The degradation of cellulose is an important factor in the life of electrical insulation in power transformers and in the longevity of paper archives. Traditionally, degradation has been studied by following the decrease in the viscometric degree of polymerisation (DP) in a solvent such as copper ethylenediamine (CUEN). In this paper, we report a study of molecular weight distribution (MWD) changes in cotton linters, measured by size exclusion chromatography in dimethylacetamide/lithium chloride (DMAc/LiCl) solvent, during accelerated ageing in the laboratory. The initial mono-modal distribution changes to a multi-modal distribution during ageing, but eventually returns to mono-modal as the DP of the cotton reaches a limiting value of 150-200. Such complex changes in the MWD cannot be reflected truly in any average value such as the DP, nevertheless we show that the number average molecular 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 trend is that the polydispersity of the material increases with ageing, as the distribution broadens, but the scatter in the data prevents any accurate trend analysis. The intermediate peak positions indicate preferential scission of molecules near the centre.