Effects of Coupling Agent and Interfacial Modifiers on Mechanical Properties of Poly(lactic acid) and Wood Flour Biocomposites

To reduce our dependency on depleting fossil fuels and their cost, biocomposites were prepared using polylactic acid (PLA) as a matrix and wood flour (WF) as filler by a twin-screw extrusion method. Because of poor wettability between wood flour and PLA matrix, the properties of the PLA/wood flour composite are not right. Thus, the silane coupling agents (as the surface treatment agent of wood flour) and the interfacial modifiers (various copolymers) have been used to improve their interfacial adhesion. The effects of wood flour content, types of silane coupling agents and their content, interfacial modifiers and their concentration on the properties and morphology of PLA/WF biocomposites were systematically studied in detail, including microstructures, mechanical and rheological properties. The results revealed that the properties of biocomposites were expected to be improved by dispersing wood flour aggregations into microfibrils and improving the interfacial adhesion between PLA and WF with the addition of epoxy silane or ethylene-methyl acrylate-glycidyl methacrylate (EMAGMA). Especially, the interficial modifier of EMAGMA could improve not only the interfacial action but also the impact strength of PLA. Further studies indicated that the co-interfacial modifiers of epoxy silane and EMAGMA could effectively enhance the interaction between PLA matrix and WF and further improve mainly the impact strength and elongation-at-break of PLA/WF biocomposites.