Effect of chemical modification of wood flour on long-term hygroscopic behavior of polypropylene composites

This experimental work is aimed at studying the effect of fiber surface modification including alkaline, acetic acid, and benzyl chloride on the long-term water absorption and thickness swelling (TS) of wood flour (WF)-reinforced polypropylene composites. The samples were made by melt compounding and then injection molding. Hygroscopic rates of the samples were evaluated by immersing them in water at room temperature and monitoring moisture sorption and thickness changes for several weeks. The results indicated that chemical modification has a significant effect on the water absorption of composites. The mechanism of water absorption of all samples followed the kinetics of a Fickian diffusion process. The composites modified with acetylation-treated fiber showed the lowest and the unmodified composites exhibited the highest water absorption coefficient. TS of the composites was clearly dependent upon the WF chemical modification. The swelling rate parameter of treated samples is less than those of untreated ones.