The Effects of Wet-Milled Wood Flour on the Mechanical Properties of Wood Flour/Polypropylene Composites

The sizes and shapes of wet ball-milled wood flour were investigated based on their average particle size, size distribution, their solution viscosity, and scanning electronmicroscopy images. The ball-milling conditions were combinations of rotational speed (150, 200, and 250 rpm) and milling time (1 to 16 h). The average diameter of the wood flours decreased and the degree of fibrillation of the wood fibers increased with the ball-milling time at each rotational speed. Ball-milled wood flours having the same average particle size had similar surface fibrils that were tens to hundreds of nanometers wide. Ball-milling at 200 or 250 rpm could pulverize just as effectively as that at 150 rpm because the size reduction and fibrillation progressed more quickly. Tensile and bending properties of the composites prepared from the ball-milled wood flour (4 wt% in polypropylene) were evaluated. Morphological changes in the wood fillers had little effect on the properties of the composites. The tensile and bending properties of the composites containing the wood filler were 10% higher than those for the unfilled resin.