Swelling of Valonia cellulose microfibrils in amine oxide systems

Abstract

Cellulose microfibrils from Valonia ventricosa cell-wall fragments were immersed into molten N-methylmorpholine-N-oxide monohydrate (NMMO·H2O), stabilized with n-propyl gallate and kept at 80 °C. The resulting ultrastructural modifications, which were followed by transmission electron microscopy and electron diffraction analysis, showed that within minutes the solvent slowly penetrated inside the crystalline microfibrils and progressed as a wedge in between the cellulose chains without cutting them. Prior to dissolution, a longitudinal subfibrillation of the initial microfibrils occurred, leading to the observation of highly swollen microfibrils, which could reach diameters up to three times larger than those of the initial samples. This mode of swelling is compared with those occurring in other systems, where the intracrystalline swelling of cellulose has been described at the ultrastructural level.Key words: cellulose swelling, Valonia cellulose, N-methylmorpholine-N-oxide.