Synergistic effect of coupling agents on polypropylene‐based wood–plastic composites

In this study, polypropylene grafted with maleic anhydride (PP‐ g ‐MA) and styrene ethylene‐ co ‐butylene styrene block copolymer grafted with maleic anhydride (SEBS‐ g ‐MA) were used as coupling agents for polypropylene‐based wood–plastic composites containing 50 wt % wood flour. Adding up to 5 wt % PP‐ g ‐MA to the composite increased the tensile strength of the wood‐plastic composite (WPC) by almost 100% and the reversed‐notch Izod impact strength by more than 100%; the modulus remained essentially unchanged. By contrast, the same amount of SEBS‐ g ‐MA had a greater effect on the impact strength but a smaller influence on the tensile strength; in addition, the modulus was reduced. On using a combination of 2 wt % PP‐ g ‐MA and 1 wt % SEBS‐ g ‐MA, the impact strength of the composite could be increased significantly, but the tensile strength and modulus were not reduced to any appreciable extent relative to the use of PP‐ g ‐MA alone. Because WPCs are building products where minimizing costs is extremely important, this finding has important commercial implications.