Controlled thermo-catalytic modification of regenerated cellulosic fibres using magnesium chloride Lewis acid

The Lewis-acid catalytic reactions of magnesium chloride with regenerated cellulosic fibres under baking conditions can be interpreted using existing semi-crystalline morphological models. Reaction at 180 °C is associated with chain scission, which takes place randomly within the accessible regions of the fibre structure. This causes a rapid reduction in the cellulose degree of polymerization, which stabilizes at a limiting value, analogous to that observed with wet-state mineral acid catalysed hydrolysis. A slower scission-reaction is also observed, believed to be due to the liberation of single glucan units from crystallite ends, again analogous to wet-state mineral acid hydrolysis. Dry-state catalysis is promoted by thermal molecular motion, allowing migration of catalyst ions and also conformational flexing of the cellulose polymer, which also induces a small amount of recrystallisation at crystallite lateral surfaces. Differences in the dry-state reaction have been observed for lyocell, viscose and modal regenerated fibres, which can be related to differences in crystallinity and resulting accessibility of the magnesium chloride catalyst. For lyocell the accessibility towards magnesium chloride is lower than found with mineral acids, which may be significant in the development of treatments to promote mechanical fibrillation, without sacrificing fibre tensile properties.