A size exclusion chromatography study of cellulose degradation

The degradation of cellulose is an important factor in the life of electric al insulation in power transformers and in the longevity of paper archives. Traditionally, degradation has been studied by following the decrease in t he viscometric degree of polymerisation (DP) in a solvent such as copper et hylenediamine (CUEN). In this paper, we report a study of molecular weight distribution (MWD) changes in cotton linters, measured by size exclusion ch romatography in dimethylacetamide/lithium chloride (DMAc/LiCl) solvent, dur ing accelerated ageing in the laboratory. The initial mono-modal distributi on changes to a multi-modal distribution during ageing, but eventually retu rns to mono-modal as the DP of the cotton reaches a limiting value of 150-2 00. Such complex changes in the MWD cannot be reflected truly in any averag e value such as the DP, nevertheless we show that the number average molecu lar weight (M-n) changes with time in very much the same way as viscometric DP and the changes can be fitted to the same kinetic model. The general tr end is that the polydispersity of the material increases with ageing, as th e distribution broadens, but the scatter in the data prevents any accurate trend analysis. The intermediate peak positions indicate preferential sciss ion of molecules near the centre. (C) 2000 Elsevier Science Ltd. All rights reserved.