Low temperature thermal degradation of cellulosic insulating paper in air and transformer oil

The thermal degradation of cellulose in the form of Kraft insulating paper has been studied in air for up to 140 h and in transformer oil for up to 3500 h in the temperature range 60–120 °C using measurements of the degree of polymerization (DP) and (in oil) analysis of furanic degradation products. Degradation was faster in air than in oil. The DP decreased from the original value of 1.2 × 10³ to a limiting value in the range of 300–900 depending on temperature and degradation conditions. The variation of the DP with degradation time was consistent with two mechanisms, one in which the first‐order rate constant decreased exponentially with time, and another in which only a limited number of chain bonds were scissionable. The degradation rate was first order in scissionable bonds. The major furanic degradation products were 2‐furaldehyde, 5‐hydroxymethyl‐2‐furaldehyde and furfuryl alcohol. Their concentrations continually increased over the timescale of the experiments. © 2001 Society of Chemical Industry