Watertrees in polyethene studied by luminescence and FTIR microspectrometry

Specific groups in water trees have been characterized by Fourier transform infrared (FTIR) microspectrometry. The stability of these groups with respect to several solvents was studied, and the luminescence of water trees was compared with their methylene blue image. The water tree samples were taken from four cables aged in the laboratory or in service. They were luminescent, although in one case very weakly, and the luminescent areas corresponding closely to the stained regions. Water trees are polar regions in polyethene, as evidenced by an immersion and evacuation experiment. The chemical components of water trees show some variety. The groups resulting from immersion could not be washed out by selected solvents. An interaction between some of these groups and the solvents could, however, be established by FTIR microspectrometry. In the cases investigated, the water trees seem to contain carboxylate groups attached to the polyethene. If so, this might be the result of an oxidation process of which carboxylate is the main product rather than ketones or aldehydes