Production of HCl and H2 in the radiolysis of PVC

Complete text of publication follows. PVC is a thermoplastic polymer commonly encountered in nuclear waste management, disposition and disposal. The effects of ionising radiation on its performance are insufficiently understood. Our study has focused on the postirradiation degradation of γ and 4He ion irradiated PVC and on the release of potentially corrosive and explosive gases, such as HCl and H2, from deaerated, aerated, and water mixtures of PVC. Experiments were performed with PVC powder samples with number average weight of 22000 D and with unplasticised PVC film. The samples were irradiated with 60Co γ-rays and 4He ions at room temperature. The production and post-irradiation release of HCl and H2 was measured using ion and gas chromatography, respectively. The post-irradiation evolution of the solid plastic was examined using GPC and EPR, FT-IR and UV/VIS spectroscopy. UV/VIS absorbance spectroscopy was performed on PVC powder dissolved in THF. FT-IR transmittance spectra were obtained from PVC powder in air. EPR spectra were taken after γ-irradiation of PVC powders in air and vacuum, and for PVC film irradiated with γ-rays and 4He ions. GPC measurements were made on both pure and irradiated PVC powder and PVC film. The yield of HCl from γ-radiolysis of PVC powder is 19.6 molecules/100 eV. Chloride ion is released from the polymer for days following radiolysis. The H2 yield with γ-rays is about 0.23 molecule/100 eV and 0.45 molecule/100 eV with 4He ion radiolysis. Visually, irradiated PVC samples change from white to a green-brown colour with the extent of discolouration dependent on the applied dose and irradiation environment. No significant post-irradiation evolution of the chromophores was observed by FT-IR or UV/VIS, but the EPR spectra obtained evolve with time. GPC analysis showed a molecular weight distribution with a smaller mean in the irradiated samples compared to pure PVC. This change is related to HCl loss and possibly to main chain scission (fragmentation). Various reaction mechanisms and possible products will be discussed. This work was supported by the UK Nuclear Decommissioning Authority and by the Office of Basic Energy Science of the US Department of Energy.