Acetylation of Ground Pulp: Monitoring Acetylation via HSQC-NMR Spectroscopy

The acetylation of ground pulp (GP) was followed by heteronuclear single quantum coherence-nuclear magnetic resonance (HSQC-NMR) spectroscopy to investigate the relationship between the degree of acetylation and the introduction positions of acetyl groups during this acetylation. We also examined the effect of acetylation on thermal stability. Seven acetyl GPs (AcGPs) with degree of substitution (DS) values of 0.19, 0.29, 0.59, 0.74, 1.04, 1.11, and 1.19 were prepared and analyzed using HSQC-NMR spectroscopy. Acetylation was found to occur first on the primary hydroxyl groups of polysaccharides and lignin, followed by the secondary hydroxyl groups of polysaccharides, and finally the hydroxyl groups at the alpha-position of lignin. The thermal stabilities of the AcGPs were analyzed using thermogravimetric analysis (TGA). The 1% weight loss temperatures of the AcGPs were higher than that of the GP. The acetylation of the primary hydroxyl groups in polysaccharides and lignin and the hydroxyl groups at the alpha-position of lignin was more effective in improving thermal stability than that of the secondary hydroxyl groups in polysaccharides.