How xylan effects the breaking load of individual fiber–fiber joints and the single fiber tensile strength

Abstract

Bleached and unrefined softwood kraft fibers were treated with aqueous solutions of xylans and potassium hydroxide (KOH) to vary the amount of xylan present on the fiber surface and within the fiber wall. This was done in order to directly measure the influence of xylan on the joint strength of individual fiber–fiber joints as well as the tensile strength of individual fibers to determine the elastic modulus. The results were compared with two unbleached and unrefined softwood kraft pulps (Kappa 42 and 54). Additional xylan had a statistically significant effect on the mean values of the breaking load of individual fiber crossings. Moreover, the breaking load was strongly affected by the cooking time during pulping. However, no correlation between the optical bonded area and the joint strength was observed. The modulus of elasticity of individual fibers was not influenced by additional xylan or alkaline extraction. The elastic modulus was influenced more by chemical pulping and bleaching. The results indicate that additional xylan on the fiber surface has a strength-enhancing effect on the joint strength individual fiber crossings which also depends on the distribution of xylan. On the other hand, the elasticity of a fiber seems to be more influenced by the morphology and the composition of the fiber walls, especially in the secondary S2 wall.