Characterization of alkali-soluble hemicelluloses of hardwood dissolving Pulps

in the first step of the viscose process, pulp is steeped in aqueous sodium hydroxide of about 18% at temperatures up to 50 degreesC removing alkali-soluble carbohydrates. After pressing off the cellulose, which is converted to its alkoxide, the so-called press lye is enriched with undesirable short chain material which is removed by membrane separation processes. A more profound knowledge of the fractions is necessary to improve the separation system and to possibly use them as source for new products. Here, hemicellulose fractions of two pulps extracted at different sodium hydroxide concentrations and fractions obtained from press lye have been characterized with respect to macromolecular properties, functionalities and carbohydrate composition. The results show that the properties of alkali-soluble hemicelluloses depend on the pulp origin and the steeping conditions. The molecular mass and molecular weight distribution were determined and detailed carbohydrate analysis revealed both the building units of the heteropolysaccharides and the amount of fragmentation products. Effort has also been undertaken to elucidate the presence of side chains in the high molecular weight fraction.