Investigations on the aging of cross-linked ethylene vinyl silane copolymer

Cross-linked ethylene vinyl silane copolymer (EVS) used as an electrical insulation in low voltage secondary cables was examined for its oxidative aging behaviour. Thermal aging of the copolymer was found to consist of three stages. The first stage consisted of an increase in the silane cross-linking induced thermally, the second stage was defined by the consumption of antioxidants with a subsequent increase in oxidation leading to brittle failure as the third stage. The type and concentration of the antioxidants determined the extent of the second stage, influencing the target application of the copolymer. For a copolymer with selected antioxidant concentration, the brittle failure occurring in the third stage could be related to an increase in cross-link density of the copolymer. Aging of the copolymer under UV conditions, resulted first in oxidation, characterized by carbonyl species and polymer unsaturation, leading to brittle failure. There was little or no increase in cross-linking. Under either aging conditions the electrical breakdown strength of the copolymer was retained to above 50% until the samples became brittle. Practical implications of the results from these investigations are discussed