Characterization of the cellulosic residues from lithium chloride N,N-dimethylacetamide dissolution of softwood kraft pulp

In contrast to hardwood kraft pulps, softwood kraft, pulps are not completely soluble in LiCl/DMAc. Characterization of the undissolved fraction was made in order to obtain an understanding of the reason for its limited solubility. It was found that the residue consisted mainly of latewood fibers. In comparison with the initial pulp, the residue contains a higher relative amount of mannan, lignin and nitrogen. The nitrogen was assumed to originate from degraded proteins retained in the pulp. In contrast, the softwood pulp xylan seems to be easily dissolved and mainly amorphous structures were present in the residue. On the addition of LiCI/DMAc, gel formation occurs, probably caused by the glucomannan content of che softwood kraft pulp. The gel formation also seems to be the main reason for the limited solubility of pulps with low lignin content. (C) 1997 Elsevier Science Ltd.