Tree growth in a propylene/ethylene copolymer: relationships between electrical activity during growth and the structure, chemistry and properties of the trees that result

In this paper, we consider electrical treeing in a clarified propylene/ethylene copolymer; our interest in this stems, primarily, from its high optical clarity, which permits the acquisition of images of evolving trees (tree structure and light emission). In this paper we consider tree growth in this material and relate the discharge activity during growth, determined both through observations of optical emission and measurements of partial discharges in the external circuit, to the form of the trees that evolve. In particular, confocal Raman microprobe spectroscopy has been used to explore the local chemical composition, since this technique has the potential to provide spectroscopic data at high spatial resolutions (lateral ∼1 μm: vertical ∼2 μm) from within optically transparent media.