Water-insoluble and soluble glucuronoxylans from eucalyptus pulp and their behavior in alkaline pulping.

Hemicellulose plays a versatile role in plant cell wall by linking cellulose and lignin or impeding lignin removal from sustainable cellulosic fibers. Herein, hemicellulose fractions (glucuronoxylans) of Eucalyptus pulp cooked to various cooking degree were extracted by potassium hydroxide solution and purified with ethanol. The glucuronoxylans are divided into water-insoluble (GXI) and -soluble (GXS) fractions. The release or degradation behavior of glycosylated side-chain of hemicellulose in alkaline cooking was explored according to the separate discussion of GXI and GXS, and take consideration of the effect of extraction temperature on polysaccharide degradation. The GXI is constructed of basically straight xylan chain with high linearity, and GXS contains multi-branches xylan chain. The harsher cooking conditions (corresponding to H factors 317, 586 and 904) and alkaline-extraction temperature significantly influenced the composition and structure, leading more glycosyl side chains removal. More content glucuronic acid (6.04–11.26%) in GXS, which may relate to high branch on xylans and great solubility, while less of glucuronic acid (MeGlcA, 2.28–5.48%) in GXI was accounting for the poor solubility. The glycosyl analyses of the two fractions extracted from different pulp showed that the hexenuronic acid (HexA) converted from MeGlcA in GXI was retained during cooking, while that in GXS was easier to be removed in pulping process. [ABSTRACT FROM AUTHOR]