Pulverization and Chemical Modification of Wood in One Pod: Acetylation Behavior of Wood by Mechanochemical Processing with Rod-Milling Treatment

The acetylation behavior of wood during mechanochemical processing, which is a solvent-free treatment involving simultaneous grinding and chemical modification in a pod, was monitored by heteronuclear single quantum coherence-nuclear magnetic resonance (HSQC-NMR). In this research, acetylated wood powders (AcWPs) with different weight percent gain (WPG) values were prepared via mechanochemical processing and monitored. First, the primary hydroxyl groups of polysaccharides and lignin were acetylated during the initial reaction process. At this stage, a small portion of the benzyl hydroxyl groups in lignin were also acetylated despite their low reactivity. Subsequently, as the WPG increased, the secondary hydroxyl groups of the polysaccharides began to be acetylated. In this middle stage, almost all primary hydroxyl groups in most of the polysaccharides and lignin, except for a small fraction of those in cellulose, were acetylated. In the final stage, almost all hydroxyl groups in the polysaccharides and lignin were acetylated, although a few hydroxyl groups in cellulose and a few secondary hydroxyl groups in xylan and lignin remained. Then, we investigated the effect of mechanochemical acetylation on thermal resistance by using thermogravimetric analysis. Overall, mechanochemical acetylation markedly improved the thermal resistance of the obtained AcWPs.