The effect of wood particle size distribution on the mechanical properties of wood–plastic composite

Commercial wood flour of pine (Pinus densiflora) was used as an experimental material. It was milled with different milling times 0, 10, 20, 30, 40, 60, and 120 min to investigate the effect of their particle size distribution on the mechanical properties of the wood–plastic composite. Two kinds of drying conditions, 7 days of freeze-drying at a temperature of −45 °C and heat drying (80 °C) for 24 h were applied. Polypropylene and maleic anhydride-grafted polypropylene were used as a matrix and the compatibilizer of the wood–plastic composite compound, respectively. Particle size analysis showed that an increase in the time of ball milling decreased the wood flour size. However, an excessive milling period of time longer than 40 min corresponded to an increase in the amount of aggregation. Scanning electron microscope images showed the existence of aggregation for the wood flour with 120 min of wet milling time. As the particle size decreased, mechanical properties of wood–plastic composite increased for up to 30 min of wet milling time and then slightly decreased. This behavior might be due to aggregation. The optimum mechanical property was obtained at 30 min of wet milling time under freeze-drying conditions.