Effects of ultraviolet photon irradiation on the dielectric properties of biodegradable polymers

Three kinds of biodegradable polymers, poly-L-lactic acid (PLLA), polybutylene succinate (PBS), and polybutylene succinate adipate (PBSA), and low-density polyethylene (LDPE) as a reference were irradiated for 30 minutes by ultraviolet (UV) photons from a KrCl excimer lamp. It has become clear that the three biodegradable polymers are far more susceptible to UV photons than LDPE since they absorb UV photons very intensely in the vicinity of the irradiated surface. Space charge distribution profiles show that charge carriers are trapped near the irradiated surface. The conduction current increases by the UV-irradiation in all the biodegradable polymers. Instrumental analyses show that the samples were decomposed by photoinduced oxidation. Furthermore, the absorption spectra indicate the appearance of conjugated double bonds. Such structural changes induced seem to be responsible for the higher conductivity and the charge trapping.