Thermal characterization and kinetic analysis of polyvinyl chloride containing Sn and Zn

Abstract

Polyvinyl chloride (PVC) films containing the mercaptan methyltin (S), zinc stearate (Z) and dipentaerythritol (D) additives were prepared. The thermal degradation kinetics of the films were investigated by nonisothermal thermogravimetry and TG–FTIR techniques. Using the nonmodel method and the Kissinger, the Friedman, the Kissinger–Akahira–Sunose and the Flynn–Wall–Ozawa methods, the average apparent activation energies of the PVC–SZD films in the first and second thermal decomposition stages obtained were 127.5 and 261.6 kJ mol−1, respectively. Compared with the experimental master plot by the generalized master plot, the experimental and theoretical master plots on the master plot of θ/θ0.5 versus α show that the thermal degradation of PVC-SZD film conforms to the chemical reaction F1.5 mechanism model. TG–FTIR analysis showed that the infrared vibration peaks ordered from strong to weak after adding SZD components were: νCO2 (638 °C) > ν(–COOR) (275 °C) > νHCl (299 °C). The thermal degradation of the film did not show hydroxyl or moisture formation compared to the blank. The removal of carboxyl groups of plasticizer dioctyl terephthalate (DOTP) in PVC was significantly inhibited, and the CO2 gas released by thermal degradation was reduced by 85.2%. This suggests that SZD has a strong interaction with the ester groups in DOTP, and there is the possibility of generating a more stable carboxyl group-containing metal complex, which creates favorable conditions for the recovery of DOTP. When the heating rates were 2.5, 5.0, 10 and 20 °C min−1, the lowest temperatures at which the conversions reached 5 and 10% were 226.1 °C and 239.1 °C, respectively.