Polarization current in gamma irradiated polypropylene: measurements and computer simulation

An investigation is carried out to verify the possibility of using measured charging current to evaluate ageing processes in polypropylene (PP) films. For the tests a well-characterized PP, doped with a known amount of hindered amine light stabilizer and aged by gamma-irradiation with Co⁶⁰. A simulation model that can be very useful for evaluating the status of the material is also discussed. This model is based on the assumption that the slow charging current transient is due to the motion, in disordered matter, of dipole orientation. Assuming that the charge of dipoles is related to the inverse of the relaxation time according to a Gamma distribution function, a good fit between computed and measured values is obtained, in both the first seconds and toward the end of the current transient