Impact of hydrothermal and alkaline treatments of birch kraft pulp on the levelling-off degree of polymerization (LODP) of cellulose microfibrils

Abstract

The levelling-off degree of polymerization (LODP) is typically considered an apodictic number of each cellulosic source that relates to the length of its cellulose crystallites. In this study, we have performed hydrothermal and alkaline treatments on bleached birch kraft pulp to adjust the xylan content, and the resulting pulps have been subjected to acid hydrolysis to determine their LODP. The results show that hydrothermal treatments promote longitudinal alterations in the supramolecular structure of cellulose, represented by a linear decrease in the LODP with lowering the xylan content in the pulp. Moreover, a decrease in LODP is also observed after alkaline extraction of the birch kraft pulp, but the decrease as a function of xylan content differs from that observed after hydrothermal treatments. The results appear to indicate that the LODP is rather an artifact introduced during processing of the material than a true measure of the length of the crystallites in the native cellulose source.