Investigation of the structural changes in LDPE and XLPE induced by high electrical stress

It is shown that the application of high electrical fields at power frequency causes dramatic changes in the spectra of LDPE and XLPE polymers. The field creates intense Raman-induced photoluminescence but this decays with time, the characteristic polyethylene Raman spectrum is suppressed and new Raman lines appear. One of these lines indicates that unsaturated C=C bonds are being generated. There is also evidence from scanning probe microscopy that the field destroys the lamella structure and can create 10 nm wide cracks. It is suggested that the high electrical fields create mechanical forces that gradually destroy the crystalline lamella structure of polyethylene by polymer chain disentanglement, the molecule scissions and free radical production. The outcome is a void network or craze conducive to tree propagation