Adsorption of cationized barley husk xylan on kraft pulp fibres: influence of degree of cationization on adsorption characteristics

A water-soluble (glucurono)arabinoxylan (GAX) was isolated from barley husk using chlorite delignification followed by alkaline extraction and enzymatic purification of the extract. The isolated xylan was shown to adsorb on bleached softwood kraft fibres, but the degree of adsorption was rather low under the applied conditions. This can be explained by the inhibited adsorption of GAX molecules with a relatively high degree of arabinofuranosyl substitution, as indicated by iodine complexation and neutral carbohydrate analysis of the non-adsorbing xylans. In order to increase the driving force for adsorption of the more highly substituted GAX, the xylan was cationized through a reaction in an aqueous alkaline medium with 2,3-epoxypropyltrimethylammonium chloride (EPTMAC). The chemical modification of xylan was confirmed by using 1 H- 13 C HSQC (Heteronuclear Single Quantum Coherence) NMR, and was quantified by using elemental analysis. The GAX cationization, which introduced cationic charge densities ranging from 110 to 740 μeq/g, was shown to increase the rate and magnitude of adsorption extensively, due to the induced electrostatic interaction between the anionic fibres and the cationic xylan. Similar to non-modified xylan, cationic xylan possessed a non-electrostatic cellulose surface affinity, as shown by adsorption at high ionic-strength and on esterified (carboxyl-free) pulp fibres. \ua9 2009 Springer Science+Business Media B.V