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

Abstract

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 wetstate 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.

Carbon-13 solid state NMR investigation and modeling of the morphological reorganization in regenerated cellulose fibres induced by controlled acid hydrolysis

“…This finding is supported by a separate kinetic analysis of the reduction in DP during hydrolysis, by previously described method, based on the Ekenstam model (Domvoglou et al 2009). The data in Table 1 also includes an estimate of LODP and the apparent fraction of reactive polymer bonds (a), which is consistent with the greater average length crystallites in lyocell compared to viscose and modal.…”

“…The viscosity average degree of polymerization (DP) was calculated as described in previous work (Domvoglou et al 2009). Measurements were carried out on water-only treated samples and on the solid residues of hydrolysed samples following neutralization, rinsing and drying.…”

Controlled accessibility Lewis acid catalysed thermal reactions of regenerated cellulosic fibres

“…Bulky, low accessibility enzyme agents are successful in achieving the desired fabric aesthetic, through attack a fibre surfaces and defects (Morgado et al 2000), but so far a replication of their mode of action has not been possible with simple organic or inorganic agents. This new study represents a continuation of previous investigations, which suggested that the local accessibility of Lewis acid salts would be reduced as a consequence of their lower diffusional mobility within the fibre structure under dry-state baking conditions, as reflected in a higher levelling-off degree of polymerisation (Domvoglou et al 2009). However, the application of salts from aqueous solution means that total initial accessibility within the fibre swollen pore structure will always be high, with sufficient polymer chains then available for catalytic attack, causing an unacceptable loss of strength.…”

“…However, the depolymerisation reaction must be carefully controlled, to reach a balance between the subsequent rate of fibrillation of the treated fibre and its tensile properties, which is difficult to achieve in practice. The application of both magnesium chloride Lewis acid and also mineral acids have been investigated (Domvoglou et al 2009;Ibbett et al 2008), which both have high accessibility within the lyocell fibre morphology. Whilst acceptable results have been achieved with both these agents under strict laboratory conditions it is considered that too many variables exist within a commercial textile processing environment for stable optimisation.…”

“…Previous work has demonstrated that the Lewis acid catalysed depolymerisation of lyocell is highly dependent on the extent of accessibility of the acid agents within the fibre (Domvoglou et al 2009). Conditions of lower accessibility are believed to be advantageous, which may allow a delamination of the fibre fibrillar morphology, but without reducing its longitudinal continuity (Ibbett et al 2008).…”