Fluorescence lifetimes and ageing in irradiated low-density polyethylene

An investigation has been made of fluorescence lifetimes in low-density polyethylene (LDPE). Samples of material 50 μm thick were irradiated in air to various doses between 0 and 1 MGy using an electron accelerator. This caused enhanced and rapid ageing of the LDPE, the behaviour of which was then investigated using a time-correlated single photon counting fluorometer. The results demonstrate that fluorescence is a function of radiation absorbed dose. The greater the dose, the more rapidly does the fluorescence signal decay. This derives from the fact that the structure of the LDPE is changing via crosslinking and oxidation and thus the aged polymer network is unable to vibrate as readily as can unaged pristine material. The results indicate that fluorescence could, in principle, be used as a tool for the condition monitoring of polymer insulation