Impact of sapwood and the properties and market

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Impact of sapwood and the properties and market utilisation of plantation and young hardwoods: Mechanical Testing of Southern & Northern Species (PART D)

PROJECT NUMBER: PNB039-0708 FEBRUARY 2010

PRODUCTS & PROCESSING

This report can also be viewed on the FWPA website

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Melbourne VIC 3000, AustraliaT +61 (0)3 9927 3200 F +61 (0)3 9927 3288

E [email protected] W www.fwpa.com.au

Impact of sapwood and the properties and market utilisation of plantation and young

hardwoods: Mechanical Testing of Southern & Northern Species (PART D)

Prepared for

Forest & Wood Products Australia

by

W. Atyeo

Publication: Impact of sapwood and the properties and market utilisation of plantation and young hardwoods Project No: PNB039-0708 © 2009 Forest & Wood Products Australia Limited. All rights reserved. Forest & Wood Products Australia Limited (FWPA) makes no warranties or assurances with respect to this publication including merchantability, fitness for purpose or otherwise. FWPA and all persons associated with it exclude all liability (including liability for negligence) in relation to any opinion, advice or information contained in this publication or for any consequences arising from the use of such opinion, advice or information. This work is copyright and protected under the Copyright Act 1968 (Cth). All material except the FWPA logo may be reproduced in whole or in part, provided that it is not sold or used for commercial benefit and its source (Forest & Wood Products Australia Limited) is acknowledged. Reproduction or copying for other purposes, which is strictly reserved only for the owner or licensee of copyright under the Copyright Act, is prohibited without the prior written consent of Forest & Wood Products Australia Limited. ISBN: 978-1-920883-96-6 Principal Researcher: Greg Nolan and Ross Farrell UTAS, Centre for Sustainable Architecture with Wood William Atyeo Department of Primary Industry & Fisheries – Queensland

Dr Graeme Siemon Forest Products Commission – Western Australia Dr Georgiana Daian and Prof. Barbara Ozarska University of Melbourne

Final report received by FWPA in February, 2010

Forest & Wood Products Australia Limited Level 4, 10-16 Queen St, Melbourne, Victoria, 3000 T +61 3 9927 3200 F +61 3 9927 3288 E [email protected] W www.fwpa.com.au

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Executive Summary This section of the project assessed a range of mechanical properties for the sapwood and heartwood of key plantation and young regrowth species. The species investigated include the following: Plantation resources

1. Gympie messmate, Eucalyptus cloeziana; 2. Dunn’s white gum, E. dunnii; 3. Shining gum, E. nitens; 4. Sydney bluegum, E. saligna 5. Tasmanian blue gum, E. globulus;

Young regrowth resource

6. Messmate stringybark, E. obliqua; 7. Blackbutt, E. pilularis; 8. Spotted gum, Corymbia citriodora; 9. Karri, E. diversicolor.

Where possible, a sample of 15 trees was selected from two sites for each species. Species sourced in the Queensland and N.S.W. (nos. 1, 2, 7 & 8) were sawn at the Salisbury Research Centre, Department of Primary Industries & Fisheries, Queensland. The remainder were sawn at commercial sawmills local to the source of log supply. Matched sapwood and heartwood samples were cut from the sawn boards to permit comparison of sapwood and heartwood of the tested properties. The sapwood samples of the species susceptible to Lyctus spp. borers (all except nos. 1, 7 & 9) were treated to prevent attack. The properties assessed included air dry density, bending strength and stiffness, Janka hardness, screw withdrawal strength, shrinkage and glue bonding. Generally, the mechanical property tests have shown that, with the exception of blackbutt, the properties of sapwood are at least equivalent to those of heartwood. Where the trees were of young age at harvest (nos. 2, 3 & 5), the strength of the sapwood was in fact superior to that of heartwood. This was attributed to the higher density of the outer wood (where the sapwood is located) compared with the heartwood in these still maturing trees. In the species represented by more mature logs, whether regrowth or plantation, (nos. 1, 6, 7 & 8), the strength properties of sapwood do not differ significantly from those of heartwood. In these species, heartwood density was slightly higher than sapwood, but this can be accounted for by the absence of extractives in the sapwood. Heartwood mechanical properties obtained in this study were compared with those reported in the literature for native forest examples of the same species. As expected, heartwood mechanical properties of the young-age species were lower than those reported in the literature, whereas those for the older ones were comparable with literature values. Bonding of heartwood in the higher density, northern region species, was inferior to sapwood when using phenolic adhesives, but was satisfactory in the lower density, southern and western region material. Dry bonding with polyurethane adhesives was satisfactory in both sapwood and heartwood in all species except Gympie messmate. Wet bonding of the polyurethane samples was unsatisfactory in both sapwood and heartwood of the high density species, but remained satisfactory in the low density ones.

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Generally, the heartwood shrinkage results obtained in this study accord with published results for the respective species, when the age of the test material is taken into consideration. Dunn’s white gum, Tasmanian blue gum and shining gum had somewhat lower shrinkages than the published data, while the other species approximated the published data more closely. Differences between sapwood and heartwood were not significant in the species sourced from older logs, except for blackbutt, where the shrinkage of heartwood was significantly greater than that of sapwood. In the species sourced from younger logs, shrinkage of sapwood was significantly higher than that of heartwood.

Table of Contents 1 Project Outline ................................................................................................................................. 1

1.1 Project Background................................................................................................................... 1 1.2 Report introduction and objectives ............................................................................................ 2

2. Material and Sampling strategy ...................................................................................................... 4 2.1 Species Selection ................................................................................................................. 4

2.1.1 Northern region species ...................................................................................................... 4 2.1.2 Southern region species ...................................................................................................... 5 2.1.3 Western region species ....................................................................................................... 6

2.2 Sampling Strategy......................................................................................................................... 6 3. Methods .......................................................................................................................................... 7

3.1 Sample preparation ................................................................................................................... 7 3.1.1 Log breakdown .................................................................................................................. 7 3.1.2 Flitch processing (northern region only) .......................................................................... 7 3.1.3 Southern region test material ............................................................................................. 8 3.1.4 Summary of Testing Schedule ........................................................................................... 9

3.2 Properties Testing ...................................................................................................................... 9 3.2.1 Moisture content ................................................................................................................. 9 3.2.2 Density ............................................................................................................................... 9 3.2.3 Bending strength and stiffness ......................................................................................... 10 3.2.4 Screw withdrawal ............................................................................................................ 10 3.2.5 Janka hardness ................................................................................................................. 11 3.2.6 Adhesive testing............................................................................................................... 12 3.2.7 Stability ............................................................................................................................. 13

4. Results and Discussion ................................................................................................................. 15 4.1 Analysis .................................................................................................................................. 15 4.3 Density .................................................................................................................................... 16 4.3 Bending strength ..................................................................................................................... 19 4.4 Bending stiffness..................................................................................................................... 22 4.5 Janka Hardness ....................................................................................................................... 25 4.6 Screw Withdrawal................................................................................................................... 27 4.7 Glue Bonding........................................................................................................................... 31

4.7.1 Phenolic Adhesive ........................................................................................................... 31 4.7.2 Polyurethane Adhesive ..................................................................................................... 32

4.8 Stability .............................................................................................................................. 33 4.9 Variability between species ............................................................................................... 36

5. Western region results .................................................................................................................. 37 6. Conclusion .................................................................................................................................... 38 7. References..................................................................................................................................... 39 Acknowledgements............................................................................................................................ 41

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1 Project Outline This project is the result of work coordinated by the University of Tasmania (UTAS), in collaboration with the Department of Primary Industries & Fisheries – Queensland (DPI-Q), University of Melbourne (UMEL) and the Forest Products Commission (FPC) in Western Australia. The objectives of the project are to:

(i) Determine and compare the physical and visual properties of the heartwood and sapwood of commercially important hardwood species grown in plantation and young regrowth regimes in Australia with accepted public data for native forest material of those species.

(ii) Determine the likely net value of retaining the sapwood in the tested species given these properties.

The project outcomes are reported in six parts as listed in Table 1.

Table 1: Overview of project reporting structure. REPORT NUMBER NAME AUTHOR/S

Part 1 Project executive summary All

Part 2 Literature review All

Part 3 Mechanical Testing: Minimum radius of bending curvature UMEL

Part 4 Mechanical Testing of western species FPC

Part 5 Mechanical Testing of southern & northern species DPI-Q

Part 6 Visual properties assessment UTAS

1.1 Project Background

The hardwood processing industry in Australia is in transition from milling predominantly native forest logs to milling a combination of plantation and native forest logs of different age and diameter. Increases to Australia's native forest reserves and a reduction in productivity of the remaining resource have reduced the supply of native forest sawlogs (for both solid wood and veneer production) from public forests. Smaller diameter native forest regrowth, and plantation sawlogs are being substituted to make up this shortfall (Nolan, Greaves et al. (2005). Mechanical properties of the Australian timber species (both hardwoods and softwoods) considered at the time to have most commercial potential are given in the standard 1960s references. These reports were prepared by CSIRO Division of Forest Products in the 1960s (Kingston and Risdon (1961) for shrinkage and density, and Bolza and Kloot (1963) for mechanical properties). The data were nearly all based on samples from mature trees. The continually changing availability of forest resources to the Australian timber industry means that it is essential to assess the properties of regrowth species from native forest and those of plantation-grown timbers.

With the transition of the log supply many challenges face the industry regarding the economics of processing the future resource and the ability of the future resource to substitute for declining native sawlog supply (Cameron and Willersdorf (2006). The industry is in different stages of this transition in different regions. Tasmania will experience this transition before others with Forestry Tasmania estimating that hardwood plantations will account for 50% of the (high quality) hardwood sawlog supply by 2020 (currently providing less than 1%). By 2010, the total national supply of hardwood plantation sawlogs will be about 358,000 cubic

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metres per year. Tasmania will produce about 53% of the total and Central Gippsland and North Coast New South Wales about 20% each. Hardwood plantation sawlog supply is forecast to exceed 1 million cubic metres per year after about 2020 and to peak at around 1.8 million cubic metres per year in 2030 (Parsons, Frakes et al. (2007).

A successful transition from native forest logging to intensively managed hardwood plantations will require not only the development of new processing techniques, but also improved knowledge of the properties of the young, fast grown wood resource. Among the attributes most critical to the successful utilisation of plantation hardwoods are the physical and mechanical properties of the wood. Studies on the utilisation properties of Australia plantation hardwoods have recently been conducted by Muneri, Leggate et al. (1998), Muneri and Leggate (2000), Muneri, Smith et al. (2003), McGavin, Bailleres et al. (2007) and McGavin, Davies et al. (2006), who have reported on a range of physical and mechanical properties.

However these studies, and most others reported in the literature, have omitted sapwood from their investigations. Among the reasons for this are:

sapwood has been regarded of such low value due to its low durability and susceptibility to Lyctus spp. (lyctid or powder post beetle) infestation in most species, that it has been regarded as a waste product;

sapwood made up only a small part of hardwood logs traditionally extracted from native forests, and little was recovered during traditional milling operations.

Hardwood producers in all states are recognizing that adjustment to the changed resource is essential. Fundamental questions raised by this adjustment include defining the properties of this new resource and comparing them to the species properties currently recognised in the marketplace. Furthermore, the sapwood of lyctid susceptible eucalypts is removed from the sawn board and veneer as standard practice. With large diameter logs sourced from mature native forests the yield losses through removal of sapwood are relatively minor. However, the recovery losses by removing sapwood become increasingly significant as log diameter decreases and the relative proportion of sapwood increases. Thus potential gains may be made by retaining the sapwood and treating the susceptible material to prevent lyctid attack.

As the sapwood is likely to differ in properties from the heartwood this project will determine and compare the physical and appearance properties of the heartwood and sapwood of commercially important hardwood species grown in plantation and young regrowth regimes with the accepted public data for native forest material of those species. For non-susceptible species and in states where sapwood is currently retained and treated, there is still significant value in clarifying the properties of the future resource. The characteristics of interest in the marketplace include mechanical properties, such as stiffness, strength, density, stability, screw holding and hardness. Appearance properties are also assessed with particular reference to colour, finishing quality and the ability to take a stain and coating.

1.2 Report introduction and objectives

This report provides Part 5, Mechanical Property Assessment of Southern and Northern Hardwood Species.

The objective of this sub-project was to evaluate whether sapwood has equivalent mechanical and physical properties to heartwood in Australian plantation hardwood species.

The properties investigated in this sub-project were:

• Air-dry density (density at 12% moisture content (mc));

• bending strength and stiffness of small, clear samples;

• screw withdrawal strength;

• Janka hardness;

• Percent wood failure of glued samples after cleavage test, dry and wet; and

• shrinkage and basic density.

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The plantation hardwood species under study represent three regions of active hardwood plantation establishment in Australia:

1. Queensland and northern New South Wales, referred to in this report as the northern region,

2. Tasmania and Victoria, the southern region,

3. Western Australia, the western region.

The species chosen for inclusion in the study, if not already major plantation species, are under consideration for extensive establishment in the future. Species representation of the regions was as follows:

Northern: Gympie messmate (Eucalyptus cloeziana), blackbutt (E. pilularis), spotted gum (Corymbia citriodora) and Dunn’s white gum (E. dunnii);

Southern: Southern blue gum (E. globulus), shining gum (E. nitens) and messmate stringy bark (E. obliqua);

Western: Sydney blue gum (E.saligna), karri (E. divericolor).

Apart from Dunn’s white gum, each species was sampled from two separate localities. Preference was for plantation material, but where this was not available, regrowth logs were selected. Fifteen trees were selected from each locality. Log selection from the tree was governed by the need for logs of sufficient size to provide adequate sapwood test material; generally a log of at least 250 mm small end diameter was required to yield a 100 mm cant for further processing. Only one site was available for Dunn’s white gum at the time of the study, but this species was also represented by 30 trees.

All logs sourced from the northern region were cut at the Salisbury Research Centre, Department of Primary Industries and Fisheries, Queensland (DPI&F). Southern and western material was selected as sawn boards during normal milling at commercial sawmills.

Apart from adhesive properties, all testing of western region material was performed by Forest Products Commission, Western Australia. These results are presented in Sub-report Number 4. Adhesive properties results for the western region species are presented in Section 4.7 along with those for the southern and northern region species.

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2. Material and Sampling strategy

2.1 Species Selection

2.1.1 Northern region species Gympie messmate, Eucalyptus cloeziana F. Muell.

Site 1

Locality: Ringtail State Forest, Pomona, Queensland

Age and type: Plantation, 48 years old

Supplier: Natural Resources and Mines, Queensland

Site 2

Locality: Yurol State Forest, Tewantin, Queensland


Supplier: Natural Resources and Mining, Queensland

Blackbutt, Eucalyptus pilularis Smith

Site 1

Age and Type: Regeneration, circa 50 years old

Locality: Coffs Harbour locality, NSW

Supplier: State Forests NSW, via Boral Timber Ltd

Site 2

Age and type: Regeneration, circa 20 years old

Locality: Wild Cattle Ck State Forest, Dorrigo, NSW

Supplier: State Forests NSW via Big River Timbers Pty Ltd

Spotted gum, Corymbia citriodora Hook.

Site 1


Locality: Casino region, NSW


Site 2


Locality: Richmond Range State Forest, Woodenbong, NSW

Supplier: State Forests NSW via Big River Timbers Pty Ltd

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Dunn’s White Gum, Eucalyptus dunnii Maiden

Age and Type: Plantation, 12 years old

Locality: Moonpar State Forest, Dorrigo NSW


2.1.2 Southern region species Tasmanian blue gum, Eucalyptus globulus Labill.

Site 1


Locality: Mt Direction, Tasmania

Supplier: Private

Site 2


Locality: Meunna, Tasmania

Supplier: Forestry Tasmania

Shining gum, Eucalyptus nitens Maiden

Site 1


Locality: Meunna, Tasmania

Supplier: Forestry Tasmania

Site 2


Locality: St George’s Rd, Ridgley, Tasmania

Supplier: Gunns Ltd

Messmate Stringybark, Eucalyptus obliqua L’Her.

Site 1

Age and type: Regeneration, 50 – 60 years old

Locality: Dip River Forest Block, Tasmania

Supplier: Brittons Ltd

Site 2

Age and type: Regeneration, 80 years old

Locality: Arve Loop Rd, Tahune, Tasmania

Supplier: ITC

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2.1.3 Western region species Karri, Eucalyptus diversicolor F. Muell.

Site 1} Refer to Part 4.

Site 2}

Sydney blue gum, Eucalyptus saligna Smith

Site 1} Refer to Part 4.

Site 2}

2.2 Sampling Strategy

It was decided to sample each species two sites located within its principal plantation region. Ideally, it would have been preferable to sample each species from plantation stands of contrasting ages, but at the time of the study such material was not available for most of the species under consideration. Hence some species were sampled from only young plantations, some from only mature plantations and some from natural regrowth stands.

Fifteen trees per stand were selected for sampling. This number exceeds the number recommended by Hamza and Lewark (1994) who calculated the number of trees per stand required to estimate various wood quality attributes in plantation eucalypts with a precision of 5% of the mean. They estimated tree numbers of 4 to 12 for a range of wood anatomical and physical properties, with coefficients of variation ranging from 3 to 8%. Blackbutt, spotted gum and Dunn’s white gum were sampled from mill stocks by employees of the collaborators. Gympie messmate logs were selected at the forest sites by the investigator during a commercial logging operation.

One flitch per log (15 per site) was prepared for the steam bending and appearance sub-projects and two flitches per site for the veneering sub-project. The sampling strategy for the breakdown of samples for this work is considered in the respective sub-project reports.

For the mechanical properties sub-project, again one flitch per site was prepared. From this, one sapwood specimen and one matched heartwood specimen of each type were prepared, as detailed in Sections 3.1.2 and 3.1.3. Matching the samples obviated the need to duplicate samples within trees, because the project objectives stressed testing the equivalence of sapwood and heartwood, rather than determining absolute values of either.

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3. Methods

3.1 Sample preparation

3.1.1 Log breakdown Logs of northern species were sawn on a Kara “Master” circular breakdown saw at the Salisbury Research Centre (SRC). The cutting pattern is shown in Figure 1.

When a veneer project flitch was being recovered, four flitches were produced per log, (two logs per site). When a veneer flitch was not recovered, 3 flitches were prepared (remaining 13 logs per site). The flitches varied in width between 80 and 120 mm depending on log diameter. The allocation of the four flitches was as follows:

• Flitch 1: sawn, dried and retained at Salisbury Research Centre (SRC) for cutting into test pieces for mechanical properties testing;

• Flitch 2: sawn, dried and sent to University of Tasmania (UTAS) for appearance property testing;

• Flitch 3: sawn and sent to University of Melbourne (UMEL) for steam bending tests in green-off-saw condition.

• Flitch 4: sent to Gunns Veneers, Somerset, Tasmania for veneer trials in green-off-saw condition (Two logs / site only).

3.1.2 Flitch processing (northern region only) Before re-sawing, two 250 mm sections were removed from Flitch 1. One was cut into a 50 x 50 x 150 mm hardness test piece, as shown in Fig 1c. This test piece was left in a 12% conditioning chamber for approximately three months until a mc of 12 ± 1 %1 was reached. The second was cut into a pair of 20 x 20 x 100 mm blocks for stability measurements (See under “Stability” in the Methodology section). The remainder of Flitch 1, and the entire Flitch 2 and 3 were re-sawn into 25 mm boards using a band re-saw, as 1 MC of the hardness blocks was monitored by weekly weighing, using a procedure similar to the sample board methodology of AS1080.1 (1997) Timber - Methods of test. Part 1: Moisture content.

1

2 3

4

waste

Figure 1a: Cutting pattern for log breakdown used at SRC .

Figure 1b: Cutting pattern for re-saw of flitches at SRC

s.w. /h.w. boundary

Figure 1c: Cutting pattern for hardness test block from section of Flitch 1

waste

s.w./h.w. boundary

50 x 50 x 150 mm hardness test piece

s.w. board

h.w. board

waste

waste

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shown in Figure 1b. The aim was to produce a matched pair of boards, one predominantly sapwood, the other predominantly heartwood, with as little separation between the sapwood and heartwood boards as possible. (In Gympie messmate, which has a relatively narrow sapwood band, some “sapwood” boards unavoidably included a section of heartwood.)

The boards cut from Flitch 3 were wrapped in plastic film to prevent loss of moisture, and immediately despatched to the University of Melbourne. All other boards were seasoned in a solar kiln to a target mc of 12% before further processing or despatch. Prior to seasoning, the sapwood boards from Lyctid susceptible species2 were treated with a boron solution at a commercial treatment plant to Hazard Level H1 in accordance with the Timber Utilisation and Marketing Act, Queensland, Anon. (1988).

After seasoning, each board from Flitch 1 was cut into test pieces as shown in Figure 2. This enabled matched pairs of sapwood and heartwood specimens to be cut from the adjacent board pairs.

Once cut, all test pieces were stored on a 12% emc conditioning chamber pending testing.

3.1.3 Southern region test material Log breakdown of messmate, shining gum and Tasmanian blue gum was undertaken at a commercial sawmill in Tasmania, detailed in the Appearance Properties Sub-report. A standard industrial cutting pattern was used, yielding mostly quarter-sawn boards. This necessitated a different approach to sawing the mechanical property specimens as was used for the northern region material, which utilised a backsawn cutting pattern. Figure 3 details the cutting of mechanical property test pieces from the southern region material.

2 The lyctid susceptible species were spotted gum and Dunns white gum. Gympie messmate and blackbutt are designated as lyctid immune and so their sapwood boards were left untreated.

Cross-section

70 to 90 x 25

Small clear bending

waste

Screw wdl Adhesive

waste

20 x 20

50 300 25 20 150 25 600

mc density

Length of section

Figure 2: Break-down of boards into mechanical property test pieces (northern species)

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The matched small, clear bending and density specimens were taken from the boards denoted as “sapwood” by the Tasmanian research team, as the boards contained both sapwood and heartwood timber. The adhesive test pair was taken from the “sapwood” and “heartwood” boards as for the Queensland species. Janka hardness specimens were also taken from the laminated adhesive material, because the sawn material proved too thin for testing.

3.1.4 Summary of Testing Schedule Sample numbers and their relationship to sites and trees are summarised in Table 2.

Table 2: Summary of test samples Sub-project Species Sites per

species

Logs per site Flitches per log Sapwood/ heartwood pairs per flitch

Bending radius (Part 3)

9 2 15 1 See Part 3

Mechanical properties (Parts 4 & 5)

9 2 15 1 1 per test type

Visual properties – Solid wood (Part 6)

9 2 15 1 See Part 6

Visual properties Veneer (Part 6)

9 2 2 1 See Part 6

3.2 Properties Testing

3.2.1 Moisture content The moisture content of all test samples was measured after test by the oven dry method of AS1080.1 (1997) Timber – methods of test – part 1 moisture content. Because the samples had been conditioned to 12% mc prior to test, actual mc at the time of test was in the range 12 ± 2%, and no correction of the results for mc was necessary. The mc data have not been reported here.

3.2.2 Density Density was determined gravimetrically as specified in AS1080.3 (2000), Timber - Methods of test. Method 3: Density. The mc of the test pieces was determined by the oven dry method at the time of measure, allowing the density to be corrected to 12% mc using the equation of Budgen (1981).

25 20 150

Small clear bending s.w.

waste

Screw wdl #1

waste

50 300 150 600

mc density

Length of section

Screw wdl #2

Small clear bending h.w. Adhesive

s.w. / h.w. boundary

Figure 3: break-down of boards into mechanical property test pieces (southern species) (Cross-sections as for Fig 2)

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3.2.3 Bending strength and stiffness Bending strength and stiffness were evaluated using the small, clear sample test procedure as defined by Mack (1979). The dimensions of the specimen were 20 x 20 x 300 mm, with the sample supported on a span of 280 mm and loaded centrally on the radial face (Fig 4). Stiffness was measured in the range 200 to 800 N, after which the specimen was loaded to failure and the peak load recorded. The failure mode was recorded using the categories defined in Figure 6 of ASTMD143-94 (2007), Standard methods for small clear specimens of timber. Specimens which exhibited cross grain fracture with a slope of grain exceeding 1 in 20, as well as any samples containing strength limiting defects not apparent before testing were culled from the analysis.

3.2.4 Screw withdrawal The methodology for the screw withdrawal test conformed to AS1649 (2001) (Figure 5). Six gauge, 30 mm plain woodscrews were used for all tests. Four screws were inserted into each specimen, 2 in the tangential surface and 2 in the radial surface3. In the species from the southern region, where sapwood and heartwood were present in the same board, a pair of test pieces was cut for the withdrawal test. The screws were inserted in the sapwood zone of the first sample and into the heartwood zone of the other, giving a matched pair of sapwood and heartwood test pieces.

3 In the northern species, which were backsawn, the tangential surface was the board face and the radial surface the edge; in the southern species which were quartersawn, the orientation of surfaces was opposite.

Figure 4: Small clear bending test

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3.2.5 Janka hardness

The Janka hardness test conformed to the procedure of Mack (1979). The test consists of measuring the force required to indent the specimen with a hemispherical tool, 11.28 mm in diameter, to a depth of 5.64 mm. Figure 6 shows a typical test sample after testing, with the indentations left by the tool visible on the sapwood and heartwood zones of the test piece.

In the northern region species, a 50 x 50 x 150 mm specimen was cut such that the specimen encompassed both the sapwood and heartwood zones, as shown in Figure 1c. In species where the sapwood band was wide enough, four determinations were made; two on the tangential face and two on the radial face in both sapwood and heartwood. In species with a narrow sapwood zone, only two determinations in each of the sapwood and heartwood zones were possible.

The southern region species were supplied as nominally 25 mm thick, quarter sawn boards, although some material was thinner. It was found that many samples split before the Janka tool was fully indented, preventing accurate testing. Therefore a section of laminated board from the adhesive test samples was used for the Janka tests, which met the thickness requirement of the test4 and prevented splitting. Because the tangential face exposed on the board edges was scarcely wider than the Janka tool, no testing of the tangential face was possible in the southern region species.

4 The minimum thickness for Janka test pieces recommended by Mack (1979) is 25 mm.

Figure 5: Screw withdrawal test

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Figure 6: Janka hardness test piece, northern region species

3.2.6 Adhesive testing Test specimens were fabricated using the laboratory pilot press shown in Figure 7.

The 600 mm test boards were cut into 2 sets of paired, 150 mm lengths. One pair was laminated using a phenol / resorcinol formaldehyde adhesive5, the other with a polyurethane adhesive6. The variables of adhesive application complied with the manufacturers’ instructions, and are listed in Table 3.

5 Dynea Prefere 4001 / 5837 6 Nightingale Grasp PUA Adhesive

Figure7: Fabricating adhesive test specimens

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Table 3: Variables of adhesive application Adhesive Type /

Variable

Phenol resorcinol formaldehyde Polyurethane

Spread rate (g / m2) 342 190

Application Brush, 2 sides Brush, 1 side

Open assembly time (min) Less than 5 Less than 5

Closed assembly time (min) Less than 20 Less than 20

Press time (min) 120 60

Press temperature (oC) 60 Ambient

Pressure (MPa) 0.5 -1.0 0.25 - 0.5

At all times, samples were machined less than 24 hours before gluing. This was done to ensure the heartwood samples were not affected by surface inactivation, which is known to impair adhesion in wood (Forbes (1998).

Two sections, 25 mm in length along the grain, were cut from each laminated assembly. A notch approximately 2 mm in depth, was cut into the glue line of each specimen. The notched specimens were subjected to the chisel test of AS/NZS1328.1 (1998) Glued laminated structural timber Part 1, Appendix B4, illustrated in Figures 8 & 9. The first specimen was tested in the dry condition, at least one week after removal from the glue press. The second was tested at a high mc after a vacuum / pressure immersion (VPI) cycle, designed to evaluate the long-term durability of the adhesive. These tests were termed the “dry bond” and “wet bond” tests respectively.

Figure 8: AS/NZS 1328.1 Chisel specimen before test

3.2.7 Stability All stability test material was cut from unseasoned material; flitch sections in the case of the northern region species, and boards in the southern region species. Heartwood material was cut into 20 x 20 x 100 mm sections, and sapwood into 10 x 10 x 50 mm sections, with the grain of the specimen faces orientated truly to the tangential and radial planes. The smaller size was used for sapwood so that 100% sapwood samples could be prepared, even in species with limited sapwood content.

The specimens were marked out with points for consistent measurement:

• Three pairs of points for radial measurement across the grain

Figure 9: Chisel specimens after test

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• Three pairs of points for tangential measurement across the grain

• One pair of points for longitudinal measurement along the grain.

Full-sized heartwood specimens (20 mm section) were measured to 0.001 mm with a digital gauge mounted in a purpose-made jig. The small-sized sapwood specimens were measured to the same resolution using a digital micrometer mounted in a clamp. These measurements are illustrated in Figure 10.

At the time of cutting, a 25 mm mc test specimen was cut adjacent to the stability test specimen for estimation of the oven-dry weight of the latter. This enabled the mc of the stability test specimen to be estimated during the conditioning regime. At the conclusion of the experiment, the actual oven dry weight of the sample was determined, allowing correction of the estimated mc’s.

After cutting, the specimens were wrapped in polythene film and stored in a cold chamber operating at 4 - 6o C to prevent moisture loss until commencement of the experiment. After initial measurement the specimens were unwrapped and allowed to air dry in the laboratory to less than 15%, before being reconditioned in a laboratory kiln under saturated steam conditions. The reconditioned samples were redried to 12% mc in a 12% EMC chamber, then reduced to 5% mc in a 5% EMC chamber. Finally, they were oven dried in a laboratory oven at 103oC for determination of oven-dry weight.

Throughout this process, each stability test specimen was measured at mc conditioning points as shown in Table 4.

Table 4: Conditioning and measurement regime for stability specimens MC condition at time of measurement Shrinkage value determined after measurement

Initial (mc > fsp) None

“air dry” (mc = 12%) Green to 12 %

“air dry” (mc = 12 %) after reconditioning (a.r.) Green to 12 % a.r.

MC = 5% Unit shrinkage between 12 & 5% mc

At the conclusion of the experiment, the specimens were inspected for unrecovered collapse, splitting and undersize. Data from affected specimens was culled prior to statistical analysis. In the case of shining gum, site one, only three specimens remained free of defect, and no statistical analysis was possible.

Figure 10: Measurement of heartwood (right) and sapwood (left) stability specimens

15

4. Results and Discussion

4.1 Analysis Box plots have been used to illustrate the data for physical and mechanical properties. A box plot indicates the central tendency of the values, their variability and the symmetry of the distribution. In this report, the box plots are drawn to the following format:

• The box itself encompasses the middle 50% of the data, and is known as the inter-quartile range,

• The upper end of the box indicates the 75th percentile (upper quartile) of the data set,

• The lower end indicates the 25th percentile (lower quartile),

• The black horizontal line represents the median,

• The ends of the vertical lines above and below the box delineate the range of the data, unless outliers are present, in which case they delineate 1.5 times the inter-quartile range.

• Outliers are shown in green if they lie between 1.5 and 3 times the inter-quartile range and red if they lie outside 3 times the range.

Test means for the paired sapwood and heartwood specimens were compared using a T-test. The null hypothesis for the test is that there is no difference between sapwood and heartwood in the measured property or test result. The alternative hypothesis used in this report is that sapwood and heartwood are not equal. The appropriate test of significance in this case is the two-tailed test. The hypothesis formula can be expressed:

Ho: µsap = µheart H1: µsap ≠ µheart

A paired T-test design was used where there was a definite relationship between the sapwood and heartwood samples under test, in that each pair originated from adjacent positions within a log. This was the case for all tests except the Janka hardness and adhesive tests on the southern region species. For these tests, the sapwood and heartwood boards were not necessarily from the same log, and a two-sample T-test was used. In the analysis of the Tasmanian hardness data, where the number of replicates per site was limited to 6, site data were pooled when neither site or site by type (sapwood / heartwood) interaction were significant.

The effect of the various sources of variation was analysed using analysis of variance (ANOVA). A 2 factor ANOVA design was applied to all the data:

Main effects:

species

wood type (sapwood/heartwood)

Interaction:

Species x wood type

It was decided to separate the northern and southern species for ANOVA analysis, because the two groups are unlikely to be considered for establishment within the same regions.

16

4.3 Density The density measurements for the northern and southern region species are illustrated in Figures 11 and 12a & 12b. Table 5 lists mean density at 12% mc, for sapwood and heartwood samples arranged by species and site and the significance when they are compared using the paired T-test. Where available, literature data for each species are included in the data tables. The literature values are shown alongside the corresponding heartwood data.

Figure 11: Boxplots of density – Northern region species

17

Table 5: Density at 12% mc. Literature figures in brackets.

Mean density @12% mc (kg / m3)

Species Site

Sapwood Heartwood

No. Obs

T stat and significance level

1 1,010 1,060 (969) 8 -4.12 ** Corymbia citriodora, spotted gum 2 951 992 ( 16 -6.66 **

1 1,020 1,030 (1,010) 15 -0.203 n.s. Eucalyptus cloeziana, Gympie messmate 2 981 985 ( 15 -0.422 n.s.

E. dunnii, Dunn’s white gum 1 736 615 (743) 30 7.58 **

1 733 724 (843) 15 0.433 n.s. E. globulus, Tasmanian blue gum 2 715 631 ( 15 5.04 **

Figure 12a: Boxplots of density, southern species

Figure 12b: Boxplots of density, southern region species

18

Mean density @12% mc (kg / m3)

1 576 490 (639) 15 5.05 ** E. nitens, shining gum

2 681 578 ( 15 4.13**

1 702 693 (713) 15 0.652 n.s. E. obliqua, messmate stringybark 2 729 728 ( 15 0.092 n.s.

1 868 905 (860) 9 -3.59 ** E. pilularis, blackbutt

2 931 975 ( 27 -5.48 **

Literature data for Gympie messmate from Kynasten, Eccles et al. (1994). All others from Kingston and Risdon (1961).

Key to significance level symbols for Table 5 and subsequent Tables:

** denotes significant at 1% level;

* denotes significant at 5% level;

n.s. denotes not significant;

n.a. denotes not applicable.

In the species where project material was sourced from regrowth or older plantations (spotted gum, Gympie messmate, blackbutt, messmate stringybark), the observed heartwood densities closely approximate published values, whereas in the species represented by younger plantations (Dunn’s white gum, Tasmanian blue gum, shining gum), heartwood densities were lower.

In comparing sapwood and heartwood densities, there are two conflicting trends to consider:

1. The influence of extractive content, which increases the apparent density of heartwood over sapwood and

2. The influence of physiological maturity, which increases the density of outer-wood over inner-wood.

typically report total extractive contents of about 7% in the outer heartwood. Thus, in logs from older trees, it would be expected that the density surfeit of heartwood over sapwood would be of this order. On the other hand, in logs from younger trees, especially from species of lower extractive content, the sapwood density may be higher than that of heartwood, because the sapwood has more mature properties than the relatively immature heartwood.

Species in which heartwood density was significantly higher than sapwood were the northern region blackbutt and spotted gum, both species of high extractive content, and represented by trees of 20 Studies on Australian plantation hardwoods, for example McGavin, Bailleres et al. (2007), years of age or older. Heartwood density of both species exceeded that of sapwood by 4 to 5%, in line with expected extractive content. The heartwood density of Gympie messmate was not significantly higher than sapwood, although extractive contents of 7% have been reported previously (McGavin, Bailleres et al. (2007). A likely explanation for this apparent anomaly was that many of the “sapwood” boards contained sections of sapwood due to the thinness of the sapwood band in the logs processed.

The species in which sapwood density was higher than that of the matched heartwood were Dunn’s white gum, and the southern-grown species shining gum and Tasmanian blue gum (site 1). In each case, trees were under 20 years old at the time of harvest. Finally, in messmate stringybark and Tasmanian bluegum (site

19

2), there was no significant difference between sapwood and heartwood densities. This can be explained the cancelling out of the opposing trends of extractive content and maturity in these intermediate-aged trees.

4.3 Bending strength Box plots of bending strength, comparing sapwood and heartwood for each of the north and south region species are displayed in Figures 13a & b and 14.

20

Table 6 lists the mean bending strength of the matched sapwood / heartwood pairs, and the significance when they are compared using a paired T-test.

Figure 13a: Box plot of modulus of rupture – Northern region species

Figure 13b: Box plot of modulus of rupture – Northern region species

21

Figure 14: Box plot of modulus of rupture – Southern region species

22

Table 6: Bending strength (literature data bracketed)

Bending Strength (MPa)

Species Site

Mean s.w.

Mean h.w.

No. obs.


1 156.6 170.5 (150) 8 -1.47 n.s. Corymbia citriodora, spotted gum

2 167.8 168.1 ( 15 -0.118 n.s.

1 173.4 176.1 (137) 15 -0.302 n.s. Eucalyptus cloeziana, Gympie messmate 2 159.7 165.0 ( 15 -0.839 n.s.

E. dunnii, Dunn’s white gum 1 110.8 94.14(135) 28 3.62**

1 130.7 131.0 (146) 15 -0.081 n.s E. globulus, Tasmanian blue gum

2 126.9 109.3 ( 11 3.88 **

1 98.26 78.86 (99) 13 3.70** E. nitens, shining gum

2 119.3 100.5 ( 15 3.03**

1 126.3 121.1 (118) 15 0.857 n.s. E. obliqua, messmate stringybark

2 131.4 126.6 ( 15 2.06 n.s.

1 148.9 157.9 (144) 8 -0.133 n.s. E. pilularis, blackbutt

2 179.7 194.7 ( 26 -4.29**

Literature data from Bootle (2005)

In the species represented by older material, heartwood clearwood rupture strength exceeded published data, while as expected, the younger plantation stock was lower in strength.

In spotted gum, Gympie messmate, messmate stringybark, blackbutt (site 1) and Tasmanian bluegum (site 1) there was no significant difference between sapwood and heartwood in bending strength. In Dunn’s white gum, Tasmanian bluegum (site 2) and shining gum, there was a significant difference between sapwood and heartwood, with sapwood having superior properties. This can be attributed to the greater maturity and higher density in the sapwood region of these younger trees.

The one exception is blackbutt (site 2) where the heartwood strength was significantly higher than that of the sapwood.

4.4 Bending stiffness Box plots of bending stiffness, comparing sapwood and heartwood for each of the north and south region species, are displayed in Figures 15 and 16a & b. Table 7: Bending stiffness (literature data bracketed) lists the mean bending stiffness of matched sapwood / heartwood pairs, and the significance when they are compared using a paired T-test.

23

Figure 15: Box plots of modulus of elasticity – Northern region species

Figure 16a: Boxplots of modulus of elasticity – southern region species

24

Table 7: Bending stiffness (literature data bracketed)

Bending Stiffness (GPa) Species Site

Mean s.w. Mean h.w.

No. Obs. T stat and significance level

1 21.4 23.3(23) 8 -1.64 n.s. Corymbia citriodora, spotted gum

2 21.5 21.9( 15 -0.697 n.s.

1 21.7 21.2(17) 15 0.836 n.s. Eucalyptus cloeziana, Gympie messmate 2 20.8 20.8( 15 0.038 n.s.

E. dunnii, Dunn’s white gum 1 14.8 11.6(22) 28 5.55**

1 18.7 17.5(20) 15 2.10* E. globulus, Tasmanian blue gum

2 17.3 13.7( 11 3.87**

1 13.1 9.7(13) 13 5.84** E. nitens, shining gum

2 17.7 13.0( 15 5.36**

1 17.5 17.5(15) 15 0.103 n.s. E. obliqua, messmate stringybark

2 17.7 18.3( 15 -1.13 n.s.

1 19.9 20.4(19) 8 -1.42 n.s. E. pilularis, blackbutt

2 23.8 26.0( 26 -4.66 **


The trends for stiffness were as for strength, and can be explained similarly, both in relation to literature data and comparison between sapwood and heartwood. . The only case of a change in significance between strength and stiffness was in Tasmanian blue gum (site 1), where sapwood stiffness was significantly higher than heartwood (5% level).

Figure 16: Boxplots of modulus of elasticity – southern region species

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4.5 Janka Hardness

Box plots of the Janka hardness results, arranged as for previous data, are displayed in Figure 17 and 18. Table 8 lists the mean Janka hardness of matched sapwood / heartwood pairs, and the significance when they are compared using a paired T-test. The tabulated data are based on the mean of the two or four determinations possible per sample (See Section 3.2.4).

Figure 17: Box plots of Janka hardness – Northern region species

Figure 28: Box plots of Janka hardness - Southern region species

26

Table 8: Janka hardness (literature data bracketed)

Janka Hardness (kN) Species Site

Mean s.w. Mean h.w.

No. Obs.

T stat7

1 12.14 11.97(11) 8 0.915 n.s. Corymbia citriodora, spotted gum 2 10.95 10.99( 18 -0.15 n.s. 1 13.73 14.10(12) 15 -0.94 n.s. Eucalyptus cloeziana, Gympie

messmate 2 11.39 12.71( 15 -4.24 ** E. dunnii, Dunn’s white gum 1 6.10 4.78(7.2) 30 8.02 ** E. globulus, Tasmanian blue gum8

1} 2}

5.99 5.33(12) 24 1.61n.s.

1 4.32 3.93(5.8) 12 0.912n.s. E. nitens, shining gum 2 5.82 4.88( 12 2.00n.s.

E.obliqua, messmate stringybark8 1} 2}

6.11 5.93(7.1) 24 0.446n.s.

1 8.60 9.16(9.1) 8 -1.00 n.s. E. pilularis, blackbutt 2 9.97 10.06( 27 -0.32 n.s.


Spotted gum, Gympie messmate, and blackbutt had heartwood hardness equivalent to the literature figures, consistent with their performance in strength and stiffness. Messmate stringybark was slightly below published results, but the remaining species were well below the literature values.

In spotted gum, Gympie messmate (site 1) and blackbutt there was no significant difference between sapwood and heartwood in Janka hardness. In Gympie messmate (site 2) however, the heartwood was significantly harder than the sapwood. This contrasts with the comparison in density, bending strength and stiffness with this material, where no significant difference was found, and is not fully understood. Nonetheless, the sapwood hardness at this site is still very high, and comparable to the published value for mature, heartwood of this species.

By contrast, the sapwood hardness of Dunn’s white gum is significantly greater than that of the heartwood. This can be readily explained by the significantly higher density of the outerwood region of these young trees.

In the southern region, the sapwood hardness was higher than heartwood in all species, although the differences were not statistically significant. This may be due to the limitations of the test samples discussed in Section 3.2.4, which precluded the use of a paired analysis design. Nonetheless, an inferior performance of sapwood to heartwood in this property has not been demonstrated.

7 Paired test for C. citriodora, E.cloeziana, E. dunnii, & E. pilularis. Two-sample test for others. 8 Data for site 1 and site 2 pooled. See Section 3.2.4.

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4.6 Screw Withdrawal

Mean screw withdrawal strength is displayed as box plots in Figures 18 and 19. T-test results for this data are summarized in Error! Reference source not found., and the resulting joint group data in Error! Reference source not found..

Figure18: Box plots of withdrawal strength, Northern-grown species

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Table 9: Screw withdrawal strength

Withdrawal (kN) Species Site

Mean s.w. Mean h.w.

No. Obs.

T stat7

1 3.04 3.04 8 -0.025 n.s. Corymbia citriodora, spotted gum

2 2.79 2.92 16 -1.81 n.s.

1 3.20 3.22 15 -0.215 n.s. Eucalyptus cloeziana, Gympie messmate 2 2.85 2.86 15 -0.17 n.s.

E. dunnii, Dunn’s white gum 1 1.77 1.53 30 4.38 **

1 1.82 1.68 15 2.66 * E. globulus, Tasmanian blue gum

2 1.70 1.42 15 5.44 **

1 1.44 1.16 15 4.37 ** E. nitens, shining gum

2 1.75 1.51 15 3.00 **

1 1.56 1.59 15 -0.71 n.s. E. obliqua, messmate stringybark

2 1.82 1.74 15 1.76 n.s.

Figure 19: Box plots of withdrawal strength – southern region species

29

Withdrawal (kN) Species Site

Mean s.w. Mean h.w.

No. Obs.

T stat7

1 2.38 2.68 9 -2.74 * E. pilularis, blackbutt

2 2.64 2.91 26 -5.61**

Table 10: Joint group by species, site and wood type

Joint Group Species Site

Sapwood Heart-wood Overall Standard Species Value, AS1720.1

1 JD1 JD1 JD1 Corymbia citriodora, spotted gum

2 JD1 JD1 JD1

JD1

1 JD1 JD1 JD1 Eucalyptus cloeziana, Gympie messmate 2 JD1 JD1 JD1

JD19

E. dunnii, Dunn’s white gum 1 JD2 JD3 JD2 JD2 8

1 JD3 JD3 JD3 E. globulus, Tasmanian blue gum

2 JD3 JD3 JD3

JD2

1 JD3 JD4 JD4 E. nitens, shining gum

2 JD2 JD3 JD3

(JD4)10

1 JD3 JD3 JD3 E. obliqua, messmate stringybark

2 JD3 JD2 JD2

JD3

1 JD1 JD1 JD1 E. pilularis, blackbutt

2 JD1 JD1 JD1

JD2

Literature data is not available for this property, however published joint group ratings, discussed below, allow the experimental material to be benchmarked against the established hardwood resource.

Results followed similar trends to the other strength properties: spotted gum, Gympie messmate and messmate stringybark showed no significant difference between sapwood and heartwood in screw holding capacity. Blackbutt showed significantly lower screw holding capacity in the sapwood samples, especially in site 2, mirroring its performance in bending strength and stiffness.

Dunn’s white gum, shining gum and Tasmanian blue gum all showed significantly higher screw holding capacity in the sapwood samples. In the southern region species, screw withdrawal was more variable within species compared with the northern ones. This can be explained by the fact that testing was limited to the radial faces of the quarter sawn boards by sample geometry. Figure 20 illustrates how screws may encounter either earlywood or latewood in a quarter sawn board, whereas in backsawn boards, the wood density encountered by each screw is more uniform.

9 JD ratings from Hopewell (2006) 10 Provisional rating based on measured mean density for this sample.

30

ii) i) Joint groups were calculated from the data according to AS1649 (2001) Timber - Methods of test for mechanical fasteners and connectors - Basic working loads and characteristic strengths. This analysis was conducted to see if the statistical differences discussed above translated into a change of joint group rating, a significant property of wood for many structural applications. Calculation of JD rating allows comparison of the sapwood and heartwood values with the Australian Standard species value Tabulated in AS 1720.1, Timber structures Part 1: Design methods.

Again there was a distinction between the older and younger material. Gympie messmate, messmate stringybark and spotted gum achieved or exceeded the Australian Standard values in both sapwood and heartwood. The observed lower sapwood withdrawal of blackbutt did not translate in a lower JD rating, because the average withdrawal strength was still well above the JD 2 threshold.

Messmate stringybark from site 2 had a lower JD rating in sapwood, even though the mean withdrawal strength was not statistically different from that of heartwood. This can be explained by the greater variability of sapwood data, evident in the box plot, which has resulted in a lower 5th percentile value and consequently JD rating. Nonetheless, the sapwood JD rating was still equivalent to the Australian Standard value.

In the younger material, the ratings of Dunn’s white gum and Tasmanian blue gum did not match the Australian Standard ratings. Shining gum is not tabulated in AS1720 (1997), but the observed rating of JD3 to JD4 is consistent with the density of the material tested.

Figure 20: Insertion of screws into back-sawn (i) and quarter-sawn (ii) boards to show the potential for higher variability in case (ii)

31

4.7 Glue Bonding

4.7.1 Phenolic Adhesive

Results for dry and wet bond scores in the chisel test for phenol-resorcinol adhesive are summarized in Error! Reference source not found.. Bond scores were recorded as percentages, which were normalised for analysis using an arcsine square root transformation. The back-transformed means are tabulated in Error! Reference source not found..

Table 11: Bond scores for phenol-resorcinol, percentage wood failure (back transformed means)

Dry Wet Species Site

Sapwood Heartwood T sig.11

Sapwood Heartwood T sig.

1 42.6 0.00 ** 0.00 0.00 n.a. Corymbia citriodora, spotted gum

2 25.4 0.14 * 0.00 0.00 n.a.

1 25.12 0.14 ** 0.00 0.00 n.a. Eucalyptus cloeziana, Gympie messmate 2 1.65 0.14 n.s. 0.00 0.00 n.a.

1 47.4 5.78 * 54.3 0.14 * E. diversicolor, karri

2 58.8 17.6 * 31.2 2.00 n.s.

E. dunnii, Dunn’s white gum 1 78.3 30.8 ** 69.5 11.7 **

1 100 97.9 n.s. 88.6 74.8 n.s. E. globulus, Tasmanian blue gum

2 88.9 68.4 n.s. 62.9 44.4 n.s.

1 98.9 94.7 n.s. 92.4 51.6 n.s. E. nitens, shining gum

2 99.4 93.4 n.s. 61.8 49.6 n.s.

1 93.3 85.9 n.s. 85.4 57.9 n.s. E. obliqua, messmate stringybark

2 97.9 91.0 n.s. 20.7 14.3 n.s.

1 40.1 3.77 n.s. 0.76 0.76 n.s. E. pilularis, blackbutt

2 63.8 4.25 ** 4.80 0.00 *

1 47.2 43.5 n.s. 37.9 28.1 n.s. E. saligna, Sydney blue gum

2 60.9 74.2 n.s. 55.2 28.0 n.s.

Bonding of high density Australian hardwoods with adhesives has long been regarded as problematic; Widsten, Gutowoski et al. (2005) reported that the lowest bond strengths were produced by species combining high extractive contents and high density. In the current study, dry wood failure in sapwood was better than that of heartwood in the higher density species such as spotted gum, Gympie messmate and blackbutt. However bonding after the wet conditioning treatment was severely weakened, with almost no wood failure observed in either sapwood or heartwood.

In most of the lower density species, bonding has been successful in both sapwood and heartwood, and there was no significant difference between the two wood types. After wet conditioning, wood failure was somewhat reduced, but still acceptable with no statistical difference between sapwood and heartwood. Dunn’s white gum and Karri were exceptions, however. In both species, dry wood failure in sapwood was better than that of heartwood, as in the high density species, but this was also the case after wet conditioning.

11 Paired T-test for northern species, two-sample test for Tasmanian species.

32

4.7.2 Polyurethane Adhesive Error! Reference source not found. reports the bond scores for polyurethane bonding in the same format as Error! Reference source not found..

Table 12: Bond scores, polyurethane adhesive, percentage wood failure (back-transformed means)

Dry Wet Species Site



1 64.8 19.3 n.s. 0.0 0.0 n.a. Corymbia citriodora, spotted gum

2 28.0 26.1 n.s. 0.0 0.0 n.a.

1 2.54 0 n.s. 0.0 0.0 n.a. Eucalyptus cloeziana, Gympie messmate 2 18.7 0.76 n.s. 0.0 0.0 n.a.

1 80.5 51.7 n.s. 0.0 0.0 n.a. E. diversicolor, karri

2 64.2 51.9 n.s. 9.0 0.9 n.s.

E. dunnii, Dunn’s white gum 1 80.5 94.2 n.s. 29.1 47.4 n.s.

1 100 93.8 n.s. 95.3 73.0 n.s. E. globulus, Tasmanian blue gum

2 100 94.1 n.s. 61.7 48.7 n.s.

1 98.5 97.2 n.s. 98.5 90.7 n.s. E. nitens, shining gum

2 98.3 100 n.s. 76.1 74.5 n.s.

1 100 95.3 n.s. 60.5 13.9 n.s. E. obliqua, messmate stringybark

2 100 99.8 n.s. 2.5 7.9 n.s.

1 81.0 32.0 n.s. 0.44 0.0 n.s. E. pilularis, blackbutt

2 58.1 50.2 n.s. 0.0 0.0 n.a.

1 47.2 43.5 n.s. 2.3 4.3 n.s. E. saligna, Sydney blue gum

2 58.7 73.9 n.s. 43.4 2.7 n.s.

Dry bonding of heartwood with the polyurethane adhesive has been more successful than with phenolic in most species. Although sapwood generally recorded higher bond scores than heartwood, the differences were not statistically significant. An exception was Gympie messmate, which did not achieve high wood failure in either sapwood or heartwood. As with the phenolic adhesives, bonding after wet conditioning in high density species was severely reduced, with little wood failure recorded in either sapwood or heartwood. However, with the polyurethane adhesive, wet bonding was also poor in the lower density species, resulting in no statistical difference between sapwood and heartwood. These findings confirm the results of Vick and Okkonen (1998), who found that polyurethanes provided equal or better bonding in yellow birch and Douglas fir to resorcinol when tested in the dry state, but recorded very low wet wood failure with these adhesives compared with resorcinol.

These experiments have shown that sapwood can be bonded at least as successfully as the heartwood of these plantation species. Excellent dry bonds can be achieved with most of the species in both sapwood and

33

heartwood, especially with the polyurethane adhesive. In the case of wet bonding, however, bonding of heartwood was less successful, especially with the polyurethane adhesive. This suggests that, where durable bonds are required under exterior exposure, careful selection of species and adhesive will be required.

4.8 Stability Stability data are summarised in Table 13. The unit volumetric shrinkage data - normalised for analysis using an arcsine square root transformation - are displayed as box plots in Figures 21 and 22, and Table 14 reports statistical analysis of these data.

Table 13: Stability data (literature data bracketed)

Shrinkage to 12% mc (%)

Unit linear shrinkage

(% per % mc)

Species

(2 sites combined)

Wood type Basic density (kg/m3)

Radial Tangential Radial Tangential

Sapwood 763 4.8 5.3 0.34 0.36 Spotted gum Heartwood 827 (790) 3.5 (3.7) 5.1 (5.0) 0.34 (0.32) 0.32 (0.38)

Sapwood 751 3.5 4.5 0.31 0.37 Gympie messmate Heartwood 832 (810) 3.2 (3.4) 4.8 (6.2) 0.31 (0.21) 0.36 (0.37)

Sapwood 577 5.4 4.7 0.24 0.34 Dunn’s white gum Heartwood 502 (625) 2.1 (2.0) 6.8 (4.1) 0.17 (0.20) 0.30 (0.36)

Sapwood 551 5.6 8.5 0.31 0.36 Tas. blue gum Heartwood 520 (681) 3.8 (3.2) 7.8 (6.2) 0.24 0.34

Sapwood 484 3.3 6.6 0.20 0.31 Shining gum Heartwood 483 (524) 3.1 (3.0) 7.8 (5.9) 0.17 (0.22) 0.29 (0.33)

Sapwood 523 3.9 6.5 0.25 0.33 Messmate stringybark Heartwood 552 (599) 4.6 (3.3) 8.9 (6.3) 0.28 (0.23) 0.36 (0.36)

Sapwood 704 4.4 5.5 0.21 0.23 Blackbutt

Heartwood 721 (698) 4.6 (3.5) 7.1 (5.8) 0.32 (0.26) 0.37 (0.37)

Literature data for Gympie messmate from Kynasten, Eccles et al. (1994). All others from Kingston and Risdon (1961).

34

Figure 21: Northern region species, unit volumetric shrinkage

Figure 21 (cont.): Northern region species - Unit volumetric shrinkage

35

Table 14: Unit volumetric shrinkage, back-transformed means

Mean unit volumetric shrinkage (%)

Species Site

Sapwood Heartwood

No. Obs.


1 0.70 0.67 8 0.83 n.s. Corymbia citriodora, spotted gum

2 0.69 0.66 13 1.54 n.s.

1 0.69 0.70 11 -0.63 n.s. Eucalyptus cloeziana, Gympie messmate 2 0.65 0.63 14 1.16 n.s.

E. dunnii, Dunn’s white gum 1 0.59 0.47 28 6.85 **

1 0.70 0.57 12 6.97 ** E. globulus, Tasmanian blue gum

2 0.60 0.58 8 0.74 n.s.

1 Insufficient data for analysis – see text E. nitens, shining gum

2 0.61 0.45 7 5.29 **

1 0.55 0.58 8 -1.66 n.s. E. obliqua, messmate stringybark

2 0.60 0.66 10 1.93 n.s.

1 0.39 0.71 8 -38.0 ** E. pilularis, blackbutt

2 0.44 0.68 19 -10.3 **

Generally, the heartwood shrinkage results obtained in this study accord with published results for the respective species, when the age of the test material is taken into consideration. Hence Dunn’s white gum, Tasmanian blue gum and shining gum had somewhat lower basic density and shrinkages than the published data, while the other species approximated the published data more closely.

The unit volumetric shrinkage, estimated from the tangential and radial shrinkages over the measured mc range, provides a convenient summary property for the stability attributes. The mean unit radial shrinkages for the sapwood and heartwood specimens were compared using the paired t-test. In spotted gum, Gympie messmate, and messmate stringybark, no significant difference between sapwood and heartwood was found.

Figure 22: Southern region species - Unit volumetric shrinkage

36

In Dunn’s white gum, shining gum and Tasmanian blue gum, sapwood shrinkage was significantly greater than that of heartwood. This would be expected, because it has long been known that lower volumetric shrinkage in eucalypts is associated with an increase in water-soluble extractives (Chafe (1987). Further, volumetric shrinkage is positively related to the polysaccharide (cellulose) content (ibid). The basic density results collected with the stability data confirm earlier observations of higher density in the sapwood region of the younger-aged test material, and hence suggest a likelihood of increased shrinkage in the denser sapwood.

In blackbutt, unit volumetric shrinkage of heartwood is significantly higher than that of sapwood. This seems to contradict the results observed for the other six species, where sapwood shrinkage, if significantly different from heartwood, was the greater. An explanation can be found in the behaviour of the blackbutt material after reconditioning. Reconditioning of the sapwood boards was commenced at a mean mc of 14.5%, whereas the mean mc of the heartwood boards was 10% at the time of reconditioning. Blackmore and Langrish (2008) note that reconditioning of hardwoods has been found to be progressively less effective at mc’s below 15%. It is thus possible that reconditioning of the heartwood samples of blackbutt was not fully effective, and the reported shrinkage values are inflated by residual collapse.

4.9 Variability between species The results for the analysis of variance are summarised in Table 15 and Table 16 for the mechanical properties measured in the project.

Table 15: Results of analysis of variance for significance of differences between means for species and wood type and the interaction between these, northern species Property Species Wood type

(sap/heart) Interaction

Density at 12% mc

** n.s. **

Bending strength

** n.s. **

Bending stiffness

** n.s. **

Janka hardness ** n.s. **

Screw withdrawal

** n.s. **

Table 16: Results of analysis of variance for significance of differences between means for species and wood type and the interaction between these, southern species Property Species Wood type

(sap/heart) Interaction

Density at 12% mc

** ** **

Bending strength

** ** n.s.

Bending stiffness

** ** **

Janka hardness ** * n.s.

Screw withdrawal

** ** *

37

In the northern species (Table 15), there is a common pattern of significance for all the measured properties. The effect of species is significant, reflecting the large difference between Dunn’s white gum and the other three species, which has been considered above. The effect of wood type (sapwood v heartwood) was not significant across the 4 species, yet there was a significant interaction between wood type and species. Again this is due to Dunn’s white gum, in which there was a larger (and sometimes significant) difference between sapwood and heartwood in the properties examined.

In the southern species (Table 16), the pattern of variation is more varied. Species and wood type were both significant main effects in all measured properties. The species by type interaction was not significant for bending strength and Janka hardness, indicating that a similar relationship between sapwood and heartwood results occurred in all species. This was not the case for density and bending stiffness, where the sapwood hardwood response was less uniform. Reasons for this behaviour are discussed under the results for each property.

5. Western region results

See Sub-Report 4, Mechanical Testing of western species.

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6. Conclusion The mechanical property tests have shown that, with the exception of blackbutt, the properties of sapwood are at least equivalent to those of heartwood. Where the trees were of young age at harvest, as was the case with Dunn’s white gum, Tasmanian blue gum and shining gum, the strength of the sapwood was in fact superior to that of heartwood. This can be attributed to the higher density of the outer-wood (where the sapwood is located) compared with the heartwood in these still maturing trees. In the species represented by more mature logs (either older plantation or regrowth logs) – spotted gum, Gympie messmate and messmate stringybark, the strength properties of sapwood do not differ significantly from those of heartwood. In these species, heartwood density was slightly higher than sapwood, but this can be accounted for by the absence of extractives in the sapwood.

A significant finding from this study, confirming indications from earlier work by McGavin, Davies et al. (2006) and McGavin, Bailleres et al. (2007), is that plantation trees will yield wood of lower density and strength if harvested before the trees approach physiological maturity. Hence the specimens of Dunn’s white gum, Tasmanian blue gum, and shining gum all averaged lower density and mechanical properties than those reported in the literature for these species. These were also the species in which the sapwood properties were found to be superior to heartwood in this study.

The blackbutt samples, especially those sourced from Big River Timbers (Site 2) did reveal lower sapwood properties compared with heartwood in a number of the tests. The material tested in this project was sourced from natural forest regrowth; when suitable plantation blackbutt becomes available, further investigation of this species is warranted.

The screw withdrawal tests showed that the sapwood of all species was equivalent to heartwood. However, joint group ratings calculated from the data for the younger material did not match the ratings published in Australian Standards for the corresponding species.

Bonding of heartwood in the higher density, northern region species, was inferior to sapwood when using phenolic adhesives, but was satisfactory in the lower density, southern and western region material. Dry bonding with polyurethane adhesives was satisfactory in both sapwood and heartwood in all species except Gympie messmate. Wet bonding of the polyurethane samples was unsatisfactory in both sapwood and heartwood of the high density species, but remained satisfactory in the low density ones.

The relationship between sapwood / heartwood and the stability properties was complicated by the effects of wood density and reconditioning. In the species represented by older re-growth and plantation material, basic density, shrinkage and stability (unit shrinkage), tended to approximate literature data for the corresponding species. Differences between sapwood and heartwood were not significant. An exception to this trend was blackbutt, where the shrinkage of heartwood was significantly greater than that of sapwood. This can be attributed to the incomplete reconditioning of the heartwood in this species. Significant differences were found between sapwood and heartwood stability in the younger aged material, with heartwood being the more stable (having lower unit shrinkage). This can be attributed to:

1. the greater basic density of the sapwood region; and

2. the bulking effect of extractives in the heartwood.

39

7. References Anon. (1988) Timber Utilization and Marketing Act Gazette Notice, 1998. In. (Queensland Government Printer) AS1080.1 (1997) Timber - Methods of test. Part 1: Moisture content. AS1080.3 (2000) Timber - Methods of test. Method 3: Density. AS1649 (2001) Timber - methods of test for mechanical fasteners and connectors - Basic working loads and characteristic strengths. AS1720 (1997) Timber structures Part 1: Design methods. AS 1720.1 - 1997. AS/NZS1328.1 (1998) Glued laminated structural timber Part 1: Performance requirements and minimum production requirements. AS/NZS 1328 Part 1:1998. ASTMD143-94 (2007) Standard methods for small clear specimens of timber. ASTM D 143 - 94 (2007). Blackmore P, Langrish TAG (2008) Effect of pre-drying schedule ramping on collapse recovery and internal checking with Victorian ash eucalypts. Wood Sci Technol. 42, 473 - 492. Bolza E, Kloot NH (1963) The mechanical properties of 174 Australian timbers. CSIRO Division of Forest Products Technol. Pap. 25. Bootle K (2005) ' Wood in Australia: Types, properties and uses.' (McGraw-Hill Book Company: Sydney NSW Australia) Budgen B (1981) Shrinkage and density of some Australian and south-east Asian timbers. DBR Technical Paper (Second Series) C.S.I.R.O. 38. Cameron J, Willersdorf R (2006) Why plantations are no substitute for native forest timber in Victoria. In 'Victorian Forest Industries Association Seminar'. (VAFI: Melbourne) Chafe SC (1987) Collapse, volumetric shrinkage, specific gravity and extractives in Eucalyptus and other species. Wood Science and Technology 21, 27 - 41. Forbes C (1998) Wood surface inactivation and adhesive bonding. Wood Products Notes, Department of Wood & Paper Science, North Carolina State University. Hamza K, Lewark S (1994) Sampling for wood properties in trial plots of 4 Eucalyptus species at Ruvu, Tanzania. Ann Sci For 51, 233 - 240. Kingston RST, Risdon CJE (1961) Shrinkage and density of Australian and other South-west Pacific woods Division of Forest Products Technological Paper C.S.I.R.O. 13.

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Kynasten WT, Eccles DB, Hopewell G (1994) Gympie messmate. Timber species notes, DPI Forest Service 64. Mack JJ (1979) Australian methods for mechanically testing small clear specimens of timber. DBR Technical Paper (Second Series) C.S.I.R.O. 31. McGavin R, Bailleres H, Hopewell G (2007) 'Wood quality and structural properties of two tropical plantation eucalypts from North Queensland.' Forest and Wood Products Australia, PN07.3022, Melbourne, Vic, Australia. McGavin R, Davies M, M.MacGregor-Skinner J, Bailleres H, Armstrong M, Atyeo W, Norton J (2006) 'Utilisation potential and market opportunities for plantation hardwood thinnings from Queensland and northern New South Wales ' Forest and Wood Products Research and Development Corporation., PN05.2022, Melbourne, Vic, Australia. Muneri A, Leggate W (2000) Wood properties and sawn timber characteristics of fast, plantation grown 4-year old Eucalyptus pilularis. In 'Opportunities for the new Millennium: Proceedings of the Australian Forest Growers Biennial Conference'. Cairns, Qld, Australia. (Eds A Snell and S Vize) pp. 64 - 72. (Australian Forest Growers) Muneri A, Leggate W, Palmer G, Ryan P (1998) The influence of age and site on wood properties of plantation grown Eucalyptus cloeziana and the implications for utilisation. In 'Managing and Growing Trees Training Conference'. Kooralbyn, Queensland, Australia pp. 290-296. (Department of Natural Resources and Mines, Qld) Muneri A, Smith G, Armstrong M, Andrews M, Joe W, Dingle J, Dickson R, Nester M, Palmer G (2003) 'The impact of spacing and thinning on growth, sawing characteristics and knot patterns of 36-year-old Eucalyptus pilularis.' State Forests of NSW and Queensland Forest Research Institute, Technical Report. Nolan G, Greaves B, Washusan R, Parsons M, Jennings S (2005) 'Eucalypt plantations for solid wood products in Australia - A review.' FWPRDC Proj. No. PN04.3002. Parsons M, Frakes I, Gavran M (2007) 'Australia's Plantation Log Supply 2005 - 2049.' National Plantation Inventory, Bureau of Rural Sciences, Canberra. Vick C, Okkonen E (1998) Strength and durability of one-part polyurethane bonds to wood. Forest Products Journal 48, 71 - 76. Widsten P, Gutowoski W, Li S, Cerra S, Molenaar S, Spicer M (2005) Relevance of wood extractive content to surface inactivation and adhesive bonding of wood. In '13th ISWFPC Symposium on the chemistry performance of composites containing wood and natural plant fibres'. Rotorua, New Zealand

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Acknowledgements The author wishes to thank the following organisations and individuals who contributed to the success of this study:

The Department of Primary Industries and Fisheries (DPI&F) for providing financial support and services to the project, especially through the infrastructure and equipment at the Salisbury Research Centre;

The Forest and Wood Products Association (FWPA) for providing financial support to the project (reference PN07.2307);

The Timber Research Unit, University of Tasmania, for overseeing the project, and especially Greg Nolan and Ross Farrell for co-ordination of the work;

Stuart Austin of Big River Timbers, Grafton for the provision of logs for the project;

Nigel Wilshire and John Norrie of Boral Timber for the provision of logs for the project;

Denis Rolfe and Lance Stumm of Department of Natural Resources and Mines for the provision of logs for the project and assistance with log extraction;

John Toole of DGI Springwood, Crestmead, Qld for advice on glue lamination and adhesives;

Martin Davies of DPI&F for conduct of the stability measurements;

Michael Kennedy, Robert McGavin, Eric Littee, Adam Redman and Daniel Field of DPI&F for technical support and sample preparation.

ii

On 26 March 2009, the Department of Primary Industries and Fisheries was amalgamated with other government departments to form the Department of Employment, Economic Development and Innovation.

© The State of Queensland, Department of Employment, Economic Development and Innovation, 2009. Except as permitted by the Copyright Act 1968, no part of the work may in any form or by any electronic, mechanical, photocopying, recording, or any other means be reproduced, stored in a retrieval system or be broadcast or transmitted without the prior written permission of the Department of Employment, Economic Development and Innovation. The information contained herein is subject to change without notice. The copyright owner shall not be liable for technical or other errors or omissions contained herein. The reader/user accepts all risks and responsibility for losses, damages, costs and other consequences resulting directly or indirectly from using this information. Enquiries about reproduction, including downloading or printing the web version, should be directed to [email protected] or telephone +61 7 3225 1398. Researcher: W. Atyeo Salisbury Research Centre, Queensland Primary Industries and Fisheries, Department of Employment, Economic Development and Innovation 50 Evans Rd, Salisbury, Qld 4107

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