Synergistic effect of coupling agents and fiber treatments on mechanical properties and moisture absorption of polypropylene-rice husk composites and their foam

Rice husks and polypropylene were applied as the fibers and matrix, respectively, to make composites. Polypropylene-grafted maleic anhydride (PP-g-MA) and styrene ethylene butadiene styrene-grafted maleic anhydride (SEBS-g-MA) were used as coupling agents. The rice husks were also treated with NaOH, silane, or NaOH + HCl + silane to enhance the effect of the coupling agents. Using a combination of 2 wt% PP-g-MA and 1 wt% SEBS-g-MA, the impact strength of the composite increased, but the tensile strength and modulus were not reduced relative to the use of PP-g-MA alone. The three treatments - NaOH, silane and NaOH + HCl + silane - and added coupling agents improved the impact strength and decreased the moisture absorption rate of the composites except for those subjected to the alkaline treatments. The foaming results showed that adding coupling agents improved the cell structure and reduced the density of the foam.