Modifying cellulose fibers by adsorption/precipitation of xylan

Abstract

Xylan was precipitated on bleached and unbleached softwood kraft pulps (SKPB and SKPUB), a bleached sulfite pulp, and viscose fibers to investigate the influence on physical properties of handsheets as well as to gain more detailed information of the distribution of adsorbed xylan on cellulosic surfaces. The adsorption step was carried out at constant conditions. The values of the parameters were chosen after a series of different adsorption steps (as presented elsewhere) also in regard as a possible industrial application. Afterwards, suspension and physical strength properties of unrefined and refined samples were determined. Refining resulted in a stronger increase in the beating degree of the pulps with additional xylan than the reference samples. The water retention value was not significantly changed. Comparing the tensile index of the handsheets versus the beating degree a remarkable increase in the strength properties was not observed. The investigation of the surface of the SKPB fibers via ATR suggests that precipitated xylan is heterogeneously and nonuniformly distributed. On cellulose model films, particles could be detected via atomic force microscopy. Phase images recorded with OH-functionalized tips suggested that these particles consist of xylan. An inhomogeneous distribution of xylan could be a reason that there is no measurable influence on the strength properties of the handsheets.