From LDPE to XLPE: Investigating the change of electrical properties. Part II. luminescence

Luminescence experiments have been used to probe the nature of trapping sites and the dynamic behavior of charge carriers in low density polyethylene (LDPE), antioxidant containing LDPE (LDPE+AO) and cross-linked polyethylene (XLPE). It is shown that deep traps of different natures are present in these materials. For example carbonyl functions provide deep traps in LDPE. New traps are seen in LDPE+AO and XLPE, associated with the anti oxidant itself or with its reaction produces, and to the by-products of the cross-linking reaction. Among those, acetophenone, cumyl alcohol and α-methylstyrene cannot account for the observed spectra. It is shown, in addition, that two XLPE compounds based on two different base resins exhibit the same behaviour demonstrating that the chemical and/or structural modifications introduced by the cross-linking process itself control the charge storage in XLPE. The electrical properties of the same materials are discussed in the light of the work reported in pt.I see ibid., vol.12 no.3 p.438-46, (2005).