Potential use of rice endosperm fibers as reinforcing material in biocomposites

Biocomposites composed of biodegradable polymer, as matrix material, and natural fibers, as reinforcing material, have attracted much attention from the environmental viewpoint and their advantages such as high strength & stiffness, low cost, and biodegradable properties [1-3]. The lack of good interfacial adhesion between natural fibers and matrix, low melting point, and water sensitivity make the use of natural fiber-reinforced composites less attractive. Various green methods have been explored in order to improve the compatibility between hydrophilic natural fibers and hydrophobic polymer matrices among which enzyme digestions [4]. Enzyme catalyzed reactions are highly specific and result in the separation of fibers from their non-fiber components [5]. Rice fibers can also be considered as important potential reinforcing filler for thermoplastic composite because of its lignocellulosic characteristics and the objective of this study is to investigate the reinforcing potential of original and enzymatically modified rice endosperm fibers. Rice endosperm fibers were biochemically characterized and enzymatically treated with Celluclast. Original and enzymatically treated rice fibers were characterized in order to know their surface morphology, thermal stability and crystallinity. Biocomposites were prepared by reinforcing poly(butylene succinate) (PBS) with original and enzymatic treated rice endosperm fibers (10, 20 and 30 wt%) by melt mixing at 160°C. Synthesized composites were subjected for water uptake test to investigate the resistance against water absorption. Thermal and mechanical characterization of all biocomposites was carried out in order to verify the effect of the dispersion of fibers inside the polymeric matrix. Analysis shows that rice fibers and PBS degrade in a single step, at different temperatures. Moreover, enzymatically treated fibers are slightly more stable than the original ones. The thermal properties of the composites do not vary with respect to those of PBS. Therefore, the crystalline structure of the polymeric matrix is not disturbed by the presence of fibers also when present in a large amount. Finally from tensile and flexural analysis, it has been observed that reinforcement of rice endosperm fibers have a notable effect on the mechanical performances of the composites. A significant increment of tensile and flexural properties is induced by both kinds of fibers, revealing a general reinforcement of the matrix in all the samples.