Structural changes of amorphous cellulose by thermal and hydrothermal treatments.

Abstract

Structural changes of cellulose molecules in non-crystalline region of cellulosic materials by thermal and hydrothermal treatments were studied by using new amorphous cellulose samples, which were prepared from cellulose/SO2-diethylamine-dimethylsulfoxide solutions. Dry-thermal treatments led to depolymerization of amorphous cellulose and a decrease in moisture contents by forming irreversible hydrogen bonds, and these changes depended on molecular weight of original amorphous samples, heating temperature, and heating time. However, no crystallization was detected by X-ray diffraction analyses. In the case of thermal treatments of amorphous cellulose samples at 80°C and 80% relative humidity for 1-14 days, no change in amorphous structure, molecular weight, or moisture contents was observed. Hydrothermal treatments of amorphous cellulose samples in water at temperature higher than 100°C brought about crystallization to cellulose IV, together with depolymerization and a decrease in moisture contents. These structural changes depended on molecular weight of original amorphous celluloses, heating temperature, and heating time. In comparison with the results of dry-thermal treatments, it was shown that the presence of water remarkably enhanced depolymerization and crystallization to cellulose IV.