Kinetics of Plasticized Poly(vinyl chloride) Thermal Degradation, Induction, Autocatalysis, Glass Transition, Diffusion

Kinetics of non‐oxidative thermal degradation of poly(vinyl chloride) (PVC) plasticized with di(2‐ethylhexyl)phthalate and epoxidized linseed oil (ELO) were studied using differential scanning calorimetry. PVC thermal degradation autocatalyzed by forming HCl is delayed in the presence of acid scavenging ELO. Direct HCl elimination rates during steady state degradation (induction period) were almost independent on ELO concentration, with rate constants ranging from ≈3.2×10 −6 s −1 at 463 K to ≈7.0×10 −5 s −1 at 503 K. Activation energy of HCl elimination increased with glass transition temperature (T g ) increase from 136.0 kJ mol −1 at T g =260.3 K to 141.9 kJ mol −1 at T g =274.2 K. Diffusion coefficients of HCl diffusion in plasticized PVC deduced using Williams‐Landel‐Ferry equation were of the order of 10 −4 cm 2 sec −1 . Calculated activation energy of HCl diffusion in plasticized PVC was ≈30 kJ mol −1 . The rate constants of PVC autocatalytic degradation were derived from the experimental data (for the 1 st time) using Šesták‐Berggren approach and ranged from 3.2×10 −2 sec −1 at 503 K to 4.4×10 −3 sec −1 at 463 K. Autocatalysis activation energies ranged from 70.4 kJ mol −1 to 85.1 kJ mol −1 and increased with increase of glass transition temperature. It was established that PVC degradation kinetics was not controlled by HCl diffusion. Compensation effect was observed for initial and catalyzed PVC degradation.