Materials and Design 33 (2012) 419–424

Contents lists available at ScienceDirect

Materials and Design

journal homepage: www.elsevier .com/locate /matdes

The effect of alkali pretreatment on mechanical and morphological propertiesof tropical wood polymer composites

Md. Saiful Islam a,⇑, Sinin Hamdan a, I. Jusoh b, Md. Rezaur Rahman a, Abu Saleh Ahmed a

a Faculty of Engineering, Universiti Malaysia Sarawak, 94300 Kota Samarahan, Sarawak, Malaysiab Faculty of Science, Universiti Malaysia Sarawak, 94300 Kota Samarahan, Sarawak, Malaysia

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

Article history:Received 13 January 2011Accepted 21 April 2011Available online 1 May 2011

Keywords:E. MechanicalG. Scanning electron microscopyG. X-ray analysis

0261-3069/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.matdes.2011.04.044

⇑ Corresponding author. Address: Department of MEngineering, Faculty of Engineering, Universiti MaSamarahan, Sarawak, Malaysia. Tel.: +60 14 992251;

E-mail addresses: msaifuli2007@gmail.com,(Md. Saiful Islam).

In this study, mechanical and morphological properties of wood polymer composites (WPCs) from fivekinds of selected tropical light hardwoods namely Jelutong (Dyera costulata), Terbulan (Endospermum dia-denum), Batai (Paraserianthes moluccana), Rubberwood (Hevea brasiliensis), and Pulai (Alstonia pneumato-phora) were investigated. Methyl methacrylate (MMA) and styrene (ST) vinyl monomer mixture (50:50;volume:volume) was used in preparation of WPCs. Before being impregnated with an MMA/ST monomermixture, wood species were chemically pretreated with 5% sodium hydroxide (NaOH) solution for thereduction of hydrophilic hydroxyl groups and impurities from the cellulose fibre in wood and toincreased adhesion and compatibility of wood fibre to polymer matrix. Monomer mixture (MMA/ST)was impregnated into raw wood and NaOH pretreated wood specimens to manufacture wood polymercomposite (WPC) and pretreated wood polymer composite (PWPC). Mechanical tests and microstructuralanalysis were conducted. Comparison has been made among the properties of raw wood, WPC and PWPC.The result reveals that PWPC yielded better mechanical and morphological properties compared to WPCand raw wood.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

Structural wood is the most preferred building and constructionmaterial due to its high physical strength, low processing cost andaesthetically pleasing character. But the physical and mechanicalproperties of wood are readily deteriorated by environmental var-iation which is the main drawback and limit of its properties [1].These troublesome inherent properties of wood can be minimizedby appropriate chemical treatment such as the formation of woodpolymer composite (WPC) [2].

Recently, wood has been treated with a variety of chemicalssuch as styrene, epoxy resins, urethane, phenol formaldehyde,methyl methacrylate (MMA), vinyl or acrylic monomers to improveits physical, mechanical and biological properties [3–5]. The physi-cal and mechanical properties of wood can also be significantly im-proved by the impregnation of vinyl monomer mixture [6].Thermosetting and thermoplastic monomers have been widelyused and achieved certain improvements in wood properties, butboth showed limitations [7]. Thermosetting-related polymer suchas phenolic resins, urea–formaldehyde and melamine–formalde-

ll rights reserved.

echanical and Manufacturinglaysia Sarawak, 94300 Kotafax: +60 82 583410.

imsaiful@pgfeng.unimas.my

hyde shows improvement in compressive strength properties andmoisture-related shrinking and swelling behaviours. However,wood polymer composite treated with these type polymers maybe more brittle, and display only marginal improvement in mor-phological properties. Thermoplastic type monomers such as acry-late or methacrylates, for case in point, do not improve dimensionalstability. It has been established that the monomer and its mixturedoes not form bonds with hydroxyl groups of the cellulose fibres.They simply bulk the void spaces within the wood structure [8].Since most of the vinyl monomers are non-polar, there is littleinteraction between these monomers and the hydroxyl groups ofthe cellulose fibre. Poor chemical and physical interfacial interac-tions between the wood surface and chemical are two of the mostimportant mechanisms of bond failure [9]. Therefore, the polymercomponent of the WPC simply bulks the wood structure by fillingthe capillaries, vessels and other void spaces within the wood.

Therefore, one can deduce that if there was the formation ofchemical bonds between the impregnated monomers and the hy-droxyl groups on the cellulose fibres, the physical and mechanicalproperties of WPC could be further improved. It has been notedthat the better adhesion and interaction between hydrophilicwood fibres and polymer can be improved by pretreatment usingvarieties of chemicals and reagents such as alkoxysilane couplingagents, diazonium salt, sodium perchlorate, dinitrophenyl hydra-zine (DNPH), sodium periodate [8,10–13].

420 Md. Saiful Islam et al. / Materials and Design 33 (2012) 419–424

However, sodium hydroxides (NaOH) are widely used to modifythe interface between dissimilar materials such as raw fibres andthermoplastic or thermosetting polymer [14,15]. Alkaline sodiumhydroxide removes natural fats and waxes from the cellulose fibresurface thus revealing chemically reactive functional groups likehydroxyl groups. The removal of the surface impurities from thecellulose fibres also improves the surface roughness of the fibresor particles thus opening more hydroxyl groups and other reactivefunctional groups on the surface [16]. Sodium hydroxide alsoreacts with accessible –OH groups according to the following pro-posed chemical reaction [15–17].

Cellulose� OHþ NaOH! Cellulose� O�Naþ þH2O

þ impurities ð1Þ

In this study, the effects of alkali pretreatment on somemechanical and morphological properties of selected tropicalWPCs in Malaysia have been investigated. Five species of selectedMalaysian tropical light hardwood were utilized as starting mate-rials, keeping in mind that they are easily obtainable in the localforests. Major drawback of using these species is their high mois-ture uptake, and physical and mechanical properties that changewith environmental factors. Hydroxyl groups are intrinsic groupsof cellulose, that are responsible for the water uptake, a negativecharacteristic to this purpose, but these groups are responsiblefor general characteristics of the wood.

In order to overcome this problem and to improve the adhesionand compatibility of polymer to the cellulose of wood, the woodsamples were chemically pretreated with a 5% alkaline NaOH solu-tion and then impregnated with an MMA/ST monomer mixture tomanufacture pretreated wood polymer composite (PWPC). There-fore, the present study dealt with mechanical and morphologicalproperties of WPC pretreated with NaOH.

2. Experimental

2.1. Wood materials

Five kinds of tropical wood species, namely Jelutong (Dyeracostulata), Terbulan (Endospermum diadenum), Batai (Paraserianthesmoluccana), Rubberwood (Hevea brasiliensis), and Pulai (Alstoniapneumatophora) were selected in this study. The densities of thesetropical wood species are 380, 450, 455, 480 and 650 kg/m3 for Ba-tai, Jelutong, Pulai, Terbulan, and Rubberwood respectively. Gener-ally these wood species are porous and contain cellulose (40–44%),lignin (18–25%) and hemicelluloses (15–35%). Other polymericconstituents present in lesser and often varying quantities arestarch, pectin, and ash for the extractive-free wood. The internalproperties of these tropical woods are high vessel diameter (90–340 lm), medium of the number of vessel present per unit area(1–10%), high fibre length (800–1800 lm), and medium cell wallthickness.

These wood species were felled and cut into three bolts of 1.2 mlength and subsequently conditioned to air-dry in a room with rel-ative humidity of 60% and ambient temperature of around 25 �C for3 month prior to testing. The planks were ripped and machined to300 mm (L) � 20 mm (T) � 20 mm (R) and 100 mm (L) � 25 mm(T) � 25 mm (R) specimens for three point bending and compres-sion parallel to the grain test.

2.2. Alkali and monomer solutions

Chemicals used for pretreatment and WPC production were 5%NaOH, and methyl methacrylate/styrene (MMA/ST, 50:50, vol-ume:volume) mixture containing 2% benzyl peroxide catalyst asa polymerization initiator.

2.3. Pretreatment of wood specimens

All oven dried raw wood specimens were placed in a 5% NaOHsolution in a reaction vessel at room temperature for 6 h. Speci-mens were then removed and thoroughly rinsed in distilled waterseveral times after which a few drops of acetic acid were added justto neutralize excess NaOH that could otherwise continue to de-grade the wood cell wall components. The extracted wood sampleswere then oven dried at 100 �C for 24 h.

2.4. Manufacturing of wood polymer composites

For WPC and PWPC manufacturing, raw wood and pretreatedwood oven-dried samples were placed in an impregnation vacuumchamber at a vacuum pressure of 10 kPa for 10 min. The MMA/STmixture was introduced into the chamber as the vacuum pressurewas released. The samples were kept immersed in the monomermixture solution for 6 h at ambient temperature and atmosphericpressure to obtain further impregnation. Samples were then re-moved from the chamber and wiped of excess impregnate. Sam-ples were wrapped with aluminium foil and placed in an ovenfor 24 h at 105 �C for polymerization to take place. Weight percent-age gain (WPG) of the samples was then measured using Eq. (1):

WPGð%Þ ¼ ½ðWi �WoÞ=Wo� � 100 ð2Þ

where Wo and Wi are oven dried weights of raw wood and mono-mer mixture impregnated WPC samples respectively.

2.5. Microstructural analysis

2.5.1. Fourier transform infrared spectroscopy (FTIR)The infrared spectra of the raw and modified WPC specimens

were recorded on a shimadzu fourier transform infrared spectros-copy (FTIR) 81001 spectrophotometer. The transmittance range ofscan was 370–4000 cm�1.

2.5.2. Scanning electron microscopy (SEM)The interfacial bonding between the cell wall polymer and

monomer mixture were examined using a scanning electronmicroscope (SEM) (JSM-6701F) supplied by JEOL Company Limited,Japan. The specimens were first fixed with Karnovsky’s fixative andthen taken through a graded alcohol dehydration series. Oncedehydrated, the specimen was coated with a thin layer of gold be-fore being viewed on the SEM. The micrographs, taken at a magni-fication of 500 and 1000, are presented in the Section 3.

2.5.3. X-ray diffraction (XRD)In order to assess the effect of alkali pretreatment on surface

morphology of the WPC, XRD analysis was applied. A SiemensD500 diffractrometer was used where Cu Ka (k = 1.54 ÅA

0

) radiationwas employed with 2h varying between 4� and 80� at 5�/min.

2.6. Mechanical test

2.6.1. Bending and compression testIn order to characterize mechanical properties of manufactured

composites, bending and compression tests were carried outaccording to ASTM D-143 (1996) [18] using a Shimadzu UniversalTesting Machine having a loading capacity of 300 kN. A cross headspeed of 2 mm/min was used during the test.

2.7. Statistical analysis

The significant difference among raw wood, WPC and PWPCwere evaluated by a computerized statistical program (SPSS) com-posed of analysis of variance (one way anova) and following Tukey

(a) 100

NaOH pretreated Wood

Md. Saiful Islam et al. / Materials and Design 33 (2012) 419–424 421

tests at the 95% confidence level. Statistical evaluations were madeon homogeneity groups (HG), of which different letters reflectedstatistical significance.

4000 3200 2400 1800 1400 1000 600 4000.0

20

40

60

80

3407

2917

17361636

15081463

1427 1330 12621055

3438

1642 14031053

Raw Wood

Tra

nsm

ittan

ce (

%)

Wavenumbers (cm )-1

(b) 100

3. Results and discussion

3.1. Weight percentage gain (WPG%)

The values of WPG for WPC and PWPC samples were measuredand are given in Table 1. From Table 1, it can be seen that the WPGof PWPC samples were higher than the WPC samples. These resultsindicate that after alkali pretreatment, MMA/ST was more easilyimpregnated in all wood species. This is expected because NaOHreacts with OH groups of cellulose and also removes all impuritiesfrom the wood fibre surfaces thus increasing the adhesion andcompatibility between wood fibres and polymer, resulting in high-er WPG.

4000 3200 2400 1800 1400 1000 600 4000.0

20

40

60

80

WPC

3438

2271

16291421

105011601265

3435

2924

16251423

13751243

1162 1112

1054

2271

1333

1736T

rans

mitt

ance

(%

)

Wavenumbers (cm )-1

PWPC

ig. 1. IR spectrum of (a) Raw wood and 5% NaOH pretreated wood and (b) WPCnd PWPC.

3.2. Microstructural analysis

3.2.1. Fourier transform infrared spectroscopy (FT-IR)The reactions of NaOH with cellulose in wood fibre yielded cel-

lulose-ONa compound and removed impurities from the fibre sur-face. This is confirmed by the FTIR spectroscopic analysis as shownin Fig. 1a. The FTIR spectrum of the raw wood clearly shows theabsorption band in the region of 3407 cm�1, 2917 cm�1 and1736 cm�1 due to OAH stretching vibration, CAH stretching vibra-tion and C@O stretching vibration respectively. These absorptionbands are due to hydroxyl groups in cellulose, carbonyl groups ofacetyl ester in hemicellulose and carbonyl aldehyde in lignin[20]. After pretreatment with 5% NaOH, the characteristic peak at2917 cm�1, 1736 cm�1 and 1636 cm�1 fully disappeared and thereis a slight shift of the AOH peak by about 31 cm�1 to the high fre-quencies obtained. These characteristic peaks may be due to theremoval of surface impurities and the formation of cellulose-ONacompound on the wood fibre surface [10,21].

Fig. 1b shows the FTIR spectra of WPC and PWPC. Comparingthe FTIR spectra between WPC and PWPC it was found that thereis a significant difference in their absorption bands. This is due tothe differences of structural and chemical composition withinWPC and PWPC. The FTIR spectrum of WPC shows the absorptionband in the region of 3435 cm�1, 2924 cm�1 and 1736 cm�1. Theseabsorption bands also existed in raw wood. Therefore, it is clearthat MMA/ST do not have the ability to remove these characteristicabsorption bands responsible for functional groups from the woodfibre surfaces. On the other hand, no absorption band was found inthese above regions for PWPC. This is due to the chemical pretreat-ment with the NaOH solution.

Table 1Weight percentage gain (WPG) of wood polymer composites (WPC) and NaOHpretreated wood polymer composites (PWPC).

Wood species Composite type WPG St. dev.

Jelutong WPC 29 2.17PWPC 50 2.52

Terbulan WPC 19 1.7PWPC 38 2.0

Batai WPC 37 2.2PWPC 57 2.53

Rubberwood WPC 13 1.2PWPC 32 1.5

Pulai WPC 25 1.3PWPC 44 2.4

Mean value is the average of 10 samples, (St. dev. = Stander deviation).

Fa

3.2.2. X-ray diffraction (XRD)The X-ray diffraction patterns of raw wood, WPC and PWPC are

given in Figs. 2–4, respectively. As seen in Fig. 2 the patterns of rawwood fibres exhibit three well defined peaks (2h) at 15.1�, 22.8�and 34.7�. The 15.1�, 22.8� and 34.7� reflections correspond tothe (1 1 0), (2 0 0) and (0 2 3) or (0 0 4) crystallographic planes,respectively [22].

On the other hand, comparing all the X-ray diffractograms (Figs.2–4) it is observed that there are some new peaks (2h) of variousintensities in the amorphous region 40–75�. These peaks may be

Fig. 2. Typical X-ray diffraction patterns of raw wood.

Fig. 3. Typical X-ray diffraction patterns of wood polymer composite (WPC).

Fig. 4. Typical X-ray diffraction patterns of pretreated wood polymer composite(PWPC).

Fig. 5. SEM photographs of (i) Raw

422 Md. Saiful Islam et al. / Materials and Design 33 (2012) 419–424

due to the incorporation of MMA/ST inside wood and the formationof wood composites. The diffraction patterns of WPC in (Fig. 3)exhibits four new diffraction peaks at 43.6�, 49.1�, 50.9�, and72.7� whereas, the PWPC (Fig. 4) shows five new peaks of highand sharp intensity at 42.1�, 43.6�, 49.2�, 51.0�, and 72.6�. This re-sult also indicates that the manufactured WPC and PWPC signifi-cantly increased the crystallinity of wood as seen by otherresearchers [23–26]. However, PWPC shows more crystallinitypeaks than the raw wood and WPC as shown in (Fig. 4). Such a re-sult is expected because the alkali pretreatment removed all impu-rities from the wood fibre surface thus increasing the impregnationof MMA/ST and the degree of polymerization inside the wood fibre[21].

3.2.3. Scanning electron microscopy (SEM)Fig. 5i shows a number of void spaces and uneven layers in the

raw wood fibre surface which is removable by the suitable chem-ical treatment [27]. Fig. 5ii depicts the micrograph of WPC whileFig. 5iii is that of PWPC.

Fig. 5ii shows clean polymer stands throughout the wood fibreswith remarkable gaps between this polymer and the cell walls,while Fig. 5iii shows no noticeable gaps and strong bonds betweenthe polymer and the cell wall. Furthermore, fibrous cellulose mate-rial adhered to the surface of the polymer stands. It is thus deducedthat the reaction of NaOH with wood cellulose had increased theadhesion and compatibility of the polymer to the cellulose fibresof the wood.

3.2.4. Three point bending testThe modulus of elasticity (MOE) and modulus of rupture (MOR)

of raw wood, WPC and PWPC were measured and results are givenin Table 2. The MOE of WPC and PWPC were higher than those oftheir raw ones. From Table 2, it is worth noting that the MOEwas more significantly affected by the NaOH pretreatment. Thisresult is expected because NaOH reacts with cellulose in woodand enhances the adhesion and compatibility between wood fibresand the polymer resulting in improved MOE. The higher MOE of

wood, (ii) WPC and (iii) PWPC.

Table 2Static Young’s modulus of raw wood, wood polymer composites (WPC) and 5% NaOH pretreated wood polymer composites (PWPC).

Wood species Composite type MOE (GPa) Static bending strength, at 10% MCa

St. dev. HGb MOR (MPa) St. dev. HGb

Jelutong Untreated (raw) 5.31 0.44 A 46 5.72 AWPC 7.9 0.39 B 62 3.02 BPWPC 8.52 0.49 C 72 5.60 C

Terbulan Untreated (raw) 7.39 1.15 D 60.5 2.46 DWPC 10.15 0.39 E 77 5.29 EPWPC 11.14 0.40 F 88 6.86 F

Batai Untreated (raw) 6.51 0.57 G 55.4 2.86 GWPC 9.30 0.48 H 73 4.64 HPWPC 10 0.40 I 83 7.31 I

Rubber Untreated (raw) 11.62 1.05 J 105.8 2.57 JWPC 15.20 0.34 K 130 1.63 KPWPC 17.24 0.32 L 150 2.03 L

Pulai Untreated (raw) 4.12 1.80 M 37.8 1.81 MWPC 6 0.26 N 50 7.11 NPWPC 6.5 0.53 O 58 6.61 O

Mean value is the average of 10 specimens.a Moisture content.b The same letters are not significantly different at a = 5%. Comparisons were done within the each wood species group. (St. dev. = Stander deviation, HG = Homogeneity

Group).

Table 3Compressive strength of raw wood, wood polymer composites (WPC) and 5% NaOHpretreated wood polymer composites (PWPC).

Wood species Composite type Compressive strength (GPa), at 10% MCa

Mean St. dev. HGb

Jelutong Untreated (raw) 2.85 0.57 AWPC 4.41 0.33 BPWPC 5.30 0.13 C

Terbulan Untreated (raw) 3.82 0.63 DWPC 5.50 0.29 EPWPC 6.50 0.20 F

Batai Untreated (raw) 3.58 0.83 GWPC 5.20 0.30 HPWPC 6.30 0.38 I

Rubber Untreated (raw) 2.68 0.83 JWPC 3.75 0.26 KPWPC 4.45 0.20 L

Pulai Untreated (raw) 2.42 1.17 MWPC 3.70 0.21 NPWPC 4.40 0.28 O

Mean value is the average of 10 specimens.a Moisture content.b The same letters are not significantly different at a = 5%. Comparisons were

done within the each wood species group. (St. dev. = Stander deviation, HG =Homogeneity Group).

Md. Saiful Islam et al. / Materials and Design 33 (2012) 419–424 423

both WPC and PWPC compared to the raw wood were due to thechemical modification and impregnation, which is in accordancewith other researchers [28].

In the wood specimens, NaOH reacts with OH groups of cellu-lose fibre and yielded cellulose-ONa compound and removes theimpurities from the wood fibre surfaces thus enhancing polymerloading and degree of polymerization which further increasedthe MOE of PWPC. It is also apparent from Table 2, the MOE ofWPC and PWPC of the Jelutong wood were highest, followed byPulai, Batai, Terbulan, and Rubberwood respectively. However,for Rubberwood, a small increase was found for its WPC and PWPCdue to high density of this species and a little amount of MMA/STincorporation inside the cell wall, as found by other researchers[29,30].

On the other hand, the MOR of PWPC was higher than those ofWPC and raw wood, which is in agreement with previous research[31]. As one can see from Table 2 there was significant improve-ment of MOR of PWPC for all wood species. These results suggestthat the pretreatment enhanced the interfacial bonding strengthbetween wood fibres and polymer. The MOR of WPC and PWPCof Jelutong was highest followed by Pulai, Batai, Terbulan, and Rub-berwood respectively. The WPC and PWPC of Rubber wood hadlowest MOR observed because of its high density. This indicatesthat MOR also depends on the wood properties [19].

3.2.5. Compression test analysisThe compressive strength results for the raw wood, WPCs and

PWPC were measured and are summarized in Table 3. From Table3, it is seen that there was a significant increase in compressivestrength for both WPC and PWPC of all species. One can also beseen that WPC and PWPC of all species exhibited much highercompressive strength than raw wood samples. These incrementswere 39.93–54.74% for WPC and 66.04–85.96% for PWPC.

It is also apparent that PWPCs had higher (18–21%) compressivestrength compared to WPCs. Of the five wood species used, thehighest increases of compressive strength were observed in Jelu-tong followed by Pulai, Batai, Terbulan, and Rubberwood for bothWPC and PWPC. Raw wood species failed in compression becauseof the bulking of relatively thin cell walls due to a long column typeof instability. The chemical modification of raw wood puts a coat-ing on the walls which thickens them, thus greatly increasing theirlateral stability [32]. This is also expected because MMA/ST mix-ture has the ability to fill the void spaces and the strong branched

polymeric situation inside wood, thus forming WPC with improvedcompressive strength. This enhances the lateral stability of the cellwall. The increase of compressive strength of WPC compared toraw wood was also reported by different researchers [8,29].

All the WPC and PWPC samples had increased in compressionresistance. This finding is expected because the incorporation ofpolymer into the wood reduced the proportion of void spaces inthe wood. Thus a greater force was required to deform the WPCspecimens. However, the PWPC had the highest compressivestrength compared to WPC. This can be attributed to two main rea-sons, firstly that NaOH pretreatment increased adhesion and com-patibility between the wood fibre and the polymer and, secondlythat NaOH removes all impurities from the wood fibre surfaceswhich led to increased degree of polymerization [10].

4. Conclusions

The results obtained in this study lead us to the conclusionsthat:

424 Md. Saiful Islam et al. / Materials and Design 33 (2012) 419–424

1. The mechanical and morphological properties of the WPC weresignificantly increased by pretreatment with 5% NaOH solution.The mechanical tests also indicated that the PWPC led to signif-icant improvements in MOE, MOR and compressive strength.

2. The MOE, MOR and compressive strength of PWPC were 48–61%, 41–57% and 66–86% higher than raw wood and 7–10%,13–17% and 18–20% higher than WPC.

3. NaOH reacts with wood fibres and yielded cellulose-ONa com-pound and also removed all impurities from the wood fibre sur-faces which was confirmed by FTIR spectroscopic analysis. Themanufactured WPC and PWPC were also confirmed by FTIRspectroscopic analysis.

4. The significant effects of NaOH pretreatment on the above men-tioned properties of PWPC could be explained by the behaviourof the monomer mixture which adhered to the cellulose fibre ofthe wood as indicated by the scanning electron microscopy andX-ray diffraction patterns.

5. The authors propose that NaOH pretreatment increased theadhesion and compatibility of wood fibre to polymer matrixthus enhancing the degree of polymerization and the degreeof crystallinity of wood composite, which significantlyincreased the mechanical and morphological properties of allselected tropical light hardwoods used in this study.

References

[1] Hill CAS. Modifying the properties of wood. In: Hill CAS, editor. Woodmodification. Chemical thermal and other processes. John Wiley & Sons Ltd;2006. p. 175–90.

[2] Kamdem DP, Pizzi A, Jermannaud A. Durability of heat-treated wood. Holz alsRoh-Werkstoff 2002;60:1–6.

[3] Islam MS, Hamdan S, Rahman MR, Jusoh I, Ibrahim NF. Dynamic Young’smodulus and dimensional stability of batai tropical wood impregnated withpolyvinyl alcohol. J Sci Res 2010;2(2):227–36.

[4] Yalinkilic MK, Takahashi M, Imamura Y, Gezer ED, Demirci Z, Ilhan R. Boronaddition to non or low formaldehyde cross-linking reagents to enhancebiological resistance and dimensional stability for wood. Holz als Roh-Werkstoff 1991;57(1):151–63.

[5] Hamdan S, Talib ZA, Rahman MR, Ahmed AS, Islam MS. Dynamic Young’smodulus measurement of treated and post-treated tropical wood polymercomposites (WPC). Bioresour 2010;5(1):324–42.

[6] Baysal E, Yalinkilic MK, Altinok M, Peker ASH, Peker H, Colak M. Some physical,biological, mechanical, and fire properties of wood polymer composite (WPC)pretreated with boric and borax mixture. Constr Build Mater 2007:1471–85.

[7] Kumar S. Chemical modification of wood. Wood Fibre Sci 1994;26:270–80.[8] Elvy SB, Dennis GR, Loo-teck NG. Effect of coupling agent on the physical

properties of wood–polymer composites. J Mater Proc Technol 1995;48:365–72.[9] Rowell RM. Chemical modification of wood for improved adhesion in

composites. USDA forest Products laboratory Madison; Wisconsin: 1995; 1:56–60.

[10] Fávaro SL, Lopes MS, Neto AGVC, Santana RR, Radovanovic E. Chemical,morphological, and mechanical analysis of rice husk/post-consumerpolyethylene composites. Composites: Part A 2010;41(1):154–60.

[11] Haque MM, Hasan M, Islam MS, Ali ME. Physico-mechanical properties ofchemically treated palm and coir fibre reinforced polypropylene composites.Bio Technol 2009;100:4903–6.

[12] Islam MN, Haque MM, Huque MM. Mechanical and morphological propertiesof chemically treated coir-filled polypropylene composites. Ind Eng Chem Res2009;48(23):10491–7.

[13] Haque MM, Islam MS, Islam MDS, Islam MN, Huque MDM, Hasan M. Physico-mechanical properties of chemically treated palm fibre reinforcedpolypropylene composites. J Reinf Plas Compos 2010;29(11):1734–42.

[14] Mwaikambo LY, Ansell MP. The effect of chemical treatment on the propertiesof hemp, sisal, jute and kapok for composite reinforcement. Die AngewMakromol Chem 2000;272:108–16.

[15] Mohanty AK, Khan MA, Hinrichsen G. Surface modification of jute and itsinfluence on performance of biodegradable jute-fabric/biopol composites.Compos Sci Technol 2000;60:1115–24.

[16] George J, Sreekala MS, Thomas S. A review on interface modification andcharacterization of natural fibre reinforced plastic composites. Polym Eng Sci2001;41(9):1471–556.

[17] Sreekala MS, Thomas S. Effect of fibre surface modification on water-sorptioncharacteristics of oil palm fibres. Compos Sci Technol 2003;63:861–9.

[18] ASTM D-143. Standard method of testing small clear specimens of timber.USA: American society for testing and materials; 1996.

[19] Yap MGS, Chia LHL, Teoh SH. Wood polymer composites from some tropicalhardwood. J wood Chem Technol 1990;10(1):1–19.

[20] Ismail H, Edyhan M, Wirjosentono B. Bamboo fibre filled natural rubbercomposites; the effects of filler loading and bonding agent. Polym Test2002;21(920):139–44.

[21] Ndazi BS, Karlsson S, Tesha JV, Nyahumwa CW. Chemical and physicalmodifications of rice husks for use as composite panels. Composites: Part A2007;38(3):925–35.

[22] Elesini US, Cuden AP, Richards AF. Study of the green cotton fibres. Acta ChimSolv 2002;49:815.

[23] Shiraishi N, Matsunaga T, Yokota T, Hayashi Y. Preparation of higher aliphaticacid esters of wood in an N2O4–DMF cellulose solvent medium. J Appl PolymSci 1979;24:2347.

[24] Marcovich NE, Reboredo MM, Aranguren MI. Modified woodflour as thermosetfillers: II. Thermal degradation of woodflours and composites. ThermochimicaActa 2001;372:45.

[25] Borysiak S, Doczekalska B. X-ray diffraction study of pine wood treated withNaOH. Fibr Text East Euro 2005;13(5):87–9.

[26] Khan MA, Ali KMI, Wang W. Electrical properties and X-ray diffraction of woodand wood plastic composite (WPC). Radiat Phys Chem 1991;38(3):303–6.

[27] Zafeiropoulos NE, Williams DR, Baillie CA, Matthews FL. Engineering andcharacterisation of the interface in flax fibre/polypropylene compositematerials. Part I. Development and investigation of surface treatments.Composites: Part A 2002;33:1083–93.

[28] Rowell RM. Chemical modification of wood. Forest Prod Abstr1983;6(12):363–82.

[29] Umit C, Yildiz, Yildiz S, Gezer ED. Mechanical properties and decay resistanceof wood–polymer composites prepared from fast growing species in Turkey.Bioresour Technol 2005;96:1003–11.

[30] Manabendra D, Saikia CN. Chemical modification of wood with thermosettingresin: effect on dimensional stability and strength property. Bio Technol2000;73:179–81.

[31] Cai X, Riedl B, Zhang SY, Hui W. Effect of nanofillers on water resistance anddimensional stability of solid wood modified by melamine urea–formaldehyderesin. Wood Fiber Sci 2007;39(2):307–18.

[32] Rozman HD, Kumar RN, Khalil HPS, Abusamah A, Abu R. Fibre activation withglycidyl methacrylate and subsequent copolymerization with diallylphthalate. Euro Polym J 1997;33(8):1213–8.