Electrical treeing in polyethylene: analysis by confocal Raman microprobe spectroscopy

Confocal Raman microprobe spectroscopy, has been used to explore the chemical nature of electrical trees in polyethylene and two distinct classes of tree have been identified. In structures where discharge activity occurs within the body of the tree, the dominant characteristic is massive fluorescence. Where discharge activity is confined to the. tips, the Raman bands of polyethylene are seen throughout the body of the tree, but superimposed upon pronounced fluorescence. Other than at the tips, the G and D bands of sp² hybridized carbon are also seen. The chemical details of both tree types are therefore consistent with the discharge patterns; channels containing graphitic carbon are conducting whereas those that merely contain fluorescent decomposition residues are not. The implications of these results are discussed.