Effects of coupling agents on thermal behavior and mechanical properties of wood flour/polypropylene composites

The efficiency of two coupling agents in wood-polymer composites was investigated in this study. Thermal behavior of neat polypropylene, wood flour/polypropylene composite, maleated anhydride polypropylene-reinforced wood-polymer composite, and oxidized polypropylene-reinforced wood-polymer composite was investigated by means of differential scanning calorimetry and scanning electron microscopy in order to obtain information on the dispersion of the wood flour in the polymeric matrix, on the crystallization kinetics of polypropylene, and the macrostructure of its composites. The results confirm the expected nucleant effect of wood with and without the coupling agents used. The wide angle X-ray diffraction patterns indicated enhanced compatibility between polypropylene and wood with the addition of coupling agent. As a coupling agent, maleated anhydride polypropylene had a better performance in wood-polymer composites than polypropylene oxide and neat polypropylene because of its stronger interfacial bonding. Coupling agents help overcome the polarity disparity increase. All the results showed that with maleated anhydride polypropylene, oxidized polypropylene or without any coupling agent, wood flour acted as nucleating agent and increased the crystallization rate of polypropylene. For the composites, wood with maleated anhydride polypropylene was a more effective nucleating agent for polypropylene than wood with oxidized polypropylene. The mechanical properties were evaluated and the samples with coupling agent showed superior results like tensile and flexural properties.