Thermal ageing of PP-EPDM thermoplastic vulcanizate: Multiscale study and kinetic modeling

• Thermal oxidation of PP-EPDM thermoplastic vulcanizate • Multiscale characterization of chemical ageing (FTIR, UV, GPC) and its consequences (tensile test, yellowing) • Significant effect of plasticizer on TPV yellowing • Predominant role of EPDM on TPV oxidation • Kinetic modelling of TPV oxidation assuming the key role of tertiary C-H present in EPDM This work presents a multi-scale study of the impact of thermal ageing of thermoplastic vulcanizate (TPV) obtained by blending a thermoplastic matrix (polypropylene), plasticizer, and dispersed crosslinked EPDM rubber particles. This study focuses on the case of TPV without pigments or stabilizers. The thermal ageing was mainly monitored by Fourier transform infrared and thermal analysis, to identify oxidation products and their kinetics of appearance, and GPC analysis performed on extracted PP fraction of the TPV. Data indicated that EPDM phase oxidizes first and drives degradation of the TPV. Appearance changes were characterized by colorimetry and gloss. Oxidation leads to strong changes of mechanical properties and aspect properties observed from the early hours of ageing, yellowing (change of Δb*) being also induced by the plasticizer. Yellowing reached unacceptable level (regarding the requirements for exterior automotive parts) before mechanical properties. The oxidation of EPDM and TPV was thus simulated by a kinetic model based on kinetic parameters already available in the literature. Its validity was verified by its capability to simulate the appearance of primary (hydroperoxides) and secondary (carbonyls) oxidation products.