Staining of water trees with methylene blue explained

摘要

Staining with a methylene blue solution, a popular technique fornachieving the required high contrast images of water trees, was carriednout at 70° C. It is shown that methylene blue stains the completentree, which justifies water tree length measurements after staining. Thenwater tree is not stained exclusively, but rather faster and probably tona higher degree than the polyethylene. Comparing optical microscopynimages of water trees before and after staining, it was found that thenentire tree becomes visible. Comparison of FTIR (Fourier-transformninfrared) spectra measured before and after staining did not indicatenthat a chemical reaction is required in the staining process. Inngeneral, the staining of water trees with methylene blue can benexplained by mere diffusion. The enhanced temperature of 70° C helpsnto increase the permeability of the polyethylene