AbstractThe effects of acetylation of wood flour with vinylacetate and the content of Maleic Anhydride Polypropylene (MAPP) coupling agent before compounding were evaluated relative to water absorption and thickness swelling. Hot water was used to extract materials of sawdust fir flour before acetylation. Fir flour was successfully acetylated using vinylacetate (VA) in the presence of potassium carbonate. The modification was confirmed by the weight percent gain (18.8%) and Fourier transform Infrared (FTIR) spectroscopy. The acetylated or control wood flour was mixed with MAPP coupling agent (0, 3, & 6 wt%) at 60 rpm and 160 °C, followed by extrusion. The wood plastic composite (WPC) was made by hot pressing at 200 °C and 25 MPa for 5 min. Specimens were exposed to white-rot decay for 16 weeks. In addition to the weight loss due to fungal treatment, water absorption, thickness swelling, and contact angle of the acetylated and decayed samples was investigated. Increasing the percentage of MAPP was found to decrease the percentage of weight loss, water absorption, and thickness swelling in all of the samples. In contrast, increasing the MAPP percentage increased the contact angle in all samples. The SEM micrographs revealed that the bonding between fibers and polymeric material was improved and strengthened by MAPP addition.