Effects of nanoparticles on the mechanical properties of rice straw/polypropylene composites

Rice straw is an abundantly available and potentially valuable biomass that is currently underexploited. In the present work, the reinforcing effects of nanoparticles (silica and clay) on the rice straw / polypropylene composites have been studied. In the sample preparation, four levels of loading (0-3 wt%) were used for nanoparticles. In order to increase the interphase adhesion, polypropylene grafted with maleic anhydride was added as coupling agent to all the composites studied. The mechanical properties, namely, the tensile modulus, flexural modulus, notched Izod impact strength, and elongation at break of the composites were determined. The results showed that while tensile and flexural moduli and elongation were moderately improved by the increase in the amount of nanoparticles in the matrix, Izod impact strengths decreased dramatically. The flexural and tensile moduli increased with increase of nanoclay up to 2 wt%. However, beyond this amount, mentioned properties decreased. Generally, high amount (3 wt%) of nano-size particles in the composites can lead to the reduction of interfacial adhesion between matrix polymer and filler, and it limits their applications. Transmission electron microscopy revealed the existence of uniform intercalated nanoclay dispersed throughout the matrix at 1 and 2 wt% loading. The mechanical properties of composites filled with nanoclay are generally greater than nanosilica composites.