Characterisation of dissolved spruce xylan in kraft cooking

Xylan dissolved during kraft cooking and later redeposited on fibre surfaces has been shown to affect the paper strength properties. Earlier studies have shown that the xylan characteristics, rather than simply the amount of xylan, influence the strength enhancing effect of xylan. In order to obtain an optimal use of the xylan, it is of interest to understand what the beneficial xylan characteristics are and how cooking conditions affect the characteristics. In this study, kraft cooking of spruce chips was performed at varied cooking conditions and the xylan in the black liquor was characterized. It was found that dissolved spruce xylan had a much higher amount of bound lignin compared to previous studies on xylan dissolved from hardwoods. The ionic strength of the cooking liquor affected the amount of xylan dissolved as well as the uronic acid content of the xylan.