Changes in H-Bonding of Cellulose During Solvent Purification Treatment (Acetonation)

Abstract

In this study, acetone was used as the solvent of purification due to the fact that acetone has the ability to penetrate into the cellulosic material and bring about considerable stereochemical changes. At the same time, acetone is classified as a dipolar aprotic hydrophilic solvent, i.e., hydrogen bond acceptor (HBA), (Frey-Wyssling 1953; Bax et al. 1972; Isaacs 1974). The changes caused in hydrogen bonding of the cellulose by acetone were irreversible. The increase of acetone concentration was found to be associated with a significant systematic increase in absorbance height of OH stretching, i.e., provision of weak hydrogen H-bond. In other words, the accessibility of cellulose was progressively increased with the increase of acetone concentration. Investigation into the solvent purification treatment has also revealed that other factors such as type of acid, acid concentration, temperature and residence time have variable effects on hydrogen bonding of the treated material. However, the solvent's (i.e., type of acid catalyst) effect on hydrogen bonding appears to be the one most crucial among these parameters when other variables are kept constant. Also, in this work normal acetone (e.g., C-13 natural abundance is 1.11 %) and C-13 labeled acetone (99%) were used in investigation of possible covalent reaction of acetone with cellulose. The C-13 CP/MAS NMR spectrum of cellulose with normal acetone has shown no signal at the methyl group region. However, remarkably, the spectrum of the residual cotton treated with C-13 labeled acetone has given two peaks at 26.5 and 31.8 ppm, respectively. These peaks have been verified to be methyl groups. This has been considered as an evidence that the acetone has reacted covalently with cellulose even in the presence of water.