Polyethylene Composites Reinforced by Kenaf Fiber Modified by Silane Grafted Low Density Polyethylene Yajuan TIAN, and Shin-ichi KURODA† Gunma University, Graduate School of Engineering Kiryu, Gunma , Japan firstname.lastname@example.org Introduction The use of natural fibers as reinforcements and fillers in natural-fiber/thermoplastic composites has become more commonplace in recent years as they have many advantageous attributes, such as low density, low cost, high specific strength and modulus, relative non- abrasiveness, and biodegrability. Kenaf bast fiber has high potential as a reinforcing fiber in thermoplastic composites because of its superior toughness and high aspect ratio in comparison with other fibers. A single fiber of kenaf can have a modulus as high as 11-60 GPa1). The main disadvantages of natural fibers in composites include incompatibility between hydrophilic natural fibers and hydrophobic polymers and potential moisture absorption of the fibers. To improve the compatibility with hydrophobic thermoplastics, many efforts for the surface treatment of natural fiber have been done2-4), such as maleated polyolefin (1-3wt%) treatment, silane coupling, silane coupling together with maleated polyolefin treatment, esterification and etherification etc.. Some improvements have been achieved to some extent by these methods. As we have successfully prepared a new polymeric coupling agent, i.e. silane grafted LDPE with relative higher graft yield by photo-grafting technique in our former studies and very strong adhesive strength to glass plate has been achieved5), it’s expectable that this polymeric coupling agent will bring good properties for natural fiber/hydrophobic thermoplastics composites. In this study, by using low molecular weight vinyl silane coupling agent and this polymeric coupling agent for the surface treatment of kenaf fiber, kenaf fiber/LLDPE composites were prepared and their properties were studied. Experimental Methacryloxypropyltriethoxysilane and 3-methacryloxypropyltriethoxysilane grafted LDPE (Si-g-LDPE, graft yield 10%-20%) prepared through photo-grafting technique in our lab were used for the surface treatment of kenaf fiber. Si-g-LDPE were first dissolved in xylene at 80℃ to form a solution, then kenaf fiber were added. After 1 h immersion and the following drying, they were subjected to soxhlet extraction with xylene for 24 h and then dried at room temperature in a vacuum oven. Some other kenaf fiber were treated by 3- methacryloxypropyltriethoxysilane by the same procedure. The surfaces of kenaf fibers before and after modification were analyzed by X-ray photoelectron spectra. LLDPE/kenaf fiber composites were prepared by hot pressing technique. LLDPE power (60wt%), Sumilizer (0.3wt%) and kenaf fiber (40wt%) were mixed together, then they were poured into the mold already preheated to 200℃ and molded at 15MPa. After the following cooling down to room temperature, they were taken out of the mold and composites were prepared. Dynamic mechanical property of LLDPE/kenaf composite were measured by a viscous-elastic device (TOYOSEIKI), and water absorbency were detected by immersing the corresponding composites in water at room temperature for 12 h and calculating the weight percentage increased. Results and discussion Figure 1 shows the kinetic mechanical behavior of LDPE and the composites reinforced by kenaf fiber without pretreatment, modified by Si-g-LDPE and modified by low molecular weight silane. Modulus of LDPE dropped very quickly with temperature increasing, while modulus of composites decreased slowly. All the composites showed a high modulus at room temperature, among which composites filled with Si-g-LDPE modified kenaf has the highest modulus. On the plot of modulus (imaginary part) against temperature, the peak appeared around -24°C for LDPE, which was assigned as the relaxation of the amorphous part of LDPE caused by branching, shifted to a higher temperature after filled with kenaf fiber, and the absolute value decreased. This suggests good interaction exist between kenaf fiber and LDPE. 3.5 3500000000 180000000 0.1 Modulus (GPa) (real part) Modulus (GPa) (imaginary part) 3.0 3000000000 160000000 8 140000000 0.1 2.5 2500000000 a 9-1 a 9月1日 6 120000000 b 24-1 2.0 2000000000 b 0.1 24-1 100000000 c 7-3 1.5 1500000000 c 4 7月3日 80000000 d LDPE d 0.1 60000000 1.0 1000000000 LDPE 2 40000000 0.5 500000000 0.1 20000000 0 0 0 0 -200 -100 0 100 200 -200 -100 0 100 200 Temperature (℃) Temperature (℃) Figure 1. Temperature dependence ofdynamic mechanical property of kenaf fiber/LLDPE composite. a--- Pretreated by Si-g-LDPE; b--- Pretreated by silane; c--- Without pretreatment; d---LDPE Table 1 shows the water absorbency of PE/kenaf fibe composites. Composite using Si-g-LDPE treated kenaf fiber has lower water absorbency compared with composite using untreated kenaf fiber. Water absorbency contributes to hydrogen bonding of hydroxyl groups on kenaf fiber with water. Lower water absorbency means difficult accessibility of water to fiber, which in turn means better interaction of fiber with matrix. Table 1. Water absorbency of PE/kenaf fiber composites Kenaf fiber Water absorbency (%) Without pretreatment 3.95 Pretreated by silane 3.39 Pretreated by Si-g LOPE 1.74 Conclusion 3-methacryloxypropyltriethoxysilane photo-grafted LDPE is a very effective coupling agent for kenaf fiber/LLDPE composites. Good interactions between kenaf fiber and LLDPE matrix has been established by this polymeric coupling agent. Improved mechanical property and water absorbency has been achieved for kenaf fiber/LLDPE composite. References 1. Shinji, O., Mechanics of Materials, 40, 446-452 (2008). 2. Mohanty, A. K.; Drzal, L. T.; Misra, M. Journal of Adhesion Science and Technology, 16, 999 (2002). 3. Gassan, J., Applied Science and Manufacturing, 33A, 369 (2002) 4. Baiardo, M., Frisoni, G., Scandola, M., Licciardello, A., Journal of Applied Polymer Science, 3, 38 (2002). 5. Tian, Y.J., Kuroda, S., to be submitted. Main Body of Text Times New Roman 12 pt The talk will present novel results relating to the pioneering work of Staudinger. 1 References superscript; total abstract length maximum 2 pages Equation 1 (1) Figure X:(Times New Roman 10 pt and bold) Insert Figures as Word Text Box; Figure Caption 10 pt Times New Roman References Times New Roman 10 pt Bold; references themselves Times New Roman 10 pt 1 Staudinger, H. Nature 1944, 30, 605-643. Citation Style 'Macromolecules'
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