Radiation-induced migration of additives in PVC-based biomedical disposable devices Part 2. Surface analysis by XPS

Extruded parts of non-sterilized and P-irradiated (25 and 50 kGy) plasticized poly(vinyl chloride) (PVC) used for disposable medical devices have been studied to investigate the effect of sterilization on surface chemical composition. The polymer surfaces were analysed using angle-resolved x-ray photoelectron spectroscopy. The inner surface of the blood tubing lines showed a fairly smooth surface both before and after sterilization, so a laterally homogeneous surface can be assumed for XPS analysis. The XPS survey spectra exhibited no signals besides carbon, chlorine, oxygen and calcium. Detailed analysis of the regions showed the C 1s, Cl 2p and O 1s signals to be multi-component, presenting signals of the PVC, the plasticizer and the other additives. Binding energies remained constant irrespective of P-radiation dosage, but the amount of chlorine component at 198.4 +/- 0.1 eV (associated with modified PVC) decreased with sterilization dosage. Angle-resolved XPS revealed that this component is located at the outermost surface of the polymer. It can be hypothesized that the production processes themselves (extrusion and/or injection molded) already induce modifications of the polymer surface and also lead to surface segregation of the plasticizer. During the subsequent thermal sterilization of the polymer dehydrochlorination continues but, because of the very short time required by the beta-irradiation technology to sterilize devices, the atmospheric oxygen is unable to diffuse into the irradiated material, thus inhibiting further side-degradation of the materials, such as thermo-oxidative degradation. Copyright (C) 2003 John Wiley Sons, Ltd.