Initiation mechanism of electrical tree and deteriorated region in polymers

A detailed chemical analysis and electron microscopic observation of the deteriorated region which is the first stage of tree initiation was carried out in LDPE (low-density polyethylene). Chemical analysis by micro FT-IR and Raman micro-probe techniques show that numbers of carbonyl groups (C=O) and double bonds of C atoms (C=C) in the deteriorated region are higher than those in normal polyethylene. This result strongly suggests that the polymer chain is scissored in the deteriorated region. It is observed by SEM that many small voids and cracks exist in the deteriorated region. TEM observation and the RAMAN difference spectrum show that the lamella of LDPE disappears and the amorphous part increases in the deteriorated region