Effect of compatibilizer on the structure-property relationships of Kenaf-fiber/polypropylene composites

Although lignocellulosic, fiber-thermoplastics composites have been used for sever-al decades, recent economic and environmental advantages have resulted in significant commercial interest in the use of these fibers for sever-al applications. Kenaf is a fast growing annual growth plant that is harvested for its bast fibers. These fibers have excellent specific properties and have potential to be outstanding reinforcing fillers in plastics. This paper reports the structure-property relationships of kenaf fiber reinforced polypropylene (PP) and its impact copolymers. The use of maleated polypropylenes (MAPP) is important to improve the compatibility between the fiber and matrix. A significant improvement in impact strengths was observed when the MAPP was used in the composites. Results also indicate that the impact copolymer blends with coupling agent have better high temperature moduli and lower creep compliance than the uncoupled systems. The coupling agent also changes the crystallization and melting behavior of these blends. Because of the better adhesion between the polymer molecules and kenaf fibers, the coupled samples have more restricted molecules than the uncoupled blends. As a result, the crystallization of the coupled high molecular weight blends is slower than the uncoupled blends, resulting in a lower crystallization temperature (TC) and reduced crystallinity. For the lower molecular weight blends, the coupling agent enhances the crystallization of polymer matrix and results in a higher crystallization temperature and increased crystallinity of the coupled blend. The coupled blends also have more defects in the polymer crystals, and the crystallinity of coupled blends is also lower than the uncoupled blends. This could explain the lower melting temperatures of the coupled samples as compared to uncoupled samples.