Controlled accessibility Lewis acid catalysed thermal reactions of regenerated cellulosic fibres

A combination of techniques have been used to characterise lyocell regenerated cellulose fibre subjected to low-moisture thermal-catalytic reactions with zinc chloride Lewis acid. Application from non-swelling ethanol reduces catalyst accessibility, but at high temperatures migration takes place through the internal fibre morphology. The extent of chain scission is reduced at lower temperatures, leading to a higher leveling-off degree of polymerisation (LODP). In contrast, application of zinc chloride from water results in a lower LODP, due to the more even distribution of catalyst. The weights of extractable polymer material increase according to two separate rate constants, following established semicrystalline models. A higher Arrhenius activation energy for chain scission is seen for zinc chloride application from ethanol, which may be due to the physical mobilisation of the cellulose polymer at high temperature, associated with a cellulose Tg. This may also aid recrystallisation. Cellulose dehydration endotherms and pyrolysis exotherms are shifted to lower temperature for application of zinc chloride from ethanol compared to water, which may be the result of a higher local concentration of catalyst and a faster reaction onset. © 2010 Springer Science+Business Media B.V.