Steam Explosion of Aspen Wood. Characterisation of Reaction Products

Abstract

Summary The steam explosion process was used to separate the components of aspen wood. The main goal was to obtain a material with a molecular weight distribution similar to that of dissolving pulp. To achieve variations in fibre structure and molecular weight, two series of steam explosions were made in which the time and temperature were varied according to factorial designs. The resulting pulps were very dark and were therefore bleached with hydrogen peroxide. The bleaching was sufficient to increase the brightness of the exploded material significantly. The resulting lignocellulosic materials as well as the washing water were characterised by carbohydrate analysis, lignin analysis and size-exclusion chromatography. A large variation in the pulp composition as well as in cellulose and hemicellulose molecular weight was obtained merely by varying the time and temperature of the explosions. The results showed that pulps with properties ranging from a high xylan content (7%) and high molecular weight cellulose (900 000) to a low xylose content (< 1%)and low molecular weight cellulose (<40 000) were produced. The exploded material consisted mainly of cellulose, hemicellulose and degraded polysaccharides. The degraded polysaccharides showed up as lignin in the Klason lignin analysis and in measurements of kappa number.