Thermal degradation kinetics study of polyvinyl chloride (PVC) sheath for new and aged cables.

The thermal degradation dynamics of new and aged PVC sheaths was studied in detail. The results illustrated that compared to new PVC sheath, the onset decomposition of aged PVC sheath mainly happened at higher temperature with larger peak value of mass loss rate. Three model-free methods most commonly used were employed to estimate the activation energy values at different conversions. It was noted that the aged PVC sheath exhibited greater entire activation energy than new PVC sheath. Two thermal degradation regions were observed based on the activation energy variation with conversion. The threshold of conversion for two regions was 0.6 for new PVC sheath and 0.5 for aged PVC sheath. The possible reaction mechanism was predicted by generalized master-plots method. The reaction model corresponding to each region showed observed difference between new and aged PVC sheaths. The compensation effect was also used to calculate the related pre-exponential factor. The variation of thermal degradation behavior could be ascribed to the changes of chemical composition, molecular structure, composition proportion and various additives after thermal aging. Besides, the thermal degradation process was reconstructed by an ANN model and it indicated that the predicted data fitted well with the experimental data.