Interfacial compatibility of wood flour/polypropylene composites by stress relaxation method

To investigate the interfacial compatibility of wood flour/polypropylene (PP) composite, compressive stress relaxation curves at different temperatures (26, 40, and 60 degrees C) were determined at various wood contents (0, 20, 30, 40, 50, 60, and 70%) without coupling agent and further determined at wood contents of 50 and 60% by using maleic anhydride grafted polypropylene (MAPP) and silane as coupling agents. The apparent activation energy (?E) was also calculated according to the Eyring's absolute rate reaction theory. The results showed that the stress relaxed faster at higher temperatures. ?E of wood flour/polypropylene composites without coupling agent showed the highest value at wood content of 40%, suggesting that the best interfacial compatibility between wood and PP occurred at 40% wood content. Adding coupling agents increased ?E obviously at higher wood contents (50 and 60%). With the increasing loading level of coupling agents, ?E increased at first and then decreased gradually or finally reached a constant level depending on the type of coupling agent. The optimal loading of coupling agent corresponding to the highest ?E value was related to wood content and the type of coupling agent. Within the experimental conditions used in this study, the optimal loading level for MAPP was 2% at both wood contents while for silane it was 1.5% and 2% at wood content of 50 and 60%, respectively. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012