Abstract:
A thermomechanical pulp, a high yield sulfite pulp, and a high yield solvent sulfite pulp from western hemlock [Tsuga heterophylla (Raf.) Sarg.] wood were investigated to determine the amount of carbohydrate material present and to elucidate the structures of the carbohydrates. The effects of the three pulping processes, which were quite different, on the carbohydrates are compared. Attempts to isolate hemicelluloses from the pulps were only moderately successful. The high lignin content interfered with hemicellulose extraction. However, a xylose-rich hemicellulose and a glucomannan hemicellulose was isolated from each pulp. Most of the pulp materials remained insoluble in the alkaline media ordinarily used for hemicellulose extractions. The structures of the carbohydrate polysaccharides were clarified by the use of the quite new technique of cross polarization/magic angle spinning nuclear magnetic resonance of solid samples. This physico-chemical spectroscopic method is a non-destructive method in which the solid samples are recovered unchanged. The method requires no preparation of derivatives and hence reduces the chance of polysaccharide degradation. It replaces, in part, the classical methylation procedure ordinarily used to determine the positions of linkages in polysaccharides. The xylan, the glucomannans, and the celluloses of the samples reported in this work were shown by carbon-13 cross polarization/magic angle spinning nuclear magnetic resonance of their solid forms to be linked by 1-->4 glycosidic linkages. In addition, peaks at 90 ppm and 85 ppm in the spectra of cellulose samples from the high yield solvent sulfite pulp indicate at least two crystalline polymorphs of cellulose.
