DIFFUSION OF OXYGEN INTO IRRADIATED POLYPROPYLENE FILMS

Polypropylene (PP) film samples were prepared using Isotactic Polypropylene (IPP) granules which were hot pressed and cooled by three different methods (annealing, quenching water+ice and quenching liquid nitrogen) in order to obtain three different crystalline states with various thicknesses (95,135,150,200 mu m). These PP films were gamma-irradiated with the sterilization dose of 25 kGy in vacuum at room temperature. The diffusion coefficient of oxygen into irradiated PP films were calculated by using Fick's second law of diffusion and by following the change in ESR spectra with time. It is shown that diffusion of oxygen has an inverse relation with crystallinity and film thickness. With increasing film thickness, it was observed that the diffusion coefficients of oxygen into irradiated PP film with different crystallinities were converging to a single value.