Effect of Chemical Modifications of Fibers on Tensile

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Effect of Chemical Modifications of Fibers on Tensile Properties of Epoxy Hybrid Composites M. Jawaid a

a b

b

a

c

, Alothman Othman , N. Saba , Y. A. Shekeil , M. T.

Paridah & H. P. S. Abdul Khalil

a d

a

Department of Biocomposite Technology, Institute of Tropical Forestry and Forest Products (INTROP) , Universiti Putra Malaysia , Serdang , Malaysia b

Faculty of Chemical Engineering , King Saud University , Riyadh , Saudi Arabia c

Department of Mechanical and Manufacturing Engineering , Universiti Putra Malaysia , Serdang , Malaysia d

School of Industrial Technology , Universiti Sains Malaysia , Penang , Malaysia Accepted author version posted online: 01 Apr 2014.Published online: 16 Jul 2014.

To cite this article: M. Jawaid , Alothman Othman , N. Saba , Y. A. Shekeil , M. T. Paridah & H. P. S. Abdul Khalil (2014) Effect of Chemical Modifications of Fibers on Tensile Properties of Epoxy Hybrid Composites, International Journal of Polymer Analysis and Characterization, 19:5, 391-403, DOI: 10.1080/1023666X.2014.904081 To link to this article: http://dx.doi.org/10.1080/1023666X.2014.904081

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International Journal of Polymer Anal. Charact., 19: 391–403, 2014 Copyright # Taylor & Francis Group, LLC ISSN: 1023-666X print/1563-5341 online DOI: 10.1080/1023666X.2014.904081

Effect of Chemical Modifications of Fibers on Tensile Properties of Epoxy Hybrid Composites M. Jawaid,1,2 Alothman Othman,2 N. Saba,1 Y. A. Shekeil,3 M. T. Paridah,1 and H. P. S. Abdul Khalil1,4 Downloaded by [Universiti Putra Malaysia] at 22:19 16 July 2014

1

Department of Biocomposite Technology, Institute of Tropical Forestry and Forest Products (INTROP), Universiti Putra Malaysia, Serdang, Malaysia 2 Faculty of Chemical Engineering, King Saud University, Riyadh, Saudi Arabia 3 Department of Mechanical and Manufacturing Engineering, Universiti Putra Malaysia, Serdang, Malaysia 4 School of Industrial Technology, Universiti Sains Malaysia, Penang, Malaysia Treatment of oil palm empty fruit bunch (EFB) and jute fibers is carried out by using 2-hydroxy ethyl acrylate (2-HEA) to increase the interfacial bonding of fibers with the epoxy matrix. Fourier transform-infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM) were used to measure the change of surface composition of the fibers after treatment. Modified oil palm and jute fibers were used as reinforcements for epoxy matrix to fabricate hybrid composites by the hand lay-up technique. Tensile and morphological properties of hybrid composites were studied, and tensile properties of hybrid composites prepared from chemically treated oil palm=jute fibers were found to be better than those of untreated hybrid composites. SEM micrographs disclose that interfacial bonding between fiber and matrix significantly improved in the hybrid composites. Developed hybrid composites can be exploited as alternative materials for development of automotive and structural components instead of synthetic fiber–reinforced polymer composites. Keywords: Fibers; Hybrid composites; 2-Hydroxy ethyl acrylate; Scanning electron microscopy; Tensile properties

INTRODUCTION Nowadays natural fibers are one of the potential biodegradable reinforcing materials capable of replacing synthetic fibers in polymer composite fabrication. Natural fibers offer various advantages over synthetic fibers such as low density, low cost, biodegradability, acceptable specific properties, better thermal and insulating properties, and low energy consumption during processing, among others.[1–3] Oil palm empty fruit bunch (EFB) obtained from oil palm tree used to extract palm oil and oil palm fibres, extracted oil palm EFB fibres, can be used as low cost reinforcement materials in polymer composites. Jute is the cheapest vegetable fiber; it Submitted 19 February 2014; accepted 3 March 2014. Correspondence: M. Jawaid, Department of Biocomposite Technology, Institute of Tropical Forestry and Forest Products (INTROP), Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia. E-mail: [email protected] Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gpac.


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falls into the bast fiber category along with kenaf, industrial hemp, flax (linen), and ramie. It has high tensile strength and low extensibility and ensures better breathability of fabrics. Researchers have done an assessment of the tensile property of jute fiber through single-fiber tensile tests.[4] Researchers studied the effect of surface treatment on structural, mechanical, and thermal properties of jute fibers and found that change in crystallinity developed after alkali treatment, resulting in improvement in mechanical strength of the fibers.[5] The effect of 2-hydroxyethyl methacrylate (HEMA) on mechanical properties of jute-polycarbonate were investigated, and the results indicated improvement in mechanical properties over nontreated composites.[6] Khan et al.[7] performed an interesting study on treatment of jute fabric (hessian cloth) with 2-hydroxy ethylacrylate (HEA) under UV radiation in order to improve the mechanical and electrical properties. Studies on the effect of acetylation on jute fibers showed that maximum weight percentage gain (WPG) was 18.0% for an acetic anhydride-pyridine system at 120 C for 4 h, whereas using only acetic anhydride, WPG was 12.3% at the same reaction conditions.[8] It was reported that chemical modification of oil palm EFB fibers by acetylation, isocynate treatment, silane treatment, acrylation, and acrylonitrile grafting leads to strong covalent bond formation and to reduction in the hydrophilic nature of EFB fibers.[9] It was observed that mechanical properties of EFB fibers can be improved by treatment with allyl methacrylate and subsequent curing under UV radiation.[10] Chemical modification of EFB fibers leads to major changes in the fibrillar structure of fibers,[11] and acetylation of EFB fibers influences the mechanical properties of oil palm fiber–reinforced polyester composites.[12] Oil palm fiber– reinforced polyester composites modified with anhydrate display better mechanical and water absorption properties.[13] Some studies reported that polymer composites fabricated with reinforcement by chemically treated alfa, coir, bagasse, and sansevieria cylindrical fibers had improved mechanical properties compared to untreated composites.[14–16] In an interesting study, other researchers fabricated jute=bagasse hybrid composites with modified bagasse fiber, and the results indicated that fiber surface modification improved fiber=matrix interaction and significantly increased mechanical properties of hybrid composites.[17] Sodium lauryl sulfate (SLS) treatment has shown improvement in tensile, flexural, and impact strength of both nonwoven and woven hybrid composites compared to alkali-treated composites.[18] Hybrid composites can be used to produce door panels, headliners, seatbacks, vehicle load floors, and other automotive parts. In the present study, oil palm EFB and jute fibers were treated with 2-hydroxy ethyl acrylate (2-HEA) to improve fiber=matrix interfacial bonding. Structural and morphological properties of 2-HEA–treated oil palm EFB and jute fiber were carried out by Fourier transform-infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM), respectively. The oil palm-jute hybrid composites were fabricated by the hand lay-up method by reinforcing modified oil palm EFB and jute fibers in an epoxy matrix. Previous work on flexural, impact, dimensional stability, and chemical resistance properties of 2-HEA–treated fiber-reinforced epoxy hybrid composites was reported.[19,20] The present work is the extension of previously published work that deals with the effect of chemical treatment of fibers on tensile properties of hybrid composites, and the results are compared with our previously published work[21] on tensile properties of untreated oil palm=jute fiber–reinforced epoxy hybrid composites.

EFFECT OF CHEMICAL MODIFICATIONS OF FIBERS

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EXPERIMENTAL SECTION Materials


The epoxy resin 331 and epoxy hardener (A 062) used in this research were obtained from Zarm Scientific & Supplies Sdn. (Malaysia). Benzyl alcohol, 2-HEA and dicumyl peroxide was supplied by Aldrich Co. (USA). Chopped jute fiber mat was procured from Indarsen Shamlal Pvt Ltd. (Kolkata, India). Oil palm EFB fiber mat was obtained from Ecofibre Technology Sdn. Bhd. (Malaysia). Chemical Modification of Jute and EFB Fiber Mat Modification of jute and EFB fiber mats was done to increase wettability of the fiber with resin and improve the fiber=matrix interface, which are critical factors for obtaining better mechanical properties of composites. Jute and EFB fibers were immersed in a solution of 3% HEA and 1% dicumyl peroxide in methanol for 5 min. Then, jute and EFB fibers were dried at ambient temperature for 24 h.[6] Preparation of Chemically Modified Hybrid Composites Using chemically modified jute and EFB fiber mat, hybrid composites were prepared according to Jawaid et al.[19] Keeping the total fiber loading at 40% by weight and weight ratio of oil palm EFB and jute fiber at 4:1, the composites were prepared by the hand lay-up technique. CHARACTERIZATION Weight Percentage Gain (WPG) The grafting of 2-HEA onto jute and EFB fibers was determined from the weight percentage gain by the samples after treatment. Weight gain (based on percentage of oven-dried weight) of the chemically modified fibers was calculated from: WPGð%Þ ¼

Weight gain 100 Original weight

ð1Þ

Fourier Transform-Infrared (FT-IR) Spectroscopy FT-IR spectroscopy was performed using a Nicolet Avatar Model 360 spectrometer and taking 32 scans for each sample with a resolution of 4 cm1. The treated EFB and jute fibers were pounded in a mortar cooled with liquid nitrogen, and 1–2 mg of the obtained powder was dispersed in 100 mg of potassium bromide. Samples and KBr were carefully dried before disk preparation and were subjected to FT-IR analysis immediately afterward.

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Scanning Electron Microscopy (SEM) Morphology of the treated oil palm fibers, jute fibers, and hybrid composites was investigated using a scanning electron microscope (Leo Supra, 50 VP, Carl Ziess, SMT, Germany). The samples were mounted onto the SEM holder using double-sided electrically conducting carbon adhesive tape to prevent surface charge on the specimens when exposed to the electron beam. The treated oil palm fibers, jute fibers, and fracture surfaces of tensile testing of hybrid composites were sputtered with gold prior to their morphological observation.


Tensile Test (ASTM D 3039) In the present work, the tensile strength and modulus of the modified hybrid composites were measured using an Instron 5582 universal testing machine. This test was conducted as per the ASTM D 3039 specifications. RESULTS AND DISCUSSION FT-IR Analysis of Treated Jute and EFB Fibers Figures 1 and 2 show the FT-IR spectra of untreated and treated jute and EFB fibers, respectively. The aim of using FT-IR is to measure the change of surface composition of the fibers after treatment. The characteristic features of the spectra of EFB and jute fibers are due to their constituent cellulose, hemicellulose, and lignin.[6] The FT-IR spectra of untreated and treated jute fibers exhibited O-H stretching of the hydrogen bond at a broad transmittance peak at 3200–3600 cm1 consistent with previous results,[22] which became less intense upon 2-hydroxy ethylacrylate (2-HEA) treatment. The reduction in intensity may be due to breaking of intermolecular hydrogen bonding between O-H groups of cellulose and hemicellulose molecules[23] and a prominent C-H stretching absorption frequency of the alkane group around 2920 cm1. The presence of this peak is mostly because of the cellulosic and hemicellulosic constituents of oil palm EFB fiber.[24] With 2-HEA treatment, the carbonyl (>C=O) band appeared at 1723 and 1736 cm1 in the curves of treated jute fibers and EFB fibers due to the presence of the ester group in 2-HEA (Figure 3). The characteristic peak between 1424 and 1428 cm1 corresponding to CH2 bending of cellulose remained unaffected after treatment.[25] The band at 1030 cm1, which is assigned to aromatic C-H- in plane deformation for primary alcohol in lignin, was found with higher absorption intensity ratio in untreated jute fiber than in treated jute fiber. The characteristic peaks of cellulose and lignin are around 1040–1060 cm1 (C-O stretching vibration of cellulose) and 1550–1650 cm1(aromatic skeleton vibration of lignin), respectively.[26,27] Positions of the two bands are approximately the same after treatment. However, the relative intensities of the band vary correspondingly. FT-IR study revealed that 2-HEA reacts with the fiber surface of both jute and EFB on account of graft copolymerization of cellulose with 2-HEA. Table I shows several major absorption bands present in jute and EFB fibers. Chemical modification of natural fibers causes an increase in hydrophobicity of the fibers and thus reduces degree of moisture absorption in natural fibers.[13]



FIGURE 1 FT-IR spectrum patterns of untreated and treated jute fibers.

FIGURE 2 FT-IR spectrum patterns of untreated and treated EFB fibers.

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FIGURE 3 Natural fiber reaction mechanisms between cellulose and 2-HEA.

SEM Analysis of Treated Jute Fibers The surface topography of untreated and treated jute fibers was analyzed by scanning electron microscopy (SEM). The scanning electron micrographs of both untreated and treated jute fibers surfaces are shown in Figures 4(a) and 4(b). The untreated jute fibers (Figure 4(a)) show some coating on the surface, which is likely to be the cementing materials (lignin, pectin, and waxy substances) present in fibers. Waxes and oil provide a protective layer on the surface of the fibers. HEA treatment appears to have removed much of the cementing materials and made the fiber surfaces rougher. It also seems that the treatment made the fiber surface very clean. The surface topography of treated fibers shows the absence of impurities (Figure (b)), which are clearly visible in the untreated fibers. Treatment of jute fibers caused the removal of impurities, noncellulosic materials, inorganic substances, and waxes and made the fiber surface cleaner and rougher than that of untreated fibers. Surface modification of fibers can also change the fine structure of the native cellulose I to cellulose II and result in stiff and strong fibers of interest in the formation of biocomposites.[28] Hence, HEA treatment causes significant changes in morphology and topography of the fiber surface and enhances the fiber=matrix interface.

TABLE I Peak assignments for several major absorption bands present in jute and EFB fibers Frequency (cm1) 3600–3200 3090–2600 1750–1700 1650–1550 1420–1430 1280–1070 1240–1250 1300–1030 1040–1060 1030

Vibration O-H stretching of hydrogen bond C-H stretching of CH2 and CH3 Stretching vibration of the carbonyl group (C=O) Aromatic skeleton vibration of lignin CH2 bending of cellulose C-O-C stretching C-O stretching in the acetyl O-H deformation bending C-O stretching vibration of cellulose C-H deformation=bending



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FIGURE 4 SEM micrograph of (a) untreated jute fibers (500), (b) treated jute fibers (500), (c) untreated EFB fibers (500), and (d) treated EFB fibers (500).

SEM Analysis of Treated EFB Fibers EFB fiber sample surfaces were observed under a scanning electron microscope before and after treatment with 2-HEA. Figures 4(c) and 4(d) show the SEM micrographs of untreated and treated EFB fiber surface under magnification (500). It is clear from Figure 4(c) that the EFB fiber surface was full of impurities and no pores can be seen. EFB fiber samples possessed a large amount of silica impurities. Changes in the surface after 2-HEA treatment are observed in Figure 4(d); the surface of treated EFB fiber was cleaner and smoother than that of untreated EFB fibers. Modification of EFB fiber with acetylation results in a smoother surface for treated EFB fiber than untreated EFB fiber.[13] Similar studies done on EFB fiber surface modification by alkali, mercerization, acetylation, silanization, and acrylated treatment show less impurities and prominent pores.[9,29]

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TABLE II Weight percentage gain (WPG) of jute and EFB fiber with 2-HEA modification Fiber

WPG (%)

EFB Jute

5 7


Weight Percentage Gain (WPG) The weight percentage gain of jute and EFB fibers increased after modification with 2-HEA. Figure 3 shows the reaction scheme for 2-HEA modification. WPG should be considered to ensure sufficient improvement in the desired properties of fibers. Besides that, proof of whether modification has taken place depends on the WPG value.[13] The results of WPG obtained after 2-HEA treatment for EFB and jute was 5% and 7%, respectively (Table II). The extent of chemical modification of EFB and jute fibers was quantitatively determined using WPG. Jute fibers show higher WPG than EFB fibers, indicating that jute fibers show better chemical reactivity with 2-HEA than EFB fibers. The reactivity of fiber with chemical depends upon the relative reactivities of the hydroxyl groups in the substrate and the rate of diffusion of the reagent into the matrix.[30]

Tensile Properties The effect of 2-HEA on the performance of tensile properties of hybrid composites was studied. Tensile strength and modulus of untreated hybrid composites and hybrid composites of 2-HEA-treated jute fibers are shown in Table III. Chemical treatment of jute fibers increased the tensile properties of the hybrid composites over those of untreated hybrid composites. From the tensile property values, it is clear that tensile strength and modulus of treated hybrid composites increased significantly as compared to untreated hybrid composites. Treated hybrid composites can withstand tensile stress to a higher level than untreated hybrid composites can. Tensile properties can be explained on the basis of changes in chemical interactions at the fiber=matrix interface.[31] 2-HEA treatment removes impurities and weaker noncellulosic fiber components from the jute fiber surface, as can clearly be seen from scanning electron TABLE III Tensile strength and modulus of untreated and treated hybrid composites having a ratio of oil palm EFB: jute fiber of 4:1 Hybrid composite EFB=jute=EFB EFB=jute=EFB (treated) Jute=EFB=jute Jute=EFB=jute (treated)

Standard error.

Tensile strength (MPa)

Tensile modulus (GPa)

25.5 0.23 29.61 0.4 27.4 0.02 32.34 0.07

2.39 0.01 2.92 0.03 2.59 0.07 3.24 0.05


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micrographs. The development of rough surface topography due to the jute surface treatment offers a better fiber=matrix interface and higher tensile properties. The increased tensile properties as well as good fiber=matrix interface bonding may be attributed to the 2-HEA, which reacted with jute and epoxy. The vinyl group of the acrylate moiety of 2-HEA reacts with the OH group of the cellulose backbone of jute fiber through graft copolymerization and, as a result, the hydrophilic nature of jute is reduced (Figure 3). Again, OH groups of 2-HEA may also react

FIGURE 5 Nucleophilic addition reaction mechanism between epoxy matrix (structure 2) and 2-HEA grafted cellulose.


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with carbonyl groups of the epoxy matrix through nucleophilic addition (Figure 5). The effect of chemical treatment on tensile strength and modulus of jute=bagasse-reinforced epoxy hybrid indicated that the treatment increased fiber=matrix interface bonding and enhanced tensile properties of hybrid composites.[17] Treated jute fiber–based jute=EFB=jute hybrid composites show better tensile properties than untreated hybrid composites because jute fiber failure transferred high stress to the less strong oil palm EFB fibers and this ultimately lead to failure of the composite. In a hybrid composite, the tensile modulus and elongation at break of individual reinforcing fibers play an important role. The modulus of jute fiber is comparatively higher than that of oil palm EFB, and because of that jute=EFB=jute hybrid composites show better tensile properties than EFB=Jute=EFB composites. It has been found that alkali-treated sisal and roselle fibers resulted in a significant increase in tensile properties.[32] Jacob et al.[33] reported that chemically modified sisal=oil palm hybrid showed better tensile properties due to better interaction between sisal=oil palm and the matrix.

FIGURE 6 Scanning electron micrograph of tensile fracture of EFB=jute=EFB (treated) hybrid composite.

FIGURE 7 Scanning electron micrograph of tensile fracture of jute=EFB=jute (treated) hybrid composite.



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The effect on the tensile properties of 2-HEA-treated jute fiber hybrid composite as compared with untreated jute fiber hybrid composites is also confirmed by the SEM micrographs showing fracture surfaces, shown in Figures 6 and 7. Scanning electron micrographs of the tensile fractured surfaces of the hybrid composites were taken to study the fiber=matrix interaction and fracture behavior. The 2-HEA modification seemed to enhance interlocking of the matrix with fibers. In the case of untreated oil palm=jute hybrid epoxy composites, the fiber=matrix interface bonding is weak.[21] It is also clear from the SEM of tensile fracture of untreated hybrid composites that the fiber surface is more or less clear and holes are also visible on the fracture surfaces, indicating fiber pull-out. Fiber pull-out to some extent was reduced in treated jute hybrid composites, as seen in Figures 6 and 7. It is also evident from SEM micrographs of treated hybrid composites that improved adhesion, crack planes, and matrix particles can be seen on the fiber surfaces. Therefore, it can be concluded that the fiber=matrix interface improved with chemical treatment due to the effective coupling action of 2-HEA. CONCLUSIONS Chemical modification of jute and EFB fibers carried out using 2-hydroxy ethylacrylate, and the modified fibers were analyzed using FT-IR, SEM, and WPG, confirming the effectiveness of chemical modification. Chemical modification of jute and EFB fibers was imperative for increased fiber=matrix interfacial adhesion. Treated jute=EFB=jute hybrid composite shows better tensile properties than untreated hybrid composites because jute fiber fails to transfer high stress to the less strong oil palm EFB fibers, and this ultimately led to failure of the composite. Therefore, it can be concluded that the fiber=matrix interface has been improved with chemical treatment due to the effective coupling action of 2-HEA with fibers. SEM micrographs of tensile fracture of treated hybrid composites also confirmed that the fiber=matrix interface has been improved with the chemical treatment due to the effective coupling action of 2-HEA. FUNDING The authors extend their appreciation to the Deanship of Scientific Research at King Saud University for funding this work through research group no RGP-VPP-133. REFERENCES 1. Jawaid, M., H. P. S. Abdul Khalil, A. Hassan, R. Dungani, and A. Hadiyane. 2013. Effect of jute fibre loading on tensile and dynamic mechanical properties of oil palm-epoxy composites. Composites Part B Eng. 45: 619–624. 2. Pinto, M. A., V. B. Chalivendra, Y. K. Kim, and A. F. Lewis. 2014. Evaluation of surface treatment and fabrication methods for jute fiber=epoxy laminar composites. Polym. Compos. 35: 310–317. DOI: 10.1002=pc.22663 3. Kommula, V. P., K. Obi Reddy, M. Shukla, T. Marwala, and A. Varada Rajulu. 2013. Physico-chemical, tensile, and thermal characterization of Napier grass (native African) fiber strands. Int. J. Polym. Anal. Charact. 18: 303–314. 4. Defoirdt, N., S. Biswas, L. De Vriese, L. Q. N. Tran, A. Van Acker, Q. Ahsan, L. Gorbatikh, A. Van Vuure, and I. Vedpoest. 2010. Assessment of the tensile properties of coir, bamboo and jute fibre. Composites Part A Appl. Sci. Manuf. 41: 588–595. 5. Sinha, E., and S. K. Rout. 2008. Influence of fibre-surface treatment on structural, thermal and mechanical properties of jute. J. Mater. Sci. 43: 2590–2601.


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