Chemical pulping: the influence of xylan on the sensitivity towards fiber damage, xylan added in the oxygen stage

The aim of this study was to investigate if extra xylan added during oxygen delignification of kraft spruce fibers could contribute to reduce the effect of fiber damage introduced during the cook. Two pulps were produced, one with and one without mechanical treatment at the end of the cook. The pulp produced without mechanical treatment was oxygen delignified with xylan added in the oxygen stage. The pulp produced with mechanical treatment was oxygen delignified both with and without xylan added. Results did not indicate that xylan added in the oxygen stage could repair the already introduced fiber damage. Added xylan had a fiber straightening effect as seen earlier when xylan was added in the cook. Xylan added in the oxygen stage resulted in improved tensile strength development. However, the negative effect from introduced mechanical treatment still influenced the strength properties more than could be compensated by the added xylan. SEM-images could not identify any differences between the investigated pulps. It seems likely that the birch xylan added forms a uniform but nonhomogeneous coating on the fiber surfaces. Possibly the xylan has penetrated into the fiber wall to a greater extent compared to previous studies when xylan was added in the cook