oil palm silane zirconate by AmirHamzah40


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                                 Polymer-Plastics Technology and Engineering
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                                 Mechanical Properties of Silane and Zirconate Coupling
                                 Agent-Treated Oil Palm Empty Fruit Bunch Fiber-
                                 Filled Acrylic-Impact Modified Poly (Vinyl Chloride)
                                                      a                 a                           b
                                 Aznizam Abu Bakar , Azman Hassan & Ahmad Fuad Mohd Yusof
                                  Department of Polymer Engineering, Faculty of Chemical and Natural Resources
                                 Engineering, Universiti Teknologi Malaysia, UTM Skudai, Johor, Malaysia
                                     Plastics Technology Centre, SIRIM Bhd. Shah Alam, Malaysia

                                 Available online: 06 Dec 2010

To cite this article: Aznizam Abu Bakar, Azman Hassan & Ahmad Fuad Mohd Yusof (2010): Mechanical Properties of Silane
and Zirconate Coupling Agent-Treated Oil Palm Empty Fruit Bunch Fiber-Filled Acrylic-Impact Modified Poly (Vinyl Chloride)
Composites, Polymer-Plastics Technology and Engineering, 49:15, 1563-1570

To link to this article: http://dx.doi.org/10.1080/03602559.2010.512336


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                                                                    Polymer-Plastics Technology and Engineering, 49: 1563–1570, 2010
                                                                    Copyright # Taylor & Francis Group, LLC
                                                                    ISSN: 0360-2559 print=1525-6111 online
                                                                    DOI: 10.1080/03602559.2010.512336

                                                                    Mechanical Properties of Silane and Zirconate Coupling
                                                                    Agent-Treated Oil Palm Empty Fruit Bunch Fiber-Filled
                                                                    Acrylic-Impact Modified Poly (Vinyl Chloride) Composites
                                                                    Aznizam Abu Bakar1, Azman Hassan1, and Ahmad Fuad Mohd Yusof2
                                                                     Department of Polymer Engineering, Faculty of Chemical and Natural Resources Engineering,
                                                                    Universiti Teknologi Malaysia, UTM Skudai, Johor, Malaysia
                                                                     Plastics Technology Centre, SIRIM Bhd. Shah Alam, Malaysia

                                                                                                                                            properties of rigid PVC. Lutz (1993) reported that these
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                                                                        The influence of untreated and treated OPEFB content on the          properties of PVC have adversely affected with increasing
                                                                    mechanical properties of acrylic impact-modified PVC was investi-        impact modifier concentration[3]. The incorporation of soft
                                                                    gated. The formulations were first dry blended before being milled       rubbery impact modifier has lowered the rigidity of the
                                                                    into sheets on a two-roll mill. Test specimens were then hot pressed.   rigid PVC and therefore, fibers are often added in the rigid
                                                                    The modulus significantly increased while the impact and flexural
                                                                    strength insignificantly improved with increasing of treated OPEFB       PVC formulations to compensate for the softening effect
                                                                    contents. The reduction in water absorption, the formation of new       caused by the addition of impact modifier. Even though
                                                                    absorption bands and the slight number of treated fiber pulled-out       fibers offer stiffness enhancement, certain drawbacks, such
                                                                    proved that there was an interaction between fiber and matrix. How-      as the incompatibility of the fibers with the polymer matrix
                                                                    ever, this interaction was insufficient to enhance the impact and flex-   and self-agglomeration of fibers, greatly reduce the impact
                                                                    ural strength significantly.
                                                                                                                                            strength or toughness of the composites.
                                                                                                                                               One of the natural fibers that have received much atten-
                                                                    Keywords Composites; Coupling agent; Mechanical properties;
                                                                             Poly (vinyl chloride); Renewable resources
                                                                                                                                            tion by Malaysian researchers for reducing the cost of pro-
                                                                                                                                            ducts is from Oil Palm Empty Fruit Bunches (OPEFBs).
                                                                                                                                            OPEFBs from the oil palm plant Elaesis guineensis is one
                                                                    INTRODUCTION                                                            of the oil palm lignocellulosic by-products generated from
                                                                       Poly (vinyl chloride) (PVC) is intrinsically more ductile            oil-palm industries in Malaysia. Most of the research on
                                                                    than other thermoplastics such as polystyrene, and in com-              OPEFB so far has dealt with polyester, polypropylene
                                                                    parison with polyethylene and polypropylene, it is more                 and polystyrene[4–7]. They focused on how fiber loading,
                                                                    rigid and stronger. However, PVC is extremely sensitive                 fiber size distribution and surface-treated fiber affected
                                                                    to stress rate, temperature, and notching.                              the mechanical properties of the composites. The decreased
                                                                       The ductility of PVC can dramatically reduce with                    strength was likely the result of incompatibility of the
                                                                    increasing the impact rate, reducing the test temperature               hydrophilic wood fibers with the hydrophobic polymer
                                                                    or providing notch as a stress concentrator[1].Therefore,               matrix.
                                                                    PVC is usually impact modified with impact modifier to                       A similar reason was also reported by other researchers
                                                                    improve its ductility. The enhancement of PVC ductility                 who used wood flour as filler in PVC[8]. To improve the
                                                                    by introduction of a rubbery phase of impact modifier is a               adhesion or compatibility between fibers and polymer
                                                                    well-known phenomenon, which has been widely exploited                  matrix, the fibers’ surfaces were treated with various types
                                                                    commercially. Basically, the effect of impact modifier is to             of coupling agents. Coupling agent is able to react chemi-
                                                                    shift the ductile-brittle transition of the PVC to the higher           cally on both ends during processing, with the fibers on
                                                                    impact rate, lower temperature, or sharper notch[2,3].                  one side and the polymer on the other, thus creating a
                                                                       While PVC ductility is improved, there are other effects,            chemical bridge at the interface. Ahmad Fuad et al.
                                                                    which must be considered such as the tensile and flexural                (1997) has explained in detail the reaction scheme of silane
                                                                                                                                            coupling agents with cellulose materials[9].
                                                                       Address correspondence to Aznizam Abu Bakar, Department                 The effectiveness of coupling agents on the wood-fibres
                                                                    of Polymer Engineering, Faculty of Chemical and Natural                 in the PVC=wood fiber composites has also been studied
                                                                    Resources Engineering, Universiti Teknologi Malaysia, 81310             by Matuana et al. (1998)[10]. The results showed that the
                                                                    UTM Skudai, Johor, Malaysia. E-mail: aznizam@fkkksa.
                                                                                                                                            adhesion between PVC and wood veneer laminates was

                                                                    1564                                               A. ABU BAKAR ET AL.

                                                                    significantly improved when wood veneers treated with            that reduced the stiffness of the composites. Another rea-
                                                                    aminopropyltriethoxy-silane, while no improvement was           son was the agglomeration of fiber into fiber bundles was
                                                                    observed for the other coupling agents such as dichlo-          still observed in the matrix[13].
                                                                    rodiethylsilane, phthalic anhydride and maleated                    The fiber bundles had exaggerated the weakening of the
                                                                    polypropylene.                                                  interfacial interaction between fiber and PVC matrix and
                                                                       The improvement was attributed to the fact that              then reduced the flexural modulus and strength of the
                                                                    aminopropyltriethoxy-silane treated wood veneer chemi-          impact-modified composites. The weakened interfacial
                                                                    cally reacted and formed an ionic bond with the polymer         regions become potential sites for crack growth, as inability
                                                                    matrix because of the highly electronegative nature of          of the fibers to support the stress transfers to the polymer
                                                                    chlorine atoms. Even though aminopropyltriethoxy-silane         matrix. Thus, for interfacial interaction improvement, the
                                                                    has the ability to modify the wood surface, investigations      OPEFB fiber was first treated with silane and zirconate
                                                                    on other coupling agents are still progressively studied in     coupling agent and followed by the incorporation of
                                                                    wood-polymer composites field. Thus, as a continuation           treated fiber into acrylic impact-modified PVC. The effect
                                                                    of their previous work, Matuana et al. (2005)[8] had used       of silane-treated and zirconate-treated OPEFB fiber con-
                                                                    chitin and chitosan coupling agents, two natural polymers,      tents on the impact strength and flexural properties of
                                                                    as novel coupling agents for PVC=wood-flour composites.          acrylic impact-modified composites was the main aim of
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                                                                    They found that the flexural strength and modulus of             this study.
                                                                    composite increased with the addition of chitin and
                                                                    chitosan coupling agents compared to composite without          EXPERIMENTAL
                                                                    coupling agent.
                                                                       Even though coupling agents have been used in various
                                                                                                                                       The suspension poly (vinyl chloride) resin used was
                                                                    natural fiber-polymer composites, the research trend of
                                                                                                                                    supplied by Industrial Resin Malaysia (IRM) Sdn. Bhd.,
                                                                    requiring composites with ultimate performance in mech-
                                                                                                                                    Tampoi, Johor, Malaysia. IRM Sdn. Bhd. also supplied
                                                                    anical properties resulted in the application of coupling
                                                                                                                                    the additives used in the PVC formulations (Table 1) except
                                                                    agents in the natural fiber composites is constantly being
                                                                                                                                    for the acrylic impact modifier and OPEFB fiber. Core
                                                                    investigated. Therefore, the use of the coupling agent-
                                                                                                                                    and shell acrylic impact modifier with a trade name of
                                                                    treated OPEFB fiber in the acrylic-impact modified PVC
                                                                                                                                    Paraloid KM355P was supplied by Kureha Chemicals
                                                                    matrix is still actively pursued, notably to strike a balance
                                                                                                                                    Ltd. (Singapore).
                                                                    between stiffness, strength, and toughness.
                                                                                                                                       Acrylic impact modifier consisted of poly (methyl
                                                                       The blend formulations used in this study were based on
                                                                                                                                    methacrylate)(PMMA) as a shell while poly (butyl acryla-
                                                                    the PVC window profile formulation, which was suitable
                                                                                                                                    te)(PBA) acts as a core. OPEFB was purchased from Sabu-
                                                                    for outdoor applications, mainly for blend formulations
                                                                                                                                    tek Sdn. Bhd., Teluk Intan, Perak, Malaysia. The Prosil
                                                                    added with acrylic impact modifier. The acrylic impact
                                                                                                                                    9234 and NZ44 coupling agents used were supplied by
                                                                    modifier is reported to be more weather resistant compared
                                                                                                                                    Kenrich Petrochemicals, Inc. (New Jersey, USA). The Pro-
                                                                    to other impact modifiers such as chlorinated polyethyl-
                                                                                                                                    sil 9234 is silane-based with chemical name is n-octyl-
                                                                    ene[11]. Therefore, in this work, the acrylic-impact modified
                                                                                                                                    triethoxysilane, while NZ 44 is zirconate-based with
                                                                    PVC was used as a matrix and then it was reinforced with
                                                                                                                                    chemical name tris (2-ethylene-diamino) ethanolate. Both
                                                                    the coupling agent-treated OPEFB fibers.
                                                                                                                                    coupling agents’ chemical structures are shown in Figure 1.
                                                                       Our preliminary studies were done on PVC composites
                                                                    filled with fiber loadings of untreated OPEFB. Increased
                                                                    rigidity of the PVC was observed as a function of fiber          Treated Fiber Preparation
                                                                    loading but accompanied by a severe decrease in impact             The OPEFB fibers used were less than 75 mm long and
                                                                    and flexural strength[12]. To minimize the impact=stiffness      were dried in an oven at 105 C for about 24 hours to a con-
                                                                    trade off, the PVC was impact modified with acrylic impact       stant weight prior to preparation of the PVC composites.
                                                                    modifier for ductility enhancement[13]. The addition of          The coupling agent treated OPEFB fibers were prepared
                                                                    9 phr of acrylic impact modifier into the untreated OPEFB        according to the procedure provided by the coupling agent
                                                                    fiber-filled PVC composite improved the impact strength           manufacturers. For zirconate coupling agent, the PVC
                                                                    but decreased the flexural strength and modulus of the           resin itself was treated rather than the fibers. This is con-
                                                                    composites[13].                                                 trary to silane coupling agent in which the OPEFB fiber
                                                                       The results indicated that even though acrylic impact        itself underwent coupling agent treatment prior to dry
                                                                    modifier had the ability to compensate the detrimental           blending process.
                                                                    effects caused by the fiber with lowering the yield stress          The dosage used for the silane coupling agent was 0.5%
                                                                    of PVC matrix by allowing shear yielding rather than frac-      by weight of the fiber. The silane was diluted in ethanol to
                                                                    ture, this mechanism had generated the softening effect         make up a 10% solution for better dispersion. The OPEFB
                                                                                                          TREATED OPEFB-IMPACT MODIFIED PVC COMPOSITES                                            1565

                                                                                                                                 TABLE 1
                                                                                                                              PVC formulations
                                                                    Ingredients                                                             Part per hundred resin (phr)
                                                                    PVC resin                             100.0                100.0                100.0             100.0                  100.0
                                                                    Tin Stabilizer                          2.0                   2.0                 2.0                2.0                    2.0
                                                                    Calcium Stearate                        0.5                   0.5                 0.5                0.5                    0.5
                                                                    Stearic Acid                            0.6                   0.6                 0.6                0.6                    0.6
                                                                    Acrylic Processing Aid                  1.5                   1.5                 1.5                1.5                    1.5
                                                                    Titanium Oxide                          4.0                   4.0                 4.0                4.0                    4.0
                                                                    Acrylic Impact Modifier                  –                    –                    9                  9                      9
                                                                    Untreated OPEFB                         –              10, 20, 30, 40             –           10, 20, 30, 40               –
                                                                    Treated OPEFB                           –                    –                    –                 –                10, 20, 30, 40

                                                                    fibers were charged into a bench-top tumbler mixer and sil-              and composites. The dry-blended formulations were then
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                                                                    ane coupling agent was added slowly over the period of 15               melt-blended and sheeted using a laboratory two-roll mill
                                                                    minutes to ensure uniform distribution of the coupling                  at 165 C for 10 min. The milled sheets were then placed
                                                                    agent. The fibers were continuously mixed for another 30                 into a mould and hot pressed at 180 C for 5 min. The
                                                                    minutes. The silane-treated OPEFB fibers were dried in                   mould was cooled for 5 min before the specimens were
                                                                    an oven at 100 C for about 2 hours.                                    removed from the mould cavities.
                                                                       The dosage of the zirconate coupling agent was slightly
                                                                    different. The manufacturer recommended that the dosage                 Mechanical Testing
                                                                    should be either 0.2% or 0.5% by weight of fiber. Since with                The Izod impact strength assessment was carried out on
                                                                    increasing fiber content, the PVC fraction decreased corre-              notched samples of dimensions 62.5 Â 13 Â 3 mm3 at room
                                                                    spondingly, the applied dosage of zirconate had to be                   temperature using an IMPats 5 pendulum impact tester
                                                                    adjusted. Thus, at lower fiber contents (at which level,                 (Vignate (MI), Italy) at an impact velocity of 3.0 m=s and
                                                                    the PVC predominated), 0.2% by weight of PVC was used.                  90o swing angle. The notch depth was fixed at 2.6 Æ
                                                                    At higher fiber contents (30 and 40 phr fiber content), 0.5%              0.02 mm with an angle of 45o.
                                                                    by weight of OPEFB was applied. The zirconate coupling                     The flexural test was conducted on the Instron Machine
                                                                    agent was diluted in propanol to assist distribution of the             Model 5567 (London, United Kingdom) according to
                                                                    coupling agent in the PVC resin prior to the dry blending               ASTM D790. The samples with dimensions 125 Â 13 Â
                                                                    process.                                                                3 mm3 were tested at a cross-head speed of 3 mm=min at
                                                                                                                                            room temperature. The support span for the flexural test
                                                                    Sample Preparation                                                      was 51 mm. All the reported values for the tests were the
                                                                       The dry-blend formulations, as shown in Table 1, were                average of 7 specimens.
                                                                    first dry-blended with a laboratory high-speed mixer for
                                                                    10 min to homogenize the dry-blended PVC compound                       Water Absorption Testing
                                                                                                                                               The specimen test bars were immersed into the distillate
                                                                                                                                            water for 60 days at room temperature according to ASTM
                                                                                                                                            D570. Water absorption was determined by weighing the
                                                                                                                                            sample before and after immersion at specific time inter-
                                                                                                                                            vals. The water absorption at any time was calculated.
                                                                                                                                            The purpose of this test was to observe the influence of
                                                                                                                                            coupling agents on the degree of water absorption of the
                                                                                                                                            specimens. As a comparative study on the water absorption
                                                                                                                                            between untreated and coupling agent treated composites,
                                                                                                                                            only the results of composites filled with 20 phr and
                                                                                                                                            40 phr OPEFB fibers were plotted.

                                                                                                                                            Scanning Electron Microscopy Study
                                                                                                                                               Studies on the composite-fractured-surface morpholo-
                                                                    FIG. 1. Chemical structure of (a) Silane (Prosil 9234) (b) Zirconate    gies were performed with a JEOL model JSM-6301 F scan-
                                                                    (NZ 44).                                                                ning electron microscope (SEM) (Illinois, USA). A small
                                                                    1566                                                     A. ABU BAKAR ET AL.

                                                                    portion of the fractured surface of impact-tested specimen             weakened the fiber-matrix interface. The weakness of inter-
                                                                    was mounted on the copper stub and sputter-coated with a               facial adhesion resulted in debonding as identified by
                                                                    thin layer of gold to avoid electrostatic charging during              pulling-out of fiber bundles in the composites, as reported
                                                                    examination.                                                           in the previous researches[12,13].
                                                                                                                                               As the coupling agent-treated OPEFB fiber incorpor-
                                                                    Fourier Transform Infrared Study                                       ated in the PVC, the impact strength of composite increases
                                                                       Nicolet 5700 (Mettler-Toledo, New York, USA) Fourier                slightly but the increment gradually decreases as the
                                                                    Transform Infrared (FTIR) was used to identify the related             denomination of OPEFB fiber in the matrix increases,
                                                                    functional groups present in the untreated and treated                 mainly at 40 phr. It indicates that both coupling agents
                                                                    composites. A small quantity of the untreated and treated              were able to improve the fiber-matrix adhesion at low fiber
                                                                    composites with fiber loading of 30 phr was used for com-               content. At high fiber content, the ability of both coupling
                                                                    paring and analyzing. The composite samples were scanned               agents to enhance the interfacial interaction fiber-matrix
                                                                    from 4000 cmÀ1 À370 cmÀ1 for 16 times to reduce the                    was reduced. The trend of this result suggests that the inter-
                                                                    noise-to-signal ratio.                                                 action between fiber and matrix was not strong enough to
                                                                                                                                           contribute tremendous increment in mechanical properties,
                                                                    RESULTS AND DISCUSSION                                                 mainly impact strength of composites. This similar reason
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                                                                    Impact Strength                                                        was also used to explain the reduction of flexural strength
                                                                       Figure 2 shows the influence of OPEFB fiber content on                which is discussed in the subsequent section.
                                                                    the impact strength of the PVC composites. The impact                      SEM micrographs of the impact-fractured surface of sil-
                                                                    strength of composites decreased with increasing untreated             ane treated-filled composites (Fig. 3) and zirconate treated
                                                                    OPEFB fiber content from 10 to 40 phr. As discussed in                  fiber-filled composites (Fig. 4) also show that the formation
                                                                    previous work[12], this trend was associated with the poor             of interaction between treated-fiber and matrix took place
                                                                    wetting of the fiber by the PVC matrix, even though                     in the composites. This is because the treated-fibers pulled
                                                                    OPEFB has the ability to form a physical interaction with              out from the matrix but a fair amount of polymeric resi-
                                                                    polar PVC. This interaction is relatively weak compared to             dues remained on the fibers (Fig. 4). It indicates that the
                                                                    the strong fiber-fiber interaction caused by hydrogen                    matrix wetted the treated fibers in composites extensively.
                                                                    bonds. The hydrogen bonds resulted in OPEFB fibers to                   Besides that the treated fibers in composites in Figures 3
                                                                    agglomerate among them into fiber bundles, which conse-                 and 4 show only slight fibers were pulled out.
                                                                    quently, lowered the contact area with the matrix and                      It is also interesting to observe that the impact strength
                                                                                                                                           of treated OPEFB fiber-filled acrylic-impact modified com-
                                                                                                                                           posites was higher compared to untreated, treated and
                                                                                                                                           impact-modified composites (Fig. 2). The ability of acrylic
                                                                                                                                           impact modifier to compensate for the detrimental effect

                                                                    FIG. 2. Effect of untreated OPEFB and coupling agent-treated OPEFB
                                                                    fiber loadings on the impact strength of unmodified and acrylic-impact   FIG. 3. SEM micrograph of the impact fractured-surface of PVC com-
                                                                    modified PVC composites.                                                posite treated with silane coupling agent (Magnification 1000x).
                                                                                                         TREATED OPEFB-IMPACT MODIFIED PVC COMPOSITES                                                   1567
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                                                                    FIG. 4. SEM micrograph of the impact fractured-surface of PVC com-
                                                                    posite treated with zirconate coupling agent (Magnification 2000x).

                                                                    caused by the fiber with lowering the yield stress of PVC
                                                                    matrix, and the improvement of fiber-matrix interaction
                                                                    by silane and zirconate coupling agents had produced the             FIG. 5. Effect of untreated OPEFB and coupling agent-treated OPEFB
                                                                    PVC composites with good in impact strength. Figure 2                fiber loadings on the flexural modulus of unmodified and acrylic-impact
                                                                    also shows that the performance of both coupling agents              modified PVC composites.
                                                                    in improving the impact strength of modified composites
                                                                    is difficult to be distinguished because of the impact                indicates that both coupling agents had an ability to bal-
                                                                    strength values obtained were relatively similar.                    ance the impact modifier softening effect by improving
                                                                                                                                         the fiber-matrix interfacial adhesion. Silane had brought
                                                                    Flexural Modulus                                                     a greater stiffness of the composites compared to zirconate
                                                                        As expected, the modulus that indicates the stiffness of         coupling agent.
                                                                    composites increases steadily with increasing fiber content
                                                                    (Fig. 5). This is due to the nature of natural fiber within           Flexural Strength
                                                                    the composite, where it appeared to act as filler within                 Figure 6 shows that the flexural strength of untreated
                                                                    the polymer, thereby increasing the flexural modulus and              composites decreases with increasing fiber content. The fact
                                                                    making the composite stiffer. Even though OPEFB fibers
                                                                    had a greater tendency to agglomerate among them into
                                                                    fiber bundles and poor interaction with PVC matrix, the
                                                                    OPEFB fibers were able to improve the stiffness by restrict-
                                                                    ing the segmental movement of PVC molecular chains by
                                                                    reducing the free volume of PVC. The use of coupling
                                                                    agent-treated OPEFB fiber in the composites had improved
                                                                    further the flexural modulus compared to untreated fiber.
                                                                    It shows that both coupling agents were able to improve
                                                                    the fiber-matrix interfacial adhesion by improving the wet-
                                                                    ting of the fibers by the PVC matrix (Figs. 3 and 4).
                                                                        Although the impact strength improved, the addition of
                                                                    acrylic impact modifier decreased the flexural modulus of
                                                                    untreated composites. As mentioned earlier, the softening
                                                                    effect generated by the rubbery phase of impact modifier
                                                                    had lowered the stiffness of the PVC[13,14]. However, the
                                                                    incorporation of coupling agent-treated OPEFB fiber had               FIG. 6. Effect of untreated OPEFB and coupling agent-treated OPEFB
                                                                    slightly increased the impact-modified composites. Even               fiber loadings on the flexural strength of unmodified and acrylic-impact
                                                                    though slight increment in modulus, the result trend                 modified PVC composites.
                                                                    1568                                                 A. ABU BAKAR ET AL.
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                                                                    FIG. 7. Effect of OPEFB fiber loadings on the water absorption of   FIG. 8. Effect of coupling agent-treated OPEFB fiber loadings on the
                                                                    unmodified and impact-modified PVC composites.                       water absorption of unmodified PVC composites.

                                                                    that the modulus increases while the strength decreases            indicates that the addition of coupling agents had little
                                                                    with increasing fiber content is in agreement with the trend        effect on the flexural strength of treated OPEFB and
                                                                    observed in other fiber-filled composites[4]. The reduction          treated impact-modified OPEFB composites. Similar result
                                                                    in flexural strength may be attributed to agglomeration             on the impact strength, the performance of both coupling
                                                                    of the OPEFB fibers in which resulted in fibers inability            agents in improving the flexural strength of impact-
                                                                    to support stresses transferred from the PVC matrix[13].           modified composites made it difficult to be distinguished.
                                                                    Figure 6 also shows that the treated fiber insignificantly
                                                                    improved the flexural strength of composites. Similar rea-          Water Absorption
                                                                    son as impact strength result, the inadequate coupling abil-          Figure 7 shows that the water absorption of unmodified
                                                                    ity resulted in the insignificant increment in flexural              and impact-modified composites was significantly
                                                                    strength. The presence of fiber bundles that remained intact        increased as the fiber content increased. This was expected
                                                                    even after coupling agent treatment had reduced the role of        due to the hydrophilic nature of the cellulosic fiber. The
                                                                    coupling agent in improving the fiber-matrix interaction.           polar hydroxyl groups in their molecular structures were
                                                                    The limited improvement on strength was also observed              able to form hydrogen bonds with water molecules. The
                                                                    by other researchers[15].                                          higher the proportion of OPEFB fiber in the composites,
                                                                       As expected, the flexural strength decreases with the            the higher possibility of water was being absorbed through
                                                                    addition of impact modifier. As discussed in flexural modu-          the formation of hydrogen bonds. Thus, the water absorp-
                                                                    lus, the softening effect generated by rubbery phase of            tion increased proportionally with the fiber content
                                                                    impact modifier had also lowered the flexural strength               (Table 2). Similar observations were reported by other
                                                                    of the composites. Unlike modulus, the incorporation of            researchers who used OPEFB fiber in different polymer
                                                                    treated OPEFB fibers had insignificantly changed the flex-            matrix[5,6]. Figure 7 also indicates that the water absorp-
                                                                    ural strength of impact modified PVC composites. This               tion of impact-modified composites was higher than

                                                                                                                            TABLE 2
                                                                                                Percentage of water absorption of untreated and treated composites
                                                                                                 OPEFB-filled composites                       OPEFB-filled acrylic impact modified composites
                                                                    OPEFB fiber
                                                                    content (phr)    Untreated     Silane-treated    Zirconate treated      Untreated         Silane-treated        Zirconate-treated
                                                                    0                   0.10            0.10                0.10                0.23                0.23                    0.23
                                                                    10                  0.74            0.60                0.72                0.95                0.65                    0.76
                                                                    20                  1.69            1.33                1.53                2.10                1.45                    1.66
                                                                    30                  2.89            2.21                2.32                3.14                2.35                    2.54
                                                                    40                  4.08            3.95                3.84                4.61                4.81                    4.14
                                                                                                           TREATED OPEFB-IMPACT MODIFIED PVC COMPOSITES                                                     1569

                                                                                                                                            less hydrophilic than zirconate as fiber content increased
                                                                                                                                            from 10 to 30 phr. Figure 8 also shows that at 40 phr the
                                                                                                                                            water absorption of fiber treated with both coupling agents
                                                                                                                                            are almost similar. Meanwhile, Figure 9 and Table 2 show
                                                                                                                                            that at 40 phr the water absorption of fiber treated with sil-
                                                                                                                                            ane are slightly higher than untreated. The ability of silane
                                                                                                                                            to reduce the hydrophilic of fiber was ineffective at higher
                                                                                                                                            fiber content (40 phr), due to the domination of fiber con-
                                                                                                                                            tent in the matrix. It indicates that the amount of silane
                                                                                                                                            used to treat the 40 phr fiber was insufficient to modify
                                                                                                                                            the fibers completely.

                                                                                                                                            FTIR Analysis
                                                                                                                                               The FTIR spectra of untreated and treated OPEFB-filled
                                                                                                                                            PVC composites are shown in Figure 10. The absorption
                                                                    FIG. 9. Effect of coupling agents-treated OPEFB fiber loadings on the    band regions at 3200–3600 cmÀ1 of untreated and treated
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                                                                    water absorption of acrylic-impact modified PVC composites.
                                                                                                                                            composites were probably due to absorption vibration of
                                                                                                                                            hydroxyl groups (-OH) and of secondary amine groups
                                                                                                                                            (N-H). The FTIR spectra band of silane-treated composite
                                                                    unmodified composites. The increase in polarity, which                   (Fig. 10(b)) at 1045 cmÀ1 was more intense compared to
                                                                    was contributed by acrylic impact modifier, was the main                 untreated (Fig. 10(a)) and it may be assigned to the Si-O
                                                                    cause for the higher water absorption of impact-modified                 stretching vibration. The presence of this functional group
                                                                    composites.                                                             is supported by the bands at 3418 cmÀ1, and 772 cmÀ1–
                                                                       Figures 8 and 9 also show that silane and zirconate sig-             835 cmÀ1, due to the OH stretching and OH bending
                                                                    nificantly reduced the water absorption of composites. The               vibration, respectively, from the functional group of
                                                                    ability of coupling agents to modify the cell wall of fiber              Si-OH.. The stretching vibration of aryl alkyl ether or ether
                                                                    made the OPEFB to be less hydrophilic. Coupling agent                   linkage (C-O-C) was also found not to differ greatly from
                                                                    had an ability to interact with hydroxyl groups of OPEFB,               that of the Si-O system. Similar to Si-O, the absorption
                                                                    thus blocking the latter from hydrogen bonding with water.              band at 1045 cmÀ1 was assigned to the C-O-C symmetric
                                                                    It was discovered that unmodified and impact-modified                     stretching vibration from the fiber. This band is supported
                                                                    composites (Table 2) treated with silane exhibited slightly             by C-O-C asymmetric stretching at 1247 cmÀ1[7]. The

                                                                    FIG. 10. FTIR spectra of (a) untreated composite (b) silane-treated PVC composite (c) zirconate-treated PVC composite incorporated with 30 phr
                                                                    OPEFB fiber.
                                                                    1570                                               A. ABU BAKAR ET AL.

                                                                    presence of these bands indicates that the silane coupling      REFERENCES
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                                                                                                                                        ANTEC ‘86. 1986, 1239–1240.
                                                                    ACKNOWLEDGMENT                                                  15. Mohd Ishak, Z.A.; Aminullah, A.; Ismail, H.; Rozman, H.D. (1998).
                                                                       The authors thank Polymer Engineering Department,                Effect of silane based coupling agents and acrylic acid based compa-
                                                                    FKKKSA, UTM for providing the technical services                    tibilizer on mechanical properties of oil palm empty fruit bunch filled
                                                                                                                                        high density polyethylene composites. J. Appl. Polym. Sci. 1998, 68,
                                                                    and equipments for this research work. The authors also
                                                                    thank Industrial Resin Malaysia (IRM), Sdn. Bhd. and            16. Matuana, L.M.; Park, C.B.; Balatinecz, J.J. (1997). Processing and
                                                                    Sabutek Sdn. Bhd. (Malaysia) for materials used through-            cell morphology relationships for microcellular foamed PVC=
                                                                    out this work.                                                      wood-fiber composites. Polym. Eng. Sci. 1997, 37 (7), 1137–1147.

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