A Review on Oil Palm Empty Fruit BunchFiber-Reinforced Polymer Composite Materials

Azman Hassan,1 Arshad Adam Salema,2 Farid Nasir Ani,2 Aznizam Abu Bakar11Department of Polymer Engineering, Faculty of Chemical and Natural Resources Engineering,Universiti Teknologi Malaysia, UTM 81310, Skudai, Johor Bahru, D’ Takzim, Malaysia

2Department of Thermofluid, Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, UTM 81310,Skudai, Johor Bahru, D’ Takzim, Malaysia

Natural fiber-reinforced polymer composite materialshave emerged in a wide spectrum of area of the poly-mer science. The composite produced from thesetypes of materials are low density, low cost, compara-ble specific properties, and most importantly they areenvironmental friendly. The composite materials pro-duced from oil palm fibers and commercially availablepolymers have offered some specific properties thatcan be comparable to conventional synthetic fibercomposite materials. However, these properties aregreatly dependent on the compatibility of oil palmfibers and matrix phase with moisture absorption asone of the critical issues that becomes the drawbacksof the oil palm fiber polymer composite materials.Apparently, it greatly affects the physical as well asmechanical properties of the composite materials. Thepresent review reports the work on oil palm empty fruitbunch (OPEFB) fiber-reinforced polymer compositeswith some interest on the OPEFB physical structure,and chemical compositions. Finally, the incorporationof OPEFB into polymeric materials leads to severalinteresting consequences on the water absorptioncharacteristics and the mechanical properties, whichhave been reviewed. POLYM. COMPOS., 31:2079–2101,2010. ª 2010 Society of Plastics Engineers

INTRODUCTION

During the past decades, natural fibers have attracted

the interest of material scientists, researchers, and indus-

tries because of their specific advantages as compared to

conventional or synthetic fibers. First and foremost is the

environmental issue that is alarming the present scenario

of the world. This issue is on the top of national and

international agenda. Hence, these natural or bio-based

fibers, which are biodegradable unlike the synthetic fibers,

have become the centre of attraction. In addition to this,

low cost, low density, specific properties comparable to

those of synthetic fibers, ease of separation, carbon diox-

ide seizure, non-corrosive, reduced tool wear, reduced

dermal and respiratory irritation [1, 2], have increased the

interest in using natural or biofibers with various available

synthetic and natural polymeric materials. The applica-

tions of these biocomposites range from household to

more sensitive and specialized areas such as in space and

aircrafts. For example, glass fibers are replaced with natu-

ral plant fibers in some parts of [3] the car such as inte-

rior panels, etc. They also pointed out that even though

natural fibers enjoy some superior properties compared to

synthetic fibers, but they also suffer from serious problem

such as polarity nature. The polarity characteristic creates

incompatibility problems with many polymers. In addition

to this, other study [4] has reported the limitations of

poor resistance to moisture, limited processing tempera-

ture, and low dimensional stability. Hence, various chemi-

cal treatments [5] have been done to improve the adhe-

sion or interfacial bonding between natural fibers and

polymers.

Composites are termed as biocomposite materials when

one of its phases either matrix (polymer) or reinforce-

ment/filler (fibers) comes from natural source. Plant fibers

including wood and non-wood such as cotton, flax, hemp,

kenaf, etc., or by-products from crops comes under natu-

ral and renewable source acting as reinforcement or fillers

in biocomposite materials. Depending on the natural fiber

origin (seed, bast, leaf, and fruit), bast and leaf are the

most commonly used in composite applications [6]. The

mechanical strength of these natural fibers is comparable

to that of synthetic fibers such as E-glass fibers on a per

weight basis [7]. Renewable or natural resins from vegeta-

ble oils and starches are gradually replacing the com-

monly used fossil fuel synthetic based polymers [8]. They

Correspondence to: Arshad Salema; e-mail: arshadsalema@gmail.com

Contract grant sponsor: Ministry of Higher Education (Malaysia);

contract grant number: 78200.

DOI 10.1002/pc.21006

Published online in Wiley Online Library (wileyonlinelibrary.com).

VVC 2010 Society of Plastics Engineers

POLYMER COMPOSITES—-2010

also have outlined the major factors influencing the per-

formance of the biocomposites materials, concluding that

future prospect of these materials remains need of further

research and development. However, the choice of suita-

ble natural fibers remains on many factors such as elonga-

tion at failure, thermal stability, adhesion of fibers and

matrix, dynamic and long-term behavior, final price, and

processing cost [9].

Keeping above in view and the factors such as easy

availability, abundantly available resource and futuristic

road to ease the commercialization, a comprehensive

review has been outlined on the research and development

activities done to date on OPEFB fibers composite materi-

als. The oil palm industries generate abundant amount of

biomass say in million of tons per year [10], which when

properly used will not only be able to solve the disposal

problem but also can create value added products from

these biomass. Oil palm empty fruit bunch (OPEFB) fiber

is one of the biomass that is presently used as a fuel in

the oil palm mills itself for generation of energy.

Attempts are also ongoing to convert the OPEFB fibers

into fertilizers for farms by burning them into ash, which

is rich in potassium. However, this raise the issue of envi-

ronmental pollution generated due to uncontrolled burning

of OPEFB fibers. The investigation of OPEFB fibers char-

acteristics such as physical and mechanical has led to

diversify there applications in the area of composite mate-

rials as well.

OPEFB fibers have depicted a great potential in use as

a reinforcing materials in a polymers [10]. This is

because, Malaysia and its surrounding South East Asian

countries generates large amount of OPEFB fiber as

waste, as mentioned earlier. Further, these OPEFB fibers

show specific properties that can be used by reinforcing

them with polymers to develop biocomposite materials.

Conversely, if these fibers are not used resourcefully, it

may not only lead to disposal problem and consequently

the environmental problems, but could also result in for-

feiture of substantial economic value, which would have

been induced by its suitable applications. Hence, palm oil

producing countries, in particular, can generate revenue

out of this waste product which till date is considered to

be challenging. The sustainable, non-hazardous, non-carci-

nogenic, eco-friendly, biodegradable product developed

from these fibers will surely benefit the human kind

across the globe in broad-spectrum. To our knowledge, at

commercial level, companies such as Sabutek Sdn. Bhd.

situated in Perak state and Ecofuture Berhad in Johore

state of Malaysia are manufacturing value added products

such as for packing from OPEFB fibers [11, 12]. Research

activities are being carried out at universities and other

research institutes as well. But the pace of the activities

was found to be gradual and confined. Despite many

efforts, hitherto the OPEFB fibers have not achieved total

commercialization. One of the major reasons is the hydro-

philic nature of the fibers. This can lead to separation of

the matrix and fiber phase in the composite materials after

aging due to poor adhesion between the resin matrix and

the fibers. Similar observation has been suggested for

other natural fibers such as jute fiber [13]. OPEFB fibers

are yet to be fully used economically because of consum-

ing unproductive cost and energy while handling it in oil

palm mills. However, this ‘‘waste" or by-product from the

palm oil mills, which was once viewed as embarrassing

liabilities are now viewed as co-products of increasing

potential value due to continual effort of research and

development on its applications. This will serve to pro-

mote a ‘‘zero-waste" concept. Current effort on R&D for

OPEFB fibers and other natural fibers is to minimize the

production of greenhouse gasses (GHG) and all existing

practices in the field are being examined. Certainly, the

reduction of GHG will assist in slowing down of climate

change and reducing the carbon footprints.

For example, over the past decades, the OPEFB

fibers have been studied for manufacturing composite

materials using different synthetic polymers for instance

polypropylene [14], polyester [15], poly(vinyl chloride)

[16], polyurethane [17], and phenol formaldehyde [18].

Basically, in these research works, the polymeric resins

were just used as binder. To our knowledge, until this

article, no study was found where OPEFB fiber was

reinforced with natural resins or bioresin. Extensive

studies based on these OPEFB fibers polymer composite

materials have been reported in the literature as shown

in Table 1 with classification of polymers. The

researchers have focused their studies on different

investigations such as water absorption, thermal stabil-

ity, physical and mechanical properties, and the effect

of pre-treating the OPEFB fibers to confirm the suitabil-

ity of OPEFB fiber as a reinforcing material in a dif-

ferent polymer matrix.

Very recently, a comprehensive and general review

article dealing with study on various aspects of cellulosic

biofibers and biocomposite materials was published [19].

The overview on biocomposite science and technology,

its environmental issues and market potential were found

in the literature [8]. In year 2000 and 2004, a review arti-

cle [20] about structural discussion on certain biofibers,

biodegradable polymers, and biocomposites, and an over-

view article [21] on pineapple leaf and sisal fiber and

their biocomposite reinforced with thermoset and thermo-

plastic polymers was published, respectively. Neverthe-

less, a specific review article on OPEFB fiber polymer

composite materials including both thermoplastic and

thermosets polymers have not been published so far to

our knowledge. Indeed, it becomes essential to assess the

previous and ongoing research for OPEFB fiber polymer

composite materials. This will surely enable the research-

ers, materialist, industrialists, scientist, and upcoming

experts to establish the lag in till date research work and

find approach for futuristic development for OPEFB fiber

polymer composite materials. This might even open room

for development of other natural fiber polymeric compos-

ite materials.

2080 POLYMER COMPOSITES—-2010 DOI 10.1002/pc

This review deals with the work of OPEFB fiber poly-

mer composite materials including both thermoplastic and

thermosets polymers. Earlier section of the article introdu-

ces the OPEFB fibers in terms of its types, physical char-

acteristics, structure, and chemical composition. Whereas

the later section of the article addresses the issues on

OPEFB fibers polymer composites. A particular attention

has been given on the effect of reinforcing OPEFB fibers

with different polymers (thermoplastics and thermosets)

on the water absorption characteristics and mechanical

properties.

OIL PALM FIBERS

It was of importance to describe the types of OPEFB

fiber and its basic fundamental properties before going

into the details of it and its composite materials. Gener-

ally, the fundamental properties of the materials can give

a far insight in developing the final products with a

desired property for a specific application. This knowl-

edge also helps in industrial processing and potential use

in value-added products [22]. Empty fruit bunch and the

OPEFB fiber are shown in Fig. 1.

Types of Oil Palm Fibers

Oil palm fibers are derived from two sources of oil

palm tree, that is, OPEFB and mesocarp. Among these,

OPEFB fibers as shown in Fig. 1b are the most commonly

used for composite materials and various other applica-

tions. This is because of OPEFB consist of a bunch of

fibers which is readily available and at low cost [10].

OPEFB fibers are extracted by retting process from empty

fruit bunch whereas mesocarp fibers are waste materials

left after the oil extraction that needs cleaning process

before its final usage. Hereafter, the article deals with the

OPEFB fibers polymer composite materials.

Physical Characteristics and Structure of the OPEFBFiber

The structure and contents of the natural fiber cell wall

depends widely on types of species and the parts of the

plants where they originate [23]. OPEFB fibers are lignocel-

lulosic fibers where the cellulose and hemicellulose are rein-

forced in a lignin matrix similar to that of other natural

fibers. Cellulose, hemicellulose, and lignin that forms major

constituents of the natural fibers might differ (see Table 2)

depending on plant age and growth conditions, soil condi-

tions, weather effect, and testing methods used. As the chem-

istry of the natural fibers is depended on plant they grow, it

changes during the course of growth [26]. The properties of

the fibers such as tensile strength, flexural strengths, and

rigidity depend on the alignment of cellulose fibrils, which

are generally arranged along the fiber length [19].

The cellulosic fibrils run parallel to each other and

form a crystalline structure in addition to some amor-

phous regions. Electron microscopy observations [25]

showed that the cell walls of the biomass fiber includingFIG. 1. (a) OPEFB and (b) OPEFB fibers. [Color figure can be viewed

in the online issue, which is available at wileyonlinelibrary.com.]

TABLE 1. Polymers reinforced with OPEFB fibers with classification.

Thermoplastics

ThermosetsSemi-crystalline Amorphous Elastomeric

High-density

polyethylene (HDPE)

Acrylonitrile butadiene

styrene (ABS)

Ethylene-propylene-diene

terpolymer (EPDM)

Diallyl phthalate (DAP)

Low-density

polyethylene (LDPE)

Cellulose acetae (CA) Ethylene-propylene

terpolymer (EPT)

Melamine formaldehyde (MF)

Linear low-density

polyethylene (LLDPE)

Cellulose acetate butyrate (CAB) Nitrile butadiene rubber (NBR) Phenol formaldehyde (PF)

Polyamide (PA) Cellulose proprionate (CP) Styrene-butadiene styrene (SBS) Urea formaldehyde (UF)

Polybutylene

terephthalate (PBT)

Polycarbonate (PC) Thermoplastic

polyurethane (TPU)

Epoxy (EP)

Polyether ether ketone (PEEK) Polyether sulfone (PES) Natural rubber SMR L Unsaturated polyester (UP)

Polyoxymethylene (POM) Polyethylene terephthalate (PET) Polyurethane

Polyporpylene (PP) Polymethyl methacrylate (PMMA)

Polyphenylene sulfide (PPS) Polyphenylene oxide (PPO)

Polystyrene (PS)

Polysulfone (PSU)

Polyvinyl chloride (PVC)

Styrene acrylonitrile (SAN)

—Studies on OPEFB fibers reinforced with these polymers have been done.

DOI 10.1002/pc POLYMER COMPOSITES—-2010 2081

OPEFB fibers are composed of two main layers or walls.

The transverse section of OPEFB fiber cell wall structure

is shown in Fig. 2a and b. The secondary (S1, S2, and S3)

thick wall is embedded in a primary wall and consists of

sub-secondary three layers. This layer consists different

orientation of cellulose fibrils. The observations [25]

proved the similarity in structure between OPEFB fibers

and coconut coir fibers. Similar observations reported [10,

27] that the OPEFB fibers are hard, tough, and analogous

to that of coir fibers in structure.

Moreover, the crystal and amorphous nature of OPEFB

fiber cell structure also plays an important role in deter-

mining the mechanical properties of the final composite

products. This is because of the crystal region that gives

the maximum value for the specimen modulus of materi-

als [23]. Studies [22, 25] have reported the morphological

and other detailed characteristics of the OPEFB fibers.

The results of these studies in connection with physical

and mechanical properties of the OPEFB fibers polymer

composite material are needed to be explored. This is

because the mechanical properties of the natural fibers are

dependent on the complex relations between external vari-

ables and intrinsic structural parameters that are at molec-

ular, macro-molecular, and microscopic level [28].

Fibers from oil palm biomass are in the form of

thread-like bundles. However, after processing, physically

OPEFB fibers are available in long as well as in short

length of about 50–60 mm and 10–30 mm, respectively.

Average fiber diameter is around 200 lm. Table 3 shows

the average diameter of commonly used natural fibers.

Except oil palm, coconut, and bagasse all other fibers are

thin in width or diameter. A recent study by Mohamed

Yusoff [37] has revealed the effect of single OPEFB fiber

diameter on the tensile property. Lengthwise, OPEFB

fiber is between hardwood and softwood [10]. The length-

weighted fiber length of the OPEFB fiber obtained

directly from oil palm mill was about 0.99 mm [22]. The

length to diameter ration also called as aspect ratio of

fiber has significant effect on the properties of final com-

posite materials. The aspect ratio of OPEFB fiber for

various length and diameter is as shown in Table 4 in

comparison with other natural fibers. Flax and hemp

showed highest aspect ratio, possibly may present higher

mechanical properties compared to other natural fibers.

Aspect ratio in parallel with mechanical property of the

OPEFB fiber can be improved by decreasing its diameter

via physical, chemical, or thermal treatments. Numerous

physical as well as chemical treatments for natural fibers

are reviewed [38], which could modify the structural and

surface properties of the fibers, consequently improving

the interfacial bonding with the polymer matrix. An

increase (25%) in aspect ratio of bagasse from 18.63 to

23.41 using alkali treatment (1% conc.), improved the

tensile and flexural properties by 14% and 16%, respec-

tively [39]. This was due to enhancement in aspect ratio

by decreasing the diameter of the fiber resulting in a bet-

ter adhesion between fiber and matrix. Similarly, the

effect of aspect ratio on the mechanical properties for var-

ious types of natural fibers such as wood, rice husk, straw

leaf, straw stem, whole straw reinforced with HDPE was

done [40]. They found an improvement in mechanical

properties of the composite materials. However, to our

TABLE 2. Chemical composition of oil palm fibers from different researchers.

Reference Hemicellulose (%) Cellulose (%) Lignin (%) Location

Hill and Abdul Khalil [24] 22 48 25 Malaysia

Rozman et al. [10] 17.1 47.9 24.9 Malaysia

Sabutek [11] 68.3 41.9 13.2 Malaysia

Abdul Khalil et al. [25]a 83.5 49.8 20.5 Malaysia

Sreekala and Thomas [18] – 65 19 India

a Oil palm fiber from oil palm fond.

FIG. 2. Transverse section of oil palm fiber cell wall structure [15]

(ML, middle lamella; P, primary wall; S1, S2, and S3, secondary wall

sublayers).

TABLE 3. Average diameter of natural fibers.

Fibers Diameters (lm) References

Oil palm (long) 358 [29]

Oil palm (short) 151 [29]

Oil palm (EFB) 300 [30]

Banana 120 6 5 [31]

Sisal 205 6 4 [31]

Pineapple leaf 50 6 6 [31]

Ramie 34 [32]

Coconut 397 [33]

Bagasse 399 [33]

Jute 20–200 [34]

Hemp 31.2 6 5 [35]

Flax 19 [36]

2082 POLYMER COMPOSITES—-2010 DOI 10.1002/pc

knowledge, till date, no such detailed study has been

performed for OPEFB fibers reinforced polymer compos-

ite materials except the research work [37] whereby the

effect of aspect ratio for OPEFB fibers was taken into

account to observe the young modulus only. In this

study [37], about 67% decrease in aspect ratio caused a

significant decrease in Young’s modulus of OPEFB

fibers. As the natural fiber polymer composite materials

undergoes several process steps before final products, the

aspect ratio or the geometry of the fibers usually gets

altered. Such modification can take place during process-

ing (injection, extrusion, etc.), swelling due to exposure

to certain compounds including water or change in cellu-

losic structure due to chemicals [41]. Joseph [42]

reported that maintaining the fiber geometry during proc-

essing of natural fiber polymeric composite materials is

vital, in view of the fact that it has considerable effect

on the property of final composite material. They even

proposed the fiber aspect ratio to be in the range of

100–200 for optimum results. Property such as fracture

in the composite materials is also governed by aspect

ratio of the fibers [43] and is defined by critical fiber

length. Most of the research work for natural fibers

polymer composite materials involves the effect of fiber

loading or content, physical, chemical, or thermal treat-

ments of fibers, treatment of matrix, using coupling

agents, etc. Few have focused on the effect of aspect

ratio or geometry of the fibers on the mechanical and

physical properties of the natural fiber polymer compos-

ite materials. Hence, controlling the physical characteris-

tics such as length, diameter, and surface of OPEFB

fibers has revealed momentous changes in the physical

as well as mechanical properties of the composite

materials.

Chemical Composition

Another important internal structural component

besides physical characteristics of fiber that affect the

overall performance of the natural fiber polymer compos-

ite materials is the chemical compositions. All the nature

fibers consist of basic chemical building block of cellu-

lose, hemicellulose, and lignin with varying proportions.

Other components such as pectins and waxes are also

present in minor quantities in the fibrous materials. The

characteristics of cellulose, hemicellulose, and lignin and

others are documented [44] and it does not need to be

explained further. Generally, the OPEFB fiber contains

about 40–50% cellulose, 20–30% hemicellulose, and

20–30% lignin with moisture content of about 10–15%.

Table 2 shows the chemical composition of OPEFB fibers

reported by different researchers within Malaysia and

India. This shows a variation in chemistry of the OPEFB

fibers within the same region as well as outside the

regional borders. Hence, the formation of internal chemi-

cal structure of the natural fibers totally depends on the

geographical and the soil conditions with other factors.

Similar variation in chemical composition was observed

in jute and kenaf fibers [45] and other natural fibers [46]

based on regional and different researcher observations.

Particularly, the percentage of cellulose can vary depend-

ing on the species and the age of the plant.

Abdul Khalil [25] revealed that OPEFB fiber from oil

palm fond contain highest composition of hemicellulose

compared to coir, pineapple, banana, and even soft and

hardwood fibers. Lignin which is also responsible for

tough and stiffness properties of the fiber was lower than

coir fibers, but still higher than other fibers. In addition,

the OPEFB fiber contains minor components of arabinose,

xylose, mannose, galactose, silica, copper, calcium, man-

ganese, iron, and sodium. Researchers [22] have done the

detailed study on the chemical composition of the OPEFB

fibers. They found that large number of silica bodies were

attached to the surface of the OPEFB fibers. According to

them, this may complicate the pulping and bleaching pro-

cess of the OPEFB fibers because the inorganic metals

and substance might react with the chemicals used for

treatment, which may possibly create undesirable results.

Comparative study is still lacking in the literature to show

the effect of inorganic materials attached to the OPEFB

TABLE 4. Aspect ratio of oil palm and other natural fibers.

Fiber type

Length

(L) (mm)

Diameter

(D) (mm)

Aspect

ratio (L/D)

Oil palm fibers

Short*

(Average) 17.5 0.1515 115.5

(Range) 10 0.12 83

20 0.15 133

30 0.16 187

Long

(Average) 142.3 0.358 397.5

(Range) 100 0.105 952

200 0.358 558

300 0.777 386

General 50 0.2 250

Banana

(Average) 45 0.15 300

(Range) 20 0.08 250

50 0.15 333

80 0.25 320

Sisal

(Average) 50 0.205 244

Pineapple leaf

(Average) 50 0.05 1000

Ramie

(Average) 50 0.034 1470

Coconut

(Average) 50 0.397 126

Bagasse

(Average) 50 0.399 125

Jute

(Average) 50 0.100 500

Hemp

(Average) 50 0.031 1612

Flax

(Average) 50 0.019 2631

DOI 10.1002/pc POLYMER COMPOSITES—-2010 2083

fibers on the chemical treatment. However, to how much

extent this inorganic components can impede the final

properties of the biocomposite materials are still

unknown. Besides this, OPEFB fiber contains about 1.5–

2.5% of ash with carbon (45–50%) and oxygen (44–48%)

as main constituents following the silica of about 5–6%

and others such as magnesium, calcium, and potassium in

minor quantities.

The properties and amount of each lignocellulosic

components contribute to the properties of the fiber as

well as the composite materials. For example, the hydro-

philic nature of the cellulose causes the absorption of

water in the fiber. This forms a major drawback for the

natural fibers since the interfacial bonding with matrix

weakens resulting in a poor physical and mechanical

properties of composite materials. This forms one of the

major disadvantages of the natural fibers reinforced poly-

mer composite materials. Properties such as biodegrada-

tion, moisture absorption [45], and thermal degradation

are shown by hemicellulose. On the other hand, lignin is

thermally stable and protects the further degradation of

biocomposite materials thermally. However, it is suscepti-

ble to photochemical degradation caused due to ultraviolet

light [45]. Once this lignin gets degrade, the inner content

becomes more prone to degradation and physically the

fiber starts losing the surface characteristics. The influence

of these components on the properties of the natural fiber

polymer composite materials is shown in Fig. 3. This

clearly shows that the lignocellulosic components of the

fiber play a major role in determining the mechanical and

physical properties of the fibers. Hence, the modification

of these components (cellulose, hemicellulose, and lignin)

was the focus of the research work until date to enhance

the mechanical and other properties of the OPEFB fiber

polymer composite materials. The chemical route to mod-

ify the natural fibers was found to be the most commonly

used technique.

The degree of polymerization (DP) determines the

mechanical properties of the fibers [47] and the degrada-

tion of cellulose caused by physical, chemical, or radia-

tion damage can be assessed with the help of DP value

[46]. As the structure of the natural fibers components

such as cellulose, hemicellulose, and lignin almost

remains the same, the DP is reported [13] to differ. To

our knowledge, a deep understanding of DP for OPEFB

fibers is still lacking in the literature. Further, its effect on

the physical as well as mechanical properties needs to be

evaluated. Of all the above, the OPEFB fibers has very

complex chemical structure which is yet to be established

in detail. The deep understanding of various characteris-

tics of OPEFB fibers will improve its applicability and

design criteria of composite materials with different poly-

meric resins.

Various advantages of the OPEFB fibers have been

mentioned, but they also show some weakness. Neverthe-

less, most of its inadequacy can be prevailed through suit-

able treatments. Another advantage of natural fibers over

synthetic is the buckling during processing and fabrication

rather than breaking [19]. Further, they also have reported

that cellulose in the natural fiber possesses a flattened

oval shape that is suitable for high stress due to higher as-

pect ratio. The present review article attempts to cover

the various polymeric materials reinforced with OPEFB

fiber and its mechanical and water absorption properties.

FIG. 3. Properties of lignocellulosic materials [17].

2084 POLYMER COMPOSITES—-2010 DOI 10.1002/pc

OPEFB FIBER-REINFORCED THERMOPLASTICPOLYMERS

Polypropylene

Effect on Water Absorption. The hydroxyl group de

facto is the main chemical entity for the attraction of water

molecules in the natural fibers. Another is the physical na-

ture of the natural fibers such as amorphous and crystalline

regions plays an important role in diffusion of water in the

fibers with later region showing less water intake because

of its relatively close packing of molecules [46].

Water absorption for different mesh size OPEFB fiber

filled PP (treated with maleic anhydride) composite mate-

rial was measured [14]. The composite samples were peri-

odically taken out of the water and its absorption rate was

measured and was immediately immersed in the water for

further evaluation. As the immersion time increased, the

water absorption for untreated and treated OPEFB-PP

composite material increased to a certain value and

thereon remained plateau. Treated composite materials

displayed lower water intake compared to untreated com-

posite. The overall reduction in water absorption was

found to be about 10% in maleic anhydride treated

OPEFB fibers as compared to untreated fibers. This also

depends on the filler size. As the lignocellulosic constitu-

ents of OPEFB fibers are responsible for water absorption

because of their hydroxyl groups, chemical treatment

replaces these hydroxyl groups with hydrophobic groups

and also form protective layer thus preventing any further

intake of water. Fiber size also plays a role in low intake

of water, for example in case of [14] 80 mesh size

OPEFB fiber filled PP composite materials showed about

55% lower water absorption rate for treated and about

25% lower for untreated composite materials as compared

to 60 mesh fiber size, respectively. For the same fiber

size, the water absorption rate was about 27% less in case

of 60 mesh size treated fibers and around 56% less in

case of 80 mesh size treated OPEFB fiber filled PP com-

posite materials. This depicts that smaller fiber size results

in strong adhesion between fiber-matrix which reduces

any possible voids or gaps that might form capillary for

water absorption in composite materials. However, the

authors [14] have not mentioned the detail reasons for

this effect.

OPEFB fibers–polypropylene composite materials was

produced by two compounding techniques and pre-treat-

ing the fibers with Epolene 43 and poly propylene acrylic

acid as compatibilizers and with 3-aminopropyltriethoxy-

silane as coupling agent [48]. Epolene 43 is maleic anhy-

dride modified polypropylene (PP). The results of this

study depicted that a slight reduction in water absorption

was attributed by 3-aminopropyltriethoxysilane compared

to other two compatibilizers. Overall, the improvement in

water resistance was insignificant compared to previous

study by the same author [14]. The rate of water resist-

ance in case of polypropylene acrylic acid treated fibers

was poor compared to 3-aminopropyltriethoxysilane

treated fibers. This shows the affinity of acrylic acid

towards the water molecules.

In another study [49], the effect of three coupling

agents, namely Epolene 43, polymethylene polyphenyl

isocyanate, and 3-trimethoxysilyl-propylmethaacrylate on

the water absorption characteristics by OPEFB fibers–

polypropylene composites was studied. The effect of fiber

loading in conjunction with concentration of chemicals

used as coupling agents to modify the OPEFB fibers was

also taken into account. Apparently, the results showed

reduction in water absorption for all the chemical treated

fibers. However, the water absorption rate was higher in

case of higher loaded OPEFB fiber in the composite

material. The reason behind this was the higher possibility

of water absorption by hydrophilic nature of fibers, which

proportionally increases the rate of water absorption with

higher fiber loading. PP shows very negligible or no water

absorption [50] and hence, it can be assumed that 99.9%

of water is absorbed by OPEFB fibers. This can also be

confirmed by studies performed for other natural fibers

reinforced with PP such as wood fiber/PP composites

[51], sisal fiber PP composites [52], and flax fiber/PP

composites [53]. In fact, it has been reported [52], PP

showed negligible evidence of water absorption even at

higher temperatures of about 908C.The increase in concentration of chemicals for modifi-

cation of fibers confirmed increase in reduction of water

absorption but approximately in range of 0.1–0.5%, which

can be considered as nominal effect. Interestingly, the

water absorption characteristics as shown in Fig. 4a–c

illustrates that higher fiber loading with increased chemi-

cal concentration results in more resistance in uptake of

water as was seen in case of 3-trimethoxysilyl-propylme-

thaacrylate and polymethylene polyphenyl isocyanate

treated fibers. In general, the reduction in water absorp-

tion for different chemicals treated fibers followed the

order: Epolene 43 [ 3-trimethoxysilyl-propylmetha-

acrylate [ polymethylene polyphenyl isocyanate. This

variation in water absorption might be attributed either

due to the nature of the chemicals or the replacement

of functional groups during the reaction of fibers with

chemicals.

Comparatively, maleic anhydride treated OPEFB

fibers–PP composite [14] revealed high resistance to water

than other chemical treatments. Likewise, in case of

maleated PP reinforced with wood fiber showed �38%

decrease in water intake compared to untreated compo-

sites [51]. This clearly shows that chemical used for fiber

modifications play an important role in determining the

water absorption rate for composite materials. Neverthe-

less, other factors such as filler size, fiber loading, chemi-

cal concentration, and temperature at which the treatment

is done equally contribute in defining the water absorption

characteristics. Tajvidi [50] reported that the water

absorption depended on the type of natural fibers rein-

forced with PP and order was kenaf [ newsprint [ wood

DOI 10.1002/pc POLYMER COMPOSITES—-2010 2085

flour [ rice hulls at 50 wt% fiber loading. Not only this

factors but also compounding techniques such as extru-

sion, two-roll mills, etc., with the shape and size of the

fibers plays a role in water absorption characteristics [51].

It was observed that the amount of water absorption for

OPEFB fiber/PP composite was almost near to that of

kenaf fiber/PP [50] as well as hardwood fiber/PP [51] at

50% fiber loading. Moreover, Tayang [54] have investi-

gated the effect of amorphous and crystallinity on the rate

of water absorption by natural fibers such as banana,

ramie, abaca, maguey, and kenaf. They concluded that the

water intake is linearly dependent on the amorphous

region or content of the natural fibers. Finally, the dimen-

sional stability of the composite materials greatly depends

on the amount of water or moisture absorbed, hence the

thorough understanding of the effect of water absorption

on the properties of the composite is vital.

Effect on Mechanical Properties. The effect of maleic

anhydride (MAH) on OPEFB fiber filled with PP compo-

sites was studied [14] to determine the mechanical proper-

ties. Flexural strength, modulus, and toughness increased

for OPEFB filled–PP composite material treated with

MAH as shown in Table 5. This improvement was due to

good adhesion and compatibility between MAH treated

OPEFB fillers and PP matrix. Because maleic anhydride

provides polar acid–base interactions and can bound with

hydroxyl group of the natural fibers covalently [55]. On

the other hand, increase in filler size has reverse effect on

the mechanical properties, except that for flexural tough-

ness, which showed significant increase as shown in

Table 6. This indicates that OPEFB fibers are tough in

nature and it increases overall toughness of the composite

materials. Flexural toughness increased considerably

for MAH treated OPEFB fiber filled with PP composite

FIG. 4. OPEFB fiber–polypropylene composite treated with (a) epolene 43; (b) 3-trimethoxysilyl-propylme-

thaacrylate; and (c) polymethylene polyphenyl isocyanate [20].

TABLE 5. Percentage gain in flexural and impact properties for treated

OPEFB filler–PP composites at 40% filler loading and filler size of

Mesh 80 [14].

Chemical concentration (%)

5 10 15

Flexural strength (MPa) 105 123 135

Flexural modulus (GPa) 36 40 59

Flexural toughness (KPa) 70 120 125

Impact strength (J/m) 13 42 44

TABLE 6. Percentage increase in flexural properties for MAH-treated

(10% chemical concentration) OPEFB filler–PP composite at 40% filler

loading [14].

Mesh 60 Mesh 80 Mesh 100

Flexural strength (MPa) 52 123 82

Flexural modulus (GPa) 65 41 55

Flexural toughness (kPa) 75 125 160

Impact strength (J/m) 76 44 27

2086 POLYMER COMPOSITES—-2010 DOI 10.1002/pc

materials as compared to flexural strength and modulus

with varying filler size. Similar study [56] was done in

more detailed for rubber fiber and powder form filler in

HDPE composites. It was found that rubber fibers filled

HDPE composites do not show good flexural strength as

compared to rubber powder filled HDPE composite mate-

rials. The reason stated by the researchers was the uni-

form dispersion of rubber powder fillers in the polymer

matrix as compared to rubber fibers. Moreover, fibers

with higher degree of lignin tend to agglomerate which

may subsequently create discontinuity in the matrix and

stress concentration points in the composite materials.

The impact strength was found to decrease in rubber–

HDPE composite materials, but fillers with powder form

depicted higher impact strength than that of rubber fibers.

This was due to higher surface area produced by powder

form than fiber which may resist the crack propagation.

From our knowledge, analogous assumption could be pro-

posed for OPEFB–PP composite materials where impact

strength was found to decrease as the filler size was

increased as shown in Table 6. Overall, two factors were

mainly emphasized for improvement in mechanical prop-

erties. First, the adhesion property between fibers and ma-

trix phase and second, the dispersion or uniformity of fill-

ers. Former factor is enhanced by either pre-treating the

fibers with chemical or by addition of coupling agents. As

can be noticed (see Fig. 5) from the study of Rozman

[56] the profile of impact strength before and after the

addition of coupling agents. This confirms that the tend-

ency of agglomeration or non uniformity and poor adhe-

sion can be reduced to a greater extent with the help of

coupling agents. The later can be improved through

proper selection and care during processing techniques for

composite materials.

Cellulose derived from OPEFB was reinforced with PP

to form composite as a potential material in packaging,

building products, furniture, consumer goods, and auto-

motive industries [57]. The mechanical properties such as

tensile, flexural, and impact tests for this composite was

compared with that of as received OPEFB fibers rein-

forced with PP composite. Cellulose as well as OPEFB

fibers were treated with alkali (NaOH) solution prior to

preparation of composite materials. Pure cellulose and

OPEFB fibers were blended with PP at different ratios

using twin-screw compounder. PP–cellulose composite

was found to have higher tensile strength compared to

OPEFB fiber–PP composite for fiber loading above 20%.

This was also observed in case of fibrous cellulose fiber

reinforced with PP with different compatibilizers [58]. In

general, increase of fiber or filler loading in composite

materials decreases the tensile strength. However, in case

of cellulose–PP composite materials an opposite trend

was observed, that is, an increase in tensile strength with

filler loading. Flexural modulus was seen increasing

steadily with filler content. For 17.5% chemical treated

OPEFB filler and 40% fiber loading the flexural modulus

was about 2.75 GPa as compared to 3.6 GPa for previous

study [14]. This also confirms that maleic anhydride treat-

ment was more effective than alkali treatment. However,

cellulose–PP composite material showed similar value of

modulus to that obtained by Rozman [14]. Similarly, the

impact strength in case of maleic anhydride treated

OPEFB fiber–PP composite was much higher compared

to alkali treated OPEFB filler–PP composite. However,

PP–cellulose composite showed high impact strength

compared to untreated OPEFB fiber PP composite. High

crystallinity fibrous cellulose of about 95% crystalline

reinforced with PP showed nearly 25% lower tensile

strength compared to neat PP [59]. However, it was

increased by using MAPP compatibilizer.

OPEFB fiber–PP composites were produced using

treated and untreated maleated PP (MAPP). In this work

[60], the PP was grafted with maleic anhydride to form

maleated PP with different proportions of PP and maleic

anhydride. The fiber loading was varied in the composite

materials in the range of 20–60%. The mechanical proper-

ties such as flexural and impact were enchanced by treat-

ing PP with maleic anhydride and higher improvement in

FIG. 5. Impact strength of rubber-filled HDPE composite materials (a) without coupling agents and (b)

with coupling agents (TPM, trimethoxysilyl propyl methacrylate; APE, aminopropyl triethoxysilane) [21].

DOI 10.1002/pc POLYMER COMPOSITES—-2010 2087

properties was noted for higher maleated PP. Neverthe-

less, the properties were observed to decrease with

increase in fiber loading except flexural modulus. The rea-

son behind this was the formation of hydrogen bond,

which reduced the ability to resists the stress transmitted

to the filler or fiber from the matrix. Moreover, according

to researchers [59] maleic anhydride moieties present in

MAPP can effectively interact with free OH group present

in the fibers. Hence, when the fiber loading was increased

the number of OH group apparently increased with the

constant MAPP amount causing poor interfacial bounding.

An improvement in tensile and flexural property of kenaf/

PP composite was reported by the addition of small

amount of MAPP [55]. Numerous researchers have

applied MAPP as compatibilizer either for modification of

matrix [53] or fiber surface [61]. Nevertheless, the later

authors have claimed that MAPP grafting of fibers are

industrially impracticable because of high expenses.

Poly(vinyl chloride)

PVC is usually reinforced with inorganic materials such

as glass fibers, calcium carbonate, and talc. However, these

types of fillers are characterized as high density materials

which might increase the overall density of the composite

materials. Hence, natural fibers are gaining importance as

an alternative to synthetic fillers. The important aspect in

the development of PVC composites by using natural fibers

was to achieve good combinations of properties at an eco-

nomical way. PVC is found in different forms such as PVC

rigid and plasticized PVC. Each has its own characteristics

and differs from one another. However, among these cate-

gories, PVC rigid and plasticized PVC are used in many

applications. The study of OPEFB fibers reinforced with

PVC was studied by present authors [16, 62] that are pre-

sented in this article. Besides OPEFB fiber, other natural

fibers reinforced with PVC are wood [63–65], bamboo and

pine flour [66], rice straw [67], sisal [68], sugarcane ba-

gasse [69], and coconut [70].

Effect on Water Absorption. To our knowledge, till

date, there has been no study found on the water absorp-

tion characteristics for PVC reinforced with OPEFB

fibers. This surely needs to be explored with its affect on

mechanical and physical properties in the composite

materials. Because most of the polymers particularly ther-

moplastics are non-polar, that is, hydrophobic in nature

[71], thus, neat PVC absorbs very negligible or no water.

It was reported by a company that PVC absorbed about

0.05% of water after 24 h at room temperature [72].

Hence, it can be assumed that all the water will be

absorbed by the fibers in the natural fiber reinforced with

PVC polymeric matrix. Nevertheless, the rate of absorp-

tion while using PVC as polymeric resin with OPEFB

fibers is needed to be investigated. This is because in the

high humidity regions such as Malaysia, use of natural

fiber polymer composite materials for the final application

must be done cautiously, because it can easily deteriorate

the composite material by absorbing the moisture from

the environment and even due to the weather condition.

However, natural fibers other than OPEFB fiber reinforced

with PVC composites are presented to get some insight

about water absorption characteristics.

PVC reinforced sisal fibers composites [68] were sub-

jected to water absorption characteristics showed increase

in water intake with increase in sisal fibers loading. How-

ever, modification of fibers with maleic anhydride

improved the resistance to water intake thereby improving

the mechanical properties.

A US patent [71] claimed that there was significant

reduction in water absorption in PVC oak wood and pine

flour composite material by using compatibilizers consist-

ing of mixture of maleic anhydride, styrene, methyl meth-

acrylate, azobisisobutyronitrile, and toluene.

Takatani [73] have studied the effect of using steam

exploded wood flour and found an excellent increase in

the water resistance in wood flour thermoplastic polymers

such as PMMA, PVC, and PS. From Table 7, it seems

clear that the technique of reinforcing steam exploded

wood fibers in to PVC polymer resin was successful in

increasing the water resistivity for the composite materi-

als. If wood flour alone were exposed to water environ-

ment, it would gain the highest amount of water intake as

studied in detail by Stark [74]. His study confirmed that

wood flour is the only component to absorb water or

moisture in wood flour/PP composite, because PP does

not absorb the moisture. As wood flour absorbed about

16% moisture at 90% relative humidity (RH) compared to

just 3.6% (for 20 wt% wood fiber loading) and 5.5% (for

40 wt% wood fiber loading) for the same exposure. This

77% and 65% drop for 20 wt% and 40 wt% fiber loading,

respectively, in water uptake in the wood flour/PP com-

posite materials was due to formation of skin layer of

hydrophobic PP on the wood fibers. Nevertheless, wood

flour reinforced PVC composites showed higher water

absorption rate compared to PMMA and PS. The authors

[73] concluded briefly that the water resistance of the

composite material dependent mainly on polymer species

and not on the wood species without giving detailed rea-

son about water absorption test.

TABLE 7. Water absorption property of steam-exploded wood flour

fiber reinforced with PVC polymer [73].

Types of

SE-wood flour

Fiber/SE/polymer

ratio (7/0/3)

Water absorption

% (15.92)

Beech 6/1/3 13.89

Japanese cedar 10.09

Red meranti 22.26

Beech 5/2/3 15.1

Japanese cedar 7.2

Red meranti 11.88

Beech 4/3/3 10.62

Japanese cedar 6.44

Red meranti 11.33

2088 POLYMER COMPOSITES—-2010 DOI 10.1002/pc

The rate of water absorption in wood fiber reinforced

with different thermoplastic polymer such as PVC, HDPE,

and PP was about 1.3, 0.7, and 1.1%, respectively, which

was much less than Oriented strandboard (OSB) and Me-

dium-density fiberboard (MDF) which is about 16.5% and

21.2%, respectively [75]. The rate of water intake depends

on numerous factors such as pre-treatment, processing

method, fiber orientation, fiber loading, and fiber nature.

It seems that better understanding of water absorption

characteristics for natural fiber reinforced with PVC poly-

mer composite materials needs to be carried out due to

unclear data reasoning. Biofiber polymer composite materi-

als faces the challenge of water absorption problems due to

degradation property of biofibers once exposed to rain, sea,

ice, snow, or humidity with possible reactions of swelling,

shrinking, and cracking of composite materials. Because

lignocellulosic materials present in the natural fibers such

as hemicellulose is reported [20] to be a major contributor

in absorbing the water or moisture followed by cellulose

and lignin to be least. Addition of crosslinking agents in the

natural fiber polymer composite materials can also increase

in water resistance of the composite materials as reported in

[76] using Ca and Zr salts. This and other possible cross-

linking agents have to be investigated for OPEFB fiber-

reinforced PVC polymer composite materials. Low water

absorption by OPEFB fiber PVC composite can be specu-

lated due to its higher lignin and lower cellulose content

compared to other natural fibers. As lignin act as capsule

for hemicellulose and cellulose, it can reduce the water

absorption into the OPEFB fibers. However, this type of

studies has not been carried out as mentioned earlier in this

section and needs to be taken into account.

Effect on Mechanical Properties. The influence of

OPEFB content on the impact strength of the composite is as

shown in Fig. 6. As the fiber content was increased from 0 to

40 phr, the impact strength was reduced by about 29%. This

reduction in strength was attributed due to two possible rea-

sons. First, there is the detrimental effect of fibers caused by

the volume take up. OPEFB fibers, unlike the matrix, are

incapable of dissipating stress through shear yielding prior to

fracture. The local motions of the PVC molecules are hin-

dered that enable the matrix to shear yield. As a result, the

ability of filled composites to absorb energy during fracture

propagation is decreased. In other words, the ductile portion

contributed by PVC matrix is reduced and the failure mode

became more brittle as the OPEFB fiber content increases.

Second, reason of impact strength reduction is the poor adhe-

sion and wetting of the fibers in the matrix phase. However,

this is the case for OPEFB fibers filled with PVC. Although

the polarity of OPEFB fibers makes them capable of forming

a physical interaction with polar PVC, it is a relatively weak

interaction. Therefore, OPEFB fibers have a greater tendency

to agglomerate among themselves into bundles which conse-

quently lowers the area of contact with the matrix phase.

Meanwhile, the moisture content may also contribute with

the physical bounding between fibers and PVC. These factors

weaken the interfacial adhesion between fiber and matrix due

to void formation as shown in Fig. 7. Once this occurs, the

crack growth may propagate because of the inability of the

fibers to sustain the stress transfer to the polymer matrix.

Similar trend of decrease in impact strength for coconut fiber-

reinforced PVC composite was observed in [70]. However,

impact strength of OPEFB fiber/PVC composite had higher

impact strength than coconut fiber/PVC composite. Another

reason for low impact strength is the dilution effect [68], that

is, increases in fiber loading decreases the PVC content

resulting in poor toughness property.

Figure 8 shows increase in flexural modulus with

respect to fiber content. Conversely, the flexural strength

was seen decreasing with fiber content. The increment in

modulus was about 22% as the fiber content increased

from 0 to 40 phr, whereas flexural strength decreased to

about 18%. The enhancement of modulus depends on a

number of factors, such as fiber aspect ratio [77, 78], fiber

modulus, and fiber content [78–80]. This result indicates

that although OPEFB fibers have low aspect ratio, they

are able to impart a significant improvement in stiffness

by hindering the movement of PVC molecules. For

instance, poor strength in wood flour–PP composite was

reported [78] due to lower aspect ratio of wood flour par-

ticles which was far below the critical fiber length

FIG. 6. Effect of OPEFB fiber content on the impact strength of

OPEFB fiber–PVC composites.

FIG. 7. SEM micrograph shows the void at fiber–matrix interface of

composite (Magnification: 20003). [Color figure can be viewed in the

online issue, which is available at wileyonlinelibrary.com.]

DOI 10.1002/pc POLYMER COMPOSITES—-2010 2089

required for reinforcement. The fact that the increase in

modulus while the strength decreases with increasing fiber

content is in agreement with the trend observed in other

natural fiber-filled thermoplastics [81]. Agglomerations of

fibers in the matrix, moisture intake by the fibers, and

interfacial defects could be the main causes of the reduc-

tion in the flexural strength. All these factors would have

restricted the stress transfer from the PVC to the OPEFB

fibers during flexural and impact testing. Nevertheless,

whenever a natural fiber composite fails, it has been

assumed that the failure was caused due to lack of suffi-

cient bounding between fiber and matrix phase. Another

important factor as discussed earlier is the water content

in the composite materials either before, during, or after

the formation of composite materials. Water is readily

absorbed by cellulosic natural fibers and is responsible for

the poor mechanical properties of the composite materials.

Better adhesion in composite materials particular natural

fiber polymeric components can be achieved by good wet-

ting of one component into another. Hence, the surface

energies of the components (fiber and matrix) play a nec-

essary role to reflect the final mechanical properties of the

composites. To achieve this compatibility between the

surface energies, either the surface of natural fiber can be

modified or the polymer matrix can be modified.

The above hypothesis of improving mechanical proper-

ties by treating natural fibers was proved by study [82].

In this study, it was observed that mechanical properties

such as tensile and bending of the alkali treated rice straw

reinforced with PVC was significantly improved com-

pared to untreated rice straw composite materials.

Effect of Accelerated Weathering on PVC–OPEFBFiber Composite.Impact Properties. The impact strength of weathered

composites for all fiber contents slightly decreased com-

pared to unweathered composites as depicted in Fig. 9.

The effect of photo-oxidative degradation process which

was initiated by UV irradiation in the presence of oxygen

and moisture in the amorphous regions of PVC was the

main cause for the decrease in impact strength of weath-

ered filled composites [83]. The rate of permeability of

oxygen and moisture is greater in amorphous region

because the molecular packing was less dense that the

degradation process was able to take place. Some photo-

oxidation processes lead to scission of the polymer chain,

while others to intermolecular crosslinking. This intermo-

lecular crosslinking is defined as the joining of two chains

or more [84], which causes material embrittlement [83].

Most researchers agreed that crosslinking and chain scis-

sion contribute to the deterioration of the impact strength

and other mechanical properties [85–87].

The suggested reaction scheme for photo-oxidative deg-

radation (similar to photo degradation) is shown in Fig. 10

[86–88]. The action of UV radiation on PVC produces the

singlet-excited state of polyene sequence, which resulted

from the absorption of conjugated double bonds and car-

bonyl groups. The most likely bond to be broken in the

excited singlet polyene sequence is the allylic C–Cl link-

age, due to its low dissociation energy. This results in the

FIG. 9. Impact strength of unweathered and weathered PVC–OPEFB

fiber composites. [Color figure can be viewed in the online issue, which

is available at wileyonlinelibrary.com.]FIG. 8. Effect of OPEFB fiber content on the flexural properties of

composites. [Color figure can be viewed in the online issue, which is

available at wileyonlinelibrary.com.]

FIG. 10. Reaction scheme for the accelerated photo-oxidation degrada-

tion [33–35].

2090 POLYMER COMPOSITES—-2010 DOI 10.1002/pc

chlorine radical being released from the excited singlet

polyene sequence and produces a polyenyl radical. The rad-

ical then reacts with the oxygen to produce peroxy radicals

on the chain and leads to chain scission (degradation) or/

and crosslinking of PVC molecular chains.

The lignin of the incorporated OPEFB filler primarily

broke down under UV irradiation leading to the genera-

tion of the chromophoric functional groups (impurities)

such as carbonyl and hydroperoxy radicals, which acceler-

ated the degradation of PVC. The increase in the intensity

of the C¼¼O stretching bands at around 1,735–1,731

cm21 as shown in FTIR spectra (see Fig. 11) provided

good evidence of the incorporation of carbonyl groups

into the PVC matrix during processing. The presence of

these groups explained the pronounced degradation

observed in the filled composites as compared to unfilled

composites [86]. As a result, the brittleness of the filled

composites increased with increasing OPEFB fiber content

as given in Table 8.

Flexural Properties. The weathered composites showed

slight increase in the flexural strength as shown in Fig. 12

while flexural modulus decreased (see Fig. 13) compared

to unweathered composites. The increase in the properties

of weathered samples was similar with the findings of

other researcher [85] whereby the tensile strength of

PVC/lignin blend increased after undergoing 120 h and

480 h of accelerated weathering. The increase in flexural

strength indicated that the influence of crosslinking and

chain scission of PVC molecular chains might cause a

slight increase in the flexural strength. However, this evi-

dence was not conclusive because of the fluctuation and

small magnitude of increase in the flexural strength and

flexural modulus as well (see Table 9), which fell within

the experimental error. Furthermore, other factors such as

filler agglomerations and filler–matrix interaction bonding

as mentioned earlier might also influence the flexural

properties results. The detailed work on effect of acceler-

ated weathering on the mechanical properties of OPEFB

fiber filled PVC composite is published elsewhere [62].

OPEFB FIBER-REINFORCED THERMOSETPOLYMERS

Polyurethane

Effect on Water Absorption. High density rigid PU

prepared from palm kernel oil based resin with diphenyl-

FIG. 11. FTIR spectra of (a) unweathered (red line) and (b) weathered (black line) composites containing

30 phr of OPEFB fiber. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.

com.]

TABLE 8. Percentage of impact strength reduction for filled impact-

modified composites after weathered for 504 h.

OPEFB fiber content (phr) 0 10 20 30 40

Impact strength reduction (%) 3 4 4 6 6

FIG. 12. Flexural strength of unweathered and weathered OPEFB

fiber–PVC. [Color figure can be viewed in the online issue, which is

available at wileyonlinelibrary.com.]

DOI 10.1002/pc POLYMER COMPOSITES—-2010 2091

methane diisocyanate was reinforced with OPEFB fibers

at different weight ratios in a hot press machine [17]. In

this, analysis of water absorption for the composite mate-

rials was done according to ASTM D570-8 method. Com-

posite samples were immersed in water for 7 days and the

reading was taken every 24 h. As expected, the composite

material with high fiber loading of 25:75 (matrix:fiber ra-

tio) showed higher water absorption compared to 30:70

and 35:65. The water absorption rate for 25:75 composite

materials was about 12.5% and 23% higher compared to

30:70 and 35:65 composite samples, respectively, at sev-

enth day. The water absorption profile was much higher

at initial 3 days but reached a stable value after 3 days

for all composite samples. This indicated that composite

materials prepared with OPEFB fibers are poor resistance

of water and can cause dimensional instability during

their applications.

Another interesting study of the above authors [89],

but incorporation of additional filler known as kaolinite

with OPEFB fiber in a PU matrix was done to study

the mechanical as well as water absorption behavior.

However, the ratio of PU to OPEFB fibers was fixed at

35:65 and the amount of kaolinite was varied by 5, 10,

15, and 20% by weight. Comparing the water absorp-

tion from the previous study [17], the present hybrid

composite material of kaolinite and OPEFB fiber

showed about 9% lower water intake. Kaolinite filler

might have filled the void space between the OPEFB

fibers and PU matrix thus decreasing the possibility of

direct exposure of OPEFB fibers to water. As a result

of this, the hybrid biocomposites materials became com-

pact and dense thus reducing the water intake. This has

to be confirmed by comparing the present data with that

of PU and kaolinite composite material which will fur-

ther confirm the degree of hygroscopic nature of the

both the individual fillers.

Effect on Mechanical Properties. Flexural and impact

properties of PU and OPEFB fiber composites was found

to decrease as the OPEFB fiber content increased [17]. At

higher fiber loading such as in case of 25:75 where 75%

of fiber was incorporated leads to weak bonding between

fibers and matrix. Void formation, adhesion properties,

fiber distribution, and other factors might also contribute

in diminishing the mechanical properties of the composite

materials. Similar effect of loading natural amorphous

silica fiber (NASF) on tensile strength and elongation for

PU/NASF composite was reported to be optimum at

17 wt% of fiber content in PU [90]. After this, value

reduction in mechanical properties was observed. It

should be noted that in former case [17], the PU was

formed from palm kernel oil polyester with crude isocya-

nate. This also affects the overall mechanical properties

of the composite materials.

Hence, development of hybrid composite materials

improved the mechanical as well as dimensional stabil-

ity of the composite [89]. Hybridizing of kaolinite filler

in PU–OPEFB fiber composite material decreased the

flexural strength until 15%. However, it increased for

15% and thereon again decreased for 20%. The trend

was different for flexural modulus where the loading of

kaolinite increased the flexural modulus linearly until

15% and dropped thereafter. It was reported that at

20% loading, problem of over packing occurs and low-

ers the plasticizing effect of the composite materials.

Impact strength showed similar trend that of flexural

strength and maximum value was found at 15% load-

ing. Among the mechanical properties, only flexural

modulus, that is, elasticity was observed to increase on

addition of hybrid filler with PU–OPEFB fiber compos-

ite materials.

Investigation of tensile properties revealed that a

threshold point or maximum value occurs for PU–

OPEFB filler composite materials [91]. This value was

reported to depend on the filler loading, filler size, as

well as % of OH group in OPEFB filler. The tensile

properties increased with filler loading and % of OH

groups in OPEFB filler to a certain point and decreased

thereon. The maximum value for tensile properties was

found at 50–60% of filler loading and at 60% with vary-

ing OH groups present in OPEFB filler with former

depending on filler size. It appeared that smaller filler

particle size showed lower tensile strength in PU–

OPEFB composite materials. However, the tensile prop-

erties were higher in this case as compared to study

done by [90]. This could be because of higher fiber con-

tent in the PU.

FIG. 13. Flexural modulus of unweathered and weathered OPEFB

fiber–PVC composites. [Color figure can be viewed in the online issue,

which is available at wileyonlinelibrary.com.]

TABLE 9. Percentage of flexural modulus reduction and percentage of

flexural strength increment of the filled composites after 504 h exposure

to accelerated weathering.

OPEFB fiber content (phr) 0 10 20 30 40

Flexural modulus reduction (%) 13 9 10 0 15

Flexural strength increment (%) 13 4 0 11 0

2092 POLYMER COMPOSITES—-2010 DOI 10.1002/pc

In another study by the above authors [92], the effect of

using OPEFB mat with PU polymer to produce composite

was investigated. Further, the OPEFB fiber was chemically

modified with isocyanates namely hexamethylene diisocya-

nate (HMDI) and toluene diisocyanate (TDI). Chemically

treated fibers composite materials showed increase in ten-

sile strength as compared to untreated fiber composite and

followed the order as HMDI treated composite (highest)[TDI treated composite [ untreated. An exactly opposite

order was observed for tensile modulus, that is, highest for

untreated[ TDI[HMDI. This might be attributed due to

increase in flexibility of the fibers which might also result

in easy mobility of fibers in the matrix phase thus decreas-

ing the tensile modulus or stiffness of the composite materi-

als. The chemical bounding between the fiber and matrix

via chemical used for treatment also plays a major role in

determining the mechanical properties. On the other hand,

the tensile toughness of the isocyanate treated OPEFB

fiber-reinforced PU composite materials was enhanced sig-

nificantly compared to untreated composite. This indicates

substantial requirement of energy is necessary to fail the

treated fiber composites than untreated fiber composites.

Moreover, flexural properties (strength, modulus, and

toughness) followed the same order as of tensile properties.

Impact strength of composite material was improved on

chemical modification of fibers, but decreased with maxi-

mum value observed at 35% fiber loading.

Figure 14a shows the probable combined flexural mod-

ulus profile of studies done by Badri [17] and Rozman

[92]. The optimum or maximum value of flexural prop-

erty can be in the range of 35–55% fiber loading, though

this value can not be conclusive. Similarly, the possible

flexural strength characteristic with respect to fiber load-

ing is shown in Fig. 14b. The studies revealed that always

an optimum or maximum value of flexural properties is

observed in the particular range of fiber loading. The

value for flexural properties increases linearly before this

optimum value and drops after it has reached the opti-

mum value. Hence, while designing the composite materi-

als particularly reinforcement with natural fibers, fiber

loading becomes a vital parameter to maximize the me-

chanical property.

Polyester

Effect on Water Absorption. Recently, in study [93] it

was proved that neat polyester resin shows very low water

absorption compared to its composite reinforced with nat-

ural banana fiber. There was about 260% increase in

water intake by polyester/banana fiber composite material

compared to neat polyester resin at 308C temperature.

The rate of water absorption mechanism was also found

to change with respect to temperature condition, besides

other factors such as fiber loading, diffusivity, etc. Very

recently Akil [94] and his coworkers revealed that water

absorption characteristics in unsaturated polyester rein-

forced with empty fruit bunch banana fibers composite

also depended on the type of water. For example, in their

study, the polyester composite materials were immersed

in three types of water, distilled, sea and acidic solution.

A pseudo-Fickian diffusion characteristic of water absorp-

tion was reported for their study with higher diffusion

rate and moisture absorption in distilled water followed

by acidic solution and sea water. However, no such study

was carried out for OPEFB fiber polyester composite

materials till date.

Several methods were implemented to minimize the

water absorption rate by modifying the natural fibers with

chemicals. For instances, chemically modified OPEFB

fibers were reinforced with polyester matrix to investigate

the mechanical and water absorption properties of the

composite materials [15]. The composite material of

desired volume was immersed in de-ionized water at am-

bient temperature and weighted at regular interval of time

in days to determine the percentage of moisture absorp-

tion. The results for moisture absorption for the composite

material were in the order of highest for unmodified fibers

[ succinic [ propionic [ acetic treated fibers. For

unmodified fibers, the rate of water absorption was about

10.5% while that for chemically treated was about 6%

(Succinic), 5% (Propionic), and 4% (acetic) after

100 days of composite immersion. Acetylation or acetic

anhydride showed the lowest rate of water absorption due

to fast rate of reaction and ultimate substitution [95]

between OPEFB fibers and acetic anhydride. Comparison

FIG. 14. (a) Flexural modulus and (b) flexural strength profile with increasing OPEFB fiber loading in a PU matrix.

DOI 10.1002/pc POLYMER COMPOSITES—-2010 2093

with previous studies [48, 49] it seems that the present

chemicals were found to be more effective in making the

composite materials resistance to water uptake, since the

previous studies reported about 1–3% reduction in water

absorption between unmodified and treated fibers. How-

ever, the study of Abdul Khalil [15] revealed about 4–6%

reduction in moisture absorption between unmodified and

treated fibers. This concludes that anhydrides are effective

among the chemicals to reduce the moisture absorption in

OPEFB fiber polymer composite materials.

Hill and Abdul Khalil [96] exposed polyester compos-

ite reinforced with modified and chemically treated

OPEFB fibers in a soil of 90% water holding capacity

and 50% moisture content for a period of 12 months.

Investigation on moisture absorption in composite samples

was done at 3, 6, and 12 month intervals. Apparently,

chemical treated OPEFB fibers composite material

showed lowest rate of moisture intake after duration of

composite immersion in sterile and unsterile soils. Among

the chemicals used for modification, acetylated fibers

showed the lowest uptake of moisture compared to tita-

nate and silane treated fibers. Since acetylation of OPEFB

fibers, results in an increase of hydrophobicity of the

fibers. The study was done [95] by reacting OPEFB fibers

with acetic anhydride that replaces the OH group of the

fiber with acetyl group. Moreover, the chemical treatment

such as acetylation changes the surface morphology of

the fibers and makes the surface much smoother. The

change in surface morphology and nature of the OPEFB

fibers can be observed using FT-IR and SEM methods.

The chemical method used to reduce the moisture absorp-

tion is not only useful in increasing the hydrophobicity of

the OPEFB fibers polymer composites but also improves

its physical and mechanical properties. In other words,

the removal or reduction in moisture creates the possibil-

ity of better adhesion between the fibers and matrix phase

consequently in better physical and mechanical properties.

Effect on Mechanical Properties. A specific mechani-

cal property shows certain behavior when composite

materials are analyzed at different parameters. For exam-

ple, study [96] on mechanical properties for polyester

filled OPEFB fibers composite materials revealed different

profiles for specific mechanical properties such as tensile,

flexural, and impact. In their studies, OPEFB fibers were

modified via different chemicals (acetic anhydride, silane,

and titanate) to determine any improvement in the

mechanical properties of the composite materials. Table

10 clearly shows the improvement in the mechanical

properties for chemical treated OPEFB fiber polyester

composite materials. The negative sign in Table 10 signi-

fies the reduction in the property. Hence, elongation at

break reduced for all chemically treated fibers. All other

properties particularly acetylated treated fiber composites

showed much better mechanical performance than other

treated composite material. Silane and titanate treatment

does not seem to give encouraging results for mechanical

properties.

Another remarkable study by the above author [24]

was performed on the mechanical properties of OPEFB

fiber reinforced with polyester upon exposure to different

environmental condition. These types of studies are im-

portant from the point of view that after exposure of com-

posite materials at different environment, whether or not

the mechanical properties gets affected and if so to what

extent. Because focusing only on the mechanical perform-

ance at normal conditions might sometime impetuous the

results. Hence, the study on different environmental expo-

sure on mechanical properties of composite materials par-

ticularly natural fibers composites are of great interest and

few studies have been accomplished. In the research work

done by Hill and Abdul Khalil [24], the polyester OPEFB

fiber composite materials were completely buried in soils

having 90% water holding capacity and 50% moisture

content at 298C temperature. Composite materials were

exposed to the soil conditions and its effect was analyzed

as percentage gain or loss on the tensile and flexural

property as tabulated in Tables 11 and 12, respectively.

Hence, acetylation treatment of OPEFB fibers was very

effective as compared to silane and titanate treatments.

This might be because of good bonding linkage between

OPEFB fibers and polyester matrix by acetylation treat-

ment. However, the authors [24] have recommended that

the silane treatment should be used because of lower cost

option.

Tensile strength and tensile modulus characteristics fol-

lowed the order as acetic (highest) [ propionic [ suc-

cinic (lowest) for OPEFB fiber reinforced with polyester

composite [15]. On the other hand, elongation at break

followed opposite order as succinic (highest) [ propionic

[ acetic (lowest). However, compared to unmodified

fibers composite material, the elongation at break for

modified OPEFB fibers composite materials was lower.

This was due to change in property of fibers to brittleness

after chemical modifications which might easily break

TABLE 10. Percentage gain or loss in mechanical properties for chemically treated OPEFB fiber polyester composite materials.

OPEFB fibers

Tensile Flexural

Impact strengthStrength Modulus Elongation at break Strength Modulus

Acetylated 7 12.5 27.2 0.5 19 12

Silane 5 9.4 24 26.7 16 2

Titanate 21.7 1.2 23 28 5 21

2094 POLYMER COMPOSITES—-2010 DOI 10.1002/pc

upon stress. Effect of anhydride modifications on OPEFB

fibers composite materials showed smaller improvement

in flexural strength and modulus. The results of flexural

modulus were significant compared to flexural strength.

The main reason behind this effect was the adhesion

property of the fibers and matrix phase. This was also

proved by impact testing done on chemically modified

OPEFB fiber polyester composite material. Increase of

about 20–35% in impact strength was observed in modi-

fied fiber composite materials compared to unmodified

composite material above 20% fiber loading. But the

impact strength starts to decline above 50% fiber loading.

An interesting investigation done by [97] on the me-

chanical properties for roselle and sisal fibers hybrid poly-

ester composite by taking into account the effect of mois-

ture condition. It clearly revealed that mechanical proper-

ties are greatly affected due to presence of moisture in

the composite materials. In case of dry condition or with-

out moisture, the mechanical properties showed improve-

ment whereas at wet condition or with the presence of

moisture in the composite it diminished the mechanical

properties. Such study in case of OPEFB fibers polyester

composite materials has to be carried out to understand

the moisture absorption characteristics of natural fiber-re-

inforced polymer composite material to develop optimized

material [97].

Even though the tensile strength of pure OPEFB fiber

[27] was found to be higher than rice straw fibers [98],

the composite material of later with polyester showed

higher tensile strength at 40 wt% fibers loading compared

to former with polyester [96]. This contradiction might be

due to the method used to test the specimen, preparation

technique, method of testing standards, manufacture tech-

niques of composite materials, fiber physical properties,

fibers aspect ratio, etc. Surprisingly, the tensile properties

of OPEFB fibers were found differing from one study to

another. For instance, the tensile strength of OPEFB fibers

reported by [27] was 248 MPa, which was about 250%

more than what reported by [37] which was just 71 MPa.

Hence, it was found that still there is not a good agree-

ment about the properties of OPEFB fibers and its poly-

mer composites which might have hold its further devel-

opment into a commercial fibers even though it is gener-

ated abundantly with inherent advantages.

Phenol Formaldehyde

Effect on Water Absorption. A comprehensive study

[99] on water absorption in OPEFB fiber reinforced with

phenol formaldehyde composite materials was done.

Water absorption rate at four different temperatures (30,

50, 70, and 908C), and modifying the OPEFB fibers by

using different chemicals (alkali, silane, acrylation, iso-

cyanate, peroxide, permanganate, latex, acetylation, and

acrylonitrile) and also radiating with Co c radiation was

analyzed. Effect of fiber loading (10, 20, 30, 40, and

50%) on water uptake by the composite was also deter-

mined.

As the temperature increases, the water absorption rate

reduces with fiber loading till the equilibrium state of

water uptake was reached. However, the characteristic of

water absorption at equilibrium were also dependent on

fiber loading and it decreased as the fiber loading was

increased till 40 wt% loading and thereon it increased sig-

nificantly. The profile of water absorption for OPEFB-

phenol formaldehyde composite material at different tem-

peratures is as shown in Fig. 15.

Hence, the lowest water absorption was found at 40

wt% fiber loading. In terms of temperature, lowest intake

of water was showed at 508C. The result reported [99]

that water absorption decreases on increase in tempera-

ture, for instance, 50% fiber loading showed highest water

absorption at 908C and lowest at 508C. The lowest water

absorption at 40% fiber loading followed the temperature

order: 30 (highest) [ 90 [ 70 [ 50 (lowest). However,

this order is contradicting with the observation made.

Hence, a general conclusion on water absorption cannot

TABLE 11. Percentage change in tensile properties of composite

materials after burial in soil.

OPEFB fibers

Time

(months)

Tensile

Strength Modulus

Elongation

at break

Acetylated 0 7 12 27

3 9 11 210

6 21 27 12

12 44 48 33

Silane 0 5 9 24

3 2 11 0

6 14 26 7

12 37 55 41

Titanate 0 22 1 23

3 23 25 20.3

6 8 7 3

12 6 10 17

TABLE 12. Percentage change in flexural properties of composite

materials after burial in soil.

OPEFB fibers Time (months)

Flexural

Strength Modulus

Acetylated 0 0.5 19

3 3 27

6 3 49

12 42 63

Silane 0 27 16

3 23 25

6 26 48

12 34 55

Titanate 0 28 5

3 28 11

6 28 27

12 23 21

DOI 10.1002/pc POLYMER COMPOSITES—-2010 2095

be drawn based on temperature since it varies with fiber

loading as well.

Water absorption rate can be minimized in the com-

posite materials via chemical treatment of fiber surface.

The free hydroxyl groups in natural fibers which are re-

sponsible to attach with water molecules and thereby

increases the rate of water uptake can be occupied by the

chemical entities. Therefore, study [99] showed that

chemical modification of OPEFB fibers improved the re-

sistance to water absorption in the composite materials.

Like alkali treatment showed the lower rate of water

absorption as compared to untreated composite material at

all temperatures as shown in Fig. 16. While other chemi-

cals depicted higher water absorption rate than untreated

composite materials. This is because the alkali treatment

creates a stronger bond between fiber and matrix thus

reducing the formation of void and possible gaps which

resists the water to flow inside the composite materials

and gets absorbed into the fibers.

From Fig. 16 it can also be revealed that temperature

of 508C shows lowest water absorption intake at equilib-

rium except for radiated and isocyanate treated fibers.

Latex treated fibers exhibited highest water absorption

rate. There was not much difference in water absorption

rate for isocyanate treated fibers at all temperatures. This

was because of the extent that a particular chemical reacts

with OPEFB fibers and occupies the hydroxyl groups of

the fibers. Hence, any reduction in water absorption by

the composite material is due to decrease in number of

hydroxyl groups of the fibers. Therefore, the strong inter-

face or adhesion between fiber and matrix is established

when almost all of the hydroxyl groups are occupied and

there is a little or no room for the water to be absorbed

through the capillary action which might have been cre-

ated due to weak interface bounding. As in most cases,

the water absorption was observed to be independent of

temperature. The kinetic study also [99] exhibited that

the untreated OPEFB fiber phenol formaldehyde compos-

ite material followed the Fickian diffusion mechanism,

while chemically treated composites deviated from the

Fickian diffusion curve. Interestingly, incorporation of

glass fibers in OPEFB and phenol formaldehyde compos-

ite to form a hybrid composite material reduced the water

absorption rate as the volume of glass fibers was

increased in the composite material. Similar results were

reported by Amin and Badri [89] while incorporating

kaolinite as hybrid filler with OPEFB-PU composite

material.

Study of Abdul Kahlil [80] showed � 36% and 29%

decrease in water absorption for acetylated and propiony-

lated treated OPEFB fibers reinforced with phenol formal-

dehyde respectively. This, if compared to results of Sree-

kala [99], showed an increase in water absorption rate of

about 166% for acetylated treated OPEFB fiber phenol

formaldehyde composite material. However, both the

studies [80, 99] used acetic anhydride chemical to modify

the OPEFB fibers except that later [99] treated the fibers

with sodium hydroxide for about half an hour with sulfu-

ric acid as catalyst before final treatment with acetic an-

hydride. This difference in water absorption characteris-

tics might arise due to the chemical used during treat-

ment, the composite preparation technique, the treatment

technique, and testing or analysis procedures.

Very recently, instead of using OPEFB fibers, Lai

[100] used OPEFB shell fillers of different sizes filled

with novolak phenol formaldehyde resin to form compos-

ite materials and its detailed water absorption study was

done. When compared to other biomass filler such as rice

husk and coconut shell, oil palm shell exhibited the low-

est water absorption rate. This was due to two reasons,

first the lignocellulosic content of the biomass fillers such

as hemicellulose and cellulose and second the hydroxyl

groups present in that particular biomass filler. They con-

cluded that the water absorption rate was not much

dependent on filler size and it becomes independent after

certain filler sizes. This study encourages to hybrid the

OPEFB fibers with oil palm shell fillers in a polymer

FIG. 15. Water absorption rate in OPEFB fiber-reinforced phenol form-

aldehyde composite at different fiber loading and at various temperatures

[42].

FIG. 16. Water absorption at equilibrium in treated and untreated

OPEFB fiber-reinforced phenol formaldehyde composite material at dif-

ferent temperatures. [Color figure can be viewed in the online issue,

which is available at wileyonlinelibrary.com.]

2096 POLYMER COMPOSITES—-2010 DOI 10.1002/pc

matrix for further investigation on water absorption and

its related work.

Water absorption characteristic is also found to be

affected due to fiber loading [101]. In their study, they

concluded that at higher fiber loading the water absorption

is mainly because of diffusion mechanism, while percola-

tion mechanism is dominant at lower fiber loading in the

natural fiber composite materials.

Basically, the water absorption test provides important

information regarding the adhesion property between the

fibers and the matrix [102]. This is because the higher the

adhesion between fibers and matrix, the probability for

the water to absorb through the sites becomes limited.

Therefore, most of the researchers have repeatedly

stressed the interface or adhesion property while discus-

sing the water absorption issue. Hence, various techniques

and methods have been used to reduce the water intake

by the natural fibers polymer composite materials. For

instance, Hydroxyl Terminated Polybutadine (HTPB)

Rubber was used [102] as coating for phenol formalde-

hyde resin and sisal fibers to decrease the water intake.

Water absorption study in fact became important for

natural fibers polymer composite materials because of

hydrophilic nature of natural fibers compared to synthetic

fibers. For example, in study of Joseph [103], clearly

the glass/phenol formaldehyde composite absorbed

lower water than banana/phenol formaldehyde composite

material.

Effect on Mechanical Properties. Considerable work

has been accomplished on mechanical properties of

OPEFB fiber phenol formaldehyde composite materials.

However, further evaluation needs to be done for com-

plete exposure of the OPEFB fiber composite materials to

different applications. The mechanical performance of

composite material being exposed to different tempera-

tures and other related studies needs to be investigated.

Acetylated OPEFB fibers showed the highest tensile

strength and modulus followed by propionylated,

extracted and non-extracted OPEFB fiber phenol formal-

dehyde composite materials [80]. However, elongation at

break was lowest for modified fiber composite materials

compared to non-modified composite. The reason for the

former improvement in tensile properties was due to more

hydrophobic nature of the fibers and better bonding nature

between fibers and matrix. Whereas the drop in elonga-

tion at break for modified fibers was due to crystalline na-

ture of the fibers which easily gets tear or split. Moreover,

chemical treatments remove the amorphous part from the

fibers or might change the amorphous to crystalline phase

thus bringing significant reduction in the elongation at

break value. Flexural properties of modified (acetylated

and propionylated) OPEFB fibers phenol formaldehyde

composite materials was enhanced than those of unmodi-

fied fibers composite. This clearly shows increase in

strength and stiffness of OPEFB fiber composite materials.

Furthermore, impact strength or toughness of the OPEFB

fiber phenol formaldehyde composite materials was also

increased particularly for acetylated treated fibers compo-

sites. Finale, acetylation treatment overall improves the me-

chanical properties of the OPEFB fiber PF composite mate-

rials significantly except elongation at break.

Effects of fiber length and loading on mechanical prop-

erties were evaluated for OPEFB fiber reinforced with

phenol formaldehyde composite materials [104]. An

untreated OPEFB fiber of 20, 30, 40, and 50 mm length

was prepared and loading was varied by 29, 38, and

53 wt% in the phenol formaldehyde resin. Fiber length of

40 mm showed maximum tensile strength and modulus

and thereafter it decreases with increase in fiber length.

Here, the critical length of the fibers to be used in the

composite materials becomes important. For elongation at

break the peak value was observed at 30 mm fiber length.

The study of fiber length was conducted with the fiber

loading maintained at 38%. On the other hand, the fiber

loading was varied by maintaining the fiber length at

40 mm. Both tensile strength and modulus depicted the

peak value at 38 wt% of fiber loading and further increase

in fiber loading decreases the tensile properties. There are

no peak observed for elongation at break property and it

increased with increase in fiber loading. Similar was in

case of flexural property whereby 40 mm fiber length and

38 wt% fiber loading showed peak values. This indicates

that the optimum or best value for mechanical properties

can be considered as 40 mm for fiber length and 38 wt%

for fiber loading.

Comprehensive study on the modification of OPEFB

fibers and reinforcing with phenol formaldehyde resin

to form a composite material was done [105]. Chemi-

cals such as acrylic acid, acrylonitrile monomer, NaOH,

KMnO4, acetic anhydride, and benzoyl peroxide were

used. Besides this OPEFB fibers were also radiated to

Co c radiation and modified by latex to study the me-

chanical property of its composite materials. Coupling

agents such as triethoxy vinyl silane and toluene 2, 4-

diisocyanate was used as interfacial bounding agent.

Table 13 shows the physical modification of the

OPEFB fibers after various chemical treatments. Almost

all the treatments results in a physical change in the

OPEFB fibers. Mostly, the porous structure of the fibers

is exposed by the treatments thereby increasing the pos-

sibility of the mechanical interlocking nature of the

fibers with the polymer matrices.

The authors [105] have reported that the chemical

compositions, chemical structure, and cellular arrange-

ments determine the mechanical performance of the

fibers. Figures 17 and 18 shows the tensile properties of

untreated and treated OPEFB fibers incorporated with

phenol formaldehyde resin with 40% fiber loading in all

cases. Whereas Figs. 19 and 20 depicts the flexural prop-

erties of untreated and treated OPEFB fibers composite

materials.

Poor performance of tensile strength was observed by

OPEFB treated fibers composite materials except in case

DOI 10.1002/pc POLYMER COMPOSITES—-2010 2097

of permanganate treatment. The possibility might be

effective fiber-matrix bounding nature due to its physical

(more porous) and chemical (radical formation leading to

firm attachments) modification as stated in Table 13.

Other chemical modification might have led to increase in

more hydrophobic nature of the fibers resulting in a loose

bonding mechanism between OPEFB fibers and phenolic

resin. This might cause weak bounding or adhesion prop-

erty between fiber and matrix. The detailed explanation

regarding the poor performance of OPEFB treated fibers

composite materials was reported by Sreekala [105].

Highest elongation at break was observed by latex treated

fiber composite material and it decreased for alkali, per-

FIG. 18. Tensile modulus of untreated and treated OPEFB fiber-rein-

forced phenol formaldehyde composite material. [Color figure can be

viewed in the online issue, which is available at wileyonlinelibrary.com.]

FIG. 17. Tensile strength and elongation at break of untreated and

treated OPEFB fiber-reinforced phenol formaldehyde composite material.

[Color figure can be viewed in the online issue, which is available at

wileyonlinelibrary.com.]

TABLE 13. Physical modifications of the OPEFB fibers after various chemical treatments [45].

Chemical

process Procedure Physical modifications Chemical modifications

Mercerization 5% NaOH at different time intervals at

room temperature

Pores on fibers become clear. Fiber surface

roughness increases and it becomes curly

and soft

Increase amorphous cellulose.

Removal of hydrogen bounding

Acetylation Acetic anhydride in acetic acid with

concentrated H2SO4 as a catalyst

Waxy layer is removed. Becomes stiffer Acetyl groups gets attached to

cellulose and lignin present

in fibers

Peroxide Benzoyl peroxide from acetone Leaching out of wax, gums, and pectic

substances. Very rough due to protruding

structures and pores

Higher temperatures are needed to

decompose the peroxides

Permanganate Permanganate solution (0.01, 0.05, and

0.1% conc.) in acetone for 2–3 min

Color changes and fibers become soft with

more porous structure

MnO3 ions add to the fiber to form

cellulose radical

Radiation 60Co c radiation at dose of 0.1 Mrad for

about 30 h

Elimination of porous structure and

disintegration of fibers. Cracks develop

Crystalline regions changes.

Interactions between bounds

Isocyanate Toluene isocyanate was added to fibers

soaked in chloroform containing dibutyl

tin dilaurate catalyst for 2 h

Irregular surface of fibers and is the

major change

��N¼¼C¼¼O groups replaces the OH

groups of cellulose and lignin

in fibers

Silane Tri ethoxy vinyl silane with pH of 3.5–4 Surface coatings Alkoxy from silanes form bound

with OH groups. Hydrolysis,

condensation, and bond

formations steps takes place

with the fibers

Acrylation Acrylic acid of different concentrations for

about 1 h at 508CSurface coatings It removes the hydrogen from OH

group and acrylation group

is attached

Acrylonitrile Oxidation of fibers with KMnO4 for

10 min. Washed fiber are again put

into 1% H2SO4 containing acrylonitrile

in ratio of 30:1. After this, the sample is

kept at 508C for 2 h without disturbance

Fibrillation and porous structure Nitrile groups are grafted on the

fiber and lignin plays an

important role in

acrylonitrile process

Latex Dipping fibers into natural rubber latex of

10% dry rubber

Smooth surface with reduction in

fibrillation. Hydrophobicity is increased

due to filling of pores with rubber

Fibers become more elastic. Peaks

of C��H stretching are observed

due to presence of natural rubber

2098 POLYMER COMPOSITES—-2010 DOI 10.1002/pc

oxide, permanganate, and radiation. Increment in tensile

modulus was depicted (see Fig. 18) by mercerization

treatment and slightly by permanganate treated OPEFB

fibers composite materials while other treatment showed

poor performance. Mainly, the failure of the composite

materials was attributed due to fiber breakage.

Improvement in flexural strength was observed in mer-

cerization and peroxide treated OPEFB fibers composite

material as shown in Fig. 19. Latex treatment showed the

lowest flexural strength. The reason for this varying prop-

erty characteristic under chemical treatment was same as

those given under tensile properties. Isocyanate, silane,

acrylated, and latex treatment showed improved flexural

at break property. This was due to gradual propagation of

crack in the fiber during stress. Conversely, radiated fibers

were observed to easily break under given flexural stress.

Peroxide and permanganate treatments showed improve-

ment in flexural modulus while a moderate decrease was

showed by alkali or mercerization treatment. It was evi-

dent from this study that chemical modification plays an

important role in determining the mechanical properties

of the OPEFB fiber composite materials. In short, the

property of the natural fiber composite materials depends

on the interfacial or adhesion strength between fiber-

matrix and interfacial property is dependent on the fiber

and matrix individual properties and the properties of the

fibers are dependent on the types of the chemicals used to

modify its physical and chemical structures.

Significant increase in impact strength was shown by

latex, acetylation, silane, and isocyanate treatments. Main

factor that contributes to such improvements as reported

by the author [105] was the fiber-matrix bounding nature

after chemical treatments.

CONCLUSIONS

An OPEFB fibers polymeric composite material finds

wide applications on account of its comparable specific

properties with that of conventional fiber polymer com-

posite materials. But at present its usage is limited and

has not taken a complete hold in the market to compete

with the synthetic fibers. This can only be done with con-

stant development and an optimized conclusive outcome

about the properties of OPEFB fibers and its composite

materials. The mechanical properties of the OPEFB fiber

polymer composites were observed to vary considerably

and depend on various factors. The impediments regard-

ing the fundamental and applied area have to be over-

come before a more rapid advancement of the OPEFB

fibers and its composite materials is taken into account.

The complex nature of the OPEFB fibers and its compo-

sites, entitles for more data on the properties to establish

the confidence in their final end use. First of all is their

thermal degradation at low temperatures, which restricts

for various applications. This issue is not well studied and

needs a substantial amount of further work, particularly

for OPEFB fibers and its composite materials at high tem-

perature. Being a hydrophilic in nature, generally OPEFB

fibers absorb water, which disturbs the interfacial bonding

between fibers and matrices in the composite material

leading to poor mechanical properties. Hence, it was

found that water absorption and mechanical properties are

inter-related to each other. Therefore, various physical,

chemical, or thermal treatments are necessary to over-

come such disadvantages of OPEFB fiber polymer com-

posite materials. This OPEFB fibers can be used as rein-

forcement with synthetic polymers as well as biodegrad-

able or bioresin including thermoplastics and thermosets.

Hybrid composites can also be prepared with synthetic

fibers to overcome the demerits of OPEFB fibers. Even

though significant amount of research has been done, still

the critical evaluation remains the question of its further

usage. Nevertheless, industries has been established to

tailor the OPEFB fiber composite and other application

such as fiber board, medium density board, fiber mat,

and others, but the collaboration between industries,

research institutes, and universities has been found to be

lacking.

FIG. 19. Flexural strength and flexural break of untreated and treated

OPEFB fiber-reinforced phenol formaldehyde composite material.

[Color figure can be viewed in the online issue, which is available at

wileyonlinelibrary.com.]

FIG. 20. Flexural modulus of untreated and treated OPEFB fiber-rein-

forced phenol formaldehyde composite material. [Color figure can

be viewed in the online issue, which is available at wileyonlinelibrary.

com.]

DOI 10.1002/pc POLYMER COMPOSITES—-2010 2099

REFERENCES

1. A.K. Mohanty, M. Misra, and L.T. Drzal, J. Polym. Envi-ron., 10, 19 (2002).

2. A.S. Singha and V.K. Thakur, Bull. Mater. Sci., 31, 791(2008).

3. B. Nadzai, J.V. Tesha, and E.T.N. Bisanda, J. Mater. Sci.,41, 6984 (2006).

4. G. Bogoeva-Gaceva, M. Avella, M. Malinconico, A.

Buzarovska, A. Grozdanov, G. Gentile, and M.E. Errico,

Polym. Compos., 28, 98 (2007).

5. X. Li, L.G. Tabil, and S. Panigrahi, J. Polym. Environ.,15, 25 (2007).

6. G.I. Williams and R.P. Wool, Appl. Compos. Mater., 7,421 (2000).

7. A.N. Netravali and S. Chabba, Mater. Today, 6, 22 (2003).

8. P.A. Fowler, J.M. Hughes, and R.M. Elias, J. Sci. Food.Agric., 86, 1781 (2006).

9. J. Nickel and U. Riedel, Mater. Today, 6, 44 (2003).

10. H.D. Rozman, Z.A. Mohd Ishak, and U.S. Ishiaku, in Nat-ural Fibers: Biopolymers and Biocomposites, A. Mohanty,

M. Misra, and L.T. Drzal, Eds., Taylor and Francis, Boca

Raton, 407 (2005).

11. Sabutek, SDN BHD, Available at: www.fiberx.com.

Accessed on 5 September 2008.

12. Ecofuture, BHD, Available at: www.ecofuture.com.my/

main.htm, Accessed on 15 October 2008.

13. A.K. Mohanty and M. Misra, Polym. Plast. Technol. Eng.,34, 729 (1995).

14. H.D. Rozman, M.J. Saad, and Z.A. Mohd Ishak, J. Appl.Polym. Sci., 87, 827 (2003).

15. H.P.S. Abdul Khalil, H. Ismail, M.N. Ahmad, A. Ariffin,

and K. Hassan, Polym. Int., 50, 395 (2001).

16. A. Abu Bakar, A. Hassan, and A.F. Mohd Yusof, Polym.Polym. Compos., 13, 607 (2005).

17. K.H. Badri and K.A.M. Amin, J. Oil Palm Res., 103

(2006).

18. M.S. Sreekala and S. Thomas, J. Polym. Eng., 16, 265

(1997).

19. M.J. John and S. Thomas, Carbohydr. Polym., 71, 343

(2008).

20. A.K. Mohanty, M. Misra, and G. Hinrichsen, Macromol.Mater. Eng., 276/277, 1 (2000).

21. S. Mishra, A.K. Mohanty, L.T. Drzal, M. Misra, and G.

Hinrichsen, Macromol. Mater. Eng., 289, 955 (2004).

22. K.-N. Law, W.R.W. Daud, and A. Ghazali, BioResources,2, 351 (2007).

23. T. Nishino, in Green Composites: Polymer Compositesand the Environment, C. Baillie, Ed., Woodhead Publish-

ing Limited, Boca Raton, 49 (2004).

24. C.A.S. Hill and H.P.S. Abdul Khalil, J. Appl. Polym. Sci.,77, 1322 (2000).

25. H.P.S. Abdul Khalil, M. Siti Alwani, and A.K. Mohd

Omar, BioResources, 1, 220 (2006).

26. R.M. Rowell, in Properties and Performance of Natural-Fiber Composites, K.L. Pickering, Ed., Woodhead Publish-

ing Limited, Cambridge, 3 (2008).

27. M.S. Sreekala, M.G. Kumaran, and S. Thomas, J. Appl.Polym. Sci., 66, 821 (1997).

28. T.G. Rials and M.P. Wolcott, in Paper and Compositesfrom Agro-Based Resources, R.M. Rowell, R.A. Young,

and J.K. Rowell, Eds., Lewis Publishers, Boca Raton, 63

(1997).

29. R. Muniandy, S. Ishak, and R.S. Radin Umar, REAAA J.,7, 19 (1997).

30. R. Zulkifli, M.J. Mohd Nor, A.R. Ismail, M.Z. Nuawi, S.

Abdullah, M.F. Mat Tahir, and M.N. Ab. Rahman, Eur. J.Sci. Res., 33, 144 (2009).

31. M. Idicula, A. Boudenne, L. Umadevi, L. Ibos, Y. Candau,

and S. Thomas, Comput. Sci. Technol., 66, 2719 (2006).

32. Y. Li, M.S. Sreekala, and M. Jacob, in Natural Fiber Rein-forced Polymer Composites: Macro to Nanoscale, Old

City Publishing, Philadelphia, PA, 202 (2009).

33. N.G. Justiz-Smith, G.J. Virgo, and V.E. Buchanan, Mater.Char., 59, 1273 (2008).

34. S. Kalia, B.S. Kaith, and I. Kaur, Polym. Eng. Sci., 49,1253 (2009).

35. S.J. Eichhorn and R.J. Young, Compos. Sci. Technol., 64,767 (2004).

36. C. Baley, Compos. Part A: Appl. Sci. Manuf., 33, 939

(2002).

37. M.Z. Mohamed Yusoff, M.S. Salit, and N. Ismail, SainsMalaysiana, 38, 525 (2009).

38. J. George, M.S. Sreekala, and S. Thomas, Polym. Eng.Sci., 41, 1471 (2001).

39. Y. Cao, S. Shibata, and I. Fukumoto, Compos. Part A, 37,423 (2006).

40. F. Yao, Q. Wu, Y. Lei, and Y. Xu, Ind. Crop. Prod., 28,63 (2008).

41. P.J.H. Franco and A. Valadez-Gonzalez, in Natural Fibers:Biopolymers and Biocomposites, A. Mohanty, M. Misra,

and L.T. Drzal, Eds., Taylor and Francis, Boca Raton, 177

(2005).

42. S. Joseph, M. Jacob, and S. Thomas, in Natural Fibers:Biopolymers and Biocomposites, A. Mohanty, M. Misra,

and L.T. Drzal, Eds., Taylor and Francis, Boca Raton, 435

(2005).

43. M. Sain and S. Panthapulakkal, in Green Composites:Polymer Composites and the Environment, C. Baillie, Ed.,Woodhead Publishing Limited, Boca Raton, 181 (2004).

44. M.J. John and R.D. Anandjiwala, Polym. Comp., 29, 187(2008).

45. R.M. Rowell and H.P. Stout, in Handbook of Fiber Chem-istry, M. Lewin, Ed., CRC Press, Taylor and Francis, Boca

Raton, 405 (2007).

46. S.K. Batra, in Handbook of Fiber Chemistry, M. Lewin,

Ed., CRC Press, Taylor and Francis, Boca Raton, 453

(2007).

47. K.E. Cabradilla and S.H. Zeronian, J. Appl. Polym. Sci.,19, 503 (1975).

48. H.D. Rozman, G.B. Peng, and Z.A. Mohd Ishak, J. Appl.Polym. Sci., 70, 2647 (1998).

49. H.D. Rozman, C.Y. Lai, H. Ismail, and Z.A. Mohd Ishal,

Polym. Int., 49, 1273 (2000).

2100 POLYMER COMPOSITES—-2010 DOI 10.1002/pc

50. M. Tajvidi, S.K. Najafi, and N. Moteei, J. Appl. Polym.Sci., 99, 2199 (2006).

51. A.K. Bledzki, M. Letman, A. Viksne, and L. Rence, Com-pos. Part A., 36, 789 (2005).

52. C.P.L. Chow, X.S. Xing, and R.K.Y. Li, Compos. Sci.Technol., 67, 306 (2007).

53. A. Arbelaiz, B. Fernandez, J.A. Ramos, A. Retegi, R.

Llano-Ponte, and I. Mondragon, Compos. Sci. Technol.,65, 1582 (2005).

54. C.E. Tayang, Y. Watanabe, and T. Hatakeyama, Sen-IGakkaishi, 47, 434 (1991).

55. R.M. Rowell, A. Sanadi, R. Jacobson, and D. Caulfield, in

Kenaf Properties, Processing and Products, T. Sellers and

N.A. Reichert, Eds., Mississippi State University, Mississippi

State, MS, USA. 381 (1999).

56. H.D. Rozman, B.K. Kon, A. Abusamah, R.N. Kumar, and

Z.A. Mohd Ishak, J. Appl. Polym. Sci., 69, 1993 (1998).

57. M. Khalid, C.T. Ratnam, T.G. Chuah, S. Ali, and T.S.Y.

Choong, Mater. Des., 29, 173 (2008).

58. K. Miyazaki, K. Moriya, N. Okazaki, M. Terano, and H.

Nakatani, J. Appl. Polym. Sci., 111, 1835 (2009).

59. W. Qiu, F. Zhang, T. Endo, and T. Hirotsu, Polym. Com-pos., 26, 448 (2005).

60. S. Mohamad Jani, H.D. Rozman, A. Abusamah, Z.A. Mohd

Ishak, and S. Rahim, J. Oil Palm Res., 18, 260 (2006).

61. C. Chuai, K. Almdal, L. Poulsen, and D. Plackett, J. Appl.Polym. Sci., 80, 2833 (2001).

62. A. Abu Bakar, A. Hassan, and A.F. Mohd Yusof, Iran.Polym. J., 14, 627 (2005).

63. F. Mengeloglu, L. Mauana, and J. King, J. Vinyl Add.Technol., 6, 153 (2000).

64. H. Jiang and D. Kamdem, J. Vinyl Add. Technol., 10, 59(2004).

65. H. Jiang and D. Kamdem, J. Vinyl Add. Technol., 10, 70(2004).

66. X. Ge, X. Li, and Y. Meng, J. Appl. Polym. Sci., 93, 1804(2004).

67. S. Kamel, Polym. Adv. Technol., 15, 612 (2004).

68. H. Djidjelli, A. Boukerrou, R. Founas, A. Rabouhi, M. Kaci,

and J. Farenc, J. Appl. Polym. Sci., 103, 3630 (2007).

69. Y.-T. Zheng, D.-R. Cao, D.-S. Wang, and J.-J. Chen, Com-pos. Part A, 38, 20 (2007).

70. J.L. Leblanc, C.R.G. Furtado, M.C.A.M. Leite, L.L.Y. Vis-

conte, and A.M.F. de Souza, J. Appl. Polym. Sci., 106,3653 (2007).

71. X. Shen, T. Bole, R.A. Iezzi, Z. Cygan, R.M. Hu, B.L.

Stainbrook, P.A. Callais, and J.S. Ness, U. S. Patent No.

US 2008/0261019 A1 (2008).

72. Harvel, Available at: http://www.harvel.com/piping-pvc.

asp. Accessed on 16 October 2009.

73. M. Takatani, O. Kato, T. Kitayama, T. Okamoto, and M.

Tanahashi, J. Wood Sci., 46, 210 (2000).

74. N. Stark, J. Thermoplast. Compos. Mater., 14, 421 (2001).

75. H. Jiang and D.P. Kamdem, J. Vinyl Add. Technol., 10, 59(2004).

76. R.L. Shogren, J.W. Lawton, K.F. Tiefenbacher, and L.

Chen, J. Appl. Polym. Sci., 68, 2129 (1998).

77. J. Junkasem, J. Menges, and P. Supaphol, J. Appl. Polym.Sci., 101, 3291 (2006).

78. H. Li and M.M. Sain, Polym. Plast. Technol. Eng., 42, 853(2003).

79. S. Joseph, M.S. Sreekala, Z. Oommen, P. Koshy, and S.

Thomas, Compos. Sci. Technol., 62, 1857 (2002).

80. H.P.S. Abdul Khalil, A.M. Issam, M.T. Ahmad Shakri, R.

Suriani, and A.Y. Awang, Ind. Crop. Prod., 26, 315 (2007).

81. N.D. Saheb and J.P. Jog, Adv. Polym. Technol., 18, 351(1999).

82. S. Kamel, Polym. Adv. Technol., 15, 612 (2004).

83. D. Gardiner, G. Pepperl, and J.D.W. Wisse, Plast. Rub.Compos. Proc. Appl., 26, 59 (1997).

84. C. Sarmoria and V. Enrique, Polymer, 45, 5661 (2004).

85. S.E. Raghi, R.R. Zahran, and B.E. Gebril, Mater. Lett., 46,332 (2000).

86. L.M. Matuana, D.P. Kamdem, and J. Zhang, J. Appl.Polym. Sci., 80, 1943 (2001).

87. E.D. Owen, Degradation and Stabilization of PVC, Elsev-ier Applied Science, New York (1989).

88. A. Torikai and H. Hirose, Polym. Degrad. Stab., 63, 441(1999).

89. K.A.M. Amin and K.H. Badri, J. Appl. Polym. Sci., 105,2488 (2007).

90. G.M.O. Barra, M.C. Fredel, H.A. Al-Qureshi, A.W. Tay-

lor, and C. Clemenceau Jr., Polym. Comp., 27, 582 (2006).

91. H.D. Rozman, K.R. Ahmad Hilme, and A. Abubakr, J.Appl. Polym. Sci., 106, 2290 (2007).

92. H.D. Rozman, K.R. Ahmadilmi, and A. Abubakar, Polym.Test., 23, 559 (2004).

93. P.A. Sreekumar, P. Albert, G. Unnikrishnan, K. Joseph,

and S. Thomas, J. Appl. Polym. Sci., 109, 1547 (2008).

94. H.M. Akil, L.W. Cheng, Z.A.M. Ishak, A.A. Bakar, and M.A.

Abd Rahman, Compos. Sci. Technol., 69, 1942 (2009).

95. C.A.S. Hill, H.P.S. Abdul Khalil, and M.D. Hale, Ind.Crop. Prod., 8, 53 (1998).

96. C.A.S. Hill and H.P.S. Abdul Khalil, J. Appl. Polym. Sci.,78, 1685 (2000).

97. A. Athijayamani, M. Thiruchitrambalam, U. Natarajan, and

B. Pazhanivel, Mater. Sci. Eng., 517, 344 (2009).

98. A.V. Ratna Prasad, K.M.M. Rao, K.M. Rao, and

A.V.S.S.K.S. Gupta, Ind. J. Fiber Text. Res., 32, 399 (2007).

99. M.S. Sreekala, M.G. Kumaran, and S. Thomas, Compos.Part A, 33, 763 (2002).

100. J.C. Lai, F.N. Ani, and A. Hassan, Polym. Polym. Comp.,16, 379 (2008).

101. W. Wang, M. Sain, and P.A. Cooper, Compos. Sci. Tech-nol., 66, 379 (2006).

102. J.D. Megiatto Jr., E.C. Ramires, and E. Frollini, Ind. Crop.Prod., 31, 178 (2010).

103. S. Joseph, Z. Oommen, and S. Thomas, J. Appl. Polym.Sci., 100, 2521 (2006).

104. A.K. Mohanty and M. Mishra, Polym. Plast. Technol.Eng., 34, 729 (1995).

105. M.S. Sreekala, M.G. Kumaran, S. Joseph, M. Jocob, and

S. Thomas, Appl. Compos. Mater., 7, 295 (2000).

DOI 10.1002/pc POLYMER COMPOSITES—-2010 2101