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 (Tg) increase from 136.0 kJ mol−1 at Tg=260.3 K to 141.9 kJ mol−1at Tg=274.2 K. Diffusion coefficients of HCl diffusion in plasticized PVC deduced using Williams‐Landel‐Ferry equation were of the order of 10−4 cm2 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 1st 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. Kinetics of thermal degradation of plasticized poly(vinyl chloride) (PVC) containing acid scavenger, epoxidized linseed oil (ELO), was investigated. ELO presence allowed to separate direct hydrochloric acid (HCl) elimination and HCl induced autocatalytic degradation regions, to obtain distinct rate constants and activation energies of both processes as a function of PVC glass transition temperature. Diffusivities of HCl in PVC were computed, showing that PVC degradation kinetics was not controlled by the rate of HCl diffusion. Kinetic compensation effect was established.