CHANGES IN H-BONDING OF CELLULOSE DURING SOLVENT PURIFICATION TREATMENT (ACETONATION)

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. Ar the same time, acetone is classified as a dipolar aprotic hydrophilic solv ent, i.e., hydrogen bond acceptor (HBA), (Frey-Wyssling 1953; Bar et a l. 1972; Isaacs 1974). The changes caused in hydrogen bonding of the c ellulose by acetone were irreversible. The increase of acetone concent ration was found to be associated with a significant systematic increa se in absorbance height of OH stretching, i.e., provision of weak hydr ogen H-bond. In other words, the accessibility of cellulose was progre ssively increased with the increase of acetone concentration. Investig ation into the solvent purification treatment has also revealed that o ther factors such as type of acid, acid concentration, temperature and residence time have variable effects on hydrogen bonding of the treat ed material. However, the solvent's (i.e., type of acid catalyst) effe ct 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 labele d acetone (99 %) were used in investigation of possible covalent react ion of acetone with cellulose. The C-13 CP/MAS NMR spectrum of cellulo se 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, respec tively. These peaks have been verified to be methyl groups. This has b een considered as an evidence that the acetone has reacted covalently with cellulose even in the presence of water.