Mechanical Properties and Dimensional Stabilities of Wood-Polypropylene Composites Prepared using Mechanochemically Acetylated Japanese Cedar (Cryptomeria japonica) Wood Meal

The scale-up of a mechanochemical acetylation operation using 100-L ball mills was performed to produce acetylated Japanese cedar (Cryptomeria japonica) wood meal for wood-polypropylene composite (WPC) production. Finely and coarsely acetylated wood meals (AWMs) were successfully produced with approximately 21% and 19% weight percent gains (WPG), respectively, which was close to the theoretical value. The mechanical properties of WPCs showed similar, rather weak strength compared with the AWM-filled WPCs without maleic anhydride-grafted polypropylene (MAPP) as a compatibilizing agent; however, coarse AWM-filled WPCs showed similar or higher mechanical properties than untreated wood meal (UWM)-filled WPCs when MAPP was added. Clear enhancements in the dimensional stability of AWM-filled WPCs were observed, but no significant differences in dimensional stability were observed between WPCs filled with fine and coarse AWMs, even when MAPP was added. Morphological analyses of the fracture surface showed the retention of some wood cell wall structures in coarse AWM, and fine loadings of the thermoplastic into the lumen were clearly observed. These properties were not found on the fracture surface of fine AWM-filled WPCs; therefore, high polymer loadings into the retained wood structure with high interfacial adhesion by MAPP could be suggested for improving the mechanical properties of coarse AWM-filled WPCs.