New results from a study on the degradation of Co60 γ-rays and 5 MeV 4He2+ ion irradiated unplasticised polyvinyl chloride (PVC) are presented with focus on the off-gassing and post-irradiation evolution of the plastic. Various reaction mechanisms and possible intermediates and products are discussed. PVC powder samples with number average molecular weight of 22, 47 and 99 kDa, and unplasticised PVC film were used. The production and post-irradiation release of HCl and H2 were measured with ion and gas chromatographic methods, respectively. Experiments employing an electron scavenger (nitrate) were made in PVC-aqueous system to investigate the origins of the radiolytically produced H2. The post-irradiation evolution of PVC was followed with EPR, FT-IR, Raman and UV/VIS spectroscopy. Thermal methods and gel permeation chromatography (GPC) were used to assess the effects of radiation on some properties of the plastic. The ion chromatography (IC) measurements were based on the assumption that the yield of Cl- represents that of HCl. In the γ-radiolysis of PVC powder mixed with water, G(Cl-) was about 13 ions per 100 eV (plateau region). The H2 yield was determined in aerated samples and in water mixtures. G(H2) with γ-rays in aqueous mixtures exhibited a maximum value at about 40 weight % water. As little as 1 mM NaNO3 reduced significantly the G(H2) values. Irradiated PVC samples changed colour with the extent of discoloration dependent on the applied dose and irradiation environment. No significant post-irradiation evolution of the chromophores was observed by FT-IR or UV/VIS. The EPR spectra evolved with time. The kinetics at the doses employed have a fast and a slow component due to formation of short and long-lived radicals. The fates of the polyenyl radical in vacuo and the peroxyl radical in air are elucidated. The GPC results showed a molecular weight distribution with a smaller mean in the irradiated samples compared to unirradiated PVC. This change is related to HCl loss and main chain scission processes. However, the thermal analysis did not show radiation-induced changes in the thermal stability of the polymer at the doses considered.
|Date of Award||1 Aug 2012|
- The University of Manchester
|Supervisor||Simon Pimblott (Supervisor)|