Abstract
This study compared different ageing parameters to promote vented water tree growth and examined staining and analysis methods to visualise water trees in PP-TPE, using homopolymer XLPE as a reference. Samples were abraded with \#120 or \#240 graded sandpaper to increase the insulation surface roughness and then aged in salt water (146 days) or tap water (161 days). Ageing in saltwater resulted in a higher density of vented water trees than in tap water. Increased surface roughness induced more inception sites and higher vented water tree density. Heating PP-TPE samples to 100∘C during slicing reduced surface stress whitening. Staining with Methylene Blue and Rhodamine B provided comparable contrast enabling visualisation of water trees in PP-TPE. However, the colour in the samples stained with Rhodamine B faded after 24 hours and required a rehydration procedure to restore the contrast.