Deposition of xylan isolated from Pennisetum purpureum on fibres of Eucalyptus globulus and characterisation of the composition of the surface xylans by immunolabelling and enzymatic peeling

Abstract

Adsorption of xylan on pulp is a potential method to improve its properties, especially refinability for high quality printing and writing (P&W) paper grades. In this study, elephant grass [Pennisetum purpureum (Schumach.)] xylan was used for this purpose. The xylan was extracted using cold caustic extraction (CCE) from P. purpureum brown pulp, produced by the Soda-AQ process (kappa 20). Xylan resorption was accomplished during the oxygen delignification phase of eucalypt [Eucalyptus globulus (Labill.)] pulp to avoid problems induced by the colour of the lignin-contaminated deposited xylan. Immunolabelling and enzymatic peeling methodologies were compared for the analysis of the spatial distribution of xylan in the fibre wall. The labelling appeared unevenly as faint and brighter patches on fibre surfaces. Increased labelling of xylan was detected on the samples with precipitated P. purpureum xylan. The enzymatic peeling method using a total hydrolysis enzyme mixture yielded a composition gradient as a function of time, showing clear xylose (Xyl) enrichment in the very beginning of the reaction, reflecting hydrolysis of fibre surfaces. Pure xylanase and endoglucanase hydrolyses yielded different product patterns and kinetics compared to total hydrolysis, but interpretation of those results in terms of xylan localisation was not straightforward.