Aggregation of cellulose in lithium chloride/N,N-dimethylacetamide

Hardwood kraft pulps can be completely dissolved in lithium chloride/N,N-dimethylacetamide (LiCl/DMAc). The cellulose and hemicellulose components can be separated by size exclusion chromatography (SEC). The molecular weight distribution that corresponds to cellulose is extended up to the high molecular weight region and the weight average molecular weight (M-w) relative to pullulan of this distribution is high. Light scattering (LS) measurements were conducted on a cotton Linters sample of a similar elution volume as the cellulose portion of the pulp. The true M-w of the cotton linters sample measured by LS was in close agreement with the M-w determined relative to pullulan using SEC. Gaussian curve fitting revealed an additional high molecular weight component, not apparent in the chromatogram of hardwood pulp. Based on this finding the high M-w is suggested to be due to aggregation of cellulose in LiCl/DMAc. The influence of dissolution conditions is discussed and a method for deaggregating the cellulose portion of dissolved hardwood pulps is proposed. (C) 2000 Elsevier Science Ltd. All rights reserved.