The influence of surface chemical composition on the adsorption of xyloglucan to chemical and mechanical pulps

Adsorption kinetics of xyloglucan (XG) onto bleached chemical and mechanical wood pulps were studied to better understand the application of this plant polysaccharide to the modification of key industrial cellulosic materials. Bleached pulps prepared by the kraft process adsorbed significantly larger amounts of xyloglucan than did thermomechanical pulps (TMP) and chemi-thermomechanical pulps (CTMP). The ability of pulps to adsorb xyloglucan was intimately related to the surface amounts of cellulose, lignin and extractives, as determined by electron spectroscopy for chemical analysis (ESCA). The distribution of absorbed XG on bleached pulp fibers was examined with an XG-fluorescein conjugate (XG-FITC), which was prepared by xyloglucan endotransglycosylase (XET, EC 2.4.1.207)-mediated incorporation of fluorescein-labeled xyloglucan oligosaccharides (XGO-FITC) into XG. Fluorescence microscopy revealed that XG-FITC preferentially adsorbed on fiber surfaces, and was adsorbed in higher amounts to chemical pulps than mechanical pulps, as observed for the unmodified parent polysaccharide. Addition of hybrid aspen XET (PttXET16A) and XGO-FITC to bleached and unbleached mechanical pulps indicated that the amount of enzyme-accessible xyloglucan presented on TMP and CTMP surfaces is low.