OSB occurs through resin droplets or particles joining one wood strand to
another. These joints distributed throughout the panel allow the transfer of stresses without
damPging the wood substrate. Ia cornparison, bonding in plywood is achieved by a
continuous layer of glue. Bond sites in OSB are smalls and more sparse than in plywood
(Hanson, 1998). Resistance to defonnation under stress and deaeaseû spring-back are
directly correlateci to the level of resin content. Incrwing OSB resin content will increase
cross-linking, whicb in tum reâuces swelling. However, resin is the most expensive raw
material in panel makuig.
Liquid resias are usually suspendeci in water. Water is the p r e f d carrier because ofits
naturai a f b i t y for wood, low cost, and high availability. Thuq resins contribute to steam
generation during pressing.
hvestigations on the chernid changes of wood d a t e d with heat exposwe wae
eonducted by Spait (1977). His results indicated that lignin tends to melt whae plastic flow
or reh t ion takes place at a specific range ofMC and elevated temperaain. This
"plasticisation" occws when the amorphous component of wooâ changes fiom a crystaüine
(or glassy) state to a rubbay state. The temperature ai i t c h lignin transitions from a giassy
state to a mbbery state is affected by moistue (Norimoto et ai, 1993). rii mechanid terms,
the compressive d u l u s of wood is ait& durhg plasticisation. This transition allows the
repositioning of the w d s intemal ce11 structure* As the wood cdls deform and reposition
they release mrne of the compressive stresses induced duriag pressing. This release
minimises the sweliing potentid of wood
2.4.3.1 Moisture Content
AeLe moisture content (MC) influences the rate of temperature increase during pressing.
hiring pressing, flake moi- is converted into stem. The panel wre region serves as a
heat sink and most of the vaporised steam migrates âom the surface to the a r e region.
Steam is an efficient heat transfm medium, and helps cure the aâhesive resins. Steam also
aids in wood plasticisation. When wood defonns plasticdly it releases energy thet would
o thbse contribute to moimre-induced swelling.
Norimoto et al, (19%) indicated that at temperatures above 170°C wood fibre behaves
thamoplasticly, which p e t s a significant level of compressive deforrnation. He also
notcd the effect of fibre moistun content and its relation to compressive deformation of the
fibres in a fibre bundle. At MC above fibre saturation point (FSP), the presence of fiee
wata acts as a lubricant allowing fibre position readjustment and reûuces fibre-to-fibre
testraint and hence, reduces void volume. At MC levels below FSP, the lumen changes in
size rapidly and compressive defonnation is govemed by the ratio of the widest cross-
sectionai dimensions of the fibre to the srnailest cross-sectionai dimensions; the occupation
ratio of the cell wall and the intercellular space.
When mats are pressed at low MC, the moisture migrates completely fiom the surnice layers
to the wre. The d a c e is left undesirably dry, leading to low plasticity. Low plasticity
limits the ability of fibres to relieve pressing forces.
The dyilsmics of steam genaation and rnovement are critical to OSB production. These
effects are discussed M e r in section 2.5.3 and section 2.5.4,
2.5 The Pressing Operation
The pressing stage determines OSB properties more than any other. Mimy cornplex physical
and chernical reactions occur during pressing. Pressing is ais0 the most costiy manufimuhg
operation. Therefore, a aund knowledge of the pressing stage is needcd before the swelling
behaviow of OSB can be fùlly undefstood or manipulated. Unfortunately, a thomugh
understanding of this stage is still lacking, especially regarding the interaction of physical
processes during hot pressing.
There are two main types of pressing used in OSB m a m i f i e : hot pressing (HP) and
Stream injection pressing (SIP). Hot pressing is the traditional method of OSB production.
M g HP, a mat of OSB strands is highiy compressed ùetween heated platens until it is
completely consolidateci. The t h e required for this process is dependent on rate of heat
transfer to the core region and on the t h e required for sufficient curing* The m a n u ~ ~ g
cycle time is dependent on target thickness desired.
Steam injection pressing uses compressed s t em or vapour to heat the mat during pressing.
This is a radically different mechanisrn compareci to hot pressing operations. Steam can
transfer heat to the a r e region much faster than layer-tdayer conduction. The panel
reaches a homogeneous temperature, moistun, and vapour pressure graâient across its
thickness more quickly then aaditional platen hot pressing* The technical ratiode for using
s t em was to reduce pressing tirne and pressure required for panel malring. The economic
advantage was the reduction in raw material input and the increased comrnodity output.
2.5.1 Coiitrolhble Pressing Variables
OSB pressing machinery is very complex and expensive. Presses are designed for high
through-put, not flexibility. nien are relatively few parameters that caa be adjusteci once
the machinery is installed. However, OSB manufwers spend a great deal of time
optimising theV produas by manipulating the few pmeters unda their control. The
primary fmors under the OSB maaufbcturer's control are the interactions of heat transfer
rnoâes, pressing temperature, press closing time, and consolidation pressure.
Strickler, (1959) indicaîed that there were thra ways to transfer heat to the mat: conduaion
(fiom platen to mat by contact); convection (steam was injectecl into mat); and internai heat
grnefafion @y high frequency electric fields). in conventionai hot-pmsed OSB
m a m f m g , conduction is the primary means of hm mfbr âom platen to mat.
However, convection is the dominant transfer mode within the mat. Rapid heat transfer
creates an transient enwonment within the mat. This phenornenon is m e r compiicated
by compressive stresses generated durhg mat consolidation. The end result is that the
degree of adhesive cure, density gradient, bond quality, and physical and mechanid
properties of the panel are altered through complex interactions. Great changes o c w in the
three dimensional variation in temperame, moishin content and vapour pressure,
pemeability, and thermal conductivity.
2.5.1.2 Pressing Temperature
Press platen temperatures of at least 1WC are used to tonsolidate wd-adhesive bonds
during pressing. Greater platen temperatures increase the rate of temperature nse and the
maximum attalliable core temperature (Kamite and Casey, 1989). Both hot pressing and
steam-injestion pressing use between 1600C to 190°C to ensure opthai curing across the
total panel volume.
2.5.1.3 Pnss Closing Time
Press closing t h e is used primarily to control to the panel's target thickness. Faster press
closing times produce panels with larga density gradients between the surfaces and m e .
The reverse is also tme, resulting in a more homogaieous panel. Longer press closing time
means more stress relaxation can o c w . Stress relaxation allows compaction pressure to ôe
nduceû, which reduces built-in messes.
2.5.1.4 Consolidation Pressure
Mat consolidation pressure strongiy influences the behaviw of OSB both during and after
production. During production, greater consolidation pressure increases mat ternpaahve
more tapidly dwing pressing. Strand plasticisation and stress relaxation are M u e n a d by
temperahire and thedore consolidation pressure. Thicker panels also typicaily requin
longer pressing time and lower maximum compaction pressure than thinner panels o n t h
rwi Kamice, 1996).
The pressure used in mat oonsolidation introduces stresses into the mat which remain
locked-in until subsequent water exposwe. Thus the swelîing behaviour of panels is directiy
related to consolidation pressure. The compaction pressure utilised for OSB production is
much higha than piywood. In plywwd manufacturing, pressures range fiom 500 to 700
kPa HP OSB pressing utilises pressures of 4000 to 6000 kPa (Geimer et al., 1998), or
roughly ten times higher than for plywood production. SIP OSB manufiicture employs 1950
kPa. The higher the compression pressure the mon energy is transferred to the panel for
Aiture swelling re1ease in response to moisture fluctuations. Mer production, wasotidation
pressure infiuences OSB spring-back Lower consolidation pressure irnparts less energy to
the mat. Less potential energy is stored in the mat and the tendency for spring-back is
redud.
23.2 Conventioiai Pressing Technology
Researchas have rigorously examined the physical processes and interactions involved in
pressing. The goal was to improve OSB performance through an understanding of pressing
operation interactions The focus was on internai temperature7 vapour pressure and
compaction. The following two sections offer the findings of this research as they apply to
hot pressing and steam-injection pressing.
2.5.3 Hot Pressing
Hot pressing technology uses heated, non-porous press platens to heat and cornpress mats of
resin-coated s&ands. Many cornplex interactions occur between temperature, water vapour,
and mat density (through compadion). These interactions are described below.
2.5.3.1 Intemai Temperature
The vertical temperature gradient within OSB during hot pressing closely follows the
pndicted profile for a body king heated tiom two sides. Thus, it can be coacluded that
most of the energy transmitted to the panel is used to heat it, and relatively little energy is
used to produce water vapour. However7 the temperature plateau seen in flakeboard indicates tht water is continuously vaporising, replacing water vapour that migrates âom
srirfirccs to the core and âom the centre escapes kough the panel edges. This is arpporied
by the large horizontal tempaaane grpdients observeci during flakeboard production-
Neither large amounts of vapour release nor such tempaatrae gradients are seen during
plywood pduction (Hwnphery and Bolton, 1989).
Durhg hot pressing, thermal energy is transmitted fkom the platens to the outamost layen
through radiation and wnduction Heat transfa within the p d occurs through thermal
conduction and the convection of energy by vapour. The rate of vapour transfa, and thus
heat transfer. is directly nlated to the panel's pemeability. As the outer layers are heated,
any water tunr, to vapour, which migrates towards the inner iayers. This vapour d e s
t h d energy with it, which in hun heats the core layers. The rate at which vapour caa
mvel to the oore detennines how quickly the core is heated. The rate of adhesive bond
strength deveiopment depends on temperature and vapour pressure.
2.5.3.2 Interna1 Vapour Pressure
Zavala and Humphrey (19%) studied the interaction of physical processes during hot-
pressing, focushg on heat and moisture movement. They concluded that water vapour
pressure accumulates and peaks in the centre of the panel, where bonds tend to be weakest.
These centre bonds may fail or "blod' during press opening. Failure is not necewwily
because of deficient o v d l strength, but instead due to the large saesses that are transferred
to them upon press opening. Vapour convection within the panel creates a moisture gradient
within the panel. This gradient affects the transfer of stress to adhesive bonds, hence
diffennt mechanical properties fonn at different panel locations.
Immediately der press closing, vapour pressure within the panel rises slowly. Pressure
inmases rapidly until t fïnaily reaches a plateau. Vapour pressure increases mainly due to
the vaporisation of liquid watcr. Water is found in the wood cell walls and in the adhesive.
Vapour pressure also increases due to the thermal expansion of air pnsent in voids and ceIl
lumens. As pressing continues, vapow migrates tiom the outer layers into the con.
For plywood, vapur pressure in the outermost layers initiaily fises more rapidly than in the
h a fayers. However, the vapour pressure in the core Iayers takes longer to stabilise and
rushes higher levels than in the outer layers. Tbis behaviour is not seen in OSB, d y
due to their greater permeability. The permeability ofplywood is oAen severai orders of
magnitude lower than OSB. The temperature gradient between OSB samples is relatively
uniform However, the vapour pressure gradient varies gnatly both within a single sample
and between samples. This da t ion is mainly due to nanirol variations in peability. The
low d i a l permeability of plywood prevents vapour itom escaping out the panel edges.
This results in a frürly unifonn pressure distribution. In cornparison, the higher pefmmbility
of OSB r d t s in a greater horizontal gradient, mostly because it is easier for vapour to
escape out the panel edges (Zavala and Humphrey, 1996).
Both OSB and plywooà m e n c e the greatest vapour pressure in the are. This is also
whae bond strength is lowest. ûnce cure4 the resin gluelines (in plywood) becorne a
formidable vapour b d , inhibiting vapour pressure telease, even &er press opening. In
plywood, the intemal vapour pressure can take severai minutes to return to ehnospheric
pressure upon press opening. Vapour pressure within plywood can place high loads on the
intemal bonds W e e n veneers and panels may experience delamination defonnation or
other mechanical failures if these intanal bonds should fail. OSB does not expnience such
shock, since its greater permeability allows the intemai vapour pressure to dissipate rapidly.
OSB ais0 acpaiences greater horizontal pressure gradients than plywood.
2.5.3.3 Intemal Compaction
The rheological behaviour of OSB is affectexi by both heat and moistwe. During pressing, a
mat of saands initially defonns elastidly and later densifies as intenial temperature
inmeases. The rate of densificaiion a f f k ~ ~ the rate of heat and moishin tramfa, which
affects the panels' viscoelastic behaviour, which in tum influences the densification process.
Pressing is the bottleneck in modem HP OSB pduction. Heathg by conduction requins
long pressing thes to cure the thermosetting resin in the con region. In contrast, stem
provides an fhster means of heat and moisture tramfer. Stearn-injection pressing (SIP) was
developed to rduce press tirne, minimise en- consumption and maximise raw materiai
mvery. The most important ktors in SIP pfodudion are intanal temperature dynamics
and vapour pressure âpamics.
To e5ciedy raise the panel temperature, pressurisecl stem is injected into the mat
introduced prior to severe compression. Upon press closure, heat transfa to the core is not
mtmtmeous due to the presence of moistwe in the cm. However, the con temperature of
SIP OSB reaches its maximum up to five times fasta than the HP methoâ, dependhg on
rate of stearn flow and the degree of edge vapour dissipation. The permeability of SIP OSB
drops rapidly as the press reaches its target thickness, similar to HP panels. Therefore,
thicker panel requires a higher stem flow rate to maintain the rate of temperame raise
(Kwon and Geima, 1998).
2.5 A.2 Intemal Vapour Pressure
Stream convection plays an important role in SIP heat transfer. The vapour pressure
gradient is more severe in SIP panels and the ratio of h e to edge plays an imporiant nile
in maximum attainable mat pressure. Peak temperature and pressure in the core depends on
steam time and pressure range. Overali, the direction of steam flow is fiom d a c e to the
core and dissipate out âom the periphery (Kwon and Geirner, 1998), which is similar to HP.
Instantaneous, localiseci changes in vapour pressure are inevitable. Fluctuations in vapour
pressure also depend on the relative distance, permeability, and the pressure d ien t i a l
between a source of high pressure and a vent.
Hpta (1993) discovered that initiation of the stem injection at the compaction ratio of 1 .O to
1.3 shoriens the total press tirne without reducing panel properties. An increase in stem
pressure and stem injection time reduces swelling bebaviow of OSB (Kwon and Geimer,
1993).
OSB panels are made to a relatively high compaction d o (the ratio ofboard density to
species density) and are prone to moisture release problems in the fom of blows or blisters.
This problem is magnifieci when additional steam is injected h o the panel (Geimer, 1985).
The SIP mat interior arpaiences a mon severe and nipid change in moisture and
tempaanin than HP OSB. However, the SIP pressing operation is more contrdlable than HP*
2.6 Dimensional Stabüisation Methods
Several processes have been developed for combating swelling in wood composites. Some
processes are applied eitha during or after pressing. Heat treatment is applied during
pnssing. The effects of steam and kat fixation wae studied both before and afker pressing.
Post-manufachuhg heat treatment is applied after pressing. These techniques an d i s a i d
below .
Roweli and Youngs (1980) oummarised wood dimensional dilisation techniques. Heat
treatment was mentioned for hygroscopicity reduction. In their technique, wood was heated
in the absence of oxygen to 350°C for a short time. This resulted in a 400/, reduction in
sweliing. This was attributed to thermal degradation of the hemicellulose component of the
d wall. They explained that during swelling, hydroxyl groups ofceliulose, hemicellulose
and lignin tend to expmd in order to accommodate wata hydrogen bonding. hernicellulose
are the most hygroscopic of the ce11 wall polymers. However, they are the most susceptible
to t h d degradation. Thus, by proloaged heat mposun, iaducing thermal degradation of
hemicellulose component teduces hydroxyl group availability, hence, rducing swelling
potential.
2.62 Stmm and Heat Fi t ion
houe et al., (1993) kstigated the eEea of s t e m or heat fixation of compresseci wood.
Their r d s indicated that both types offkation gave almost wmplete fixation of
compression set. Tanahashi (1989) explained that the cellulose cqstaliinity, microfibril
width and micelle width inmeases when compressed wood is subjected to stem fixation.
As temperature increases, water escapes while hydrogen ôonâing is re-established beiween
polymers within the 1ign.h-hemicellulose ma& When the tempaahuc decreases, the
amorphous region resumes a glassy state and loclcs in the plastic defonnaton of the
microfibrils, and reduce dimensional instability.
2.63 Post-Miaufacturing Heat Tmtment
In 1986, Dr. Hsu at Forintek C d Corp. patented a mahod of maLing dimensionally
stable OSB by a direct contact heat treatment. In his technique, temperatures bawem
230°C and 2S0°C were utilised to heat-treat panels for various duration. In 1989, Hsu et al
identified that a mjor contribution to TS was due to spring-back, which can be several
times greater than the nahiral swelling of wood. His team examined the chernical and
physical change requirements for dimensionally stable wood composites. An initiation of
big& temperature contact treatment created dimensionally stable OSB. His results regarding
board propaties indicated tbat the bottorn layer of a 19. lm-thick OSB panel experienced a
reduction in thichess swell. A 1% ceduction in spring back was also roughly
amibutable to the pst-treaûnent. The streagth promes of MOE and IB results were
comparable to conml panels. However, MOR was slightly reduced. Chernical anaiysis
indicated t h t changes in Klason lignh and carbohydrate contents were aegligible. Physicai
changes likely causecl the reduction in sp~g-back. Effective post-manufaauring heat
treatment utilises temperatures above the soflening point of the &hydrate components of
lignin.
2.7 Summary
Al1 OSB swells in thickness when exposed to moisture. The portion of swelling that is
directly cuised by the presence or wata is called reversible sweliing, since it can be
reversed by drying the OSB. Reversible swelling is strongiy affected by the hygroscupicity
of the wood used. heversible swelling can not be undone, and is mainly causeâ by the
release of compressive stress stored in the panel duriag the pressing stage. OSB swells in
uiickness up to thne times more thon plywood. Such swelling reduces the mechanical
~eength of OSB and limits its pradcal application.
OSB exhibits a characteristic vatical density profile, whae the panel d & e s are densa
than the con. Studies have shown that the densa surface layers swell more than the core
zone. Thus thickness swelling was show to be proportional to density. The profile of this
distribution is stn,ngly afkted by the pressing technology employed Hot-pressed panels
show a -ter diffaence in density between the s u r f i s and core than steam-injection
pressed panels. The more homogemxis density profile of stem-injection press shodd
produce less tbickness swelling tbat hot-pressed panels.
As the OSB mat is compresseci, heat and pressure are applied to cure the aâhesive resins and
consolidate the panel. During pressing, steam is either naauplly generated within the panel
or artificially i n j d . The rapid combination of -me heat, pressure and moime within
the OSB panel create a complex transient environment and forms localised equilibrium.
This induces ôoth temporary and parnanent cbanges in the mat As the wood strands am
heated in the presence of moisture, they plasticise and becorne pliable. This pliability ailows
them to be compresseâ more eady. Although the strands are mon flexible they stiil resist
compression, and retain some of the stresses generated during pressing. niese stored
stresses are released later during swelling are a major cause of spring-back. The pressing
process detemines the amount of strand plasticisation. Many other factors influence OSB
swelling behaviow, including the nature of the wood useci, the geometry and q d i t y of the
wood sirands, min content, and the final panel b c e conditions.
The pressing stage of OSB manufacture is the single most infiuential stage for swelling
behaviour. The size anci cosnplexity of pressing equipment b i t s the variables OSB
manufa~tllfers can adjust when optimising production. The miables that most influence
swelling behaviow are the modes of heat transfer, the pressing temperature and closing the,
and the consolidation pressure.
There are two types of pressing: hot pressing and stem-injection pressing. Hot pressing
uses heated platens to wami the OSB mat through conduction and later by stem vapour
co1wection. Most of the energy transmitted to the mat is used to heat the panel, and
relatively linle energy is usad in creating stem. The genaated steam escapes through the
panel eâges, taking thamal energy with it. The grrot pemieability of OSB resuhs in large
vapour pnssun and temperature Merences bnwem the panel centre and edges. Tlnu the
swelüng behaviour of h o t - p r d panels varies gnatly in both the verticai and horizontai
directiona.
Steam-injection pressing heats the mat through pressuised steam injected into the mat
through paforations in the press platens. Stem is a more efiicient heat transfer mechuiisrn
than the conduction employed by hot-pressing. The pressing time and energy is thus
reduced. Stem is contiauously pumped into the surfke layas as it escapes into the core
and out the edges. Thus t h e is las diffennce baweea the surface and core iayer
enviroments. The contiwous addition of s t e m also inmeases wood plasticisation and
reûuces required consolidation pressure. Thus steam-injection pressed panels retain less
pressing stress and exhibit las spring-back and thickness sweliing.
Severai proasses have ban deveioped to redua the degree of sweliing in OSB. These
dimensional stabilisation techniques may be applied during or der the pressing stage. Heat
treatment applies high temperatures to wood in the absence of oxygen. Steam and heat
W o n reduce thickness swelling and spring-back almost oompletely by replasticising the
wood. P o s t - ~ u f ~ g heat treatment uses hot platens to heat panels under moderate
temperatures and pressures. The panels are not compressecl iuiy fkther but are prevented
Born exparidhg as well. This process is simple and the reductions in thickness swelling and
sp~g-back of up to 20% are possible.
Despite extensive research on the swelling behaviour of OSB, several key are85 have not yet
b#n addressed. First, thae was very linle data available on the swelling behaviour of the
dSerent vcrticaî density zones (derived fkom l d s e d equilibnum). No research
investigated the swelling stress of OSB by dewity zone. Second, although hot-pressed and
steam-injection pressed panels exhibit dflerent density profiles, no studies compared the
l a y d swelling behaviour (eidier thicknessswell, spring-back, or sweliing stress) of these
panels by layer. It was unclear whether the difkences in swehg behaviour were due to
density variations between the puseleentypes or to some otha layer properties. Third, despite
the work into stabiiisation tnatments, the foais was on the tnetment conditions and the
effects to o v d panel sweîiing behaviour. No attention was given to the meIIhg
behaviow of the individuai density zones or to swelling stresses. Overail, the effects of
différent pressing technologies and treaîments on the thichess swelling, spring-back, and
swelling stress in different density zones is poorly understood. Lady, although the effect of
heat stabilisation was effective in reducing thickness swelling of OSB, its enect on laye
sweliing behaviow was not investigated.
3. OBJECTIVES
Thae wae two primary objectives for this researcb. The nrSt objective was to address the
lack of information on the layer-by-layer swelling behaviour of OSB. The second objective
was to m d e understanding on the effects of pressing and stabilising techniques on layer-
by-laya OSB swelling behavbur.
To satisfy the first objective, three swelling parameters were me8su~ed: thickness swell,
spring-ba& and swelling stnss. Panel samples were divided into tbree layers (top, bottom,
and are) and the swelling behaviour of these samples were measured. Bnween ten and
thirty-two (32 for the hot-pressed panels and 10 for the steam-injection pressed) OSB
samples wae gathered fiom each of two panel areas (the adge and centre) and fiom each of
five dEerent panels (four hot-presseci panels and one stem-injection pressed panel).
The effécts of pressing and stabilising techniques were dso studied. Two pressing
techniques, hot-pressing (HP) and steam-injection-pressing (SIP) were shidied. A single
type of pst-manufacniring heat treatment (Pm was also studied. Daia on the bebaviour
of ho t -prd and steam-injection-pressed pawls was gatheted during experiments
addressing the kst objective. In a subsequent acpallneat, the eEécts of PMIIT was studied
by subjecting the poorest perfonning of the sample panels to two diffcrent test conditions
(treatment for 7.5 minutes and 1 5 minutes).
The experimental investigation was divided into three parts. Each part is designecl to gather
Mirent swelfing behavïour data and involves diffenm experimental procedures and
apparatus. The nrSt studies the thickness swelling and spring-back of OSB layers. The
swclling strsss of OSB loyers are measured in the second part. The third expaimental part
studies the effect of PMHT on the swelIing behaviour of a single manufacturer's panel.
3.1 Justification of Experimentd Variables
Three miables wae measured throughouî in this research: thichiess swell, springhck, and
swehg stress. Thickness swelling is the primyr behaviour exhibited by OSB. Thickness
swelhg indudes the effects of both recoverable and irrecovaable sweiling. Spriag-back
represents the irrecoverable sweliing, and iadicates the proportion of overall thickness
swellkg attributable to d c n u i a g effects. This malces sp~g-back a useftl additional
variable to thicLness swelling data. Third, OSB swelling is fundamentally Qiven by the
release of stresses storecl in the panel. These stresses were storeci in the panel eitha as
matter of natural behaviour of the wood or through energy imparted d u ~ g the pressing
stage. As OSB swellq it presses on the sumunding materials. The amount of sweUing
stress determines the darnage done to these materials. Thus, swelling stress in a panel is a
usefbl parameter to measure.
Linear expansion was not atamined in this study due to its low swelling tendency. Linear
expansion is restrained by the longitudinal sweiling of wood, which is typically 0.5% (Wu
and Sucôslanâ, 1996). At less than 12% MC, the rate of LE is proportional to longitudinal
swelhg. At greater that 12% MC the LE rate stabilises and transverse swelling dominates,
making LE relatively unimportant. Overaii, LE is not a significant pedormance issue for
OSB products. The greatest conceni is moisture-induced thickness swelling. Siau, (1971)
indicated that hydroxyl groups providing hydrogen bonding sites to wata molecule are
lomed on the side of the cellulose chah When water adsorption o«ws, adjacent chains
are pushed aput refiected hcrease in thickness. Because the sites are located on the sides of
the chah, its uifluence on length is minimal.
3.2 Objectives of Part 1
The thickness swelling and spring-back behaviour of samples taken Born five panels are
me8su~ed in Part 1. The density and volume of the samples is also measured. Besides
ftIfiIling the primary objective of gathering data, Part 1 has several subsbjectives. These
are:
To pnsent and validate an inexpensive and efficient technique for separasuig OSB
panels into individual layers.
To deamine ifthe density variation between the thnt density zones of HP and SIP
OSB conforms to the g e n d J-shaped distribution indiatecl in the literatwe.
To test the hypothesis tbaî demity is strongiy positively conehted with thickness
sweIliag (TS) and spring back (SB).
To determine the difference in TS and SB h e e n edge and centre samples for HP
panel.
To identify those panel(s) which exhibit the poorest overall swelling behaviour. The
panel(s) which exhibit the greatest swelling will be used in Part 3, pst-manufachiriag
heat treatment.
3.3 Objectives of Part 2
Part 2 stucfies the swelling stresses exerted by OSB. This data has never been gathered on a
laya-by-layer basiq and gathering it is a major objective of this study. This data will also
be used to:
Characterise swelling stress behaviour over time. Of particular interest are the
maximum swelling stnss acbined, the rate of stress release, and the tirne to equilibrium.
Study the relationship betwan density and swelling stress. Thickness swelling and
spring-back are ihenced by density. It is not knom if swdling stress follows the
same behaviow.
3.4 Objectives of Part 3
nie objective of Part 3 w u to daemiine how pst-manufacni.ing k a t treatment (PMHT)
affeas the sweliing behaviow of commercial OSB. By measuring the efficis of PMHT, its
potential benefits to existing manufachiring processes could be assessui. PMHT wu bc
useâ to try to improve the swelling behaviow of a single mzuiuf~er 's commercially
produceci panel. Sample panels were subjected to the treatment for diffetent periods.
A f t m d s , their thickness sweiling, spring-bac4 and swelling stnss behaviour was
m d and discussed.
4. PART 1: THICKNESS SWELLING AND SPRINGBACK
The purpose ofthis experiment is to characterise the swelling behaviour of four
commercially manufactureci hot-pmseâ OSB panels and one experimental steam-injection-
pressed OSB panel. Samples are takm fiom the antre and edge regions of the panel and
then mechanically layered into top, core and bottom layers. The thickness swelling and
spriag-back of these layers is measwed and presented.
4.1 Materiab and Methods
Fou commercial Hot-Ressed (HP) 0-2 Grade OSB panels were aquired âom four
diffaent indusaiai manufmers. The manuhctures will be designated A, B. C, and D.
Each panel was 1.22m by 2.44m (4' by 8') and 18.26mm (23"/32") thick. The edges of
several panels were acposeû to the elunents during shipping and had already begun to sweii.
A 10.0 cm wide perimeter was trimmed off each panel to remove any damaged materiai.
Two 7.5cm by U.Ocrn (3" by 10") sample areas were selected âom each panel, one near the
centre and the otha at the panel's edge. Refer to Figure 1 for the locations of each region.
The letters "C" or 'Z" will be appended to the mawfacturer designation to indicate sample
ma, Le. "BC' indicates a centre sample from manufacturer B. The centre and edge regions
of luge panels typically exhibit diffarnt swelling properties. The swelling behaviour of any
region within the panel should Ml within the extrema set by the centre and edge samples.
The homogeneity of the manufhCtUnng proces cm also be observeci. Each sample ana was
bther ait into three 2.5cm by 25.0cm (1" by 10") stsîps. The first süip was wed to prepare
the top layer samples, the another for the core layer, and the third strip for the bottom layers.
This is repeated on the second panel.
A single 3 8 m square (15") Stem-Injection Pressed (SIP) laboratgr OSB testiag panel was
acquind and similady prepared. Again, a lOcm perimeter was removeci. The panel was too
smdi to dinde iato centre and edge regions. Samples wae instead nit ftom a single 7.5cm
by 2S.ûcm (3" by 10") area. Steam-injection pressed panels tend to be more homogeneous
and JO las intra-panel variation is expected. 28
Figure 1. Sample preparatioo and location
The panels were divided into three cross-sectional layers: the top, core and bottom layers.
This was done for severai rrasons. First, =lier investigations by Xu et al (1995) indicated
bat thickness swelling was not homogenous dong the vertical axis, but instead was
positively m l a t e d to density. Thus the thin, high density panel regions (the outer
surnices) contribute a signifiaint &action of the panel's overall thickness swell. By
measwing the sweiling and density of each layer, this effect wuld be confinned. By masurin8 the welling behaviour of individual dmsity zones in the thickness direction the
relative dimensional stability of the wrresponding layss in the eaual composite panel could
be clearly isolated. Measuring the swelling of each layer allows us to idemify the
contribution of each layer to the panel's o v e d swelling, both in absolute thickness iacrease
and in relative change. Seconci, layering the panel allows faster water uptake ami thus more
cornpiete thickness swelling in a shorter tirne.
A mechanical layer separation technique was used to isolate the top, core d bottom panel
layas. A thickness planer was used to graduaily peei off the ummted layers ûom each
strip. For example, to p d u c e the ''top layef' &p. the bottom and wre layers wen
removd and discardeci. This techaique produces very little damage to the samples, and
generally retains the panel integrity. Conventionai methods of vertical density
determination use electromagnetic radiation densitometer to provide a contiauous density
profile. However, such methods nquire a sophisticated equipment and tnhed pefsome1 to
achieve precision. Often, both an hard to acquire. The procedure used in this stwly does
not provide a continuous vertical deasity profile. Rather, it m e s as a fast and
economically efficient technique for measu~g panel density profile, albeit with less
resolutioa. By dividing the panel dong its thichess into the top, wre and bottom regions,
this meuiod produces a "the zone" density. This method does not rquire exotic
equipment and cm be used by manufactwers as a convenient means of checking the density
profile of their proâucts.
The top and bottom layen were approximately 4mm thick, and the a r e layer was lOmm
thick. These thickness were chosen by "eyeballing" the approximate thickness of the
panels' density zones. Each layer strip was then sawn into ten 2.5cm by 2.5cm (1" by 1")
blocks. For the HP panels, a total of 128 blocks were produceci, whae a block consists of
one sarnple each fiom the top, m e , and bottom layers, fonnuig 384 layers. Each
manufacturer was represented by 32 blocks (96 layer samples): 16 representing the panel
centre area, and 16 blocks representing the edgcs of the panel. Due to the much smaller
panel dimensions of the SIP sample, a single area was chosen to represent the entin panel.
The SIP panel was prepared into a total of 10 blocks (30 layers). There is typically a natural
30% variation between different panels fiom the same mmufacfwer, as well as within a
single b o d itseîf. Thuq using a kger number of panel samples wouid not inaease the
acairacy of the acpaimental fesults. Each sample was uniquely marked and its density and
thickness recorded before any testing.
Caution should k wed when cornparhg the HP and SIP panel datP The SIP data came
fiorn a single small laboratory-prohced while the HP data cornes fkom four large
commercially m a n u f " panels. Despite the M e r e ~ l c e s in the two panels, comparing
the rmks does shed some light on the relationship between layer density, spring-bwk, and
pressing technologies.
ALI laya samples was subjected to a 24 hou. water soak test in conformance with CAN3-
0437. bM85 spacifications. After soaking, the thickness swell of each block was measund
and recorded. Twenty four hours might seem like an umecessarily long duration. However,
Winistorfer and Xu (1995) shidied layer thickness swelling and its contribution to the
overali board thickness expansion. They suggested that thickness expansion was attributed
to the uptake of bound water. The ceii wall is fully satwated and reaches d m u m and
stabilisation afta 8-12 hours of water exposure. Further acposure results in free water
entering the ceIl lumen. Examining the maximum thickness swelling and sp~g-back
provides a more reliable index for characterising the dimensional stability of wood
composite p d s . By exposing the samples to test conditions for 24 hours, maximum
expansion of the panels is asmeci.
Immediately after completing the water soak test, the samples were placed in oven set at
10S°C S O C for 24 hours. M e r oven drying the thickness is again measured and recorded to
caldate the amount of spring back.
4.2 Results
The experirnental data was used to calculate the thickness swell and spring back properties
of each manufactu~er's board. The data were also analyseci using statisticai techniques to
detamine the relationship between differeat panel properties. The results of the density,
thicicness swelling and spring-back measurements are premted in Table 2 to Table 4.
These data are also presented graphicafly in Figure 2 to Figure 3. The volume of
arpaimental data malces presenting the rmlts difncult. Thenfore, dl data presented will
be the average values of al1 samples which fit the category in question.
Tabk 1. OSB Pand hyer demsities
Vahe in each ce11 is the mean value of 16 samples; whole values are the mean of 10 SaInples.
Sample Location Top dge Top centre Core edge Concentre Bottom edge Bottom centre
Whole
S a Appendix D for wrreîation coefficient and variance analysis.
Mill A Mill B Mill C MiUD Experimentai SIP Panel
686.3 kglm3 746.6 kgM 670.3 kgh3 666.1 kg/m3 880.7kgh3 683.1 kglm3 730.4 kg/& 646.4 kg/m3 728.3 kg/m3 619.3kglm3 548.8kgh3 551.2kglm3 475.5kg/m3 608.8kg/m3 602.9kglm3 549.8kglm3 468.7kg/m3 519.7kglm.3 698.2 kgh3 658.7 kglm3 592.0 kg/m3 643.0 kglm3 748.7 kg/m3 578.0 kgh3 604.0 kg/m3 578.0 kglm3 619.4 kglm3 680.0kgM 664.2 kg/rn3 608.2 kdm3 602.5 kgh3 676.1 kg/m3
Table 2. Tbickness nvdling upcrimenW msults
Sample Location
Manufacture Manufacture Manufacture h f a c t u r e SIP P d A B C D
Top Edge Top Centre Con Edge Core Centre Bottom Edge Bottom Centre
-- --
Pa Value in &h ceIl is the mean value of 16 ~amples; whole vdues are the mean of 10 ssmplss.
See Appendix D for codation coefficient and variance d y s i s .
Whole 1 638 20.9% 14.1%
Table 3. Average sweiiing behaviour of four manufactum'r hot-pmeâ pan&
Vduc in each cell is the mean of dl samples fiom diffennt mills.
HP Samples only
TOP
Core
Bottam
See Appendk D for correlation cafncient and variance analysis.
Density Thîckness Swelling Spring-back kg/m3 (Stdev) (Stdev) (Stdev)
699 35% 22Yo (61.61) (9.64) (9.18)
543 20% 12% (46.3 1) (4.49) (4.09)
630 27% 18% (58.52) (8.61) (7.36)
Whole 1 19% 16.2% 14.5% 9.5% 8.6%
Table 4. Spring-back upenmenW results
Value in each cell is the mean value of 16 samples; whole values are the mean of 10 samples.
Sample Location
Top Edge Top Centre Core Edge Core Centre Bottom Edge Bottom Centre
See Appenâix D for correlation coefficient and variance anaiysis.
Mill A Mill B Mill C Mill D Experimentai SJP
26.2% 17.5% 32.6% 17.00h 4.5% 24.W 17.5% 12.2% 27.7% 17.8% 13.8% 12.5% 5.1% 10.8% 17.9% 14.3% 5.8% 8.8%
18.6% 16.00h 24.7% 13.6%
17.3% 25.4% 11.0?? 22.8%
TOP
Core
Bottom
Tabk 5. Average meühg bcbavkrr o f s t m m ~ o a pi#red paneis.
I
Value in each ceIl is the mean o f d samples fi0111 different W.
See Appendix D for correlation coefficient and variance analys!&.
SIP Samp1es only
H Top € d g e O T op Centre O Core Edge Core Centre 8otkom Edge Q Bottom Centre Whole
WtY Thickness Swellmg Sp~jng-back w m 3 (St&v)
(S*)
Figure 3. Sprhigbadr b i a y r and m~nib1Ct\Yer
SIP
4.3 Discussion
Figure 4 graphicaiIy pnsents the average panei demity data. Most samples obtained h m
the edge region of the panels are slightly denser than centre region samples. AU HP and SIP
samples exhiôited a predominantly J-shaped daisity distriiution, where the &es are
dawr than the core hyer (density decreases from top to bottom to me). in general, the
laya deosity and whole pmd Qnsity of the SIP panels are higher than HP panels.
AU surface laya densities are higher than the density of whole sample, wMe the core laya
daisity is lower than the whole sample density.
Figure 4. Demlty prrllk by hyer and moiiufoe2iwr
A 6 C O Panel M mufacturer
1
i Top 6dge a Top Centre i Cae Edge Pi Car a n t r e
4.32 DeosMy, TMckness Sliall aud Spring Back
Table 1 to Table 5 and figures 2-5 presents data on the thickness swelling and spmig-back
pdmnance of each mdcturer's panels by layer. Overd, the &ta shows that although
the SIP Iaya samples were denser than HP samples, the layer thickness sweiiing of the SIP
panels were lower t h HP samples. The spring back of SIP samples were lowa as weU
Data fiom Table 3 and Table 5 (and Figure 2 and Figun 3) show that the wble SiP spmple
swelled 17.0% while the whole HP sarnples swded 20.9%. The spring-back of the SIP
samples was 8.6% compared to 14.1% for the HP samples. nie SIP amples & i e d
18.6% reduction in thiclatess swell and a 39.h reduction in sprkig back compared to the HP
samples.
Average of individuai layer to whole sample cornparison (top to whole, con to whole,
bottom to whole) Table 3 and Table 5 show that the average thicbess swell of the top and
bottom layers of HP samples are 67?h and 29?% bigha than the whole semple, respectively.
The average spring-back of the top and bottom layers were 56% and 27% hi* than the
whole sample. The core layer values were similar to the whole values. In gaierai, HP OSB
surface layers swells and s p ~ g back more than the whole samples while the are exhibits
similar vaiues,
The thickness swell of SIP sarnples was diffaent. Only the boaom layer was much higher
than the whole @y 88%), while the top layer (17?h) was nearly identid to whole values of
16.96%. The core layer had the lowest sweiling, l7?h lower than the whole. The spring
back of SIP sampies indicated that bottom had the highest value, followed by core, whole
and the top layer exhibited lowest spring back.
4.3.4 Cornparison %y Layer
Tables 2 and 3 indicated that the s u c f i layers of the HP and SIP sarnples exhibited 1.3 to
1.8 times higher swelhg and spring-back than the con layas nie trend is that top swells
the most foilowed by bottom then the con rwlting in a J-shaped swelling distribution
(top>bottom>çon). This means that most of the built-in compressive stress or potential
energy (as a result of mat consolidation) are stored in the surfiice layas and released in the
fonn of thickness swell and spnng back. The top and bottom laya also on average show
twice as much spring back as the core, regardes of the press type.
SIP samples also followed the same J-shape distribution. However, the bottom showed the
most spdg back, foilowed by top, and lastly the core layer.
4.3.5 Cornparison of Ceabc Region to Edge Region (HP muples oniy)
Figure 2 and 3 showed that most of the top layas fiom the edge region had higher thickntss
swell and spring-back then f?om the centre. The edge region bottom and core layers
exhibiteci less thickness meIl tban h m the centre region ofthe panel.
Ail the centre region core sbowed higher spring-back tban the edge region. In general, some
panel swelling and spring badc values were d o n n regardless of sampling location while
other p d behaviour was location dependent.
4.3.6 Cornlition between Density and Thichus Swelling and Spring Bick
Figure 5 and Figun 6 depid the relationship betwan the thickness swelling anci density of
the HP and SIP panels respectively. The HP panels showed an overall average correlation
d c i e n t of 0.78, hdicating that density and layer thickness swelling are positively
associated. Approximately 6 1.3% of the o b s e d variation in thickness swelling is due to
density.
Table 6 to Table 8 present the correlation coefficients between density, tbickness swelling,
and spring-back by layer. Each value is the mean of 16 samples. The label "Ae" represents
the mean value of the panel samples obtained fiom the edge location of mi11 A, while "Ac"
represents samples fiom the centre location of mil1 A panels. Some of the denser outer
d a c e s are only loosely clustered (low layer correlation) indicating either great natural
variation in these layer's swelling behaviour or that density is only one of many faors at
play. Of the layas, the core layer is most saoa@y influenced by density (largest deasity to
spring back correlation). The comesponding probabilities that detamine the acceptana of a
linear relationship of each table is presented in Appendix. In g a i d , al1 the sweIIing
behaviom of HP ssmples revealed strong linear relationship (refîected by high probability),
while SIP samples showed the reverse. S p ~ g back of con layers wae linesrly corrdated
to density and showed high pvalues among both the HP and SIP samples.
Table 7. Cornlition caCTcitnt betweca dewity and spring-bick by Iayet
Sample 1 Ae Ac Be Bc Ce Cc De Dc SIP
Table 6. Cornlitloi cacMcient between demity md thicicnus swtlüng by hyer
Sample TOP Core Bottom
Ae Ac Be Bc Ce Cc De Dc SIP 0.837 0.603 0.248 0.115 0.167 0.171 0.514 0.513 4.113 0.500 0.204 0.778 0.689 0.411 0.304 0.376 0.699 -0.125 0.499 4.150 0.209 0.212 0.766 0.277 0.289 0.308 0.203
TOP Core Bottom
See Appendix D for cordation coefficient analysis for tables 6 to table 8.
0.499 0.563 0.350 -0.204 0.167 0.226 0.152 0.3 11 -0.064 0.687 0.703 0.753 0.539 0.411 0.619 0.682 0.473 0.537 0.494 0.088 -0.203 -0.093 0.766 0.227 0.191 0.603 0.371
Table 8. Correlation cafficicnt ôetween thicknus swdling and sprinpbrck by Lyer
Sample
TOP Core Bottom
Ae Ac Be Bc Ce Cc De Dc SIP 0.259 0.810 0.650 -0.307 0.620 0.583 0.453 0.788 0.553 0.864 0.207 0.857 0.545 0.706 0.699 0,765 0.773 4.152 0.740 0.376 0.212 0.255 0.706 0.634 0.765 0.656 0.175
Figure 5. Tbiclmas swtüing vs. dmsity for hot-pmsed prndr
The statisticai analysis in (presented in Appendix D) inâicated that the z-due was 13.98.
This amesponds to a 100036 confidence level that thae is a linear rdationship bn\keen the
thickness swell and density.
Figure 6. Thicknaa sweiiing va density for stmin-injection-ptcsscd pan&
60 -.
Top Layer 40 Core Layer
A Bottom Layer
30 - Linear (Seriets7)
The SIP panel showed a correlation 0.217 (for aiî layers combined) and the probability of
75% chance tbat the layer thickness swelling behaves linearly with the density. This
indicaîes that layer thickness swelling is largely dependent on density. A linear regression
line shows only 4 % of the obsemed variation in thickness swelling can be explained by
density. M e n cornparing o v d dope of HP and SIP amples, the HP showed greater
change in thickness swell with density than SIP. This shows that HP is more stn,ngîy
amciated with density.
Figure 7 and Figure 8 illustrate the nlationship between hyer spcing back and density. The
HP samples show a positive correlation of 0.60, which indiaes that density and layer
spring badc are strongiy assaciated. A confidence level of nearly 1 W ? nllects that there is
a stmng dependency on density. The hear regression iine showed that 36% of the observeci
variation in spring back is due to density. The SIP panel showed a weaker correlation than
the HP samples. A correlation of 0.29 indicates tbat layer swelling stress showed weak
linear association with density. The linear regression line explains only 8% of the obsaved
variation in spring back over density. However, the probability test revealed thet there is
88% c h c e that a linear reletionship exists in the SIP samples.
Figure 7. Sp~g-back vs. denrity for hot-presscd paneh
60 -
6 0 Top Lapr 4 0 a Con Layer
Figure 8. Sp~g-back va density in SIP pan&
Dm* (k01ni3)
4.4 Analysis of Correlation Coefïicient and Variance
Stgtistical analysis of thickness swelling and spring back data, including standard deviatl
test statistics, and confidence Ievelq are presented in Appendix D. The cornparison ofthe
edge and centre swelling behaviours against the mean properties of al1 samples produced
widely varying results. The TS and SB of the top layas were ahost arfeinly affecteci by
sample location @mer than 95% confidence levels), while density seemed les dependent
on location (kss thsn 3W confidence levels). Confidence levels of the core and bottom
layers were nesrly identical. VMations in density between edge and centre were 88% to 99% signifiant, variations in TS were less than 7@!% signifiant, and variritions in SB were
roughly 50036 signifiant. It appears that the swelling behaviours to the top layas an
signincantiy affeaed by their position, ahhough density is not. Just the opposite cra be srid
of the core and bottom layen, theh swelling behaviow does not vary signincrmly with
position but thir densities do.
Cornparhg the top, core and bottom layas reveals that nearly al1 properties are significantly
infiuenccd by vertical position. Confidence levels in the variatioas in the TS and SB of al1
layers are al1 greater than 97%. Merences in the top and core layer densities are also more
t&an W ! significant. However, the bottom layer is only 24% signifiant, implying tbat the
Merences in density are not statisticaiiy significant. This low confidence level is ükely
because of the bottom layer densities are close to the population mean and have a large
standard deviation. Since the top and core layers are significantly diffaence than the mean,
i.e. the bottom layer, we can infer that the bonom layer is also sign8cantiy different fiom
the top and con. Thus it can be concluded that both deasity and swelling behaviour are
heavily innuenced by the vertical density profile. This evidence confirms the J-shaped
distribution profile seen in the data.
Analysis of the correlation d c i e n t s between density, thickness swelling and spring back
by layer and location of panels from diffaent OSB manufhctwers varied wideiy. Most
confidence levels an greater than 8W, aithough some signincance levels are as low as 14%
(from the SIP panel). The four manufmer's HP panels generaily showed strong
correlation and high significance levels bawan propeities, although some low significance
levels appeared as well. It is difncult to draw any solid conclusions fiom the lower-
significance levels, and additional panels would have to be testeci to meLe any meaninBful
statments. However, the low correlation coefficients my be due to l d s e d phenornenon
in the test panel and not indicative of the whole panel's behaviour.
The HP and SIP wrrelation coefiicients reveaied that aü the HP simples showed nearly
1000/o confidence that thm is a linear relationship which did not bappen by chance alone.
The correlation of SIP samples showed lower confidence levels for the correlation
coetncients, baween 75% and 89%. The HP test staîistics are greater than 14, wbich are
v a y large. There is ovenuhelming evidence of a strwg linear relationship between density
and TS and SB. The SIP test statistics are ali less than 2, wlicating much less support of a
linear reiaîionship. Thus, not oniy is TS and SB in SIP less affecteci by density than HP, but
tbae is also si@cantiy l a s support for any linear reiationship in SIP at ail.
Finally, the coritrol samples of each panel mawf-er showed moderate cunfidence levels
(al1 between 68% and Wh). Thus each whole panel shows signincant diaetences with
respect to the mean density and swelling behaviour. However, the popdation standard
deviaîions are fairly large and the population is Uely composed of five tightly clustered
sub-populations. SpeciGcally, the panel densities are clustaed around either 670kg/m3 or
605 kgW, the TS mund 16% or 24% and the SB arouml either 1W or 17%.
Unfortunately, there are no obvious trends between derisity and swelling behaviours. Thus
the whole panel sample's physical properties are much las homogenous then those if their
cornpanent layers.
5. PART 2: SWELLING STRESS OF OSB
This expairnent memues the stress exerted by the individuai OSB layers as they d
dunng moisture iexposufe. The samples are selected using the same panel samples and layer
sectionhg techniques as presented in section 4.1.1. The results are presented and briefly
discussed.
5.1 Materiab and Methods
. . The apparatus for measuring sweiling stress consisteci of a mechmical restrainibg system,
five elect10nic load cells, and a data acquisition cornputer system. The restraining
equipment wnsisted of stainless stal blocks, five stainless steel "S-beam load cells (2000
Ib. capacity each), and a Tinius Olsen electricallycontrolled mechanical press (Figure 9).
The press was used to applyiag the bias force to the samples. This bias force also held the
"Sn berun load celis in place. The OSB samples were amnged in a shallow aluminium pan.
Stainless steel blocks were then placed on top of each specimen. The pan (which sat on top
of a large, smooth iron block) and the steei block acted as press platais. These platens
e n m tbat the force applied to the samples was completely uniform. The "S' beam load
cells wae placed on top of the sted blocks, and a flat-headed bolt and nut assembly was
loosely fitted to the top of each load cell. The nut-and-ôolt assembly was used to finetune
the bias force on each sample before beginning the -ment. By monitoring the load ceil
reridings, the bias force on each sample could be adjusteci using the scnw assemblies. A
bias force of20 lbs. was used with ail sarnples. The experiment was starteci by triggerin8
the data acquisition qstem, and then filling the aluminium pan with water. The testing
apparatus wuld accommodate up to five OS% samples at a the. Each OSB sample was ait
into a 1" by 1" blodr. The OSB samples were then cut into three layer specimens using the
sepadon procedure describecl previously. Tûe swelling stress of each specimen was then
rntaaured.
Figrnu 9. Swcaing stress mersurement apparatus
+ metal block + load celi
Load Cell
Panel
Aluminum Pan
The enagy r e f d by the samples upon swelling could be useâ to either change the
sample's thickness or increase the stress applied against the load ceii. The press had a
maximum capacity of s e v d tons. The load cells' maximum vertical deflection under a
907kg (2ûûûlb) load was less than 0.254mrn (0.0 1"). However, the bias force applieû to the
samples was ody 9.07kg (20 lbs.). The entire mechanicd system was strong enough to
withstand s e v d tons with out mechanicaily defonning. This, the panel semples wcrc
mechanically prevented from chmghg thickness. Refb to Figure 10. Practicaily ail of the
lateral hygroscopic expansion energy of the specimens was used to incfease the force
appîid to the load ceiis. The 9.07kg (20 Ibs.) bias force was chosai to stabilise the materiai,
and doej not exceed the mshing strength of w d . Each "Sn beam load cell containeci
electrical sensors which were in turn ~ ~ e c t e d to a multicbannel data acquisition system.
The system measund ad recordeci the sweîling force at 10 minute intervals. The
experiments were conducted for ôetween 24 to 168 hours.
48
Figure 10. Typid griph of tbicknea displacement vs. pressing fornt
stress
The results of the swelling stress measurements are presented in Table 9, and graphed in
Figun 11.
Table 9. Snlllag Stress nmsuilltmenb
TOP W e Top Centre Con Edge Core Centre Bottom Edge Bottom Centre
Sample Location
Whole 1
MiUA Mill B Mill C Mill D AW- Experimental (MPa) @Pa) (MPa) @Pa) (MP~) SIP Panel (MPa)
B C Panel M anuf'turer
0
5.3 Discussion
5.3.1 Whole SMple Cornpiriion
From table 9, sweiling stress was quite similar between the two types of OSB. For HP
samples, all top layers have hi* swelîing stress than whok samples, while most ofthe
core and bottom layers are lowa. In contrast, all SIP layers showed l es swelling stress than
the whole samples.
For HP samples (average column), the sweUing stress of top layer were higher than whole
sample @y 16%). The bonam and the core w a e 0.5% and 11% lower than whole samples.
he top layer exated more swelling stress than whole samples.
Table 9 indiateci that for HP amples, mfbces showed much higher swelling stress t h the
core. The top meus the most, followed by bottom and then the core. Al1 the HP layer
samples foiiowed a J-shapeû swelling stress distribution, w h m the con stress is lower than
either the top or bottom This means that most ofthe built-in compressive stress or potential
enagy (as a result of mat consolidation) is stored in the surfàce layers.
The SIP samples showed greatest sweiling pressure in the bottom layer, followed by core,
and last the top layer. Then was no observecl J-shaped pattern to the SIP sample swelling
stress.
5 Cornparison of Centre to Edge region of panel HP umple oaly
Most of the edge region samples exhibiteci higher swellhg mess than the centre samples.
53.4 Cornlition berneen Dcnsity and Tbichcr, Swtlliag and Spring Back
Table 10 provides the correlation coefficients for sweiiiag stress to density in HP and SIP
samples. Figure 12 and Figure 13 plot the sweIIing stress @si density by layer for the HP
and SlP samples respectively. The HP samples shows a positive correlation of 0.725 over
the whole panel, which indiates that density and layer swelling stress are strongîy
associated. The linear regression he explains 52.6 % of the obsaved vpiation in swelling
pressun by density. SIP sbowed a weaker whole correllition of0.093, indichg that iayer
swelling pressure is nearly independent of density. The linear regression line explains oniy
0.8% of the obsaved variation in sweiiing pressun is contrdled by density.
The HP sampies exhibits a much stronger corndation and regression tban SIP samples.
Table 10. Comhtion bctween density and swdaag strers by hyer
Con laye 1 0.696 0.788
Panel Type Sample Location Top layer
HP* SIP Correlation Coefficient Correlation Cdcient
0.525 0.267
*mm of al1 HP samples.
S a Appendix D for correlation coefficient anaiysis
Bottom layer Mole
Figure 12. Deasity vs. Swding Stress in Hot Rcsseâ Pmds
O. 706 0.543 0.725 0.093
A gmeraiised swelling pressure vs. t h e relationship is plotted representing an union of four
types of cwes: exponential-Uic1e8~e, concave, linear, and convex (Figure 14). Both the HP
and SIP samples foilowed this trend. The swelling pressure curve can be divided into the
fouowhg stages:
0.7 - 0.6
Top kyer m i C O C ~ I ~ ~ -
(1) Rapid increase of swelling pressure: At initial MC of 8- 12% (beiow fibre satwation
point), an exposure to moistun Uiduces rapid moisture uptake. Densified wood substrates
adsorb water and initiate hygroexpansion as the hydrogen bond between the hydroxyl
groups of wood fibres break. Mona-Iayer water adsorption is fomed by the m n g
hydrogen-oxygen fora of amaction. This is refiected in rapid increase in swelling pressure
and this segment takes its dect dunDg the first 8-12 hours dependhg on thickneu. When
mrption sites are completely occupied, multi4ayer dominates.
(2) huease at a decreasing rate: The climax of rapid increase of swelling pressure
continues until the available sites for M e r sorption bemme scarce and the number of
watcx moldes attached exceeds six layers. This stage is accomponied by a graduai
reduction in amaction force which is reflected in a decteased rate of sorption.
(3) Plateau: At this segment, stress release reaches the peak between 20-27 hours
(Merence of 2 psi. or 0.0 13 MPa). Core layen release maximum sweiling pressure before
20 hours of soalcing., wbile surnlce layers require a longer exposute. No comiation is
evident between rate of sweliing pressure release and the dauity. Maximum pressure
persist for 8 hom until internai support fails to withstaad e x t d restrainin . .
8 Pr-e (201bs of stabilisiag metai blocks).
(4) Deche: A decline in sweliing pressure dominates the latter part of the cycle. Wate~ up-
take is by capillasy filling ofceil lumen exertiag Wle swelling pressure.
The putpose of this study was to aamine the effect of density on their sweliing behaviour,
not to ranL commercial OsB. However, an informal rank system was used to compare the
different panel's pafommce. Oniy the HP samples wae includeâ, because of their
obviously infaior swelling behaviour. The purpose of identifyng the %orst" panels was to
select the panel most likely to show improvement fiom pst-manufiactuhg heat treatment.
The rank system is based on the overall panel pedormance. Each average layer b r n
diérent location of the same panel is assessed based on the t h swehg behaviom. The
favoured characteristics are lower swelling behaviour. The layer with highest swelling
values receives lowest score while the layers with lower velues gets assigneci higher score.
At the ed, all scores are oummed up and the one with lowest score reflects wom
performance. M e r to Table 11, Table 12, and Table 13 for the panel scores by thickness
stress, spring-back, and swelling stress. The panel âom rnanuf&~tu~er "A" received the
lowest score in every category representing worst pafommce and will be used for the pst-
rnanufacturing heat oeatment expriment (section 6).
Tabk 11. Rank of pmd manufactunrs by thickna, swtUing
Sarnple Location 1 Mi11 A Mill B Mill C Mill D
Core Edge Core Centre Bottom Edge Bottom Centre
Top Edge Top Ceme
Score Rank
4 7 I 16 5 10 20 2
1
Corresponds to table 1.
Table 12. Rank of pana maaufactunn by sprinpback
Core Edge 1 18 20
Sample Location Top Edge
Mill A Mill B Mill C Mill D 1 3 11 1 13
Rank 1 *q** 3 2 1
Battom Centre mole Score
Corresponds to table 2.
16 5 23 7 8 14 22 27
64 91 117 120
Cornspomls to Table 9.
Table 13. Rank of prnd utanufactaren by nrdüng d m
5.4 AnalysW of Correlation Coefficient and Variance
Sample Location Top Edge Top Centre Con Edge Core Centre Bottom Edge Bottom Centre Whole Score Rank
Sta3istical analysis of the sweiling stress data is presented in Appendix D. Analysis of the
eâge and centre swelling stress behaviour revealed that both deasity and swelling stress are
significantly affeaed by sampling location. The sigaificana levels by sample location (edge
to centre) of density versw swelling stress are very high. Density-significance confidence
levels are greater than 98% and strongly suggest that there are statistically important density
diffaences between the panel edge and centre. Swelîing stress confidence levels are only
slightly lower, ranging between 83% and 990% Thus, the statisticai evidence implies that
dwerences W e e n the edge and centre swelling stress are also caused by physicai eEéczs,
and not by -dom chance. The standard deviations of the sample populations are lowest in
the cors layen and generally highest in the top layer, although the confidences levels are
xmgid ly highest in the bottom loyer. It was previously obsexveû that the centre top
samples tend to release mon stress than the edge top samples, although the Merence is
small. The opposite & i is seen in the core and bottom layers. Ahhough the mean
dEerences in swelling stress between a given layer's centre and edge samples is only
Mill A Mill B Mill C Mill D 13 3 2 7 4 8 1 5 22 28 20 14 19 26 27 25 23 14 16 9 10 24 18 21 6 11 17 12 87 114 101 93
**4** 1 2 3
roughly 4%, statistical analysis suggests that these s m d diffennces are signifiant.
Comparing the comlation d c i e n t s of the top, are , and bottom layers revds much the
same story. Confidence levels ofthe core and bottom layers are greater than Wh, stmngly
bdicatiiig a linear relationship between density and swelling stress. The top laya was only
71% signifiant, implying density lus a significant, but weaker, &éa on swelling stress.
Last, the He aud SIP sweliing stress correlation are quite dEerent The comlation
coefficient betwœn daisity and sweiiing stress in HP panels indicated a strong lineu
relatioaship baween swelling stress and density. Hypothesis testing revealed a nearly lW?
confidence level that this linear relationship exists. Thus, we confidently conclude that
density and sweliing stress are lineariy related. This conclusion confinns other works.
However, the confidence level of a iinear relationship between density and sweiling stress in
SIP samples was only 38%. This suggests that the effeds of density on swelling stress in
SE panels are largely irrelevant. In wnclusion, although the SIP and HP sample swelling
stresses wae rougbiy equal, the influence ofdensity on each panel type is much différent.
6. PART 3: POST-MANUFACTURLNG HEAT TREATMENT .
Al1 commacial panels used in this research were manufactured ushg industriai or
"primary" production processes. The ps t heat treatment proass is wnsidered a
"secondary" process* The heaî treatment used in this research was a contact treament
employed by Hsu (1986). hiring this heat treatment process, OSB panels are reheated under
low pressure. This process is designed to reduce thickness swell, and spring-back, and
welling stress by facilitating the release of resiciual stresses.
6.1 Matenais and Methods
The h o t - p d panels âom four different manufhctum were rated using the rank technique
presented in section 5.3.6. The panel from mamû- A displayed the poorest swelling
pedormance and will be expasai to the post-manufactwing heat treatment process. A single
panel from rnanufhwer A was ait into three 38cm by 3&m (1 5" by 15") subpanels. One
panel was used as a control, and the other two wae exposed to the heat treatment processrOceSS
After cutting, the subpanels to be tested were then fitted to the platens of a Wabash
Hydrwlic Ress. The press platens were heated to 240°C and set to exert 0.24 MPa of
pressure on the subpanels. Each panel was pressed for either 7.5 minutes or 15 minutes.
The pressing conditions were formulated basexi on a patent document by Hsu (1986). and
were nlatively mild. Post heat-treated sample panels were not hot-stacked. It was assumed
thst the majority of the postaaing was completed during primary prdubion. After
pressing, the subpanels were conditioned et m m temperature and humidity for 24 hours.
W h subpanel was then ait into 25.4 mm by 25.4 mm (1" by 1") testing specimens. Each
specimen was divided into three layen, using the proceâure described in section 4.1.1.
The swelling behrviour ofeach specimen was measured. Spedïcally, the mount of
thickness swelling, spring back, and swelling stress were measurd using the techniques
presented in earlier sections.
The resuhs of the thickness swelling measurements are presented in Table 14, and graphad
in Figure 15.
Table 14. Post b a t treatment thicbncss swtll data
Untrea!ed 7.5 minutes 15 minutes Trutmants
Tiiickness Sweii (W
Untreated 7.5 minutes 15 minutes
Figure 15. Post h u t treatmut effect on tbiclmcw rndl
40.0
The results of the spring-back mearnuemeas are presented in Table 15, and graphed in
Figure 16.
Top Layer Core Layer Bottom Layer Whole
34.3% 27.2 % 28.5% N/A 23 9% 15.9% 18.4% 22.1% 9.3% 1 1.2% 12.4% 8.1%
35.0 -
Figure 16. Post beat trtiitment eflects on spring-back
Table 15. Post heat miitment spnng-back data
Untraated 7.5 minutes 15 minutes Tmtmmts
Spring-back Untreat ed
7.5 minutes 15 minutes
The r d t s of the sweiling stress measurements are presented in Table 16, and grapheâ in
Figure 17.
Top Layer Core Layer Bottom Layer Whole 26.2% 17.8% 18.% N/A 18.9% 9.4% 10.m 16.W 2.1% 3 2% 2.4% 2.W
Table 16. Post heat treatment d i n g stress data
SweNing Stnss va
Untreated 7.5 minutes 15 minutes
Top Layer Core Loyer Bottom Layer Whole
0.43 0.32 0.37 0.38 0.40 0.25 0.29 OS0 0.25 0.23 0.23 0-40
Figure 17. Port heat treatPent sndüag s t r a s
0.60
Untreated 7.5 minutes Trwtmmts
6.3 Discussion
Top Wge Core Edge
rn Bottom Edge h Whde
15 minutes
A compressive force of 0.24 MPa was applied during post rnanufacniring heat treatment and
this force did not induce any additional panel compaction. Sina no additionai potentid
energy was introâuced to the panels the swelling stress is expected to be the seme or less
than non-pst heat treated OSB. The select4 pressing force should have had no effect on
the panel's thichess swelling behaviour. Aay changes in swelling behaviour wae oniy a
fiinction of temperature and the.
6.3.1 hyet Tbickness swell
Table 14 presented that al1 samples aeated for 15-minutes exhibited the least TS while the
untreated samples showed the greatest TS. Specifically, the 15 minute top, con and bottom
layers showed a 72%, 55% and 56% reduction relative to the comsponding untreated layen.
Similarly, the 7.5 miaute top, con and bottom layas showed a 300/4 42% and 35%
rduction in thickness sweliing respectively.
For the 15 minute samples, laya thickness swell does not foiiow the expeded J-shsped
disaibution. The bottom layer swells the most, followed by con and thai the top layer. The
7.5 and untreated samples follows a J-shaped swelling behaviout.
6.3.2 h y e r Spnag Back
Table 15 presented a similar trend in SB. The 15-minute tneted samples showed the most
reduction in SB by 91% in the top, 81% in the a r e and 87% in the bottom when compand
ta the untreated samples. The 7.5 minute top, core and bottom layas showed a 27 %, 47 %
and 46 % reduetion in spring back.
For 15 minute samples, spring-back does not follow J-shaped distribution. The core iayers
spriag back the most, followed by bottom and top. Both the 7.5 and non-treated samples
followed a J-shape spring-back distribution where the top showed the most spring-back,
foilowed by bottom, then core.
Table 16 shows that the sample tieated for IS minutes ahibited a 41% sweiiing stress
duction in the top, 28% in the core, and 37% in the bottom layer cornparrd to umreated
samples. Ofthe 7.5 minute sarnpleq only the core layer showed a 21% reduction in
swelling stress.
For 15 minute samples, the top layer released most of mess while core and bottom laysrs
are airnoat equal. Both the 7.5 and non-treated samples follows a J-shape spring back
distribution .
6.3.4 Cornparison of h y m d TS, SB, and SS to whok srimple
Table 17 compares layer swelling values to whole sample of the same treatment. TI"
repfcsents swelling d u e s of t h par&icular layer is higher than the whole, while '2"
represent sweiling vaiues of the particular layer is lower.
Table 17. Port b a t trmtment a i c h e s mell data (corresponds to Table 14.)
Thickness Swell 1 Top Layer Core Lay= Bottom Layer Whole
AU layers TS of 15 minute treaûnent samples are higher than whole values. For 7.5 minute
treatment sarnples, oniy the top layers are higher in TS while other layers are lower. Same
behrviour trend is found in the SB values presented in Table 18.
Table 18. Post heat treatment sprlng-back data(comsponds to Table 15.)
As seen in Table 19, al1 treated layen exhibit lower SS values than the whole values.
s@ing-bick 7.5 minutes 15 minutes
Table 19. Post heat treatment swdling stress data (corresponds to Table 16.)
Top Layer Core Layer Bottom Layer Whole H 18.1% L 41.% L 37.5% 16.W H 5.m H 60.0% H 20.W 2.0%
6.4 Analysis of Correlation Coefïicient and Variance
Sweiling Stress W a )
7.5 minutes 15 minutes
Statistical analysis of the PMIFT data via standard deviation, test statistics, and confidence
lmls are presented in Appendix D. The density test statistics of all samples are almost
always les than one, and the mean is roughly 0.5. Tbese srnail test statistics imply thas
density is not significantly altered by the treatment process. This is consistent with
prediction, which re850ned that the low PMHT pressing force would not appreciably
in- panel density.
Top Layer Core Layer Bottom Layer Mole .
L 20.00/a L 50.W L 42.00h O. 50 L 37.5% L 42.5% L 42.5% 0.40
The test statistics of the changes in TS, SB, and SS are al1 large (bnween 1 .S and 13). This
impiies thst the changes in swelling behaviour are not caused by mdom flucniations and an statisticaily very signincant. Spccindy, thickness swelling and spring back confidence
leveis are d gteater than %%, and swelling stress confidence levels are greater than 85%.
The test thidawss swelling and s p ~ g back test statistics of the 15 minute amples arc
generally a -or of two targer than the 7.5 minute sarnples. Thus, longer P m & m e n t
times produce changes in TS and SB which are more statistically predictable and consistent.
In contras&, the swelling stress test statistics an nearly constant in magnitude. Not only is
swelling stress g e n d y unchaaged by PMHT (the two treaîments dEered by less than 1.6
times), but we can infer that the statistical distribution of swelling stress is also d ê c t e d .
7. SUMMARY OF RESULTS
In generai, the sweliing behaviour of the HP and SIP OSB samples can be classifieci imo the
folîowing trends listed in the swnm~ry table.
Density
Correlation
Coenicien t
Sample location
Edge : Centre
Layer : Whole
Proportional to
density
Sîrong
@ density
Sample dependent
Surfaces > Whole
Core Whole
SIP
Independent of density
Weak
$ plasticisation
NA
Bottom > Whole
Top, Core < Whole
7.1 J-Shaped Distribution
. The vertical density distributions of the HP samples exhibited a preâominantly J-shaped
density distribution. That is, the d k e s are denser than the core layer (descendhg fiom
top to boaom to are). The SIP samples showad a J-shaped demity distribution having
greater density diflerence between the Surchce and core densities than the HP samples. The
SXP samples were expected to have a more homogeneous density distribution. The ody
atplanation for this discrepancy is that the SIP panel was producad in a laboratory, aad as
such would show have greater variation in pressing parameters relative other SIP panels.
7.1.2 Layer to Layer Sweiiing Bebaviour
Aimost ail panel types' layer to layer behaviour showed a J-shaped swelling dismbution.
The suffie layers of the HP and SIP samples reveal higher swefling, spring-back and
swelling stress thaa the core layers. For the HP samples, the top sweb the most, followed
by bottom, while the con sweUed the least (hence, reverseâ-J-shape). The bottom layer of
the SIP panel swelled the most, followed by the top and con layers. The spring badc and
swelling stress of the SIP panels did not follow the distribution. The sweL1ing stress was
greatest in the bonam layer, followed by the core and top layas.
7.2 Comiation to Density
The HP OSB panels showed bigh overall correlation to density. Density and layer thicLaess
swelhg are positively associaîed and most of the thickness swelling is attributable to
density. The SIP samples showed negligible correlation, rdecting that laye thickness
swelling is largely independent ofdensity. The swelling propaties of the denser outer
surfàces of HP samples are loosdy dependent on density, indicating eitha great naairal
variation in these layer's swelling behaviour or that density is only one of many firctors at
pîay. For density to spring back correlation, the con layer is most strongly influencexi by
dmsity. Ali layers swelling stress is strongly correlated to density.
7.3 Edge to Centre: Edge gmter than Centre
Most laye samples obtaiaed fiom the panel edge regions are siightly de- than their
counterparts in the centre regions. There was great variation in the swelling behaviour
baw#n the centre and edge regions of diff'erent m8n\lfactuter's panels. Some panels
showed more sweliing and spring-back in the edge, while others swelled more in the cena.
Still others showed w Merence between the two regions. The edge regions gendly
showed slightly more swelling stress than the centre regioas. In general, some panel
swclling and spring-back values were d o m regardless of the sample location while other
panel promes varied 4th location. Almost al1 the centre core layer have higher thickness
me11 and spring back than the edge con layas. Swelling stress is higher in the edge con
thrur the centre core.
7.4 Individual Layer Behaviour Relative to Whole Panel
The thicbiess swelling and spring-back of the HP surfâce layers were higher than the whole
samples. The core thickness swelling and spring-back behaviour was very similar to thas of
the whole panel sample. The bottom layer of the SIP panels swelled more thau the whole
panel sample, while the top sweîled about the same and the core swelied slightly less. The
bottom layer of the SIP panels alw showed the most spring-back than the whole panel, as
did the core although to a lesser degree. The top layer showed much less spring-bacl than
the whole panel.
The swelling stress was quite similar ôetween the HP and SIP paaels. AU HP top layers had
higher swelling stress than whole samples, while most of the core and bottom layers were
lower. The SIP samples in contrast showed that aii layer swelling stnsses are lower than
whole samples.
The SIP laya density a d whole panel density are pater than HP panels. The SIP samples
exhibited las thickness swell and spring back compared to the HP samples. The SIP pane1
samples do na support the theory that bigher density conesponds to higher total thickness
swelîing, while the HI? samples does. The "low swelling with hi@ daisity" behaviour of
SIP samples must be caused by fktors other than density.
7.6 PMHT: Tmtment Reduces TS and SB
In general, r d t s of all tested samples (layered or whok) indicated tbat samples treated for
15 minutes showed signiricant reduction in al1 sweiling behaviours, while sarnples p r d
for 7.5 minutes exhibited less reduction. The untreated samples showed poorer sweiling
bebaviour thsn either of the treated samples. The swelllng stress of kat-treated samples
was either unchanged or slightly nduced relative to the untreated sample. The J-shape
swelling distribution was only retained âom unveated to 7.5 minute treatmentq not in the
15 minute tfeatment.
8. GENERAL DISCUSSION
8.1 Variations in ExperimentaI Data
8.11 Flrke Distribution
A curious effeçt was observed once the acperimental daîa was plotîed. The data fkom
samples within a simple category (e.g. core iayer of edge ara of panel C) were scattaed
when plotîed against density. This variation is evident in the scattered distributions in the
plots of swelling behaviwr vasus density in Part 1 and Part 2, and scattering wes
particularly severe in the top and bottom layers. This behaviour is particularly strange since
the samples were physically adjacent to each other in the panel. The question was how
could samples so near each other have such varying properties? At first glance this variation
mi@ be amibuteci to experimental error. In fact, wide variation in the swelling behaviour
of samples in close prownity was expecteû, and has even been indirectly preâicted. The
explanation lies in the fiake distribution, wûich is deterxnined during mat formiag.
Lu et al. (1998) studied the effects of non-unifonn wood dement (strand) average in wood-
fiakt composite mat structures. Through cornputa simulation, they modelled the variation
in density aaoss OSB panel due to the natural variation in strand sise, shape, orientation and
l-tion. T'heu modtl incorporated these irregularities and generated charts of density over
the panel surface. As the OSB mat is built up, strands overlap randornly and the amount of
wood matter tluough a random cross-section of the panel is alw random. This results in
variation in panel density ove its area. After râhng to Figure 18, the effects ofstrand
variation on density becorne evident. Note thet deasity varies g r d y and rapidly across the
panel d k e . Density differences of more than 35W an fouad las than 25mm apart.
Thus, the density of adjacent panel samples can vary widely.
During pressing, the amount of wood matter in a given a m strongly determines that am's
swelling b e h a h . The entire OSB panel is pressed to the same thickness but arcas with
pater strsad concentration experience more stmses and compression. These de- areas
-ence more swelling stress end t h s main more stress, aü else behg equol. Thickness 69
sweUing, sprhg-back and swelliag stress are ali closely tied to the amount of stress stored in
the panel during pressing. Thus the wide variations in panel density between adjacent
samples should aiso create wide variation in panel swellhg behaviour between the same
samples. This is exactly what was obsewed in this research
The random strand distribution helps explain the sample to sample sweIiing variation, but
the wider variation in the top and bottom core layers have yet to be explained. The solution
to this problem lies in the thickness differences in the core and surface layer samples. The
core layers were roughly lOmm thick and the surfece layers wae each 4mm thick. The
obsmed sample density and swelling properties were the average behaviour across the
sample's thickness. The thicker the sample was, the mnger this averaging effect was.
Similarly, thinner somples should show more deviation in density and swelling behaviour
from the average. Thus, the thinner samples taken âom the top and bottom layers should
show more variation in density and swelling behaviour than the thicka are layer. Again,
the experimentai rmlts match this hypothesis.
There are other effects that can contribute to the variations in sample-to-sample panel
swelling behaviour, but the localiseci density mechanism clearly predicts the effects
observed in this work. Overall, localiseci density concentrations can explain much of the
variation in panel sample swdüng bebaviouf.
Figure 18. Demitg vs. panel location (fmm: Lu et ai, 1998)
81.2 Diflrerence in Swdling Stms o f OSB vs. Solid Wood
The swelling stresses measured in this shidy w a e nlatively low values compared to past
findings (Stamm, 1%4). This is expected and caa be explained by the following. Samples
in this study were compresseci ody in the verticai direction, perpendicular to the top and
bottom ditces. Readings were ody obtained from thickness sweliing, lateral displacement
and swelling stress were not meamed. The strands in OSB wen not resirained
mechanicaliy to sweU in the lateral direction. The duration of these experiments varied fkom
one to seven days compared to 270 days for Stamm's expaiment. Therefore, a lack of
attajnment of complete equilibrium may have OCCUI~T~~. Stamm's (l%4) experhents were
conduaed in the absence of adbesives, which would increase swelling pressure s k
i n t d mitraining effects of the resin are eliminated. M y , the sample density in this
expairnent was only half of Stamm's samples. Thus, amount of spring-back and hence,
sweiiing pressure is also expected to be lower.
8.2 Factors and Interactions
This section discusses any significant issues that have contributeci to swelling behaviour of
OSB. Figure 19 presents factors and their interactions that give rise to these issues.
Figure 19. Factors Interactions
1 Dgnimia of Stmm Flow
Steam is generated throughout the OSB panel duriag pressing as moisture in the tcsins and
wood vaporises. Steam migrates during compression dirougûout the pauel tranafening heat
and moime. In p d d a r , steam is fint generated in the Surface layers and mimes to the
con. nie panel edges are rarely sealed, and steam escapes out the edges during pressing.
Steam vapour rapidly moves fiom the surkces to the centre core, and mntually moves
fkom the p d antre con region to the edge a r e region ofthe panel. Thus, the edge eoie
region is exposed to more Seam longer than any other region. The edge core region
experiences higher levels of steam and thus greater plasticisation and more cornplete nsin
curing than the ceme mie layers.
Al1 OSB samples used in these experiments were bonded with phenol-fonnaldehyde (PF)
resins. A disadvantage of using PF resins is that the rapid s t em migration during mat
consolidation tends to dilute and wash out the resin, particularly in SIP OSB manufircture
(Geimer and Price, 1986; Walter, 1992; and Ho and Vinden, 1996). Resin is depleted in the
centre con regioa wbich results in weaker bonds. The resin removed fiom the centre a r e is
deposited in the edge samples and creates stronger bonding thae. As previously discussed,
the edge core region also experiences the longest heating and thus the resin is more
completely med. The combination of longer heating and the deposition of extra resin
nsults in greater bond s~ength in the core edge regions and correspondingly lower strength
in the centre core region. The resulted in a stronger, mon thorougbiy bonded edge con
layer.
AU OSB swelling behaviour me8sufed in this study is &mec! by bonding strength. When
the cell walis expand during swelling, compressive stresses are relessed and induce tension
between adjacent layers. When this tension can no longer be comtered by the bonding force,
layer sepamion begins. Thus, low bond strength results in a highu degree of thicknes
sweliing and spring-back* Suchsiand (1973) explaineci that s p ~ g back usuaily aaompanîcs
permanent strength loss via adhesive bond delamination. Fwthermore, aithough the
rdhesive bonds between strands and the diffaeat straad oneneiilioas of different layas in
OSB are an ecowrnical means of mechanically staôilising the panel, these same meaas ai=
facilitaie outof-press spring-back.
As previowly mentioned the dynamics of OSB pnssing resuits in a centre region that is
more w d y bonded than the edge region. The weaker centre region is more susceptible to
out-of-press spring back I irreversible release of mechanid stress (Zavala and
Humphrey, 1996). Upon press openiag, the panel inmeases thichiess u ~ i l the intanal strand
stress reduces and is countehalanced by the forces carrieci by the adhesive bonds. Howeva,
delamidon or blowing can occur if the bond *en@ is low (Geimer et al, 1993).
Delaminrition is particularly evident in the centre region due to the weaker bonds there. Out-
of-press spring back is more Iürely to occur in HP samples than SIP samples because the
magnitude mch of spring-back force varies directly with the compaction pressure utiiised.
Outof-press spring back is inevitable. Unfortwiately, the data in this research do not
provide any Monnation on the extent of such effects in the sample panels. However, high
out-of-press spriag back is causeci by low adhesive strength. Such low-sirength joints also
serve as seed-points for M e r delamination. Delamination nui be caused by moisture
induced swelling, and the amount of bond strength can be inferred &om the amount of
swelling-induccd delamination. In fact, severe swelling and delamination was observeci in
some of the test specirnens during the water-aposure testing.
8.2.4 Cd1 Wd1 Fracture and Caul Scrttn Effkt
S e v d variations in layer swelling behaviour were obsuved. SpeciGcdiy, al1 top layers in
the HP samples swelled more than the bonom layers and the thicker a r e amples exerted
less swelling stress than the thinner d a c e samples. These behaviour cm be explainecl by
ce1 wall h u m e and by the distribution of voids within the panel.
Bolh of the sdbce layers are theoretically subjected under the same platen temperature and
platen pressure. One w d d expect both d e s to bthave identidly. However, aU the HP
sampie top layen reveaied mer sweiiing than the bottom layers. This may be causeâ by a
higha I m i of ail wall fhcture, hence, higher density in the top layem.
Carll and Wang (1983) indiateci that SIP induces las ce11 d l fracnire than HP due to low
compaction used during mat consolidation. They found tbat a higher proportion of ce11 w d
fhctwe reduces the streqth ofthe straads in tension peqmdicuiar to the grain which then
incnases thickness expansion. Furthemore, fractures increase the surface ana available
for water attachent to the ceil wall. Thus contributes to the grmer sweiling behaviour of
HP samples. Geimer et al, (1998) indiatexi thet severely crushed and coilapsed ce11 walls
can absorb wata and retum to their original shape when moiahire is reintroduced. Such
celis can becow fully saturated revealing maximum thichess sweliing of 35%. Thus celi
damage can sevaely inaease the amount of thickness swelling.
During HP manuhcture, OSB mats are transporteci to the press on a caul. The caul is a
large, flexible, nibbery sheet upon which the OSB mat is fomed. During consolidation
pressing, the bottom layers are compressed against the cal. The caul may offer a
cushioning effect to the bottom strands, reducing the pressing force and the level of ce11
âacture. In contras, the top mat layers are pressed against a nonampliant steel platen,
without any extra cwhioning. The top layer dries rapidly and expaiences the ttll platen
pressure, which in tuni caused more breakage. Thus, the top layer experiences more
thickness swelling and spring-back than the bottom layer.
8.2.5 Void Volume Effkct
In the 1990s' researchers began foasing on the three-dimensional density distribution
concept, incorporating both the vertical and horizontal density distribution of the panel.
Marra (1992) indicated tbat strands vert idy halfway between the surfes Md the wre encouter an environment where the best consolidation (resin auing) ocaus as a r d t of
heat waves transmitting thamal energy fiom the surâice to the con. Observations by Chang,
(1997) of a vertical cross-section of microtomed 18.26mm(23"/32") tbick OSB wae
consistent with Marra's findings. Chang's results revealed that adjacent to the d e layer,
a partidarly well adhaed 3-4 mm thick laye of m d s was evident without visible
delaminated air pockets. The core region exhibited higber delamination and larger air
pockets or "voids", reflecting Iowa compaction and densification in the c m zone. A thin
iayer of higbly densified straads exhibiting high degne of ce1 Wall breakage, cracks and
deformation was present in the surhice layers. This layer would dlow eaPy access to water.
ûveraîl many variations in sweiiing behaviour between panel sample categories have been
ob~aved. The con layas of centre samples generally swelled more thaa the core layas of
edge samples. This is attributed to the dynamics of steam flow and the migration of resins
during pressing- Resin migraies because of steam flow. Changes in resin content affect the
bonding strength of the diErnent panel areaq which then affect the panels swelling
behaviour and out-of-press sp~g-back tendencies.
An equation for void volume prediction is Fv = 1 - (plpu), where p represents local board
density and p* wood substance density (roughly 1500 kg/m3) measured in oven dry
conditio~~ Kamke and Casey (1988) indicated that void vo1ume of h a l mat thichiess is
roughly 0.5m3 per cubic meter of panel volume. The distribution of voids within a panel
affects the panel's swelling stnss. In this study, a rnicroscopic examination of OSB
revealed voids dispersed aaoss panel thickness. More voids were concentrated in the core
region, usuaily accompanied by thick strand ends or fhctures, while fewa voids was located
in the surfas layers. The o v d l verticai void distribution can be thought as an upside
down J-shape, whae void population is higha in the core than in the surfaces. By
definition, void volume directly results in lower density. Thus the con layer is necessariiy
leu dense than the surface layers.
In addition to lowa density, the higher void volume also explains why thichess swelling
and sprhg back is Iowa in the con layer. Regardless of panel density, void volume in a
pend detamines the available space for mat interaal swelüng. Mat intemal swelling is
defmed as swelling inward into voids d e r than outwardly as thickness expansion. When
sweiling is restrained by the outer ceIl wall layer, inward d l i n g ocaus. Cellulosic
material in the core layer releases more swelling stress through intanal swelîing- Thus the
con a r a t s less swelling stress than the surfàce layers.
Although the wre layer generally exhibits les thickness swellin& sp~g-back, and swelling
stress than the top aud bottom layen, its importance to sweiling behaviour shouid not be
undcrestimated. The core layer swells las than the surfàce layers per unit thickness.
However, the con also ~ompnse~ roughly W ? of the sample by volme. Thus, the core
coatributes more absohite increase in thickness to the total panel than the surfas layas.
Thus the con domhates changes in absolute thichiess of the panel which are csusal by
tbickness swelling and spring-back. The core also absorbs some of the swelling stress of the
surface layas tbrough imanal swelfing. Thus the con laya moderates some swelling
behaviows and is the prime contributor to otbers.
Plasticisation is one of the most important effeas in OSB mamûechire. Briefly,
plasticisstion is the enect whereby wood under elevated temperature and rnoisture
conditions softais and becornes able to mechanicaiiy deform without âamage. The wood
retains its new shape once returned to cooIer and dryer conditions. Plasticisation is the
eEect that aiiows OSB strands to be defoimed duriag t&e pressing process without
destroying the strand's mechanical strength. However, a swad background to mechanical
defocmation is needed before the importance of plasticisation can be fully grasped.
Wood is a deformable solid substance. Wood c m be cornpressed and stniched, although
the force required to do so is not trivial. As a deformable solid, the behaviour of wood cm
be described using established mechanical theory.
At a given MC and temperature, as wood is cornpressed, it defonns. At low pnssure the
amount of defonnation is proportional to the force applieû, and the deformation is reversible
by removing the force. This is elastic compression, and the amount of deformation pa unit
force is a constant, the modulus of elasticity (MOE). Elastic deformation ody ocairs up to
a point, d e d the proportional limit. As the applied force exceeds the proportionai limit,
the wood no longer defonns elasticaily. Some of the applied force is used to change the
w d ' s physid structure, permanently d n g the wood in its aew shape. Ifthe applied
force is increased mer, the wood nipaires, losiag al1 of its mechanid strength. Thus
th- is a range of applieâ force (beyond the proportionai limit and before the point of
rupture) that causes the wood to pemmently change shipe without loshg mechanical
smogth-
OSB matlufkturers strive to permanentiy change the sbape of the mat strands without
damage. Thus, their goal is to apply enough force on aU the panel strands to bhg them into
the permanent set region during pressing. Fominately, the m e n t set region cm be
enlarged through plasticisation (that aUows matrDr changes and lignin flow).
û.2.7 Mahi. Cbmga and Lignh Flow
Examinhg the microscopie structure of wwd reveals the mechsnisms responsible for
plasticisation. Norimoto et al (1993) offer an excellent description:
"The ce11 wall is a fibre-reinforad composite with a cornplex, rnulti-layaed
structure. In each layer, cellulose molecules are grouped togeâher to form
long filaments calleci microfibriis, separated by a matrix containhg
hemicelluloses and lignin. Both moistun and temperature act Werently on
matrk and microfibrils. The elevation of temperature in the wet condition
sofiens the matrix and its two main constituents, hemicelluloses and lignin,
shift &om the glassy to something near a nabbery state. On the other hand,
cellulosic microfibrils because of the crystalline naaire remain in the glassy
state and are almost completely udected by moisaire and heet."
As the OSB strands are heated in the presence of moisture the ügnin and hemiceiiulose
softens. Miaofibrils are then fhe to shift and redistribute in response to the forces applied
during pressing. On the macroscopic level, the w d strands becorne mon pliable. They
deform more easily, and rd i ly diston during pressing. Once pressing is complete and the
strands cad, the matrix solidifies and the strands are set in their new sbape. Tbuq
plasticisetion has the effect of retiucing the limit of proportionality of wood. The permanent
set region becornes larger, and las force is required to permanently distoct sbgnds in the
OSB mat,
Even though the pîasticised OSB mat is more readily defonned, it inevitably nta ins some of
the pressing force in the form of elastic storage and in min bonds. This storeci en-
contributes to swehg stress, and is released during swelling as spring-back. Howewr, as
the mat stranâs are more completely plasticised, pressing them to the desired thichmrr
mpks l e s platen force. The magnitude of the force applied can be n d u d , ami thus the
magnitude offorce stores and iata released is also reduced. Hsu (1988) iadicated the
combined effécîs of hemicellulose hydrolysis ad plasticisation @y obsenhg SIP samples)
tends to reduœ the moleailar weight of lignin. As a result, the 1igni.n softening point is
reduced, and the amount of spring back is diminished. Thus greater plasticisation contributes
to betta swelling behaviour.
8.3 Expianation of SIP Performance
The SIP panel paformed better than any of the HP panels. This section discusses the
diffaences in SI? production that contribute to the improved pafomance.
8.31 Lower Compaction Pmsure
The Iowa spring back of Sm panels cm be partially attributed to the Iowa closing pressure
used. SIP utilises roughly one tenth of the pressure of HP (8.9 MPa to 700 kPa
respectively). This represents significant reduction in potential energy stored for spring
back. The poor codation between density and swelling behaviour in SIP samples also
reflects the effects ofreduced pressure. The elevated pressure used in HP explains why the
swelling pressure of HP panels are dependent on the density. This effect was seen in both
the layered and controlled HP test samples.
8.3.2 Reduced h a Closing Time
Press closing t h e affects the final OSB density gradient. Stem injection pressing uses
steam to rapidly increase temperature, moisnire and vapour pressure transfer fiom the
surfâce to the con. As a result, press cfosing tirne is reduced by 400/r. A reduction in press
closing time resuits in a more uniform density distribution and a reduction in the overalî
swelling behaviour of the controlled sample.
8 Efféct of Maximum AttUniblt Core Temperihire
nie resuits indicated that SIP core semples exhibiteci l a s thickness swelling. This is
attributable to the higher maximum temperatwe, humidity attainaûle in this region coupled .
with the longer duration at such temperature. Kwon and Geimer (1998) concluded that the
maximum con temperature in SiP panels (specidy bonded with isocyanate) can reacb
bctween 152°C aad 172OC. where as the con region in HP reaches only 1 l4T. The tirne
required for reaching maximum temperature in the con of SIP samples is only 1/5 that of
HP (Geimer et al, 1988). This meam the SIP simples had a higher level of adhesive aire
and plasticisation due to longer exposure to high temperames in the are region tban HP.
This is reflected in the reduced core layer swelling.
8.3.4 Effects of Steam Dumtion
The lower thickness swell of SIP samples can also be explained by the effect of steam-to-
panel behaviour. Hsu et ai, ((1988) indicated that thickness swelling decreased with
inaeased steam treatrnent tirne. In addition, partial hydrolysis of hemicellulose can incrase
the compnssibility of wood and hence, reduce intemaily stored stress.
The amount of thicluiess swelling reduction in SIP panel is proportional to the degree of
steaming. Higher stem injection inmeases strand cornpliance and aliows more complete
stress relaxation (fibre reamngement) and strand plasticisation (with redud glas
transition temperature of ligain). in generai, steam stabilisation (of SIP) was more efficient
than heat stabilisation (of HP). Hemicelluloses are the most hygroscopic of aii ceil wall
pdymers and an highly susceptible to thermal degrdation. The products of thermal
degradation polymerise under heat and produce a wata-insoluble polyma which exhibits
reduced swelling behaviout. Thus the more complete heating of SIP thennally degrades
polymers more than HP.
8.3.5 E f f m of Simple Pinel Size
The majority of the SIP sample swelling data confonns to other research. However, because
of the r d u d panel sue, the variation in measurement is probably lower that wodd be
o b m d in commercial panel. In contrast the HP samples were taken âom commercial
panels, and showed greater variation.
The SIP OSB sampie used in this study mnaled a more heterogenmus daisity gradient than
arpected. This can be putislly explained by the higher level of permeability of the small
panel size. The surface to edge ratio of the SIP panel is much lower than HP samples
allowing more latenl a d horizontal steom escape. The edge to surfke ratio oflaboratory-
sized SIP mat is higha than commercial-sizeâ panels (4' by S'), which increased edgewise
mat pameabiiity. Permeability determines the stem pressure sustainable within the panel
and affects the level of stem mobility and bond curing. High permeability, resulting a great
loss of heat (via stem) during consolidation can cnate an intanal mat condition similar to
HP whae heat migrates fiom s u r b to are at a rduced rate, fonning mon sevae
rnoisiure and temperature gradients. The r d t i n g density gradient is also more severe.
8.4 Post-Manufactu~g Heat Treatment
Results from the post-manufacDuring heat treatment (PMffT) arperiment confinneci Hsu's
(1989) finding in bat the high temperature prescribed stabiliseci commercial OSB quite
effbctively. The maximum thickncss swelling of OSB fiom oven-dry to moisture-saturation
is roughly 35%. Plywood and solid wood swell ody 6% to 12% (Geimer a ai, 1998).
However, OSB treated in this study swelled only 8.5% (whole sample, 15 minute treaîrnent).
The test rewihs revealed the following. First, the most obvious observation was the
darkening of the panels. Second, the quantifiable reduction in swelling behaviw with
incrrased tregtment time was quite siiificant. The following phenornena and mechanisms
are expected ta have interacted and contributed to these two results: reduction in EMC,
reduction in hygroscopicity via hemicellulose degradation, increased crystailinity and
acidity, increased resin setting, and halIy stress redistribution (Figure 20).
Figure 20. PMHT Facton and Interactio~~s
set \ bution&-& A
8.4.1 Colour Changes
The reduction in hygroscopicity of the PMHT panels is indicated by the reduction in
thickness swelling behaviour and by an examination of panel colour (darkening). Th level
ofdarkening is directly related to the duration and temperature of the treatment. Colour
changes can be aaributed ta two mechanisms: air-oxidation of phenoiic extractives and
lignin, and the decomposition of the hemicellulose to fiuhiral as hot pressing continues
(Sekino a d Me, 19%). Ahhough the amount of change can be determined using colour
system on a colour Metence meter, prominent derkenhg of heated panels in the PMHT
expairnent wu readily visible âom both treatments. Refa to Figure 2 1.
83
Figure 21.0SB colour changcs nith PMHT exposure time
The result of the PMHT sarnples indicated that colour change is proportional to treatment
tirne. As expected. the samples treated for 15 minutes turned dark brown. A prominent
reduction in hygroscopicity can be inferred by the reduction in swelling behaviour and the
change in colour. The samples treated for 7.5 minutes showed sorne browning.
Unfortunately, hygroscopicity reduction usually cornes at the expense of strand thermal
degradation and hence strength reduction (Sekino and Irle, 1996). Al1 the sample panels had
a MC of 7% to 8% below the fibre saturation point. Since the PMHT treated panels started
with such a low initial MC (from primary production) the reduction in strength is expected
to be minimal.
8.4.2 Local Variation
The degree of swelling behaviour varied with location (vertical axis) within the panel
relative to the heated platen. The farther the sample was from the piatens, the Iower was
reduction in swelling behaviour. The surface layers are in direct contact with the platen and
reach the prescribed temperature rapidly. The PMHT experiment used pressed platens
heated to 240°C, and the nsults of the OSB testing indicated that a least partiai
hemiceliulose degradation occmed. Past findings (Wood Haadbook, 1980) indicated that at
a given moistwe content, heat application can have either a reversible or irreversible eEect
on w d ' s properties depending on the temperature. At temperatures exceeding 100°C,
parnenent changes in wood composition in the form of hemicellulose degradation take
place. Less reduction in the core region swelling behaviour can possibly be explained if
these areas either did not reach 100°C or did so for less t h e than the sudiace layers. The
stabilisation effea dimssed above is proponional to tirne. Iasufficient treatment time does
not aliow the required phys id changes to thoroughiy take place.
8.4.3 Dependence on Treatment Duration
Temperature and -sure duration play critical roles in the degree of co~l~~lidation.
(Norimoto et al, 1996). This is also m e for the PMHT process. In this study, the
temperature was constant while treatment duration increaseù âom 7.5 minutes to 15
minutes. Swelling behaviour decreased dramatically with incfeased treatment duration. The
surface layers experienced more reduction than the core layers. The J-shape swelling
behaviwr in the untreated sample persisted to 7.5 minutes treetment but was lost in the 15
minutes treemient. This suggests that the results are dependant on location w i t b the mat
and on time. The following section describes the effects of PMHT on various OSB panel
properties and the mechanisms behind the effects.
8.4.4 EMC Rtduction
Moi- adsorption changes inversely with pressing temperature and the . This can be
obswed in the panel's thickness swell and spring-back. PMHT shows a similar influence
of temperature and pressure on adsorption propaties. huiag the P m experiment, the
pressing temperatute remsined constant and pressing time was varieci. The longer, (15
minute) trament tirne dlowed more water sorption site elimination Ma hemicellulose
degradstion. Fewer sorption sites result in OSB with lower EMC. Thus, changes in EMC
are strongly influenced by maximum tempefanire obtained duriag pressing. The surface of
OSB expaiemes more EMC reduction than the con. This explains why a reduction in
swelling behaviour ofthe sutface was more pronounced than in the core layers. The EMC
gradient between the surEaa and core layers ais0 diminishes as press time increases as the
nimba of sorption sites in the d k e s and core reacb an equilibrium population at the
8.4.5 Hygorropicity Rcduction and Hemicdlulose Degradation
8.4.5.1 Hygroscopicity
The swelling of OSB under savice conditions is the result the OSB panel taking up moisture
due to cheaging environmental conditions (Norimoto et al, 1993). The rate and mount of
mer adsorbeû is determined by the wood's hygroscopicity, which is controlled by the
number of bonding sites available to water molecules. The hydrogen atoms of water
molecules are attracted to the hydroxyl groups of hemicellulose molecules in the cell wall.
As the hemicelluloses take on wata molecules, they expand in al1 directions, causing
swelling. As OSB takes up watq swelling occurs perpendicular to the wood fibre
longitudinal direction. Hence, the OSB primarily increases in thickness during sweliing.
8.4.5.2 Hemicellulose Degradation
As wood is heated under dry conditions, the hemicellulose molecules give up any bound
water molecules, leaving fkee hydroxyl sites. The activation temperature of hemicellulose
degmdation is 130°C to 180°C. If the wood is heated enough for pîasticisation to occur, the
hemiœllulose molecules can move about h l y . They may bond to each other via the
amilable hydroxy1 sites, reducing the munba of sites available for water adsorption. This
degradation of hemicellulose bonding sites results in wood that has a lower equilibnum
moisture content and lower hygroscopicity. Such wood sweils less and is more
dimensionaliy stable than normal wood.
8.4.6 Iocrrucc in CrystaUiiiity and Acidity
Exposing OSB to heat rfter manufacming can resuh in iacreased acidity and crystallinity,
es well as hemicellulose degradation. Altûough a chernical analysis was not conducted,
such increases are expected in the samples. W i s (1982) arplained that hot pressing induces
deroaylation of acetylgulucomanrian. This, is in tum, aliows the release of acetic acid.
Deacaylation of aatylgulucomannan also aiIows isolated acetyigulucomannan to
crystaüise. These changes are sccornpanied by reductions in hygroscopicity and new EMC
levels.
The panel samples treated for 15 minutes showed almost no visible edge fiaring (or sevae
delmination) after the 24 hour soaking test, while the samples treated for 7.5 minutes
showed a higher degree of edge flaring. However, the extent of tlaring of eitha tteaîed
sample was less severe than in the unueated samples. A possible increase in min cross-
linking may cause the reûuction of swelling behaviour as well as diminished edge
delamination.
The PF resins used in OSB are thermosetting, and requin thermal eneqy for initiating min
polymerisation. When Ning is complete, an insoluble and inttsible cross-linled matrix is
fonned. Polymerisation cecises, even with eievated temperature. With complete curing, the
wood subsüate and adhesive bond together to pafonn as a single unit. Ifthe activation heat
aiergy is not attained during primary production incomplete auing ocairs. Thus, resin in
the treated OSB may not have complaely cwed. Further curing can be accomplished by
reintroducing the panel to temperatures above the threshold temperature of phenolic resin.
The PMEIT heated the OSB to 240°C, which is above the threshold temperature of PF resins
(1 50-190°C). The uncured resin was able to set and the additional bond strength improved
the panel's swelling behaviour. Howeva, commercial OSB contains roughly 5% phenolic
min, and the P m d a s not increase resin cantent. Thus, the effects of increased band
strength due to increased resin d n g on overaii swdling behaviour may be less than the
effects of hygroscopicity reduction.
The results of PMHT show thot the reduction in swelling stress is proportional to treatment
time and that the ciifferences in laya-to-layer swelling stress was diminished. The
distribution was lost in the -ples tregted for 15 minutes. Tbickness well and spring-back
bebaviour showed similar reductions in layer-to-layer diffaences. This wi be attributed to
stress reûistnbuition causeci by P m .
The PMHT process is analogous to clothing ironhg effect. The application of heat to the
panel temporanly soAens the panel matrk through plasticisation. Within the soAened panel,
highly saesstd areiu, of the matrix are able to SM. As these areas shifk, bey teltase and
redistribute the local stresses fiom areas of high mess to lower stress areas both vertidly
and horizontally. This distribution results in a more uniform stress gradient throughout the
pand. The panel becornes more dimensionally stable, and such stabilisation is reflected in a
reduction of al1 swelling behaviours. The application of a moderate pressing force to the
panel during PMHT forces the panel retain its original dimensions without M e r
compacting the panel. The final result is a more d o m , dimemionaily stable panel while
reducing its internul stress.
9. CONCLUSIONS
The density, thickness sweiling, spring-back and swelling stresses of HP OSB were greatest
in the outer surface layers, producing a J-shaped vertical distribution profile. The vertical
profile of the SIP panels was J-shaped only foi density and thickness swelling. SIP spring '
back and swelhg stress increased fiom the top layer to the bottom layer. Thickness
swelling, spring back and swelling stresses were positively correlated with density in HP
samples.
Spring-back contributed significantly to the total thickness increase in both panel types.
Both panel types exhibited simiiar swelling stresses. No significant trends in swelling
behaviout were found between the panel centre and edges. Swelling stress was positively
conelated with density in the HP samples and uncorrelated in the SïP samples.
The experimental data showed considerable lateral variation even over small areas. This
was probbly cawd by uneven strand distribution during mat fonning. The core layer
swelling data varied least because anomalies in flake distribution are averaged across the
thicker core samples.
The swelling behavhur of stem injection panel was superior to the hot pressed panels
likely due to the lower compaction pressure, reduced press closing tirne, greater core
temperature, and increased steam exposure time relative to hot-pressing. Steam-injection
pressing requires less compaction pressure than hot pressing. Swelling behaviour is
positively comlated to compaction pressure and thus SiP is less prone to swelling. Swelling
is positively correlated to press closing tirne. SIP pressing time can be reduced because
steam is a more eficient heat transfer mechanism than conduction. Stem heats the core
five times faster than HP, which cures the core resin more completely and produces stronger
bonds. SIP prolongs stem exposure increasing hemiceilulose hydrolysis and stress
relaxation through plasticisation. Panels with reduced fibre stress swell less severely.
The pst-manuf'tUi.ing heat-treated panels exhibited consistently reduced swelling, which
c m k amibuted to rrductions in hygroscopicity, reducition in EMC, increased resin setting,
and increased stress redistribution as well as increased hemicellulose degradation. First,
PMHT chemidly nmoves -ter sorption sites through hypscopicity and hemicellulose
degradation. Reducing the sorption sites (hydroxyl bonds available for water bonding) also
reduces panel EMC. Third, the PMHT temperature was high enough to trigger min
additionai curing, increasing the integrity of pertially cured bonds. Last, layer-to-layer
swelling sûess was diminished because PMHT tempody plasticises the panel and thus
reducing sweliing. The effects of PMHT are proportional to matment duration. Extendhg
exposure time bad the greatest effact on the sd'e layers, indicating that strarids closest to
the heat source are most affected.
The goal of tbis research was to better understand the swelling behaviour of OSB in oder to
dtimately duce thickness sweliing. The following pmblem areas would benefit from
knowledge and require M e r research and development.
Then is a need to understand the mie of plasticisation in swelling and its reduction
Computer simulation and powerfùl programming rnay generate fiture insights into
swelling equations capable of predicting OSB sweiling behaviour under service
conditions.
Rocess complications regarding rate of heat transfer, vapour dissipation, degree of cure
with respect to rate of heat -fer are still lacking and optimai conditions between these
phases is cornplex and has yet to be determined.
A bdamental principal of heat, m a s and mornentum transfer with the reaction lrinetics
relationship to describe the polymerisation of the adhesives is required.
The closing rate has a significant karing on final vertical density disaibution and
internsl structure of the panel, and how this affect swelling behaviour still require more
d y *
More understand regarding surface changes as a result of kat exposure would aid
understanding of water adsorption, hence, swelling behaviour of OSB.
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Appendu A. Data From Expriment Part 1
Tbickness swell, s p ~ g back of HP and SIP samples
Part 1 - HP LAYER DENSm, THICKNESS SWEU AND SPRlNG BACK
Mills A Location Edge samples Centre samples Layer Density (kglm3) T.S. % S.B. % Density (kglm3) T.S. % S.B. % TOP 694.28 34.08 25.70 750.30 33.79 24.83
Mean 686.26 SM Dev 69.27 Variance 4798.07
Part 1 - HP UER DENSIPY, THICKNESS SWELL AND SPRING BACK
Mills A - - - - - - - -
Location Edge sampks Centre samples Layer ûensity (kglm3) T.S. % S.B. % ûensity (kglm3) T.S. % S.B. % Core 609.52 24.28 15.14 603.68 28.95 18.16
Mean 61 9.34 Std ûev 32.55 Vatiance 1059.38
Part 1 - HP LAYER DENSITY, THlCKNESS SWELL AND SPRlNG BACK
- - - - - - - - -
Location Edge sampks Centre samples Layer ûensity (kdm3) T.S. % S.B. % Densdy (kgh3) TS. % S.B. %
Mean 698.1 6 28J3 17.35 58û.84 28,70 t8.54 Std Dev Tl.72 4.68 3.77 63.39 7.69 5.81 Variance 8010.86 21.89 14.23 4 1 7.73 59.19 33.77
Part 1 - HP LAMR DENSITY, THICKNESS SWELL AND SPRINO BACK
Mern 746.56 28.W 17.52 730.38 28.36 17.52 Std Dev 64.93 5.03 4.03 U.49 3.80 5.27 Variance 421 6.09 26-27 16.21 1878.W 14.41 27.77
PI^ 1 - HP UYER DENSITY, THICKNESS SWEL AND SPRlNG BACK
Mills B
Mean W.84 Std Dev 36.94 Variance 1364.24
Part 1 - HP LAYER DENSIW, THICKNESS SWELL AND SPIUNG BACK
Mills B Location Edae sam~les Centre sam~îes - - - - - - -
Layer Mnsity (kglm3) T.S. % S.B. % Densdy (kglm3) T.S. % SB. %
Mern 658.66 25.30 15.98 60339 25.67 25.43 Std Dev 43.42 3.32 3.16 156.70 SwS2 4.70 Variance 1 ûû5,65 11.00 10.01 245S6.05 30.42 22.1 1
Piit 1 - HP LAYER DENSITY, THHICKNESS SWELL AND SPWNO BACK
Mills C Lmüon Edge samples Centre samples Lapr Density (kplm3) T.S. % S.B. % Density (kglm3) T.S. % S.B. % Core 580.24 21.20 14.21 443.25 10.84 2.89
Part 1 - HP UYER DENSITY, THJCKNESS S M 1 1 AND SPRING BACK
Mills C Location Edge sarnples Centre samples Layer Density (km3) T.S. % S.B. % Density (kglm3) T.S. % S.B. % TOP 730.60 39.43 32.00 61 8.27 20.33 17.03
Mern 670.31 41.58 32.62 651 .58 21.16 12.17 Std Dw 68.84 5.62 5.03 M.% 2.87 3.14 Variance 4738.52 30.43 25.30 3020.90 8.23 9.M
104
Put 1 -HP LAYER DENSIW, THICKNESS SWEU AND SPRING BACK
. - - . . . - - Location Edge samples Centre samples Layew Density (kghn3) T.S. % SB. % Density (kgJm3) T-S. % S.B. %
PI^ 1 - HP LAYER DENSITY, THICKNESS SSmL AND SPRING BACK
Mills D Location Edge sampks Centre sarnples Layer ûensity (kglm3) T.S. % S.B. % Density (kglm3) T.S. % S.B. % TOP 809.33 32.94 17.65 7 17.88 45.65 35.87
PI^ 1 - HP LAVER DENSTTY, THICKNESS SWEU AND SPRlNG 8ACK
Mills D
Part 1 4 P LAVER DENSi'W, THICKNESS SWELL AND SPRING BACK
Mills D - - - - - - - - Location E d ~ e amples Centre samples Layer Density (kglm3) T.S. % S.B. % Density (kIJm3) T.S. % S.B. %
Mern 642.95 Std Dev 54.38 Variance 2966.94
Edw Den* (kdm3) atdw T.S (%) Wev S.B. (%) stdeu Dsn:TS Dsri:SB TS :SB Top 686.260 71.218 34.305 5.69026.174 7.454 0.837 0.499 0.259
Mill A Corrsl Corrl Coml Ceiibs Dsn8iW (kdm3) stdw T.S (%) Wev S.B. (%) stdev Dsn:TS Dsn:SB TS : SB Top 683.081 84.819 34.W 6.014 23.998 7.845 0.603 0.563 0.810
Mill 0 COCCbl conl C m i EW Density (1tairn3) r ~ v T.S ('16) atdm SB. 0%) a v ~ : T S SE TS : SB Top 746.556 66.920 28.959 5,156 17.522 4.125 0.248 0.350 0.650 c0k 548.840 37.746 22.315 4.850 13.792 3 . W 0.n8 0.753 OB57 ûûüûm 658.661 43.424 25.298 3.317 15.979 3 . W 0.209 -0.203 4.008
Top 730.382 187.581 28.363 3.894 t7.522 5.445 0.115 -0.297 4.308
Edge Deri8ity (kdm3) W o u 1.S (%) ddev S.B. (%) stthv ûun:fS h : S B TS : SB TQP 670.312 68.837 41.562 5.516 32.616 5.0% 0.167 0.167 0.û2û
Ew Dsnisty (Km31 rMIv T.S (%) Wev S.B. (%) 8tdev Dsir:fS Dsn:SE TS : SB TOP 666.Oô3 52.454 24.886 5.616 16.988 2 . W 0.514 0.152 0.453
Conlm Dsriirty ( M 3 ) 8tdev T.S (%) sîô8v SB. (%) s?dev b : T S ûen:SB TS : SB TOP 728.262 38,200 35.263 6279 27.667 5.499 0.514 0.311 0.788
Pas 1 - SIP LAYER DENStlY, THICKWESS SMLL & SPRING BACK
Lam Density (K~im3) T.S. % S.B. % TOP 926.343 15.139 5.179
m o n 939.922 928.382 614.992
1005.392 893.023 839.336 947.71 2 937.472
Mean 880.664 Std Oev 1 13.01 9 Variance 12773.260
61 2.892 528.879 645,iî 1 629.- 650.095 670.769 61 0.286 678.425 528.879 608.780
Maan 616.463 Std Dev 52.077 Varfance 2712.004
Bottom 705.882 1022.201 665.856 684.622 699.586 823.380 828.976 696.258 681.588 678.400
Mean 748.675 Std Dev 1 12.662 Varknce 12692.783
Part 1 - StP MEAN LAVER DENSITY, THICKNESS SWELL & SPRlNG BACK CORREîAïîON AND S-DAW) VARIATION
E Correlation Mean Density (Kglm3) Stdev TS (%) SMev SB (%) Sddev Den: TS Den:SB TS:SB TOP 880.884 107.219 16.671 4.808 4.501 1.163 -0.113 -0.064 0.554
Mills Dmay 1-S. (96) S.E. (%) A 600.304 23.207 16.586
Plrt 1 - SIP MOLE SAMPLE DENSIW, THICKNESS SWEU M D SPRINO BACK
Lob samm T.S. (%) S.B. (%) E 717.927 15.155 6.736
637.6 663.4 735.1 758.6 610.8 686. t 648.6 663.4 630.1
Wkrn 676.1 Std DW 474 v8-rn 22s8.8 c ~ k t i o c i 0.1
Part 1 - WHOLE SAMPLE MEAN DENSITY, THlCKNESS SWELL AND SPRING BAC
HP SAMPLES Comlation Mills Density(kgtm3) Stdev T.S.(%Stdev S.B.(%:Stdev DWI:T.S.~~:S.~TS:SB A 674.36 58.23 26.64 2.85 19.67 2.79 0.79 0.87 0.88 B 664.20 35.26 23.95 1.59 16.20 1.67 0.68 0.60 0.71 C 608.20 45.34 47.75 4.78 11.04 3.39 -0.67 -0.65 0.96 D 602.50 51.45 15.12 2.53 9.48 2.66 4.44 4.40 0.99 All HP 637.31 56.39 20.87 5.58 t4.10 4.06 0.45 0.50 0.97
SIP SAMPLES Correlation Mills Density (kNrn3) Stdev T.S. (% Stdev S.B. (96: Stdev m: T.S. m:S.B TSSB E 676.10 47.52 16.97 1.93 8.64 1.44 0.19 0.21 0.83
Appendu B. Data From Expriment Part 2
Swelling sûess of HP and SIP samples
C Miri Sm-
a n ÿ ( i r g h n 3 ) S1.719 616.WS 619.153 536,382 511.407 574,261 46.1914 --Y 2S.220 40.263 23.000 18.683 10.- m m w 48.228 80.2M 43.- 36.083 3O.m hi -+ P i (&604.757) 31tê33.587 41S635.25O 3Wô11.574 2Sî918.826 213ô4ZMs P i ~ m s i ( l l o a a i 0 0 ) 0.312 0.416 0.301 0.253 0,214 Om 0.07613
Mill A thickm 0.74 0.74 0.72 0.71 0.70 0.73 -lm 543.48 045.86 701 -14 763.68 602.91 702.48 pii 13.43 26.86 55.34 79.75 29.30 28.35 M d 20 pii 33.43 46.86 75.34 90.75 49.30 48.35 Pd -> Pa 230475.1 8 323055.22 51 9437.1 2 687764.47 339887.95 333360.78 Pa -> MPa 0.23 0.32 0.52 0.69 0.34 0.33
Mill A Average Stdev thickmm 0.73 0.74 0.74 m* 651.54 599.00 701.14 1 95.47 52-57 157.73 PM 23.01 42.30 29.21 9.45 9.85 19.57 M d 20 psi 43.01 62.30 49.21 29.45 Psi -> Pa 296539.95 42951 9.80 338308.57 108536.83 67885.76 152038.06 Pa -* MPa 0.30 0.43 0.34 0.1 1 0.07 0.1 5
Mill 6 t h i c k m 0.73 0.72 0.73 0.73 0.72 0.73 dmaity 668.48 807.20 681 .O2 661.98 659.43 610.26
20.70 26.04 42.32 32.96 31 .O5 28.1 3 Add 20 mi 49.70 46.04 62.32 52.96 51 .O5 48.1 3 Pu' -> Pa 342693.41 37 7444.31 429662.54 3651 37.06 351 973.90 331 81 0.1 8 Pa -> MPa 0.34 0.32 0.43 0.37 0.35 0.33
Mill B Average Sîdev o i i d t m 0.72 0.73 0.73 0.73 -flw 651.99 675.38 677.44 655.70 654.89 28.02 Psi 33.01 43.73 28.94 27.01 32.29 6.1 1 Add 20 psi 53.01 63.73 48.94 47.01 52.29 Psi -a Pa 365467.27 439369.36 337459.39 324096.67 36051 1-41 42127.78 Pa -3 MPa 0.37 0.44 0.34 0.32 0.36 0.04
Mill C thkknelm 0.73 0.73 0.73 0.74 0.73 0.73 âenaity 578.20 604.03 568.65 745.89 875.89 591.23 Pi 24.82 31 33 20.75 32.14 22.52 29.56 Add 20 pi 4.82 51.33 40,75 52-14 42.52 49.56 psi -3 ~a 309027.94 35391 5.23 280073.38 359526.14 293147.53 341707.93 Pa -a MPa 0.31 0.35 0.28 0.36 0.29 0.34
Mill C Avm()e Stdw th ickm 0.74 0.74 0.74 0.73
570.65 614.27 645.89 599.39 181.59 37.97 Pù 31 .31 33.85 20.45 32.95 8.47 6.79 M d 20 p* 51.31 53.85 40.45 U.95 28.47 Psi -> PQ 353774.59 371303.58 278904.01 365068.94 99774.83 46828.24 Pa -> MPa 0.35 0.37 0.28 0.37 0.1 0 0.05
Part 3 - WHOLE SAMPLE SWEiLlNG STRESS - CONTINUED
Mill D
-'w 575.22 722.55 582.91 567.75 722.1 3 632.61 mi 21.57 55.74 23.19 27.37 25.05 30.16 Aûd 20 psi 41.57 75.74 43.1 9 47.37 45.05 50.16 Psi -3 PO 286584.29 522242.58 291806.12 328572.96 310576.55 345ô39.14 Pa -a MPa 0.29 0.52 0.30 0.33 0.31 0.35
Mill C Avemgu Stdev Chkkm8~ 0.70 0.73 0.75 0.73
702.83 600.42 609.95 598.00 631.44 61.23 Pi 39.46 27.40 33.44 28.49 31 .19 10.05 Add 20 psi 59.46 47.40 53.41 48.49 51.19 Psi -a Pa 409977.58 328796.83 368434.73 334304.94 35291 3.57 69258.44 Pa -> MPa 0.41 0.33 0.37 0.33 0.35 0.07
Mill E ai&mss 0.78 0.77 0 .n 0.78 0.77 0.78 m* 71 2.51 706.83 691.78 722.88 701 .14 732.86 Pi 36.82 29.70 35.40 39.88 33.43 29.47 Add 20 psi 56.62 49.70 55.40 59.88 53.43 49.47 Psi -a Pa 390386.16 342893.41 381 969.79 412829.80 368421.30 341074.89 Pa -> MPa 0.39 0.34 0.38 0.41 0.37 0.34
Mill E A w m Stâev
densiîy 71 6.83 719.84 716.44 706.23 71 2.73 1 1.73 psi 27.89 32.40 28.95 30.79 30.1 2 4.06 M d 20 psi 47.99 52.40 48.95 58.79 50.1 2 Psi -a Pa 330854.88 361 2ô4.17 337482.87 391 549.55 365854.68 27761.45 Pa -a MPa 0.33 0.36 0.34 0.39 0.37 0.03
Appendix C. Data From Expriment Part 3
Post Mmufacniring Heat Treatment
Part 3 - PMHT - LAVER THICKNESS SWELL AND SPRING BACK
7.5 minute 15 minute Layer Density T.S. (SC) S.B. (%) Density T.S. (%) S.B. (%) COR€ 560.194 19.3705 10.6538 5r12.005 1 1.221 9 3.491 27
Part 3 - PMHT - LAVER THICKNESS SWELL AND SPRING BACK
Bottom 603.742 14.1631 13.3047 577.67 17.8261 1 1.7397
691.484 19.5556 7.llf 11 61 3.937 18.0995 9.95475 530.807 1 0.5263 7.89474 556.743 14.1593 6.6371 7 639.143 21.4286 8.0357 1 525.938 26.2222 13.7778 623.316 24.359 8.97436 525.55 12.1622 7.20721
694.261 25.5435 13.587 604.932 17.8082 9.58904 540.475 1 1.8644 t 0.1 6% 594.872 20.9402 14.5299 522.906 1 1.2108 7.17489 561.143 13.3929 7.58929 575.446 16.4502 10.3896 695.71 4 1 9.6429 6.69643 525.938 26.2222 1 3.7778 627.862 27.1 552 10.7759
Mean 563.423 1 7.5587 9.4721 9 Std 08v 57.758 5.4528 2.69769 Varknce 333539 29,733 7.2ï752
P ~ l t 3 - PMHT - LAYER THICKNESS SWELt AND SPRlNG BACK
Treatment 7.5 minute 15 minute - - - - - - - - - - - Layer Density T.S. (%) S.B. (%) hnsity T.S. (%) S.B. (%) TOP 662.943 32.5472 26.8868 720.658 7,76256 0.45662
Part 3 - PMHT - LAYER SWELLING STRESS
Treatement: Layered - 7.5 minute TOP
densiîy 851.31 5 714.478 733.1 17 636.29 661 .O45 71 0.661 726.974 Psi 53.7104 27.2621 56.5587 29.2966 30.9242 33.7724 50.8621 add 20 p: 73.7104 47.2621 76.5587 49.2966 50.9242 53.7724 70.8621 psi->pa 508215 325861 527853 339888 351 110 370748 408577 Paœ> Mp 0.50822 0.32586 0.52785 0.33989 0.351 1 1 0.37075 0.48858
TOP Mean Stde D a Variance Correl thickness 0.22 0.228 0.223 density 694.691 61 3.333 730.404 707.231 65.4567 4284.58 0.7491 2 psi 40.6897 26.0414 41.91 04 39.1 028 add 20 p: 60.6897 46.0414 64.9104 59.1028 psi->pa 41 8441 31 7444 426857 407499 pan> Mp 0.41 844 0.31 744 0.42686 0.4075 0.07858 0.00556
CORE
denstty 481.162 489.631 501.56 527.192 502.988 526.833 567.457 psi 17.0897 19.1242 18.3104 16.6828 16.7984 11.826.8552 add 20 p: 37.0897 39.1242 38.3104 36.6828 36.7984 31.8 46.8552 psi-+pa 255724 269752 264141 25291 9 25371 6 21 9253 323055 pa-> Mp 0.25572 0.26975 0.26414 0.25292 0.25372 0.21 92s 0.32306
CORE Mean Stde û e ~ Variance Correl thicùness 0.436 0.427 0.423 density 457.835 565.208 548.898 516.876 36.6007 1339.61 0.65505 psi 8.1 3794 27.669 13.8754 1 7.6343 add 20 p: 28.1 379 47.669 33.8754 37.6343 psi-spa 1940W 328666 233563 259479 pa->Mp 0.194 0.32867 0.23356 0.25948 0.04166 0.00156
thicknesr 0.237 0.232 0.234 0.23 0.212 0.2 0.231 densiîy 587.899 573.793 848.479 582.4 631.547 614.72 643.602 psi 17.4966 38.2483 24.8207 21 .9724 19.1 242 5.28966 36.21 38 add 20 p: 37.4966 58.2483 44.8207 41 .9724 39.1242 25.2897 56.21 38 psi->pa 258530 401608 309028 289390 269752 174366 387581 pa-> Mp 0.25853 0.40161 0.30903 0.28939 0.26975 0.17437 0.38758
Part 3 - PMHT - LAVER SWELLING STRESS
Treatement: 7.5 minute BOTTOM Mean Std ûev Variance Coml thidcnes 0.228 0.224 0.227 density 637.474 581.429 605.322 608.666 30.762 946.299 0.1081 9 psi 26.8552 19.531 1 1 7.4966 22.7049 add 20 p: 46.8552 39.531 1 37.4968 42.7049 psi->pa 323055 272557 258530 294440 pan> Mp 0.32306 0.27256 0.25853 0.29444 0.06608 0.00393
Part 3 - PMW - LAER SWELLING STRESS
Treatment: 15 minute TOP thicknes 0.18 0.209 0.192 0.193 0.217 0.2 0.225 density 692.267 647.043 787.333 672.829 755.61 3 760 787.342 psi 26.4483 14.6483 22.7862 6.91 725 25.2276 6.1 0345 30.9242 add 20 p: 46.4483 34.6483 42.7862 26.9172 45.2276 26.1035 50.9242 psi-rpa 320250 238892 295001 185588 31 1833 179977 351 110 Paœ> Mp 0.32025 0.23889 0.295 0.1 8559 0.31 183 0.1 7998 0.351 1 1
TOP Mean Stde De\i Variance Correl thicùnesr 0.226 0.178 0.217 density 576.85 627.416 808.349 691.504 77.2181 5962.64 0.47783 psi 19.1 242 6.91 725 7.93856 16.7035 add 20 p: 39.1242 26.9172 27.9388 36.7035 psi-spa 269752 185588 192630 253062 pa-a Mp 0.26975 0.18559 0.19263 0.25306 0.06491 0.00379
COR€ thickness 0.412 0.412 0.409 0.416 0.412 0.408 0.413 density 466.951 507.1 84 479.1 39 539.846 579.728 524.706 548.1 07 psi 9.76553 6.91 725 5.69656 16.2759 21 S655 1 3.0207 20.3440 add 20 p: 29.7655 26.9172 25.6966 36.2759 41.5655 33.0207 40.3448 psWpa 205226 185588 177172 250113 286584 227670 278168 pan> Mp 0.20523 0.1 8559 0.1 771 7 0.2501 1 0.28658 0.22767 0.2781 7
CORE Mean Stde De\i Variance Correl thickness 0.409 0.408 0.41 1 density 522.1 71 541 .O2 530.21 9 523.907 33.0315 1091 .O8 0.86969 psi 14.2434 13,4276 13.8345 13.509 add 20 p: 34.2414 33.4276 33.8345 33.509 psi->pa 236086 230475 233281 231036 pa-> Mp 0.23609 0.23048 0.23328 0.23104 0.03551 0.001 13
Part 3 - PMHT - LAER SWELUNG STRESS
Treatrnent: 15 minute
density 623.464 653.231 667.636 574.852 568.216 630.986 541.333 psi 1 7.0897 8.951 73 1 8.71 73 16.2759 25.6345 26.8552 1.22069 add 20 p: 37.0897 28.951 7 38.71 73 36.2759 45.6345 46.8552 21.2207 psi-spa 255724 199615 266946 250113 314639 323055 146312 pan> Mp 0.25572 0.19962 0.26695 0.2501 1 0.31464 0.32306 0.14631
BOTTOM Mean Std Dev Variance correl thicknes~ 0.21 0.22 0.218 density 545.524 539.345 566.01 8 591 .O61 48.31 1 2333.95 0.4751 5 psi 6.10345 7.73104 1 1.8 14.0379 add 20 p: 26.1035 27.731 31.8 34.0379 psi->pa 179977 191 199 21 9253 234683 pa-* Mp 0.17998 0.1912 0.21925 0.23468 0.05782 0.00301
Pla 3 - PMHT - WHOLE SAMPLE THICKNESS SWELL AND SPRlNG BACK
7.5 min Density T.S. (%) S.B. (%) 669.9209 22.45763 18.22034 65t.1344 21.35785 11.5983 687.5248 19.66054 16.97313 671.5926 26.1669 19.51909 620.447 23.05516 16.83168 675.887 21.75141 16.24294
595.6436 20.79208 1 1 .O3253 686.9575 20.821 53 1 S. 15581 632.21 5 23.33805 17.39745
680.1018 22.06506 18.2461 1 652.8 21 36028 1 1.06383
687.5248 19.66054 16.97313 671 At 16 25.88402 18.95332 620.447 23.05576 16.83168
677.3484 21.81 303 16.43059 676.5714 21.64074 15.841 58 596.4873 20.9631 7 1 1.1898 686.9575 20.821 53 15.15581 632.396 23.47949 l7.2566l
678.6535 21.35785 18.2461 1 Main 687.ûôl1 22.ûMl 18.86798 Std h v 30.57822 1.72û23S 9.676878
15 min DensQ T.S. (%) S.B. (%) 670.4673 8.272859 1.5965f7 626.0058 8.163265 1.74927 1 612.8092 8,092486 2,745665 549.7293 7.714702 1.45- 609.071 3 8.005822 1.746725 684.6145 8.1 15942 2.310841 610.4615 7.837446 l.59851? 624.8642 8.759124 2.1 89781 666.1 1 87 8.53835 2.749638 626.7328 7.591 241 1.89781 612.8092 8.092486 2.745665 559.3693 8.175182 2.043796 673.094 6.410256 0.569801
635.8343 9.171598 3.106509 633.3134 11.9403 5.8208% 689.2896 10.29851 4.477612 026.0058 8.163265 1.749271 610.7562 8.029197 2.043796 631 S543 8.651 O26 2.346041 626.6003 8.63836 2.489019
lllkrn 628.0878 8.109124 2 . m 7 SM0.V 36.m618 1.1031li 1.12Ms1
Appendix D. Statistical Analysis
TS, SB kyer u m p k location comprikon - VARIANCE: M L HP TOP LAYERS conesponds to tables 1,2 and 4
Density T.S. (%) S.B. (%) Avmge of al1 Top Iayrr (Centm+Edg.) 695.31 4 31,085 21,833 Std b v of al1 Top I a y m (CantwEdge) 78.1 36 4.T18 5.t 12 S m p k population average Location Sample Size Density T.S. (%) S.B. (%) Edge 64.000 692.303 32.428 23.325 Centre 64.000 698.325 29.742 20.340
Estimation of population stâ dev basd on sample population Location Density T.S.(%) S.B.(%) Edge 64.857 5,495 4.742
Null Hypottmir: sampk populatîon mern k not dHhmnt from whok population m r n Alternative Hypothesis: u m p k population mean k staüstically 8ignHiantly dHhnnt from whole population m r n Estimation of z, the tast sbtistic
Test Strtistics of Population means Location ûensity T.S. (%) S.B. (%) Edge -0.371 1.955 2.51 8 Centre 0.264 -2.646 -2.178
Smrll pinlurr hidiate gnabr support of th alternative hypothesis, the u m p k pop is not signifitrntly difbmnt fiom the mean Large piralues indiate rûong support of tlw nuIl hypothesk, the sample pop b not 8IgnHiantIy d$ffemnt from th. mern
p-Valu# of u m p k population mns Location Degrees of Freedom Density T.S. (%) S.B. (A) Edge 62.000 0.71 2 0.055 0.014 Centre 62.000 0.793 0.010 0.033
Piobrbility thrt we accept the hypoth.ris thit the u m p k pop k not mmn signifbntfy dîffemnt from the mean Location Density T.S.(%) S.B.(%) Edge 71 .16% 5.51% 1.44% Centre 79.30% 1.03% 3.32%
Piobability thrt wa accept the hypo(hrrk ümt th u m p k pop b signilîantly dHhrisnt tram the msrn Location ûensity T.S.(%) S.B.(%) Edge 28.04% 94.49% 98.56% Centre 20.70% 98.97% 96.68%
TS, SB Iiyw rrmpîe lacation cornparison - VARIANCE: AU HP COR€ corresponds to tables 1,2 and 4
ûensity T.S.(%) S.B.(%) Awraga allcorr kyei (Cmûe+Ed@a) 541 398 20.583 12.003 SM Dev aII con tayen (CentwEdge)
Location Sample Size Density T.S. (%) S.B. (SC) Edge 64.000 548.712 20.582 12.273
Estimation of population std dev basd on umple population Location Density T.S. (%) S.B. (%) Edge 34.060 3.550 2.91 5 centre 28.920 2.595 2.91 O
Null H y p o ü ~ ~ ~ b : umpk population mean k not dHhnnt fiwn whok population mwn Albmrtive Hypothesk: umpk population mean k rtitkticrlly significantly dHhmt fiom whole population mean
Location Oensity T.S. (%) S.B. (%) Edge 1.577 -0.002 0.741 Centre -1.857 0.004 -0.745
Smrll pvalurr indicab gnabr support of th. alternative hypothesb, th. srmple pop k significantly dllhnnt fonn the m a n Urge pinlues indlcate stmng support of th. nuIl hypothesk, the u m p k pop k not signifian* dîffemnt hwn the m r n
p-Values of u m p k population mwns Location Degrees of Freedom ûensity TS.(%) SB.(%] Edge 62.000 0.120 0.998 0.462
Pmbrbility thrt nn accept thr hypothak that the u m p k pop k not signifitrntly difhmnt fiom th. mun Location Density T.S.(%) S.B.(%) Edge 1 1.99% 99.84% 46.18%
Probability thrt m rccept the hypothmk tht the u m p k pop b signHicrntly dHhnnt fiom the mean Location Densîîy T.S.(%) S.B.(%) Edge 88.01 96 0.16% 53.82% Centre 93.20% 0.3596 54.12%
TS, SB Iryer umpk location cornpubon - VARIANCE: ALL HP BOrTOM comspanûs to tabies 1 2 and 4
Density T.S. (%) SB. (%) Average of rll bottom kyac (CenûwEdgo) 621,831 27.641 18.238
Location Sampb Site Density T.S. (%) S.B. (%) Edge 64.000 647.934 27.546 17.889
Ert)IIUd/on of population rtd dev birrd on umpk populrtkn Location Density TS. (%) SB. (%) Edge 54.907 4.623 4.223
Null Hypoth..b: umpk population maan k not dHhnnt fiom whok popuhtîon maan
rignhntly ditbnnt fiom whoîa popuhîion maan Estimation of z, the tost rbtktîc
Test Sbtirtkr of Population man8 Location Density T.S. (%) SB. (%) Edge 3.789 0.009 -0.661 Centre -2.624 10.088 0.594
Smll p-values indicab gmatar rupport of th. abmative hypoth~k, thr urnpk pop ir rignificantiy di(hnnt form the man Large piralwr indiorta r-ng support of th. nuIl hypotlmb, the umpk pop h not rignMerntly dWhnnt fiom Ihe maan
pVrlu# of u m p k popuhîion man8 Location Degrees of Freedom lknsity T.S. (%) SB. (%) Edge 62.000 0.000 0.993 0.51 1
Pmbabllity that m accrpt th. hypothrrb that th. umpk pop k not
Location Oensity T .S. (96) S.B. (%) Edge 0.03% 99.31 % 51 -1 0%
Pmbability tMm ncrpt th. hypoth#b that th. m p k pop k rbni(itrntîy di(hnnt fiom th. nnrn
TS, SB m i n piml conipiiiion - VARUNCE: HP rll hyam corresoonds to table 3
Densiîy T.S.(%) S.B. (%) 618.687 26.393 17.387
Layer Sample Size Density T-S.(%) S.B.(%) M L TOF 128.000 695.31 3 31 .O85 21.832 M L COF 128.000 541.998 20.582 12.003 ALL BOT 128.000 621.390 27.514 18.238
Wnutkn of popuktion aîd dov ô8nd on nmpk populilkn Layer Density T.S. (%) S.B. (%) AL1 TOP 78.1 36 4.777 5.111 M L CORE M L BOîTOM
Cayer Density TS. (%) S.B. (%) ALL TOP 10.968 11.112 9.906 ALL CORE ALL BOl-rOM
Smll pvrluos indicatm gmtrr support d tk. rlbmithn hypothwb, th0 u m p k pop h rignntcrnüy dl(l.mitl tioni th. nwrn Largo p"viIua8 indiata rtiong ruppoit d th, nul1 hypothmim, th0 umpk pop Ir not rignl(lcrntîy dYhmit tron (In nmn
Layer ôegrees of Frwâom Density T*S.(%) SB.(%) M L TOF 126.000 0.OOO 0.000 0.000 ALL COF 126.000 0.000 0.000 0.000 M L BOT 126.000 0.765 0.01 3 0.027
îayer Den@ T.S. (%) SB. (%) A L TOP 0.00% 0.00% 0.00% M L COR€ ALL BOITOM
îayer Oensity T.S. (%) S.B. (%) AîL TOP 100.00% 100.00% 100.00% A U COR€ ALL BOrrOM
TS, SB IWU umPk location commrbon - CORRELATîON: M L TOP EDGE
c o ~ n d a to tables 6 , f and 8 Comlation Codkkntr
Mills Sampls Sue TS vs. Density SB vs. Mnsity TS vs. SB A 16.000 0.837 0.499 0.259
E8timation of z, th0 cornlrtion codickrtt t a t statküc Tœt StatWc8 of Cornlrtiom Codlïckna
Mills tprees of Freedom TS vs. Density SB vs. Density TS vs. SB A 14.000 5.721 2- 1 55 1.005
Smdl p-valuu indicatm ~ n r t r r support d tk. iîtomathm hypoth.ih, that thon h r linoar nldonrhip Largo pirrluaa inâlc8to rtiMig rupport of th0 nuIl hypothk, that thon k no linmr nlrtiomhip
Mills grses of Ftwdom T S vs. ûensity SB vs. Dsnsity TS W. SB A 14.000 0.000 0.049 0.332
ProbrMllty mit m w p t the hypothnb that th0 rrmplm pop b not $igniflcrntly dHhnnt from th. maan Mills TS m. ûenaity SB m. Density TS vs. SB A 0.01% 4.91 % 33.20%
Pmôability (hrt m ro#pt th. hypotlnrk that tha r m p k pop h 8ignHicrntty dHhnnt from t)n mmn M~ÜS TS vs. ûensiîy SB m. ûensity TS MI. SB A 99.99% 95.09% 66.80%
TS, SB Liyw uinpk locrtkn ~oniprrlron - COWIEUTION: AU TOP CENTRE Mmrtlon of ho, tho popukfkll comkdion wdticknt cortesponds to tabies 6,7 and 8 Carnlrtion Caaffkkntm Mills Sample Site TS vs. ûensity SB vs. ûensity TS vs. SB A f6.000 0.6034 0.5632 0.8099
Null Hypothab: ppuktion cornktion c#nlcknt b n r o Altamlthro Hypothwk: popuktion cornktkri cod?kknt b not uro
Mills Degrees of Freedom TS vs. üensity SB vs. Density TS vs. SB A 14.000 2.831 2.550 5.166
Smll pvrlu#rgn8t8r support of the altornitlvr hypahasb,thmm b Yneu nMknrhip
Large pvrlws-mtmng wppoit of the nuIl hypothuis, thm h no linerr nlrtionhip ~ V ~ I U O S c~m~rtloii c-kntr
Mills Degrees of F W o m TS &. Density SB vs. Density TS vs. SB A 14.000 0.01 3 0.023 0.000
Piobrbilw that m accrpt the h y p t h h thit th. uniph pop h not aignbntly dHhnnt h m tln nmn Mills TS vs. Density SB vs. Density TS vs. SB A 1.33% 2.31% 0.01 %
Piokblllty that rn rempt th. hypottlab thit th. ~ i p k pop h signîfbntly difhmnt fnmi th@ m n ~ i l l s TS vs. DensÎty SB vs. Density TS vs. SB A 98.67% 97.60% 99.99%
conesponds to tabks 6,7 and 8 CowmJrtion CoMcktvb
Mills Sampb S K ~ TS vs. Dsnsity SB vs. Density TS vs. SB A 16.000 0.500 0.687 0.864
Null Hypoanrk: population comlrtion c d c k n t k zom Abmative îiypoth.rk: population comhtkn codficknt k not uro
Mills ames of Freedom TS M. ûensity SB va. Dansity TS vs. SB A 14.000 2.1 58 3.533 6.420
Mills iprees of Fmedom TS vs. ûensity SB m. ûenrity TS vs. SB A 14.000 O. 049 0.003 0.000
Piokbility th8t we accopt th. hypothrrk that th, nrnpk pop fa not signifltrntly dHhnnt M m tha m.rn
Pmkbility th* wa mwpt the hypothmb th& thr mmpk pop h rlgninmntly dllhnnttmni th, mean Miils TS vs. hnsity SB W. ûensity TS vs. SB A 95.12% 99.67% 100.00%
TS, SB kyrr u m p k locrtion complikori - CORRELATION: AU CORE CENTRE Wmrtion of ho, the popuktion cornlation wdficknt corresponds to tables 6 ,7 and 8
Mills Sampk Size TS m. b s i t y SB W. Wnsity TS m. SB A 16.000 0.2043 0.7026 0.2067
Mills ûegiwcr of FWom TS W. Density SB m. ûensity TS S. SB A 14.000 0.781 3.695 0.791
Mills ûegm of F m d m TS W. Cknrity SB va lknsity TS m. SB A 14.000 0.448 0.002 0.442
Probabilÿ that m .cm@ the hypothak that th. u m p k pop h not rignHlcrntty dilhnnt from the mmn Mills TS vs. DentMy SB m. Density TS m. SB A 44.80% 0.24% 44.24%
Mills TS vs- ûensity SB vs. ûensity TS m. SB A 55.20% 99.76% 55.76%
TS, SB byar runpk location cornparison - CORRELATION: ALL BOrrOM EDOE Estimation of ho, an popuktion comlrtion coefficient cornponds to tables 6,7 and 8
Cornlrtkiicœtnckiit,
TS, SB byar mmpk W o n cofnparkon - CORREUTION: A U BOTfOM CENTRE btimrtlon of rho, tha population cornhtion wdiclant conasponds to tables 6,7 and 8
Conrlrtion CoHcknb Mills Sample S b TS vs. ûensity B vs. Density 7s vs. SB A 16.000 -0.150 0.088 0.376
Null Hyp#hmk: population cornlrtion codficiant h zero Attornrthra Hypot)iais: population conrlrtion coofTkknt h not zero
EItimrtion of z, the carnlation cdficient tut atmüdc T a t Strtktim of Cornlrtiom CoMcionta
Mills ûegm of Freeâm TS vs. lknsity B m. ûensity TS W. SB A 14.000 -0.568 0.332 1.518
Smrll pvrlurr Indicatm gnrtrr 8upport of th. ritamathm hypothmb, th. u m p k pop is rignif-.ntiy dllknnt form the m r n Large pvilw Indicab m n g supgoct of the nuIl hypothœk, the wmpk pop b not signllicantly di(hmnt fmn the marn
pvrlurr of CornIrfion Codfîciant, Mills Wrws of Freedorn T& W. ûensity B vs. ûensity TS m. SB A 14.000 0.579 0.745 O.tS1
Pmkbllfty th* m aeerpt th@ hYPoa#rk thit th umpk pop h not dgnificrntly dHhnnt tram th momn M~IS TS M. ûensiîy SB W. ûensity TS vs. SB A 57.93% 74.51 % 15.74%
TS, SB laye? .unpie comprkon - CORREîAflON: M L LAYERS corresponds to figures 5 and 6
Press Type Ssrnpk She TS vs. Wnsity SB va ûensity TS vs. SB HP 388.000 0.783 0.6W 0.831 SIP 30.000 0.21 7 0.291 0.268
Press Type Degrses of Freedom TS vs. Density SB vs. ûensity TS vs. SB HP 386.000 24.731 14.890 29.350 SIP 28.000 1.176 1.609 1.472
pValwr d Comhtkn CoefTickntr Press Type ûegrees of Freedom TS vs. Density SB vs. Density TS vs. SB HP 386.000 0.000 0.000 0.OOO SI? 28.000 0.249 O,? 19 0.152
TS vs. DenMy SB m. Deneity TS vs. SB HP 0.00% 0.00% 0.00% SIP 24.94% 1 1 -87% 15.22%
Probibillty thrt m mcwpt the hypothak that the u m p k pop & rignifhntiy dllhmit fmn the mmn Press Type TS vs. Derisiîy SB vs. Density TS vs. SB HP 100.00% 100.00% 100.00% SIP 75.06% 88.13% 84.78%
Milb Smph Size A 10.060
~ ~ o f & t t m t o a t ~ T œ t S ~ ~ P ~ n n n r
Milb T.S. (%) S.6. (%) A 3.921 4.281
Milk Dspiws of Frmdom aitrity m T.S. (%) S.8. (%) A 8.000 0.140 0.004 0.003
58 laye? rrmpk location comprikon - VARWTION: M L TOP LAYER corresponds to table 9
Oensity S.S. (MPa) Average of .II Top kyw (CmtmEdge) 849.414 0.41 8 Std D.v of all Top laym (Canb.+Edg.) 60.706 0.070 S m p k populrtkn avamge L d o n Sample Size Oensity S.S. (MPa) Edge 40.000 570.47 1 0.401 Centre 40.000 728.358 0.432
Estimtion of populrtion rtd dmv brwd on umpk population Location Density S.S. (MPa) Edge 36.575 0.067 Centre
Nu# Hypothesh: mmpk population imin k mot difhmnt fiom whok popuîation miin AltrmYfhlo Hypothmsh: umpk populitkn nnrn k rfati8tically rignifiuntly difforant fiom whok populatton man Estimation of z, tha brt stiblrtic
T n t Stitkticr of Population ni«ins Location Oensiîy S.S. Edge -1 3.651 -1 .41 6 Centre 7.701 1.446
SmiW pvrluu indimto g m b r support of th@ abmathm hypothosk, th. wmpk pop is not rignificrntîy dHhnnt from the mmn Large pvrluro indiutr sliong support d th. nuIl hypothmk, th. mmpk pop is not significantly dHhnnt fiom th. nwui
pValwr of mmpk popukdkn muns Location Degrees of F d o m ûensity S.S. Edge 38.000 0.000 0.165 Centre 38.000 0.000 0.1 56
Piobabilÿ thit wa rccapt th. hypoth.r& tM the umpk pop k not nnrn rignitiointly dHnmit h m th. maan Location Oensity S.S. (96) Edge 0.00% 1 6.40%
PmbibiIÿ thrt wr retrpt th. hypothrrk thit tho runw pop b rignlflcantly
Location DensÎty S.S. (96) Edne 1 00.00% 83.57%
SS layar umpk kcrtion cornpubon - VAWATDN: M L CORE UYER conesponds to table 9
Density S.S. (MPa) Avamga of rll COR€ kyar (CentrwEdg.) 682.706 0.263 Std 0.v of al1 COREliyan (CentwEdg.) 43.324 0.0Sf SImpk population m m - Location Sample Size Density S.S. (MPa) Edge 40.000 603.726 0.271 Centre 40.000 561 -687 0.235
Eetimrtion of population 8td dev b m d on umpb population Location Density S.S. (MPa) Edge 51 .174 0.067
Null Hypothuis: u m p k population m n k not dmnnt from whok population iman Abmath@ Hypoth.ri8: umpk popuMon m u n h stitistically rigniliundy dHhnnt from whok population man Eatlirutkn d z, th. Clt rbtkdic
Tast Stitkticr of Popuküon means Location Density S.S. Edge 2,508 1.699 Centre -3,747 -3.253
umpk pop k mot signMerntiy dmnnt trom thr man Large pvlilim indicab stiong support of th0 nuIl hypothmir, Ih. umpk pop i8 not 8ignbntly dWnnt tiom th. nnin
pValrm of u m p k population munr Location Degrees of Freedom Oensity S.S. Edge 38.000 0.01 3 0.097
Pmbabilÿ that m accopt th. hypoth.ris tM Ih. umpl. pop k not nnin rbni(ic8ntiy difhnnt fiom th. m i n Location Oensity S.S. (%) Edge 1.33% 9.75% Centre 0.06% 0,24%
Pmbability th.t m rccopt th. hypoth.rk thrt th. umpk pop k signMuntly
Locaüon Oensity S.S. (%) Edge 98.67% 90.25%
$5 byer umpk location comprison - VARIATION: M L 6OmOM LAYER corresponds to taMe 9
Density S.S. (MPa) Average of rll BOTTOM Iryw (ContrwEdge) 690.298 0.314 SM D.v of al! BOHOM layon (CentwEdge) 65.675 0.064 Sampk population rven@e Location Sample Size Density S.S. (MPa) Edge 40.000 71 8.596 0.348 Centre 40.000 662.002 0.283
Estimadon of population std dev b.ud on runple population Location Density S.S. (MPa) Edge 62.1 25 0.072 Centre 69.224 0.056
Null Hypothrrk: runpk population m r n k not dmmnt from whd. population m«n Albmt ive Hypothesis: umpk population mean h sfrtktically rigniflcrintly dHhmit fiom whok population m r n Estimation of z, the test strtktic
Teat Stltisticr of Population means Location ûemiity S.S. Edge 2.881 2.987 Centre -2,585 -3.727
Small p-values indicab grniter 8upport of t)n albmrtive hypothrais, the umph pop k not 8ignifÏcantly dHlmnt fnnn the mein Large pvrlues indicab stiong support of th. nuIl hypoümia, the rrimple pop is not rignificantly dHhnnt fiom the maan
pValues of rrmpk population meam Location ûegrees of Fresdom bnsity S.S. Edge 38.000 0.006 0,005
Probbillty that we accept th. h-k thrt the umpk pop mwn b not signi(i~~ntiy dllhnnt fi#n th population mean ~ k t i o n ûensity S.S. (%) Edge 0.65% 0.49%
Pmbibility thit m rcorpt the hypoth.rb thrt th. umpk pop mun k slgnifluntly diWonnt from th. population mrrn Location Densiîy S.S. (%) Edge 99.35% 99.51 %
SS hyar eonipirison - C0RREUTK)N: LAVER8 conesponds to table 10
Densiîy Correlation Coefficient Avomge of dl (hm k y ~ ~ 67&231 oms11 Std ûw of rll thm hyan 104.926 0.072
Layer Sampie Size Density Correlation Coeftbnt ALL TOP 41,000 747.662 0.525 ACL COR€ AL1 BOTTOM
btimrtion d population 8td dev b a r d an urnple populrtion Layer Density Comîation Coefficient ALL TOP 78.597 0.083 ALL CORE ALL BOTTOM
fast Sfitktics d Population m a n Layer Density Conelation Coefficient ALL TOP 5.81 9 t .O80 ALL COR€ ALL BOlTOM
Srmll pvalws indic& gmabr 8upport of the abrnrtiva hypoth.ris, th. r m p k pop i8 8ignHicrntây di(hnntl fiom the man Large pvaluu indlcato atrong rupport of (hm nuIl hypothnb, the umph pop 18 not signilicrnüy di(hnnt fmm th. n n n
pValun of sampk population nnrm Layer Degrees of Freeâom Density C o n e l a t i o ~ ~ ~ n t ALL TOP 39.000 0.000 0.287
Layer Oensity Correlaüon CoedWmt ALL TOP 0.00% 28.68% AîL COR€ ALL BOTTOM
ProbabilMy tM m aecapt the h-h tM th. urnph pop mun h rigni(krntty dl(hirnt tmm î h popuMko mwn L a w msity C o m m i o n ~ AîL TOP 100~00% 71 32% ALL COR€ AL1 BOrrOM
SS layer sample cornpariaon - CORRELATION: ALL LAYERS - - - - - .
Estimation of dto, the population comlation coefficient conesponds to figure 72
Press Type Sam* Size SS vs. Oensity HP 112.000 0.725 SIP 30.000 0.095
Null Hypothnk: popuktiori camktkn codkknt k u r o Aîtornrttva Hypothesk: poeulrtkn comktkn c d f k k n t k not uro
P m Type Degrees of Freedom T S vs. Oensity HP 110.000 11 .O40 SIP 28.000 0.505
Press Type Degrees of Fnredom TS vs. Density HP 110.000 0.000 SIP 28.000 0.61 8
PiohMIRy that m accopt th. hypotlirrh th& t k m Ir no Iinmr nlitkn (th. nul hyPoth.rW Press Type TS vs. ûensity HP O. 00% SIP 61 -75%
Piobrbillty thrt m accopt th. hypothuia th8t (hm Ir Iinmr robtkmhip (th. rltmrnath hyPd)HIb) Press Type TS vs. ûensity HP 100.00% SIP 38.25%
PMHT TS $8 kyw rrmpk camporison - VARUTION: TOP LAYERS corresponds to tables 14 and 15
Density TA(%) SB.(%) Avengr of al1 TOP kyer (tm5+16)cninubr 671.283 15.786 10.028 Std Dw of al1 TOP layon (7.6+16)minutes 60.616 4.900 3.1 61 Sunple population avoraga Minutes Sample Sue tknsity T.S. (%) S.B. (%) 7.5 20.000 673.750 22.71 5 17.985
Estim~tion of population SM dev burd on umplr population Minutes Density T.S.(%) SB.(%) 7.5 56.037 4.91 9 4.183 15 64.996 4.880 2.139
Null Hypatlmis: ample populrtlon mean is not dHknnt from whok r
population mean Abmative Hypothrris: umpk population man is stitistiully signiflcantly diffennt from whok population m a n
Test Stitisbicr of Population mmns Minutes Oensity T.S.(%) SB.(%) 7.5 O. 199 6.300 8.509 15 -0.172 -6.349 -16.638
Small p i r a b indierte gnrtrt support of th. alternative hypothnb, the m p k pop ir not rignifiuntly difibrunt fi#n th. mean Lam p-values indiute strong support of the nuIl hypothuis, the rrmple pop is not signili«intly difbmnt fiom the man
pVaIuea of m p k population man8 Minutes ûegm of Ftwdom Density T.S. (%) S.B. (%) 7.5 18.000 0.844 0.000 0.000
Probibility that m acwpt the hypdh.rk that the runplr pop i8 not mean
Minutes Oensity T.S.(%) SB.(%) 7.5 84.43% 0.00% 0.00%
Pmbrbility thit we accrpt th. hypdmsb thrt tl» 8ampk pop k signiflunlfy dHhnnt h m th. mcrn Minutes Densiiy T*S*(%) S.B.(%) 7.5 1 5.57% 100.00% 100*00%
PMHT TS SB hyar u m p k comp.ikon - VARJARON: CORE LAYERS corresponds to tables 14 and 15
ûensity T.S.(%) S.B.(%) Avemga of rll COR€ Iryetr (7.W 5)minutt 500.960 12.89t 6,003 Std D.v of rll COR€ layen (7m5+1S)minut 38,441 2.370 2,283 Slmpk population average Minutes Sample Size Density TS.(%) S.B.(%) 7.5 20.000 495.480 15.1 17 8.972
Estimation of population std dev based on sample population Minutes Densiîy T.S.(%) SB.(%) 7.5 45.236 2.963 3.506
Null Hypothesb: umple popuktîon m r n b not d m n n t fiom whok population mean Abmative Hypothrrk: u m p k population nnrn b statistically aignifhntiy dHhnnt fiom whok population m a n Esümrtion of z, the test sbartic
Minutes Density T.S.(%) SB.(%) 7.5 -0.542 3.360 3.787
Smrll p-vrlues indicrit. gmtmr support of th rlbmrtive hypothesh, the u m p k pop is not rigniRcrntly diffennt fiom the main Large p-values indicab sbong support of th. nuIl hypothesb, th. u m p k pop is not rignitlcrintly difforent fiom th. mean
p-Values of u m p k popuktion m-nr Minutes Degrees of Fmâom Oensity T.S. (%) S.B. (%) 7.5 18.000 0.595 O. 003 0.001
Probability thrt wa accept th hypothrrb thrt the u m p k pop b not m.rn signifiantly diffonnt fiom th. mean Minutes Density T*S.(%) SB.(%) 7.5 59.46% 0.35% 0.13% 15 44.87% 0.00% 0.00%
PmbabilHy that we acmpt the hypothnk tht th. u m p k pop k rignHicanüy diffennt ftom îhe mern Minutes Oensity T.S.(%) S.&(%) 7.5 40.54% 99.65% 99.87%
PMHT Tb SB Iiyer u m p k cornparison - VARîATiON: BOTTOM LAYERS corresponds to taMes 14 and 15
Densiîy TS. (%) S.B. (%) Average of dl BOTTOM lryer (7.û+lb)ininute8 566.887 14.689 6.866
Minutes Sampk SPe Density T.S.(%) SB.(%) 7.5 20.000 563.420 17.555 9.472
btirnrtion of population std dev biwd on umpk population - -
Minutes Density T.S. (%) S.B. (%) 7.5 57.758 5.452 2.697
Null Hypothesk: r m p k popuktion nnin ir not di(hnnt from whde population mmn
Test Sfitktiu a# Populrtion msrns Minutes Density T.s.(%) SB.(%) 7.5 0.583 2.351 5.979
Srnrll p-values Indicab anater support of the rlbmi(lw hypothuh, the umpk pop k not slgnikantiy difinnt fron\ the mean Large pvaluri indicrt, stmng support of the nuIl hypothnk, the r m p k pop Ir not rignlllcrntly dilhnnt fioin the niun
Minutes Degreesof Freedom ûensity - T:s.-(%) S.E.(%) 7.5 18.000 0.567 0.030 0.000
ProbibiMy that w, accrpt th. hypoth.rk thit the u m p k pop b not nwin significintly difhrent froni the nnin
Pmbability (Mm rccopt th. hypoümsb that (hr umpk pop h 8ignMcrntly
Minutes Density T.S.(%) S.B.(%) 7.5 43.31 % 96.97% 100.00%
PYHf 88 kyar u m p k complrbm - VARlATîOY TOP LAYERS conesponds to table 16
Densiîy S.S. (%) 699.370 33.0%
Minutes Sampk Sue Density S.S. (%) 7.5 20.000 707.230 40.7%
Eatimrdion of population 8td drv buad on u m p k populatbn Minutes Densiîy S.S. (%) 7.5 65.456 7.8%
Null Hypothasb: u m p k popuktion m i n h not dithnnt fioin whd. population man
Minutes Deirsity S.S. (96) 7.5 0.537 4.415
Smrll pvrlurr indlub gnrbi ru- of the rtêarnr(hn hypoümk, tha
p-Valun of u m p k population m m Minutes De~g~ofFrsddom Densiîy S.S. (%) 7.5 184ûû 0.598 0.000
Piobrbilÿ that m rccrpt the hypo(h.rk tht th. mpk pop k not m i n rignifiuntîy diffamit tiom th. mun Minutes ûensiîy S.S. (%) 7.5 59.78% 0.03%
Minutes Density S.S. (%) 7.5 40.22% 99.97% 15 34.58% 100.00%
PMHT SS Iayer runpte comprrison - VARIATION: CORE LAYERS comaponds to t a b 16
Density S.S. (%) Average of al1 COR€ Iryw (7.û+l6)minut.r 620.423 24.5%
Minutes Sample Sue Density S.S. (%) 7.5 20.000 516,876 25.9%
Estimation of population rtd dev burd on umpk population Minutes Oensity S.S. (%) 7.5 36.600 4.1 % 15 33.031 3.5%
Null Hypothesir: sample population mean is not dhrent fmm whoh population man Abmative Hypothesis: rrmpk population mean is strtisticrlly signHiantly dHhnnt fmrn whok population mean Estinution of z, the tnt rbtistic
Test Strtistics of Population I Minutes Density S.S. (%) 7.5 -0.433 1.527
Smill pvalues indicate gmtw support of the altemative hypothds, the rrmple pop is not signifïcntly dHhnnt from the mrui
Large p-values indicab smng support of th. nuIl hypothusk, th. mmpk pop h not rignificrntly dHhnnt fmm the nwin
p-Values of smpk popuktion means Minutes ûegrees of Freedom Oensity S.S. (%) 7.5 18.000 0.670 0.144
Pmbabilÿ thit w, acwpt the hypathesk thrt the sampk pop is not rmrn significrntly dHlbrent from the mean Minutes Density S.S. (%) 7.5 66.99% 14.41 %
PmbrMlity thrt m accept the hypoShrrb Mt thr umpk pop b rignticrntly diffemnt from the mean Minuîes Densi&? S.S. (%) 7.5 33.01% 85.59%
PMHT SS I.yrr r imph compmrhon - VARIAtlON: BOTTOM UYERS conesponds to table 16
Dsnsiîy S.S. (%) Avamga of a l BOrrOM Iryw (7.S+lb)minubs 698.880 26.4% Std Dav of rll BOnOM layen (7.WS)minub. 39.636 5.6% Sampk populPtkn avemg. Minutes SampleSize ûensity S.S. (%) 7.5 20.000 608.666 29.4%
Estimation of population stâ dav basad on umplo popuhtion Minutes ûensity S.S. (%) 7.5 30.761 6.0%
Null Hypoth..k: rrmpk populition nwui im not dHI.nnt fiom whok population maan
T u t Strtisîiu of Popukdkn mana Minutes Density S.S. (%) 7.5 1.280 2.236
Snwll p i n l m indicat. gnatat rupport of th. aIbmiativo hypothrrk, th0 rrmpl. pop k not rignifiuntly di(hnnt hom th. nwrn Large pvrlri.r indicatm strong support of th. nuIl hypothds, th. umpk pop
>-Valim of umpk populition man8 Minutes bgrees of Frwdom Density S.S. (%) 7.5 t 8.000 0.21 7 0.038
PmbaMlity that m accrpt t)n hypothrrb thatm u m p h pop b not mmn
Minutes Den* S.S. (%) 7.5 21.67% 3.82% 15 42.59% 1 52%
dMbnnt from tha mean Minutes ûensiîy S.S. (%) 7.5 78.33% 96.1 8%
