Poly(vinyl chloride) degradation: identification of acidic degradation products, their emission rates, and implications for heritage collections

The degradation of poly(vinyl chloride) (PVC) is a potential risk to the objects themselves and their surroundings. In this work, we study the acidic emissions produced during the thermal degradation of PVC to assess their contribution to indoor pollution and to improve the understanding of hydrogen chloride (HCl) emissions. With surface emission experiments, we have shown that the process of HCl emissions exhibits a two-phase behaviour. Prediction of HCl emission rate at 25 °C and modelling the steady-state concentration of HCl in a museum storage box enabled us to conclude that PVC objects emit HCl at rates that are too low to significantly contribute to environmental pollution in heritage collections. However, we demonstrated significant formation of formic and acetic acid. The latter is likely the main acidic compound responsible for the negative impact in the paper Oddy test, observed for all the tested PVC materials.