TG-FTIR analysis of PVC thermal degradation and HCl removal

The pyrolysis of polyvinyl chloride (PVC) was qualitatively analyzed by TG-FTIR, and HCl removal efficiency of Ca-based additives were semi-quantitatively studied also by means of TG-FTIR. Additionally, the thermodynamic equilibrium modeling was also carried out to understand the formation of HCl from PVC and from mixtures of PVC with different additives. Experimental results showed that the pyrolysis of PVC took place in two steps accompanied by the release of HCl and hydrocarbon, respectively. Almost all Cl transformed to HCl, and hardly any other kinds of Cl compounds were detected. The addition of Ca-based additives extended the second weight loss step of PVC, but they did not affect the release time when the maximum HCl concentration appeared. The maximum HCl concentration decreased according to the increase of additive amount, that is to say, the HCl removal efficiency increased as the Ca/Cl molar ratio increased, however when the Ca/Cl ratio increased to a certain value, the increase of HCl removal efficiency was not proportional to the increase of additive amount. For different additives, different Ca/Cl ratios should be chosen based on the cost, HCl removal efficiency and utilization efficiency of additive.