Thermal degradation of γ-irradiated PVC: II-Isothermal experiments

A previous study carried out using dynamical thermogravimetry showed that radio-oxidation enhances the thermal degradation of poly(vinyl chloride) (PVC). In order to gain a better understanding of the mechanisms responsible for this thermal instability, a series of isothermal treatments were performed on radio-oxidized PVC. Two materials were studied: additive-free PVC and plasticised PVC. The samples were pre-degraded using γ-radiation under air at room temperature. The isothermal degradation at 120 and 150 C of radio-oxidized PVC was then investigated using thermogravimetry followed by mass spectrometry, in-situ infrared spectroscopy and thermodesorption coupled with gas chromatography mass spectrometry. For both pre-irradiated polymers the major weight loss appears after 30 min of heating at 120 C or 150 C. The gases responsible for this weight loss are mainly HCl, a small amount of benzene and CO₂. Desorption of degradation molecules resulting from radio-oxidation also contributes to the weight loss. (authors)