Kinetics of poly(vinyl chloride) thermal and thermo-mechanical degradation in the presence of epoxidized plasticizer. Induction effect

Kinetics of thermal and thermo-mechanical degradation of poly(vinyl chloride) (PVC) plasticized with di-(2-ethylhexyl)phthalate and epoxidized linseed oil were monitored using differential scanning calorimetry, thermogravimetry-mass spectrometry and viscosity and temperature change during high shear mastication. Linear dependence of induction period prior to PVC chain-degradation on epoxidized plasticizer concentration was observed using each method (not reported previously). Zero-order degradation kinetics controlled by the rate of hydrochloric acid elimination from saturated PVC molecules and consequent fast 2nd order scavenging of HCl by oxirane groups were consistent with experimental data. Apparent activation energies of 128.6, 146.3 kJ mol(-1) for thermal degradation and 164.4 kJ mol(-1) for thermo-mechanical degradation were deduced from the temperature dependence of the degradation induction time detected using thermogravimetry-mass spectrometry, differential scanning calorimetry and mastication, respectively. Change of activation energy with degradation mechanism is examined.