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 DOI: 10.1177/0021998310373520

2011 45: 219 originally published online 1 September 2010Journal of Composite MaterialsH.P.S. Abdul Khalil, M.R. Nurul Fazita, M. Jawaid, A.H. Bhat and C.K. Abdullah

Empty Fruit Bunches as a Reinforcement in Laminated Bio-composites  

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Empty Fruit Bunches as a Reinforcementin Laminated Bio-composites

H. P. S. ABDUL KHALIL,* M. R. NURUL FAZITA, M. JAWAID, A. H. BHAT

AND C. K. ABDULLAH

Division of Bioresource Technology, School of Industrial Technology, Universiti Sains

Malaysia, 11800 Penang, Malaysia

ABSTRACT: In this article, we study laminated bio-composites that were reinforcedwith empty fruit bunches. Five-ply veneer laminated bio-composites were preparedby alternately arranging oil palm trunk veneer and empty fruit bunch mat.Composites were made with a gluing layer of 250 or 450 g/m2 of phenol formalde-hyde. The mechanical, physical, and thermal (TGA) properties of the composite werestudied. Results indicated an improvement in mechanical, physical, and thermalproperties of the laminated bio-composites with the use of empty fruit bunches asreinforcement. The water absorption and thickness swelling of laminated bio-com-posites that were reinforced with empty fruit bunches were better than bio-compo-sites not reinforced with empty fruit bunches. Laminated bio-composites with the useof empty fruit bunch as reinforcement showed better bending strength, bendingmodulus, and screw withdrawal. Thermal stability for laminated bio-compositeswith empty fruit bunch also improved. Images taken with a scanning electron micro-graph indicated an improvement in the fiber�matrix bonding for the laminated panelglued with 450 g/m2 of phenol formaldehyde.

KEY WORDS: laminated bio-composites, oil palm trunk veneer, empty fruitbunch.

INTRODUCTION

THE OIL PALM (Elaeis guineensis Jacq.) tree cultivation in Malaysia originated fromWest Africa where it was growing wild and later developed into an agricultural crop.

The oil palm is a tropical palm tree therefore it can be cultivated easily in Malaysia. Thefirst commercial oil palm estate in Malaysia was set up in 1917 at Tennamaran Estate,Selangor [1]. Oil palm industries in Malaysia generate about 90 million tonnes of renew-able biomass (trunks, fronds, shells, palm press fiber and empty fruit bunches) per year,including about 8.2 million tonnes of oil palm trunks, 12.9 million tonnes of pruned andfelled fronds, and 15.8 millions tonnes of oil palm empty fruit bunches (EFB) [1,2]. The oil

*Author to whom correspondence should be addressed. E-mail: akhalilhps@gmail.com

Journal of COMPOSITE MATERIALS, Vol. 45, No. 2/2011 219

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palm biomass (OPB) is classified a lignocellulosic residues that typically contain 50%cellulose, 25% hemicellulose, and 25% lignin in their cell wall [2]. These excess materialshave the potential to be used as raw materials in wood-based industries. As such, the oilpalm industry must be prepared to take advantage of the situation and utilize the availablebiomass in the best possible manner [3].

A lot of construction material consists of engineered wood products. As such, theintrinsic variability is stabilized, precise specifications are met, and by-products of woodmanufacturing can be processed. An important representative of this group of materials isplywood showing excellent physical and mechanical properties [4]. Conventional plywoodconsists of a flat panel built from sheets of veneer referred to as plies. Multiple plies areplaced under pressure with a bonding agent, producing a panel with an adhesive bondbetween plies as strong as, or stronger, than wood. Plywood is assembled from anodd number of layers, with the grains of adjacent layers arranged in a perpendicularfashion [5]. More recently, new innovative bio-composite products based on naturalfibers, such as agricultural fibers or residues, or wood with natural fiber laminates, havebeen introduced in the market and directly compete with traditional wood composites [6].

The first wood adhesive matrix material used in the mass production of plywood panelswas phenol formaldehyde (PF). Phenol formaldehyde is widely used in applications thatrequire stability in severe weather conditions, such as plywood for exterior construction [7].Despite the emergence of several new classes of thermosets, high-performance polymersand several other new generation materials that are superior in some respects, phenolicresins retain industrial and commercial interest a century after their introduction. Thisrecognition emerges from the fact that these resins have several desirable characteristics,such as superior mechanical strength, heat resistance and dimensional stability as well ashigh resistance against various solvents, acids, and water. They are inherently flame resis-tant, and evolve low smoke upon incineration [8]. PF type adhesives are environmentallyacceptable because of the negligible formaldehyde emission. They are structurally durable,provide high quality wood bonding, and are suitable for use under all climatic conditions.However, conventional PF adhesives are slow curing, require higher curing temperature,and are less tolerant to variations in anatomical features and wood substrate [9].Phenol�formaldehyde adhesives are used to glue the veneer plies of exterior-grade ply-wood panels, the flakes of oriented strandboard (OSB) panels and particleboards panels.PF resins provide high strength and are extremely resistant to moisture, which preventsdelamination and gives excellent temperature stability and low initial viscosity. This is inpart due to the more flexible nature of phenolic resins [10].

There is currently considerable research concerning the use of oil palm biomass as thestructural component in various products, with results showing that these materials havethe potential to replace traditional wood and fiber derived from forests. Previous workusing laminated bio-composites made from only oil palm trunk veneer did not achievesatisfactory properties. Therefore, we investigate the properties of experimental low matrixbio-composites using oil palm trunk veneer reinforced with oil palm empty fruit bunches ina phenol�formaldehyde matrix in this study. Among the other oil palm fiber residues,OPEFB offers the best prospect for commercial exploitation since it is readily available atthe palm oil mill which can minimize transportation and procurement costs. In Malaysia,OPEFB is one of the biomass materials, which is a by-product from the palm oil industry.This OPEFB has high cellulose content and has potential as natural fiber resources, buttheir applications account for a small percentage of the total biomass productions. Severalstudies showed that OPEFB of oil palm with the average of cellulose content of 49�65%

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has the potential to be an effective reinforcement in thermoplastics and thermosettingmaterials [11,12]. In this study, the physical, mechanical, and thermal properties of thislaminated bio-composite were evaluated.

EXPERIMENTAL

Materials

Phenol formaldehyde was supplied by Hexion Specialty Chemicals Sdn. Bhd. Oil palmempty fruit bunch fiber (OPEFB) mats were obtained from Ecofuture Berhad. Oil palmtrunk (OPT) veneer was supplied by Kin Heng Timbers Industries Sdn. Bhd., Perak,Malaysia.

Preparation of Laminated Bio-composites

The OPT veneers were cut to 600� 300� 4.0mm3 samples and dried to approximately10�12% moisture content. The determination of moisture content was carried out inaccordance with BS EN 322 : 1993. The moisture content of the samples measured byplacing the samples in a drying oven at a temperature of 103� 2�C until a constantmass was reached. The reinforcing empty fruit bunches was cut into mats600� 300� 6mm3. The OPT veneer and EFB fiber mat were then impregnated with PFresin. The samples were then arranged into 5-ply laminated bio-composites, consisting ofalternating OPT veneers and EFB fiber mats with the veneer was arranged in differentdirection for EFB-reinforced laminated bio-composites and for the OPT laminated bio-composites, each veneer was arranged also in different direction as shown in Figure 1.Four types of bio-composite samples, which are OPT composite and hybrid composite(OPTþEFB) with glue spread level (250 g/m2) and glue spread level (500 g/m2) were pre-pared by mixing two type of materials, OPT veneer and EFB fiber mat impregnated with

Oil palm trunk laminatedbio-composites

EFB-reinforced laminatedbio-composites

Parallel veneer

Perpendicular veneer

Nonwoven EFB mat

Figure 1. Arrangement of OPT and EFB-reinforced laminated bio-composites.

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PF resin. Composite was then cold pressed for 10min and then it was placed in hotpressing machine with processing temperature of 150�C for 25min under pressure of200 bars (3000 psi).

Mechanical Testing

Three types of mechanical testing were conducted: flexural, shear, and screw with-drawal. A minimum of 10 samples were tested in each case.

FLEXURAL TESTThe flexural tests were performed according to BS EN 310 : 1993, using an Instron

Testing Machine Model 4204. Samples for flexural testing were cut into rectangularstrips with dimensions of approximately 240� 50� 12mm3. The exact lengths, widths,and thicknesses of the samples were measured and recorded. Samples were tested at acrosshead speed of 10mm/min over a span of 240mm. All the specimens were conditionedat ambient temperature (25� 3�C) and at relative humidity of 30% (� 2%) before testing.

SCREW WITHDRAWAL TESTThe screw withdrawal tests were performed using an Instron Testing Machine Model

4204. The length, width, and thickness were measured and recorded. The tests were carriedout in accordance to BS EN 320 : 1993. The screw withdrawal tests were carried out onsamples with dimensions of 75� 75� 12mm3. The test pieces were conditioned to constantmass in an atmosphere with a mean relative humidity of 65� 5% and a temperature of20� 2�C. For this test, a steel screw, nominal size 4.2� 38mm2 was used. The screw wasinserted into the hole to the full thickness of the board. The testing machine was set to acrosshead speed of approximately (10� 1)mm/min and until maximum load is achieved.

SHEAR TESTShear tests were performed according to BS EN 314-1 : 2004, using an Instron Testing

Machine Model 4204. The shear tests were performed on rectangular strips with dimen-sions of approximately 135� 25� 12mm3. The length, width, and thickness of eachsample was measured and recorded. Samples were tested at a crosshead speed of1.5mm/min. All of the specimens were conditioned at ambient temperature (25� 3�C)and a relative humidity of 30% (�2%) before testing.

Prior to shear tests, phenol formaldehyde laminated bio-composites were subjected to awater boil proof treatment (WBP). Samples were immersed for 4 h in boiling water, driedin a ventilated drying oven for 16�20 h at 60� 3�C, immersed for a second time in boilingwater for 4 h, and finally cooled in water at a temperature of 20� 3�C for at least 1 h.Before the water treatment, the length and width of the shear area were measured withaccuracy to within �0.1mm. The shear tests were carried out on wet test pieces, allowingfor the use of a wiping based process. The shear test pieces were arranged in the center ofthe clamping devices in such a way to allow the load to be transmitted from the testingmachine, through the ends of the test pieces and to the shear area without any transverseloads. Slipping is only allowed in the initial stage of the loading. The clamp is positionedon the sample faces. The load was applied at a constant moving rate, designed to inducerupture within 30� 10 s. Samples were tested at a crosshead speed of 1.5mm/min.

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Physical Testing

Four different physical tests were conducted in this study to test the following proper-ties: density, water absorption, thickness swelling, and delamination.

DENSITYThe densities of the bio-composites were determined by measuring the mass and volume

of each sample. Each test sample was weighed with an accuracy of 0.01 g. The mass of eachsample was obtained by calculating the arithmetic mean of the mass of all of the testsamples taken from the same board. Accurate determination of test sample dimensionswas made using a sliding calliper, in accordance with BS EN 325 : 1993. The volumes of thesamples were obtained using the measured dimensions. The density, D was then calculatedusing the formula in Equation (1):

D ¼m

v

g

cm3

� �, ð1Þ

where m is the mass and v is the volume of the bio-composite sample.

WATER ABSORPTION AND THICKNESS SWELLINGTo test water absorption and thickness swelling, samples were soaked in water for seven

days. The rate of water absorption initially increased with immersion time, until eventualstabilization. The absorbed water in the samples (A) and the thickness swelling of thesamples (G) was calculated as a percentage according to the procedure given in BS EN317 : 1993. The amount of absorbed water was calculated using Equation (2):

A %ð Þ ¼M1 �M2

M2

� �� 100, ð2Þ

where M2 is the weight before the test and M1 is the measured weight (g).The thickness swelling was calculated using Equation (3):

G %ð Þ ¼A1 � A2

A2

� �� 100, ð3Þ

where A2 is the thickness before the test and A1 is the thickness (mm) after the test.

DELAMINATION TESTThe delamination test was done following the standard BS EN 391 : 2002. It measured

the perimeter of failed glue line over the total perimeter of glue line available. The delam-ination results are evaluated using Equation (4):

D ¼PglF

Pgl �N� 100, ð4Þ

where D is delamination; PglF is the perimeter of failed glue line and Pgl the perimeter ofglue line, and N the number of gluelines.

Ten replications of bio-composite panels were constructed with OPT veneers and oilpalm EFB layers, using phenol formaldehyde resin. Samples were made in dimensions of50� 150mm2 and were pre-treated. Test pieces were impregnated with water (vacuum at

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70�85 kPa for 5min, pressure at 500�600 kPa for 1 h, vacuum at 70�85 kPa for 5min,pressure at 500�600 kPa for 1 h), drying at 60�70�C for 21�22 h.

Thermogravimetric Analysis

Thermal stability of the bio-composites panels was investigated using thermogravimetricanalysis (TGA). Thermograms were obtained with a Perkin Elmer (TGA-6) instrumentwith a heating rate of 20�C/min, over a temperature range of 25�900�C. All TGA runswere performed under a nitrogen atmosphere.

Scanning Electron Microscopy

A scanning electron microscope (SEM; Leo Supra, 50VP, Carl Ziess, SMT, Germany)was used to analyze the morphology of the bio-composites materials. A thin section of thesample was mounted on an aluminum stub using conductive silver paint and the samplewas sputter-coated with gold. The SEM micrographs were obtained under conventionalsecondary electron imaging conditions using an acceleration voltage of 15 kV.

RESULTS AND DISCUSSION

Mechanical Properties

FLEXURAL PROPERTIESFlexural test results were obtained for OPT laminated bio-composites and EFB-rein-

forced laminated bio-composites using phenol formaldehyde. Tests were performed toinvestigate the effects of reinforcing oil palm trunk veneer with EFB on the mechanicalproperties of the laminated bio-composites. Figure 2 shows the flexural strength andflexural modulus of EFB-reinforced laminated bio-composites compared to OPT lami-nated bio-composites.

Clearly, the flexural strength of the EFB-reinforced laminated bio-composite panels ishigher than that of OPT laminated bio-composites. This can be attributed to the higherdensity of the EFB-reinforced laminated bio-composites, compared to OPT laminated bio-composites (Table 1). Overall, the results showed that laminated bio-composites usingphenol formaldehyde exhibited high flexural strength. Interaction between cellulose fiberwith PF resin is excellent due to the hydrophilic nature of cellulosic fiber and PF resin.Cellulosic hydroxyl groups (�OH) and lignin hydroxyl groups are the major component ofthe fibers. These can easily form hydrogen bonds with the methylol and phenolic hydroxylgroups of the resin and at 100�C these group can undergo condensation reaction leading tothree-dimensional network between fiber and matrix [13].

The flexural strengths of the laminated bio-composites and EFB-reinforced laminatedbio-composites that used a higher glue spread level (450 g/m2), were found to be higherthan the flexural strengths of the laminated bio-composites that used a lower adhesivespread level (250 g/m2). The higher spread level allowed adhesive that was spread on thesurface of the OPT and EFB to enter the pores, where it solidified and anchored. Thisimplies that the lower glue spread amount of 250 g/m2 is inadequate to form full adhesionbetween laminated bio-composite layers (both reinforced and not).

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As shown in Figure 2, EFB-reinforced laminated bio-composites using phenol formal-

dehyde possesses a higher flexural modulus than OPT laminated bio-composites. Theelastic properties were enhanced when the laminated bio-composites were reinforcedwith EFBs, which increased the total fiber content and allowed the panels to withstand

a higher load. Among the different natural fibers, OPTs appear to be a promising materialbecause of their higher toughness [14,15].

High values of flexural modulus were obtained for panels made using phenol formal-

dehyde. When properly cured, phenol formaldehyde resin can be tougher than wood itself,resulting in an impressively high flexural modulus [16]. The results showed that, as

expected, the flexural modulus was generally higher for the laminated bio-composites

Table 1. Physical properties of OPT laminated bio-composites and EFB-reinforcedlaminated bio-composites.

Adhesive Sample Physical properties

Density (g/cm3)Water absorption(%) (After 7 days)

Thickness swelling (%)(After 7 days)

PF OPT 250 0.6616 (0.05) 58.2614 (4.4) 12.8360 (1.2)OPT 450 0.6410 (0.02) 56.6674 (3.9) 11.1814 (1.2)

OPTþEFB 250 0.7261 (0.04) 50.4972 (3.2) 9.8509 (1.2)OPTþEFB 450 0.7414 (0.08) 43.6164 (4.2) 7.4136 (1.4)

40F

lexu

ral s

tren

gth

(MP

a)

30

20

10

0OPT 250

g/m2OPT 450

g/m2OPT+EFB 250

g/m2OPT+EFB 450

g/m2

Samples

OPT 250g/m2

OPT 250g/m2

OPT+EFB 250g/m2

OPT+EFB 450g/m2

Fle

xura

l mod

ulus

(G

Pa)

0

1

2

3

4

Figure 2. Flexural strength and flexural modulus for OPT and EFB-reinforced laminated bio-composites withdifferent glue spread level using phenol formaldehyde (PF).

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that were made from a higher glue spread level, regardless of the adhesive used.This is again attributed to the improved fiber-adhesive contact when a higher gluespread level is used.

SCREW WITHDRAWAL PROPERTIESScrew withdrawal strength varies with the type of tree from which the materials were

produced, the moisture content, the orientations of grains within a section, the duration ofextraction, the method of screwing, the panel dimensions, and the surface roughness [17].The resistance of a screw shank against the direct withdrawal from a piece of wood dependson the density of the laminated bio-composite material, the diameter of the screw, and thedepth of penetration. The surface condition of the screw at the time of driving and the gluethickness also serve to influence the initial withdrawal resistance. The screw will fail intension when its strength is less than the withdrawal strength of the bio-composite.

Resistances of laminated bio-composite specimens to screw withdrawal were compared,with constant screw diameters and screw types. Screw withdrawal strength properties areshowed in Figure 3. The results show that the screw withdrawal strength of EFB-rein-forced laminated bio-composites is higher than OPT laminated bio-composites. FromFigure 4, we see a strong correlation between the screw withdrawal strength and thespecimen density. The limiting length for tension failure decreases as the density of thelaminated bio-composites increases, since the withdrawal strength of the laminated bio-composites increases with density.

From the results, it can also be seen that laminated bio-composites with the higheradhesive spread level (450 g/m2) show higher screw withdrawal values compared to lam-inated bio-composites with lower adhesive spread level (250 g/m2). More glue will increasethe thickness of the layer, which influences the withdrawal strength of the nail and screw.

OPT 250 g/m2 OPT 450 g/m2 OPT+EFB 250 g/m2

Samples

Scr

ew w

ithdr

awal

(N

)

0

200

400

600

800

1000

OPT+EFB 450 g/m2

Figure 3. Screw withdrawals of OPT and EFB-reinforced laminated bio-composites with different glue spreadlevel using phenol formaldehyde (PF).

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SHEAR PROPERTIESThe shear properties of OPT laminated bio-composites and EFB-reinforced laminated

bio-composites were also studied. Figure 5 shows the shear properties for samples using

phenol formaldehyde, with different glue spread levels. From Figure 5, it can be clearly

seen that bond strength of laminated bio-composite panels was less for the samples using a

glue spread level of 250 g/m2.Poor wettability is considered an indicator of poor bond durability. Wettability is rec-

ognized as an important criterion in evaluating the bonding ability of wood. The contact

angle that a drop of adhesive makes on a surface reflects the physical and chemical affinity

between the surface and the adhesive. In addition to chemical affinity, the rough surface of

the EFBs was a factor affecting adhesion because it was an obstruction to intimate contact

between veneer surfaces and adhesive molecules. Phenol formaldehyde adhesive showed

poor wettability and a hydrophobic surface; hence, the wettability and adhesion properties

of the surface were influenced negatively [18].As expected, the shear strength was higher for the samples without pretreatment, com-

pared to samples that underwent pretreatment for WBP tests. Samples that underwent the

pretreatment experienced a drastic change in condition, which probably caused more

moisture to penetrate into the laminated bio-composites and those areas that were heavily

exposed to moisture, the strength weaken particularly during the WBP pretreatment,

because the bond type will affect the adhesive bonding and consequently reduce the

shear strength.Figure 6 shows the shear strength for laminated bio-composites of WBP test, using

phenol formaldehyde as the adhesive resin. This test is designed to simulate exposure to

weather over sustained periods. From Figure 6, it can be seen that the shear strength

decreases after the WBP test. This may be due to swelling of the fibers during the treat-

ment, which will eventually lead to a reduction of the mechanical properties and shear

strength of the laminated bio-composites.

1000

800

600

400

200

00.62 0.64

Density (g/cm3)

Scr

ew w

ithdr

awal

(N

)

0.66 0.68 0.7 0.72 0.74 0.76

PF

Figure 4. Relationship between screw withdrawal strength and density for phenol formaldehyde (PF)laminated bio-composites.

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OPT 250 g/m2 OPT 450 g/m2 OPT+EFB 250 g/m2 OPT+EFB 450 g/m2

Samples

DRY

She

ar s

tren

gth

(MP

a)

2.0

1.5

1.0

0.5

0.0

WBP

Figure 6. Comparison of shear strength between dry and WBP treatment test of OPT and EFB-reinforcedlaminated bio-composites with different glue spread level using phenol formaldehyde (PF).

2.0

She

ar s

tren

gth

(MP

a)

1.5

1.0

0.5

0.0

OPT 250 g/m2 OPT 450 g/m2 OPT+EFB 250 g/m2 OPT+EFB 450 g/m2

Samples

Figure 5. Shear strength of OPT and EFB-reinforced laminated bio-composites with different glue spreadlevel using phenol formaldehyde (PF).

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Physical Properties

DENSITYTable 1 shows the density of OPT laminated bio-composites and EFB-reinforced lam-

inated bio-composites with different glue spread levels of 250 and 450 g/m2 using phenolformaldehyde. During the experiment, it was observed that the amount of glue resin andthe extent of compression of the veneer during hot pressing affect the density of thelaminated bio-composites, as seen in Table 1.

The characteristic property of laminated bio-composites strength is density. A higherdensity corresponds to a higher laminated bio-composite strength, as seen in Table 1 andFigures 2�6. Results showed that reinforcing laminated bio-composites of OPT with oilpalm EFBs using resin as an adhesive have higher densities than the laminated bio-com-posites made from OPT using the same resin. This may be due to the difference in thedensity of the raw materials that ultimately affects the laminated bio-composite density.The density of OPT veneer is 0.15�0.4 g/cm3 and that of EFBs is 0.7�1.15 g/cm3. It isobvious that the laminated bio-composite manufactured from layers of OPT will have alower density than the EFB-reinforced laminated bio-composites.

In addition to the raw materials density, the adhesive properties of the resin also con-tribute to the density of the laminated bio-composites. The sample using phenol formal-dehyde with a spread level of 450 g/m2 showed higher density compared to the sampleswith different glue spread levels. This is due to the enhanced interfacial adhesion betweenthe phenol formaldehyde and the laminated bio-composites, attributed to the cross linkingreaction between the hydroxyl groups of the laminated bio-composites and the formalde-hyde moiety of the resin [19].

WATER ABSORPTIONTable 1 shows the percentage of water absorption of OPT laminated bio-composites and

EFB-reinforced laminated bio-composites with different glue spread levels. Results indi-cate that OPT laminated bio-composites have higher water absorption capacity comparedto the EFB-reinforced laminated bio-composites.

The higher uptake of water in OPT bio-composites may be due to the development ofboth external and internal micro cracks in the material and/or the natural fiber swellingdue to moisture. This phenomenon maybe due to the theory that moisture absorption intothe composite materials is based on three major mechanisms, which are diffusion of watermolecules inside the microscopy between polymer chains; capillary transport of watermolecules into the gaps; and flaws at the interface between fibers and the polymer dueto the incomplete wettability; and also transport of water molecules by micro cracks in thematrix formed during the compounding process. Fiber swelling will result in the fiberdebonding from the matrix due to the moist, high temperature environment [20].Besides, this is also because OPT contains higher parenchyma which leads to the higherwater absorption. This can be explained by the greater affinity of the parenchyma toabsorb water as compared to the fiber bundles [21].

The percentage of moisture uptake decreased as reinforcement of OPT with EFBs. Thiswas expected due to the hydrophilic nature of the lignocellulosic fiber. The polar hydroxylgroups in their molecular structures are able to form hydrogen bonds with water mole-cules. The possibility of water being absorbed through the formation of hydrogen bondsincreases with fiber content. This phenomenon suggested that the OPT contains the max-imum number of free hydroxyl group, OH while the minimum number of free OH group

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are present in EFBs. This is due to the presence of OH group that enhances the waterabsorption by forming the hydrogen bonding with water molecules [22].

The panels using a higher adhesive spread level (450 g/m2) have lower water absorptioncompared to panels using a lower adhesive spread level (250 g/m2). This may be due to thehigher compatibility between the hydrophilic fiber and adhesive in the panels that usehigher adhesive spread level. The weak compatibility between the fiber surface and adhe-sive could lead to the formation of void structures within the composites, which facilitateswater absorption [23].

THICKNESS SWELLINGMany physical properties of laminated bio-composites are affected by the amount of

moisture present in the laminated bio-composite. Laminated bio-composites exhibitgreater dimensional stability compared to most other wood-based building products.Thickness swelling is independent of panel size and veneer thickness [24].

Table 1 shows that the OPT laminated bio-composites made with phenol formaldehydeadhesives exhibited a higher degree of thickness swelling than EFB-reinforced laminatedbio-composites. This may be due to the structure of oil palm EFB mats, which have higherdensities, leading to a decrease in thickness swelling.

This test also showed that the thickness swelling of the composites increases with anincrease in the period of water exposure. The increase in water exposure time allows asignificant amount of water to be absorbed, resulting in fiber swelling. The EFB-reinforcedlaminated bio-composites using phenol formaldehyde, a resin with an aromatic backbone,showed a decrease in thickness swelling. The hydrophilic nature of the fibers that arisesfrom an abundance of hydroxyl groups makes them incompatible with the hydrophobicmatrices of phenol formaldehyde, resulting in lesser water absorption [19].

DELAMINATION TESTThe performance of laminated bio-composite panels depends a great deal on the bond-

ing strength between the resin and the substrate. Any failure in the glue bond weakens themechanical strength. Furthermore, good durability is associated with the absence ofdelamination of laminated bio-composites samples [25]. Typically, in such an outdoorout of ground application, plywood is not continuously wet but can be subjected to fre-quent wetting and drying subsequently. It is generally known that moisture has a signif-icant influence on the mechanical and physical properties of wood, plywood, and otherwood-based materials. As wood-based panels are hygroscopic and since their surface tovolume ratio is very high, physical deformations and cracks are possible. In the case ofplywood the strength properties of the glue lines are affected by changing moisture, result-ing in a risk of delamination and panel failure [4].

Delamination assessment on 10 specimens from each OPT laminated bio-compositesand EFB-reinforced laminated bio-composites with different glue spread level revealedthat all of the laminated bio-composite panels presented almost no delamination.

It was observed that the laminated bio-composite specimens delaminated at the glue lineand cracks occurred on the edge of the sample. One in 10 samples of OPT laminated bio-composites with glue spread level 250 g/m2 presented 0.6% delamination; and three in 10samples of EFB-reinforced laminated bio-composites with glue spread 250 g/m2 presented1.9% delamination as shown in Table 2. The samples of EFB-reinforced laminated bio-composites with glue spread 250 g/m2 presented the highest delamination. No delamina-tion was observed in the OPT laminated bio-composites with glue spread level 450 g/m2

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and EFB-reinforced laminated bio-composites with glue spread 450 g/m2. The proportionof samples (each combination was done with 10 replications) affected by the delaminationalso is presented in Table 2. This result indicated that the laminated bio-composites withhigher glue spread (450 g/m2) exhibited better bonding strength between resin and thesubstrate with no delamination compared to laminated bio-composites with lower gluespread (250 g/m2).

Thermogravimetric Analysis

Thermogravimetric is a method to investigate the thermal stability of materials used forvarious applications. In this work, TGA was used to investigate the thermal degradationproperties of laminated bio-composite panels.

From Figure 7, it is clear that all of the samples, regardless of the panel type, initiallyundergo a loss of moisture at a temperature near 100�C. For the EFB-reinforced laminated

Table 2. Delamination and proportion of samples affected bydelamination test for OPT laminated bio-composites and EFB-reinforced

laminated bio-composites.

SampleProportion of samples affected by

delamination test Delamination (%)

OPT 450 0/10 0OPT 250 1/10 0.6OPTþEFB 450 0/10 0OPTþEFB 250 3/10 1.9

100

90

80

70

60

50

40

30

20

0 200 400 600 800 1000

110

Temperature (°C)

OPT 250OPT 450

OPT+EFB 250

OPT+EFB 450

Inte

nsity

(a.

u)

Figure 7. Thermograms of laminated bio-composites panels glued with phenol formaldehyde (PF).

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bio-composites, the initial degradation temperature occurs at a higher temperature com-pared to the OPT laminated bio-composite materials. The EFB-reinforced laminated panelwith a phenol formaldehyde glue spread of 450 g/m2 did not show signs of initial degra-dation until approximately 245�C, indicating good thermal stability. The EFB-reinforcedlaminated bio-composites with 450 g/m2 of phenol formaldehyde had a final degradationtemperature of 350 �C and an ash content of 32%. Both the degradation temperature andthe ash content were higher for the EFB-reinforced laminated sample, compared to theOPT panels (Table 3). For the EFB-reinforced laminated samples, the thermograms showdegradation upto a temperature of around 370�C, after which the thermogram plateaus, asonly ash is remaining.

Overall, panels glued with phenol formaldehyde with a spread level of 450 g/m2 had thebest thermal stability.

Scanning Electron Microscopy

SEM was used to conduct morphological analysis of the bio- composite panels. Theinteraction of the adhesive in OPT laminated bio-composites and EFB-reinforced lami-nated bio-composites, as observed from the FESEM, are shown in Figures 8(a) and (b)and 9(a) and (b).

Views of EFB-reinforced laminated bio-composites using adhesive spread level of250 g/m2 is shown in Figure 8(a). The adhesive can be seen filling up the available spacein the glue line, with some glue penetrating through the vessel lumen as mentioned bySulaiman et al. For the samples with the lower glue spread level, there are some spaces thatare not filled with adhesive and the presence of these voids can lead to poor adhesion. TheEFB-reinforced laminated bio-composite panels using phenol formaldehyde with a spreadlevel of 450 g/m2 showed a well-dispersed glue line (Figure 8(b)). The adhesive can be seenfilling up the available space in the glue line, with some glue able to penetrate through thevessel lumen adjacent to the glue line. This spreading probably occurred during the glueapplication. For samples with the higher glue spread level, there was enough adhesive tofill up the lumen void, which probably improves the adhesion. The adhesive also pene-trates between the OPT and the oil palm EFB fibers.

Figure 9(a) shows that less adhesive fills the spaces and parenchyma cells in the poroussurface of the OPT veneer. The SEM image revealed voids between OPT veneer and EFBmat layers (Figure 9(a)). These voids may arise due to the inadequate amount of adhesivein the 250 g/m2 glue spread level. For the samples with a glue spread level of 450 g/m2, itwas observed that the adhesive filled the lumen in the OPT laminated bio-composite panels

Table 3. The degradation temperature and ash content fromthermograms of laminated bio-composite panels glued with

phenol formaldehyde.

Sample Ti (�C) Tf (�C) Ash (%)

OPT 450 220 340 23OPT 250 213 335 22OPTþEFB 450 245 350 32OPTþEFB 250 225 343 30

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and filled the parenchyma of the OPT veneer (Figure 9(b)). The fact that the adhesivefills the small cavities probably serves to improve the adhesion between the surfacesof the OPT.

CONCLUSIONS

In this article, we report on the use of EFBs as a reinforcement in OPT bio-compositesand the potential of EFBs to be high performing raw materials for bio-composites usingphenol formaldehyde resin. The aim of this study was to characterize the mechanical,thermal, and physical properties of EFB-reinforced laminated bio-composites. Fromour results, we conclude that laminating EFB with OPT improves some properties of

(a)

(b)

No spaces betweenOPT veneer and EFBmat layers

Spaces betweenOPT veneer and EFB mat layers

Figure 8. Scanning electron micrograph of EFB-reinforced laminated bio-composites with (a) 250 g/m2 and(b) 450 g/m2 spread level (50�magnifications).

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bio-composites, such as bending strength and modulus, screw withdrawal. EFB-reinforcedlaminated bio-composites also showed better physical properties than OPT laminated bio-composites. It is obvious that the laminated bio-composite manufactured from layers ofOPT have a lower density than the EFB-reinforced laminated bio-composites. The thick-ness swelling and water absorption of OPT laminated bio-composites was higher than thethickness swelling determined in EFB-reinforced laminated bio-composites. The bio-com-posites constructed with OPT and laminating EFB with OPT presented almost no delam-ination. After the testing according to BS EN 391, the laminating EFB with OPT seemedto have no negative effect on the quality of the glue line. In addition, laminated bio-composites made using a glue spread level of 450 g/m2 have better mechanical and physicalproperties than laminated bio-composites using a glue spread level of 250 g/m2. Besides,the higher adhesives spread level (450 g/m2) samples showed lower water absorption and

Spaces which did not filledup with the adhesives

Resin filled up the availablespaces of the surface

(b)

(a)

Figure 9. Scanning electron micrograph of OPT laminated bio-composites with (a) 250 g/m2 and(b) 450 g/m2 spread level (50�magnifications).

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thickness swelling from the samples with lower glue spread level (250 g/m2). The thermaland morphological analysis of the EFB-reinforced laminated bio-composites glued withphenol formaldehyde confirmed that the panels have good thermal resistance and goodadhesion, with a well-dispersed glue line. In conclusion, EFBs can be used to substituteraw materials to produce laminated bio-composites.

ACKNOWLEDGMENTS

The researchers would like to thank the Ministry of Science, Technology andInnovation (MOSTI) and the Universiti Sains Malaysia, Penang for providing the researchgrant EScience Fund (RM-9) 03-01-05-SF0334 and 305/PTEKIND/613323 that made thiswork possible.

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