Mechanical properties of wood flour/poly (lactic acid) composites coupled with waterborne silane-polyacrylate copolymer emulsion

Wood flour/polylactic acid (WF/PLA) composites were produced with a WF content of 50% based on three types of waterborne polyacrylate (PA) emulsions including a PA homopolymer emulsion and two types of silane-PA copolymer emulsions as coupling agents. Two silanes were in focus, namely, gamma-methacryloxypropyl-trimethoxysilane (silane-1) and vinyltrimethoxysilane (silane-2). The emulsions and the modified WFs were characterized, and the effects were investigated in terms of emulsion type and their loading levels on the mechanical properties of WF/PLA composites. (1) Both types of silanes could be successfully copolymerized with PA to form stable emulsions. (2) With increasing PA loading, the mechanical properties (except for flexural modulus) of the composites increased at first before reaching the maximum values at 4% PA loading and then the properties worsened. However, these values were larger than those of pure composites, especially in cases when PA-silane emulsions were applied. (3) PA modified with silane-1 showed the best coupling effect among all the three PA emulsions. The results can be interpreted that PA emulsions are effective coupling agents for the preparation of high-performance WPCs.