The effect of barley husk arabinoxylan adsorption on the properties of cellulose fibres

This study investigates the adsorption of (glucurono)arabinoxylan (GAX) on cellulose fibres and the properties thereof. A water-soluble GAX, from barley husks (Hordeum vulgare), was isolated using chlorite delignification and alkaline extraction followed by enzymatic purification. The isolated GAX fraction showed an arabinose to xylose ratio of 0.22 and a weight average molar mass of 20,200 g/mol, as determined by size exclusion chromatography (SEC) in DMSO:H₂O. The GAX was adsorbed on cellulose fibres under well controlled conditions, where temperature and initial concentration of GAX proved to be important parameters in controlling the level of adsorption. The adsorption process was also dependent on xylan molecular structure. Carbohydrate analysis on the modified fibres showed a preferential adsorption of low substituted xylans (arabinose to xylose ratio of ∼0.10). During the adsorption process the GAX solution was analyzed using SEC-RI-MALLS in aqueous solvent, which demonstrated a molecular xylan adsorption on cellulose fibres. Additionally, a decrease in light scattering responses, which corresponds to an adsorption of aggregated xylan and/or xylan with a great tendency towards self-association, could be observed during the adsorption process. This was demonstrated by adsorption of GAX on regenerated cellulose fibres (Lyocell), which compared to native fibres possesses a relatively smooth fibre surface. Atomic force microscopy analysis visualised a heterogeneous decoration of the Lyocell fibres with xylan agglomerates. The effect of GAX adsorption on paper strength was also investigated. A GAX modified kraft pulp showed an evident increase in tensile strength, which might be due to a retained fibre–fibre bonding ability for xylan coated fibrils after drying and rewetting.