Materials and Design 32 (2011) 246–254

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Materials and Design

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Characterization of raw materials and manufactured binderless particleboardfrom oil palm biomass

Rokiah Hashim a,*, Wan Noor Aidawati Wan Nadhari a, Othman Sulaiman a, Fumio Kawamura b,Salim Hiziroglu c, Masatoshi Sato d, Tomoko Sugimoto e, Tay Guan Seng a, Ryohei Tanaka b

a Division of Bio-resource, Paper and Coatings Technology, School of Industrial Technology, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysiab Forestry and Forest Products Research Institute (FFPRI), Tsukuba, Ibaraki 305-8687, Japanc Department of Natural Resource Ecology and Management, Oklahoma State University, Stillwater, OK 74078-6013, USAd Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo 113-8657, Japane Japan International Research Center for Agricultural Sciences, 1-1, Owashi, Tsukuba, Ibaraki 305-8686, Japan

a r t i c l e i n f o a b s t r a c t

Article history:Received 9 April 2010Accepted 31 May 2010Available online 4 June 2010

Keywords:A. CompositesB. Particulates and powdersG. Scanning electron microscopy

0261-3069/$ - see front matter � 2010 Elsevier Ltd. Adoi:10.1016/j.matdes.2010.05.059

* Corresponding author. Tel.: +60 4 6535217; fax: +E-mail address: hrokiah@usm.my (R. Hashim).

The objective of this study was to examine the extractive, holocellulose, alpha cellulose, lignin, starch,and sugar contents of oil palm biomass and to evaluate its suitability in binderless particleboard produc-tion. In this study, bark, leaves, fronds, mid-parts and core-parts of the trunks were used to produceexperimental binderless particleboard panels. Binderless particleboard panels were made with a targetdensity of 0.80 g/cm3 at a temperature of 180 �C and a pressure of 12 MPa in a computer controlledhot press. The modulus of rupture, the internal bond strength, the thickness swelling and the waterabsorption of the panels were evaluated. Fourier transform infrared spectroscopy and field emissionscanning electron microscopy were used to characterize the properties of the raw materials and the man-ufactured panels. The chemical composition of the oil palm biomass consisted of high holocellulose, lig-nin, starch and sugar contents that have been found to aid in the production of binderless particleboard.The core-part of the trunk contained the highest amount of starch and total sugar. Samples made fromthe core-parts and fronds had sufficient modulus of rupture and internal bond strength to meet the Jap-anese Industrial Standard. The internal bond strength of the mid-part panels also met the standard. How-ever, binderless board prepared from bark and leaves showed poor modulus of rupture and internal bondstrength. Samples from the core-parts had the lowest thickness swell and water absorption but did notmeet the above standard. The Fourier transform infrared spectroscopy spectra did not show any substan-tial difference between the raw materials and the manufactured panels. Field emission scanning electronmicroscopy indicated that the compressed cells varied between raw material types and showed the pres-ence of compressed cells with some starch granules that facilitated adhesion. Based on the findings of thisstudy, oil palm has the potential to be used to manufacture binderless panel products, and further studyis required to improve its dimensional stability.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction

Particleboard is a wood-based composite consisting of varyingshapes and sizes of particles of lignocellulosic material bonded to-gether with an adhesive and consolidated under heat and pres-sure. The worldwide demand of particleboard has been growing[1]. The adhesives used to bond the particles come from syntheticor natural adhesives derived from the wood itself by chemicalreactions. Currently, most of the commercially produced particle-board is bonded with formaldehyde-based adhesives. The globaltrend indicates that the marketplace is moving towards using

ll rights reserved.

60 4 6573678.

particleboards with reduced or no formaldehyde [2]. The indus-trial use of wood as a raw material for particleboard is well estab-lished. However, with the increasing price of wood, there is aneed to find alternative sources of raw materials for particleboardmanufacture. The decreasing supply of raw materials and theneed for formaldehyde-free particleboard has led to studies ofparticleboard manufacture without synthetic adhesives and tothe investigation of raw materials other than wood such as kenaf[3,4] and bark [5].

Bonding is an important aspect of binderless boards. Self-bond-ing can be achieved by chemical activation reactions and physicalconsolidation of particles under applied heat and pressure. Degra-dation of hemicelluloses and partial degradation of cellulose toproduce simple sugars has been reported to contribute to bonding

R. Hashim et al. / Materials and Design 32 (2011) 246–254 247

[3]. Bonding can also be caused by cross-linking carbohydratepolymers and lignin [4]. Binderless boards have been developedfrom sugar-containing lignocellulosic materials such as sorghum.Free sugars, carbohydrates, or saccharides in lignocellulosic plantsserved as bonding and bulking agents [6]. Chow [5] concluded thatbonding in binderless panels made from bark arose from particleconsolidation.

Oil palm is a lignocellulosic material rich in carbohydrates inthe form of starch and sugar and containing cellulose, hemicellu-loses and lignin [7]. It is an abundant waste material at replanta-tion and harvesting sites in Malaysia and in many parts of SouthEast Asia [8]. Large quantities of this waste are left in the field asunderutilized resources. Oil palm is now considered to be one ofthe most promising non-wood lignocellulosic raw materials forvarious types of wood-based panels [9].

The abundance, sustainability and carbohydrate richness of oilpalm makes this biomass an ideal raw material for the produc-tion of value-added, environmentally friendly, binderless com-posite panels. Therefore, the objective of this study was toexamine the extractive, holocellulose, cellulose, lignin, starchand sugar contents of different parts of the oil palm and to eval-uate its suitability in binderless particleboard production. Bark,leaves, fronds, mid-parts and core-parts of the trunks were usedto produce binderless particleboard panels. The physical andmechanical properties of the panels including the modulus ofrupture (MOR), the internal bond (IB) strength, the thicknessswelling (TS) and the water absorption (WA) were determined.Fourier transform infrared (FT-IR) spectroscopy and field emis-sion scanning electron microscopy (FESEM) were used to charac-terize the differences between raw materials and samples frommanufactured panels.

Table 1Chemical composition of different parts of the oil palm.

Parts of oil palm Extractives Chemical composition (%)

Holocellulose Alpha cellulose Lignin

Bark 10.00 77.82 18.87 21.85Leaves 20.60 47.7 44.53 27.35Frond 3.50 83.13 47.76 20.15Mid-part of trunk 14.50 72.6 50.21 20.15Core-part of trunk 9.10 50.73 43.06 22.75Frond [22] 1.40 82.2 47.60 15.20Trunk [23] 5.35 73.06 41.02 24.51Kenaf [4] 82Hardwood [19] 0.1–7.7 71–89 31–64 14–34Softwood [19] 0.2–8.5 60–80 30–60 21–37

Table 2Starch and sugar content of different parts of the oil palm.

Oil palm tree by parts Starch (%) Sugar composition (mg/ml)

Glucose Xylose Arabinose Fructose

Bark 4.14(0.30)a 3.53 6.55 1.15 0.22(0.61) (3.25) (0.57) (0.38)

Leaves 2.53 2.17 3.79 1.70 –(0.12) (0.17) (3.72) (0.69)

Fronds 3.10 5.31 6.50 1.33 –(0.09) (0.95) (3.42) (0.49)

Mid-part of trunk 12.19 5.97 6.61 1.09 –(0.63) (0.65) (3.51) (0.55)

Core-part of trunk 17.17 6.55 6.20 1.31 0.04(0.40) (0.58) (3.71) (0.60) (0.07)

a Values in parentheses are standard deviations.

2. Materials and methods

2.1. Sample collection and preparation

Oil palm biomass in the form of trunks, fronds and leaves wasobtained from a local plantation in Northern Malaysia. Three typesof materials, i.e., core-part, mid-part and bark particles, were pro-duced from the trunks. Fronds and leaves were also cut from thetrees. All five different particle types were reduced to chips inthe field using a commercial chipper. The chips were then reducedto coarse particles in a laboratory-type hammer mill. An oven wasused to reduce the moisture content of the material to 7–8%. Allcoarse particles were ground into fine particles of less than 1 mmin diameter with a Willey Mill.

2.2. Determination of the chemical composition of the raw materials

Different parts of the oil palm were ground to pass through a40-mesh screen size. The sampling and the preparation of woodfor analysis were performed according to TAPPI T257 cm-02 [10],and the preparation of wood for chemical analysis was performedaccording to TAPPI 264 cm-97 [11]. Extractive components weredetermined according to TAPPI T 204 cm 97 [12] with a modifica-tion of the ethanol-toluene ratio of the solvent to 1:2. Holocellulosecontent was measured by the method of Wise [13]. Alpha cellulosecontent was determined by the extraction of the holocellulose with17.5% sodium hydroxide. Lignin content was determined based onthe Klason method [14].

Starch analysis was performed based on the method of Hum-phrey and Kelly [15]. Each type of raw material was ground andsieved through a 200-mesh sieve size and dried in a desiccator overconcentrated sulfuric acid. After the addition of 4.7 ml of 7.2 Mperchloric acid to an approximately 0.4 g sample, it was allowedto react for 10 min with periodic shaking. The sample was then di-luted with an equal volume of distilled water and centrifuged. Adrop of phenolphthalein was added to the 10 ml aliquot. The solu-tion was made alkaline with 2 N NaOH. Then 2.5 ml of acetic acidwas added, followed by 0.5 ml of 10% potassium iodide and 5 ml of0.01 N potassium iodide. The color was allowed to develop for15 min, and the absorbance was measured at 650 lm with a UVspectrophotometer, Shimadzu UV-1201. The percentage of starchwas then calculated.

The total and types of sugar were measured by the phenol–sul-furic acid method and by high performance liquid chromatography(HPLC), respectively. Each type of raw material was first hydro-lyzed according to the method used by Jeung-yil et al. [16] priorto sugar determination. About 100 mg of each milled particle typewere hydrolyzed in 1 ml of 72% (w/w) H2SO4 at 30 �C for 1 h. Themixtures were diluted by adding 7 ml of distilled water and hydro-

Total sugar (mg/ml) Total sugar using phenol sulfuric acid method (mg/ml)

11.42 13.67(0.90)

7.66 9.29(0.39)

13.14 14.29(2.74)

13.67 14.45(1.02)

14.06 16.56(1.15)

248 R. Hashim et al. / Materials and Design 32 (2011) 246–254

lyzed in an autoclave at 121 �C for 1 h. The mixtures were centri-fuged at 10,000� for 3 min. The supernatant was filtered using amicrofilter with a pore size of 0.45 lm and centrifuged for 5 minat 7.5 rpm. The total sugar content was then determined for eachsample according to the method used by Dubois et al. [17]. Briefly,10 ll of each sample was added to 0.5 ml of phenol and vortexed.Then, 3 ml of concentrated sulfuric acid was added and vortexed.The mixture was left to stand around 45 min before the absorbancewas read at 492 nm from the UV spectrophotometer. Pure glucosewas used as a standard for the test.

Analysis on the types of sugar in the hydrolyzed samples wasdone by Shimadzu High Performance Liquid Chromatography(HPLC). The column used was CARBOSep: CoreGel 87P (CHO-99-9864) from Transgenomic for carbohydrate applications with amobile phase to deionized water ratio of v/v, a flow rate of

Fig. 1. Modulus of rupture of

Fig. 2. Internal bond strength o

Fig. 3. Thickness swelling and water abs

1.0 ml/min, a temperature of 85 �C, and a total retention time ofabout 20 min. Pure glucose, xylose, galactose, arabinose, riboseand fructose were used as standards.

2.3. Production and testing of binderless panels

A total of 20 single-layer panels, four of each type of raw mate-rial, with dimensions of 20.50 cm � 20.50 cm � 0.48 cm, weremanufactured. Manually formed mats were compressed in a com-puter controlled hot press using a temperature of 180 �C and apressure of 12 MPa for 20 min. All the panels had a target densityof 0.80 g/cm3. Pressed panels were cut into test samples based onJIS A-5908 [18] after they were conditioned in a climate chamberat a temperature of 20 �C and a relative humidity of 65%.

the experimental panels.

f the experimental panels.

orption of the experimental panels.

R. Hashim et al. / Materials and Design 32 (2011) 246–254 249

Nine MOR and three IB samples were cut from each panel toevaluate their mechanical properties. Both tests were carried outon an Instron Testing System Model UTM-5582 equipped with aload cell capacity of 1000 kg. Six samples with dimensions of5 cm by 5 cm were used for determination of thickness swelling

A- Raw material B- Panel

A

A

A

A

Bark

A

B

B

B

Leaves

Fronds

Mid-p

Core-p

B

B

Fig. 4. FT-IR spectra of particles and samples from exper

(a) Cross section of the bark showing fibers (

(c) Fractured surface of the bark panel (

Fractured surface

fibers

Fig. 5. Micrographs of the bark cross-section and the bark panels. (a) Cross-section of thepanel. (d) Close-up view of the fractured surface.

(TS) and water absorption (WA). The thickness of each samplewas measured at four points: midway along each side and 1 cmfrom the edge. The samples were submerged in distilled waterfor 24 h, and thickness measurements were then taken at the samelocations to calculate the thickness swelling values. Each sample

art

art

imental panels from different parts of the oil palm.

b) Close-up view of the bark

d) Close-up view of the fractured surface

Fiber wall

Fractured surface

bark showing fibers. (b) Close-up view of the bark. (c) Fractured surface of the bark

(a) Typical cross sectional profile of a leaf (b) Surface of a leaf showing stomates

(c) Fractured surface of the leaf panel (d) Loosely bound particles in the panel

Epidermis-EP

Vascular bundle

Hypodermis-h

H

EP

Stomata-S

S

Fractured surface

Mesophyll

Fig. 6. Micrographs of oil palm leaves and of leaf panels. (a) Typical cross sectional profile of a leaf. (b) Surface of a leaf showing stomates. (c) Fractured surface of the leafpanel. (d) Loosely bound particles in the panel.

250 R. Hashim et al. / Materials and Design 32 (2011) 246–254

was also weighed to an accuracy of 0.01 g before and after submer-sion to determine the water absorption values.

2.4. Spectroscopic study

The functional groups existing in each type of oil palm particlesand in samples from pressed panels were evaluated using Fouriertransform infrared (FT-IR) spectroscopy. Pellets were prepared bymixing approximately 5 mg of powder of each sample type with95 mg of finely ground potassium bromide (KBr) and pressed intopellets of about 1 mm in thickness. The FT-IR spectrum of eachsample was then analyzed using the Nicolet infrared spectropho-tometer (Avatar 360 FT-IR E.S.P) between wave numbers of4000 cm�1 and 470 cm�1 with a resolution of 4 cm�1 to detectthe functional groups of the compounds of each material.

2.5. Microstructure study

Field emission scanning electron microscopy (FESEM) was em-ployed to investigate the morphological properties of the differenttypes of raw materials and their bonding before and after theexperimental binderless panels were manufactured. Micrographswere taken from cross sections of 0.5 cm by 0.5 cm of the differenttypes of raw material before and after the panels were made. Thesamples were coated with gold by an ion sputter coater PolaronSC515, Fisons Instruments, UK. A Field Scanning Electron Micro-scope LEO Supra 50 Vp, Carl-Zeiss SMT, Oberkochen, Germanywas used.

3. Results and discussion

3.1. Evaluation on chemical analysis

The chemical composition of different parts of the oil palm ispresented in Table 1. Values obtained by previous researchers onsome parts of oil palm, hardwood, softwood and other non-woodwere also tabulated for comparison. The chemical contents deter-

mined in this work were similar to those of different species ofhardwood, softwood and kenaf [4,19]. Therefore, the chemicalcomposition of oil palm biomass should not result in any problemsfor the manufacture of composite panels. Of the parts of the oilpalm, leaves had the highest amount of extractives, about 20%,while the frond had the lowest extractive content. The presenceof extractives could have a negative or a positive influence onthe properties of the panels [20,21]. Generally, different parts ofthe oil palm have lignin amounts ranging from 20–27%. Ligninhas been reported to play an important role in self-bonding boards[4]. Oil palm fronds have the highest amount of holocellulose andalpha cellulose. Similar holocellulose and alpha cellulose contentsin oil palm fronds were observed in another study [22]. The holo-cellulose content of the trunk has been reported to be 73.06% [23],which agrees well to the values found in mid-part of the trunk inthe present study. However, the holocellulose values of core-partof the trunk were different from those of the mid-part and fromthose reported elsewhere [23]. High holocellulose content that isrich in hemicelluloses and cellulose is a desirable property for bin-derless panel production. The kenaf plant has also been reported tohave a high holocellulose content of 82% [4].

Table 2 shows differences in starch content, sugar content andtypes of sugar between different parts of oil palm. The carbohy-drate contents of starch and sugar were expected to play an impor-tant role in providing adhesion in binderless panels [6]. Starch andsugar contents were highest in the core-part of the oil palm trunk.This result agrees with the high starch and sugar contents in suchportions of the oil palm reported by Murai et al. [7]. Based on theseresults, the core-part and the mid-part of the trunk and the frondsseem to be suitable raw materials for binderless panel production.

3.2. Evaluation on some mechanical and physical properties

The average modulus of rupture (MOR) and the internal bond(IB) values of the specimens are depicted in Figs. 1 and 2. Samplesmade from the core-part of the trunk had values of 13.37 MPa and0.71 MPa for MOR and IB, respectively, the highest among all the

(a) Frond with the typical features of a vascular bundle consisting of fibers (F), vessels (V) and phloem (P) embedded in parenchymatic ground tissue (PG)

(b) Thick wall of fibers (F) with tubular arrangement

(c) Thick-walled fibers (F) in thepanel made from fronds

F

P

V

PG

F

F

Fig. 7. Micrographs of the frond cross-section and the frond panels. (a) Frond withthe typical features of a vascular bundle consisting of fibers (F), vessels (V) andphloem (P) embedded in parenchymatic ground tissue (PG). (b) Thick wall of fibers(F) with tubular arrangement. (c) Thick-walled fibers (F) in the panel made fromfronds.

R. Hashim et al. / Materials and Design 32 (2011) 246–254 251

samples. The panels made from particles of the fronds and the mid-part of the trunk had lower values. Frond samples had the secondhighest MOR value of 11.52 MPa followed by the mid-part samples.The mid-part samples had the second highest IB value followed bythe frond samples. Panels made from particles of the bark and theleaves did not exhibit satisfactory mechanical properties.

The Japanese Industrial Standard, JIS A-5908, Type-8 [18] mini-mum requirements for MOR and IB are 8.0 MPa and 0.15 MPa,respectively. As shown in Fig. 1, core-part and frond panels satis-fied the Japanese standard. The core-part and frond panels alsomet the requirement for IB strength (Fig. 2). The total starch andsugar contents of each part of the oil palm, shown in Table 2, were

relatively high, especially for the core-part of the trunk followed bythe mid-part of the trunk. The pseudoplastic behavior of the core-part of the trunk’s parenchyma cells that are rich in starch contentexplains the high MOR and IB obtained from the core-part samples[24]. Bark and leaf panels performed poorly (Fig. 2).

The thickness swelling and the water absorption of the differentpanels ranged from 20% to 130% (Fig. 3). A typical Type-8 particle-board should not have more than 12% thickness swelling based onthe Japanese Industrial Standard [18]. Therefore, none of the sam-ples satisfied the TS requirements. The lowest TS value of 20% wasfound for core-part panels. High thickness swelling in productsmade from oil palm materials have also been reported in otherstudies and may be due to the anatomical structure of the oil palm[9].

3.3. Evaluation of functional groups

Fourier transform infrared (FT-IR) spectroscopy was employedto observe any differences between the FT-IR spectra of the rawmaterials and their manufactured panels. The spectra are pre-sented in Fig. 4. The functional groups are generally similar forall the samples. There is no substantial difference in peaks of theraw materials and the experimental manufactured panels. Thepeak at 3423 cm�1 corresponds to intermolecular hydrogen bond-ing and C-H stretching [25]. The peak at 1732 cm�1 was detected inthe mid-part of oil palm trunk before and after panel manufacture.This peak was assigned to the C@O stretch in unconjugatedketones, carbonyls, and ester groups frequently of carbohydrateorigin. The C@O was assigned to the xylan acetates (hemicellu-loses) [26]. The peak at 1037 cm�1 was present in the bark andin the core-part of the pressed panels. It can be assigned to the lig-nin unit and hydroxycinnamic acids [27].

3.4. Evaluation on the microstructure of samples

The micrographs of particles and manufactured panel samples ofthe bark, the leaves, the fronds, the mid-part and the core-part ofthe trunk are depicted in Figs. 5–9. The FESEM micrographs of thebark samples are shown in Fig. 5. The micrograph indicates thepresence of fibers in bark with thick cell walls as shown in Fig. 5aand b. The micrographs of the manufactured samples, Fig. 5c andd, reveal a compressed cell microstructure. Some void spaces orfractured surfaces are seen in parts of the compressed cells. Thisprobably contributes to the lower mechanical and physical proper-ties obtained for panels made from bark. This may be due to the lowtemperature used that was not sufficient to plasticize the oil palmbark particles [5,28]. The glass transition values of cellulose, hemi-celluloses and lignin in the dry state, were reported to be approxi-mately 220 �C, 170 �C and 200 �C, respectively, by Anglès [28].

The MOR and IB values of the bark panels were 1.60 MPa and0.05 MPa, respectively. Bark panels also exhibited high values ofthickness swelling (93.8%) and water absorption (120.8%). The ana-tomical features of bark create less mechanical fiber interlockingthan other palm oil parts. In addition, the chemical componentsof bark may also contribute to this phenomenon [5], and furtherstudy is required to understand this issue.

Fig. 6a and b shows the microstructure of the leaf cross-sectionconsisting of epidermis, hypodermis on both adaxial and abaxialsides, mesophyll, vascular bundles and stomates [29]. The crosssections of the leaf panels are illustrated in Fig. 6c and d. Large frac-ture surfaces or voids are seen in the pressed panels in Fig. 6c.Close inspection shows that some of the particles were compressedand some were loosely bonded. Even though there was a highamount of lignin in the leaves, about 27.4% as shown in Table 1,the adhesion mechanism was probably hindered by the presenceof chlorophyll in the leaves [30]. The low amount of starch and su-

(a) Parenchymatic tissue (b) Pressed fibers and parenchyma cells

(c) Pits of the vessel in a ladder-like arrangement

(d) Pressed thick-walled fibers

(e) Starch granules in the mid-part portion (f) Pressed fibers

Fig. 8. Micrographs of the cross section of the mid-part of the oil palm trunk and the mid-part panels. (a) Parenchymatic tissue. (b) Pressed fibers and parenchyma cells. (c)Pits of the vessel in a ladder-like arrangement. (d) Pressed thick-walled fibers. (e) Starch granules in the mid-part portion. f Pressed fibers.

252 R. Hashim et al. / Materials and Design 32 (2011) 246–254

gar found in leaves, as reported in Table 2, could also contribute tothe poor bonding [6].

Fig. 7 shows the frond cross-section and the frond panels. Thevascular bundle consisting of fibers, phloem and xylem embed-ded in a matrix of ground tissue consisting of parenchyma cells[9] can be clearly seen in Fig. 7a. The thick fiber walls of thefrond before (Fig. 7b) and after compression (Fig. 7c) probablyexplain the high MOR and internal bond strength of frond pan-els. The high lumen to cell wall ratio increases the ability ofthe particles to compress closely together, leading to betterbonding [9].

Fig. 8a, c and e shows the cross-section of the mid-part of the oilpalm trunk. Parenchymatous tissue with starch granules was gen-erally present in the cells. The pits of the vessel in ladder-likearrangement could be seen in Fig. 8c. The starch granules were lo-cated on the parenchymatous ground tissue. Compressed cells offibers, ground parenchymatous tissue and starch granules areshown clearly in Fig. 8b, d and f in the manufactured panels. Thesecells probably contribute to the improved interfacial adhesion thatprovides good bonding between the fibers [9].

The cross-section of the core-part of the trunk and the core-partpanels, showing ground parenchymatous tissue and fiber wall fea-tures, are shown in Fig. 9a–f. In the pressed panels, more starchgranules could be seen in core-part of the trunk than the mid-partas shown in Fig. 9. This trend is consistent with the values of starchanalyzed chemically. The starch granules filled up the voids in be-tween the cells and facilitated the interfacial adhesion between thefibers. These features were not seen in the leaf panels in Fig. 6. Thework of Noor et al. [24] showed that starch molecules becomeunstable at high temperatures and their molecular chains break-down, increasing the chain mobility. The authors also reported apeak melting point of 67.3 �C for the starch from the oil palm trunk.At high temperatures the hydrogen bonding in the starch and thewater molecules of the particles decreases, resulting in pseudo-plastic flow behavior.

Therefore, binderless particleboard panels from the oil palm of-fer a promising solution to a significant ecological problem via theconversion of biomass into a value-added product. A limitation ofthese experimental panels is their dimensional stability. Steamtreatment, chemical treatment or a combination of both may im-

(a) Core-part with the typical features of a vascular bundle consisting of fibers (F), vessels (V) and phloem (P) embedded in parenchymatic ground tissue (PG)

(b) Panel with starch granules (S) in parenchymatic ground tissue (PG) and pressed fiber (PF)

(c) Starch granules (S) in the parenchymatic ground tissue (PG)

(d) Panel showing pressed fibers

(e) Thick-walled fibers (F) in the core-part (f) Starch granules (S) in the manufactured panels

F

PV

PGS

SPFPG

PG PGPF

S

S

F

S

Fig. 9. Micrographs of the cross-section of the core-part of the oil palm trunk and the core-part panels. (a) Core-part with the typical features of a vascular bundle consistingof fibers (F), vessels (V) and phloem (P) embedded in parenchymatic ground tissue (PG). (b) Panel with starch granules (S) in parenchymatic ground tissue (PG) and pressedfiber (PF). (c) Starch granules (S) in the parenchymatic ground tissue (PG). (d) Panel showing pressed fibers. (e) Thick-walled fibers (F) in the core-part. (f) Starch granules (S)in the manufactured panels.

R. Hashim et al. / Materials and Design 32 (2011) 246–254 253

prove thickness swelling and water absorption properties of thepanels [3,4].

4. Conclusions

Oil palm biomass waste is a suitable material for the produc-tion of binderless particleboard composite panels. The chemicalcomposition of the oil palm biomass consists of high holocellu-lose, lignin, starch and sugar contents normally required forself-bonding adhesion. The core-parts, mid-parts and frondsmay be used to produce binderless boards with acceptable MORand IB strength. Panels made from bark and leaves had poorMOR and IB strength. All parts of the oil palm had poor waterabsorption and thickness swelling properties. The FT-IR spectrashowed little difference between the raw materials and the man-ufactured panels. FESEM showed the presence of compressed cellswith some starch granules that facilitated adhesion. Differenttypes of raw materials result in different properties in binderlessparticleboard.

Acknowledgements

The authors would like to acknowledge the Universiti SainsMalaysia for Graduate Assistantship Support for Wan Noor Aidaw-ati Wan Nadhari, and financial support for Rokiah Hashim’s sabbat-ical leave to be part of the International Visiting Scholar atOklahoma State University, USA. The Japan International ResearchCenter for Agricultural Science (JIRCAS) for partially sponsoringthis research (304/PTEKIND/650478/J122) is also acknowledged.We would like to acknowledge Advanced Agriecological ResearchSdn. Bhd., Malaysia and Kuala Lumpur Kepong Bhd., Malaysia fortheir assistance in acquiring the oil palm samples.

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