This article was downloaded by: [Temple University Libraries] On: 15 November 2014, At: 02:47 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Polymer-Plastics Technology and Engineering Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/lpte20 Maleated Natural Rubber as a Coupling Agent for Recycled High Density Polyethylene/Natural Rubber/ Kenaf Powder Biocomposites a a a b Xuan Viet Cao , Hanafi Ismail , Azura A Rashid , Tsutomu Takeichi & Thao Vo-Huu c a School of Materials & Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia , Malaysia b Department of Environmental and Life Sciences , Toyohashi University of Technology , Japan c Department of Polymer Materials, Faculty of Materials Technology , Ho Chi Minh University of Technology , Vietnam Published online: 27 Jun 2012 To cite this article: Xuan Viet Cao , Hanafi Ismail , Azura A Rashid , Tsutomu Takeichi & Thao Vo-Huu (2012) Maleated Natural Rubber as a Coupling Agent for Recycled High Density Polyethylene/Natural Rubber/Kenaf Powder Biocomposites, PolymerPlastics Technology and Engineering, 51:9, 904-910, DOI: 10.1080/03602559.2012.671425 To link to this article: http://dx.doi.org/10.1080/03602559.2012.671425 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis The accuracy of the Content should not be relied upon and should be independently 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Hanafi Ismail1, Azura A Rashid1, Tsutomu Takeichi2, and Thao Vo-Huu3 Downloaded by [Temple University Libraries] at 02:47 15 November 2014 School of Materials & Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia, Malaysia Department of Environmental and Life Sciences, Toyohashi University of Technology, Japan Department of Polymer Materials, Faculty of Materials Technology, Ho Chi Minh University of Technology, Vietnam Kenaf powder (KP) was incorporated into recycled high density polyethylene (rHDPE)/natural rubber (NR) blend using an internal mixer at 165 C and rotor speed of 50 rpm The tensile strength and elongation at break of the composites decreased, while the tensile modulus increased with increasing filler loading The water absorption was found to increase as the filler content increased The maleic anhydride grafted natural rubber was prepared and used to enhance the composites performance The addition of MANR as a coupling agent improved the tensile properties of rHDPE/NR/KP biocomposites The water absorption was also reduced with the addition of MANR Keywords Biocomposites; Kenaf powder; Maleated natural rubber; Naturalrubber; Recycled high density polyethylene INTRODUCTION The development of polymer composites using recycled or recyclable polymers and natural organic fillers is very actively pursued due to threats of uncertain petroleum supply in the near future and environmental concerns This class of composites indicated as biocomposite, which shows various benefits and good properties inherited from its constituents Fillers (bio-fibers or powders) used in polymer composites mainly include banana, sisal, hemp, jute, pineapple, bamboo, cotton, coconut, rice husk, and kenaf These fillers offer several advantages such as large quantity, annual renewability, low cost, light weight, competitive specific mechanical properties, reduced energy consumption, and environmental friendliness[1–3] Address correspondence to Hanafi Ismail, Polymer Division, School of Material and Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong, Tebal, Penang, Malaysia E-mail: hanafi@eng.usm.my Kenaf is gaining a lot of attention in the composite industry, since they can be applied as filler in polymer composites It is widely planted in Malaysia and was found to be the most suitable crop for commercial-scale production due to the climate in Malaysia[4] Kenaf stem is composed of two distinct fibers, bast and core The average stem composition is 35% bark and 65% woody core by weight The bark contains a long fiber called bast fiber, whereas the woody core contains short core fibers[5] The abundance of kenaf core combined with the ease of its processability is an attractive characteristic, could make it a desirable substitute for synthetic fillers that is a potentially toxic Due to the difference in the composition of recycled plastics, the performance of composites from recycled plastics is expected to be different from those of the corresponding virgin plastics Some work has been carried out on natural fiber reinforced of recycled PE[6–10] However, work done on natural fiber filled recycled PE=natural rubber (NR) blend is still very limited In this study, the potential of using kenaf core and recycled HDPE=NR blend for making biocomposites was examined The main problem that has prevented a more utilization of natural fiber in TPE composites is the lack of good adhesion between the hydrophilic fillers and hydrophobic matrixes This results in poor mechanical properties of final products It was found that the interfacial adhesion can be improved by using coupling agents.It is well known that maleated coupling agents have been widely used for various single polymer composites (both plastic and rubber composites)[11–15] However, its utilization in thermoplastic elastomer composites has been less studied and remained promising In previous study[16], the authors reported that maleic anhydride grafted polyethylene which is more favorable for rHDPE phase was successfully used as a 904 rHDPE=NR=KP BIOCOMPOSITES Downloaded by [Temple University Libraries] at 02:47 15 November 2014 compatibilizer to enhance the properties of rHDPE=NR= KP biocomposites To the best of our knowledge, no attempt has been made towards the employment of maleated natural rubber (MANR) as a coupling agent in polyolefin natural rubber composites In the present work, (MANR) was prepared and used as a coupling agent for this system MANR was expected to facilitate the interactions between rubber phase (NR) and filler (KP) as well as plastic (rHDPE) and rubber (NR) phase The effect of MANR on the mechanical properties, water absorption, and morphology of the biocomposites was investigated EXPERIMENTAL Materials and Chemicals Recycled high density polyethylene (rHDPE) was obtained from Zarm Scientific and Supplies Sdn Bhd, Penang with melt flow index of 0.237 g=10 Natural rubber used was SMR L grade from the Rubber Research Institute of Malaysia (RRIM) Maleic anhydride (MA) was supplied by Sigma Aldrich Kenaf powder was produced by grinding kenaf core in a table-type pulverizing machine and sieved to obtain the powder size in range of 32 to 150 mm Preparation of Maleic Anhydride Grafted Natural Rubber Maleic anhydride grafted natural rubber (MANR) was prepared in an internal mixer (Haake Rheomix) at a temperature of 135 C for 10 and a rotor speed of 60 rpm according to a procedure reported by Nakason et al.[17] The maleic anhydride content used in this study was phr Preparation of rHDPE/NR/KP Biocomposites Formulation of rHDPE=NR=KP biocomposites is given in Table Prior to compounding, rHDPE and KP were dried by using a vacuum oven at 80 C for 24 h Mixing process was carried out at 165 C and a rotor speed of 50 rpm The rHDPE was first charged into the mixer and melted for NR was added at third minute The MANR and KP were added at the 6th min, respectively The blend was allowed to further mixing for another to obtain the stabilization torque The total mixing time was 12 for all samples The blends were then compression molded in a hydraulic hot press into mm sheets for preparing test samples The hot press procedure involved preheating at 165 C for followed by compressing for at the same temperature, and subsequent cooling under pressure for Fourier Transform Infrared Spectroscopy (FTIR) FTIR (Perkin Elmer System 2000) was used to confirm the grafting reaction between NR and MAH Sample was 905 TABLE Formation of rHDPE=NR=KP biocompositesà Materials Composition (phr) Recycled high density polyethylene (rHDPE) Natural rubber (SMR L) Kenaf powder (KP) MANRa 70 30 0, 10, 20, 30, 40 Note (phr)-part per hundred resin a 5% of KP à Similar biocomposites but without MANR were also prepared extracted the unreated MAH by Soxhlet extraction in acetone for 24 h, and further dried in a vacuum oven at 40 C for 24 h prior to FTIR measurement FTIR spectrum was recorded in the transmittance range from 4000 to 600 cmÀ1 with a resolution of cmÀ1 There were scans for each spectrum All FTIR spectra were obtained using attenuated total reflectance (ATR) Tensile Properties The tensile properties were measured using an Instron 3366 machine at a cross-head speed of 50 mm=min at 25 Ỉ 3 C according to ASTM D 412 Tensile strength, tensile modulus, and elongation at break of the each sample were obtained from the average of five specimens Water Absorption A water absorption test was carried out by immersing the samples in distilled water at room temperature (25 C) The water absorption was determined by weighing the samples at regular intervals on an electronic balance The percentage of water absorption, Mt, was calculated by Mt ¼ 100  ðwt À wo Þ=wo ð1Þ where wo and wt are the original dry weight and weight after exposure, respectively Scanning Electron Microscopy (SEM) The morphology of the composites was also analyzed with a Supra-35VP field emission scanning electron microscope (SEM) The objective was to get some information regarding filler dispersion and bonding quality between matrix and filler The fracture surfaces obtained from tensile test were coated with gold=palladium by a sputter coating instrument (Bio-Rad Polaron Division) for 45 to prevent electrostatic charging during evaluation Downloaded by [Temple University Libraries] at 02:47 15 November 2014 906 X V CAO ET AL RESULTS AND DISCUSSION FTIR Analysis The FTIR spectra of NR and MANR are shown in Figure The peaksat 1662 cmÀ1 and 833 cmÀ1 were corresponded to C ¼ C of NR and observed for both cases For the MANR spectrum, the absence of the absorption peak at 698 cmÀ1 suggested the unreacted MAH has been completely removed from the MANR A broad and intense characteristic peak at 1779 cmÀ1 and a weak absorption peak at ca 1862 cmÀ1 were observed These peaks were assigned to grafted anhydride, which are due to symmetric (strong) and asymmetric (weak) C ¼ O stretching vibrations of succinic anhydride rings, respectively[18,19] Therefore, it can be confirmed that the MAH was successfully grafted onto NR backbone.A possible reaction mechanism can be found elsewhere[17] Processing Characteristics The torque development provides information regarding the effectiveness of mixing, thermal and mechanical shearing stability of the composites The addition of compatibilizers or coupling agents can also be studied through the torque versus time curves Figure shows the torque behavior of rHDPE=NR=KP biocomposites with MANR as a coupling agent Generally, a similar pattern of torque curves was observed for all composites (except for the rHDPE=NR blend) The first rise in torque was attributed to the resistance exerted by solid rHDPE against the rotors The torque decreased as rHDPE melted with mechanical shearing and the rise of internal temperature The second peak was detected corresponding to NR charging These two peaks were obtained for all composites and expressed the different amount of rHDPE and NR charged into the mixing chamber However, the change of torque observed as MANR added was unobvious The third peak appeared at around the 7th due to the introduction of KP, which presented proportionally to the filler content Upon completion of filler dispersion, the torque started FIG FTIR spectra of NR (a) and MANR (b) FIG Torque development for rHDPE=NR=KP biocomposites with MANR at different KP content to decrease gradually due to a reduction in viscosity as the stock temperature increased The stabilization torque of the composites is presented in Figure It can be seen that stabilization torque increased gradually with increasing filler loading This was due to the higher the filler content the lower the mobility of polymer chains and thus increased the viscosity and stabilization torque However, stabilization torque of composites with MANR was found to be higher than that of composites without MANR Therefore, the addition of MANR improved the filler-matrix interfacial bonding, which resulted in the higher stabilization torque in the composites with MANR[20] Tensile Properties The typical stress-strain curves of rHDPE=NR blend, rHDPE=NR=KP composites with and without MANR at FIG Stabilization torque at 12 of rHDPE=NR=KP biocomposites Downloaded by [Temple University Libraries] at 02:47 15 November 2014 rHDPE=NR=KP BIOCOMPOSITES 907 FIG Stress-strain behavior of rHDPE=NR=KP biocomposites at various filler content (Color figure available online.) FIG Elongation at break of rHDPE=NR=KP biocomposites at various filler content 10 and 40 KP content are depicted in Figure The difference originated from the incorporation of filler and the addition of coupling agent was evident from these curves The curve of rHDPE=NR blend displayed typical yield behavior and ductile nature However, rHDPE=NR=KP composites exhibited more brittle behavior under tensile load, which expressed shorter elongation and higher initial slope (higher tensile modulus) This is common effect of incorporation of short fiber into a thermoplastic or rubber matrix Due to the weak interfacial bonding between the hydrophilic lignocellulosic filler and the hydrophobic polymer matrixes, the stress propagation was obstructed Therefore, the composites could not elongate and broke when internal stress increased at interface of filler and matrix, resulted in lower tensile at break compared to yield strength and yield strength then was reported as tensile strength As shown in FIG Tensile strength of rHDPE=NR=KP biocomposites at various filler content Figure 5, tensile strength of rHDPE=NR=KP biocomposites decreased gradually with increasing filler content Increasing filler content from 10 phr to 40 phr, yield strength was slightly reduced; hence tensile strength was only decreased ca MPa The other reason caused poor stress transfer in composites was the irregular morphology of KP This hindered the KP orientation during tensile test and resulted in the deterioration of elongation of the composites This explained the rather lower elongation at break of composites after 20 phr KP compared to 10 phr KP as shown in Figure As expected, the addition of MANR as coupling agent enhanced the composites properties MANR improved interfacial adhesion between KP and matrix by forming hydrogen bonding between KP and MANR Coupling mechanism of MANR in rHDPE=NR=KP composites is proposed in Figure The better interfacial bonding also prevented fiber-fiber contact, hence gave the better filler dispersion As a result, tensile strength and elongation at break increased with the addition of MANR This was also responsible for the higher tensile modulus for composites with MANR As shown in Figure 8, at a FIG Possible hydrogen bonding formed between KP and MANR Downloaded by [Temple University Libraries] at 02:47 15 November 2014 908 X V CAO ET AL FIG Tensile modulus of rHDPE=NR=KP biocomposites at various filler content similar filler loading, composites with MANR exhibited higher tensile modulus than those without MANR The incorporation of KP was expected to increase the modulus resulting from the inclusion of rigid filler particles in the soft matrix These results indicated that tensile modulus of the KP filled rHDPE=NR biocomposites followed the same trend with the filled plastic and rubber composites Water Absorption Water absorption of rHDPE=NR=KP biocomposites without MANR is presented in Figure All rHDPE= NR=KP biocomposites with MANR also displayed a similar pattern of sorption, where the samples absorbed water very rapidly during the first stages, followed by gradual increase until reaching a certain value (saturated point) Obviously, the water uptake of the composites increased as filler content increased The hydrophilic character of natural fiber was responsible for the water absorption in FIG Water absorption of rHDPE=NR=KP biocomposites without MANR the biocomposites by forming hydrogen bonding between water and the hydroxyl group of cellulose, hemicellulose in the cell wall As KP content increased, the number of hydrogen bonding also increased In rHDPE=NR=KP biocomposites without MANR, because fiber-matrix adhesion is weak, water can easily enter into the interfacial gaps Figure 10 presents equilibrium water uptake at 63 days of rHDPE=NR=KP biocomposites with and without MANR It is clear that the addition of MANR resulted in lowering of water uptake compared to the composites without MANR As mentioned here, the water absorption is dependent on the availability of free –OH groups on the surface of the fiber In composites with MANR, the number of –OH groups could be reduced via the hydrogen bond between MANR and –OH of KP fiber The improvement of interfacial adhesion between fiber and matrix also reduced the water accumulation in interfacial gaps, hence, limiting the penetration of water into the composites[21] Morphology of Biocomposites SEM was used to evaluate the effect of filler content and the addition of coupling agent on the morphology of the composites These morphology observations are correlated to the mechanical properties as well as the water absorption of the biocomposites as discussed earlier Tensile fracture surfaces of the biocomposites with and without MANR at 10 and 40 phr of KP are shown in Figure 11 In the case of composites without MANR at 10 phr (Fig 11(a)), the composites had matrix fibrillation and deformed in ductile mode However, the fibers were not well oriented and the poor adhesion at the interface can be deduced from the clean surface of the fibers This poor adhesion is clearly visible at 40 phr (Fig 11(b)), where some fibers were pulled out FIG 10 Equilibrium water uptake at 63 days of rHDPE=NR=KP biocomposites with and without MANR rHDPE=NR=KP BIOCOMPOSITES 909 Downloaded by [Temple University Libraries] at 02:47 15 November 2014 CONCLUSIONS Maleated natural rubber was prepared and used in this study to improve the interfacial adhesion between hydrophilic kenaf powder and the rHDPE=NR hydrophobic matrices The SEM micrographs showed the better adhesion at the fiber-matrix interfaces as MANR was added to the composites It was attributed to the hydrogen bonding formed between the hydroxyl groups of fiber and the maleic anhydride of MANR rHDPE=NR=KP biocomposites with MANR provided an enhancement in tensile strength, tensile modulus, elongation at break, and water absorption compared to the biocomposites without MANR REFERENCES FIG 11 Tensile fracture surfaces of rHDPE=NR=KP biocomposites at 200X: (a) 10 phr of KP, (b) 40 phr of KP, (c) 10 phr of KP with MANR, and (d) 40 phr of KP with MANR or remained loosely with the matrix Voids were also presented in the samples These features were evidences for poor mechanical properties and high water uptake of the uncoupled composites The addition of MANR significantly improved adhesion to the fiber Figures 11(c) and (d) shows the microstructure of KP filled rHDPE=NR composites with MANR at 10 phr and 40 phr, respectively The morphology was clearly different compared to the composites without MANR All the micrographs of the composites with MANR also showed better dispersed fillers compared to the composites without MANR The better fiber-matrix adhesion can be measured by the fact that more matrix fibrillation, rougher fracture surfaces, and less fiber pull out were observed Interestingly, the improvement of the adhesion at the interface was still obvious at 30 phr by looking at a 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Xuan Viet Cao1, Hanafi Ismail1, Azura A Rashid1, Tsutomu Takeichi2, and Thao Vo-Huu3 Downloaded... increased with increasing filler loading The water absorption was found to increase as the filler content increased The maleic anhydride grafted natural rubber was prepared and used to enhance