Swelling Behaviors of Thermoplastic Vulcanizates (TPVs): Modified Extended Flory- Huggins Model

Abstract

This study examines the swelling behavior of thermoplastic vulcanizates (TPVs) from a 60/40 wt% of ethylene propylene diene monomer (EPDM) and polypropylene (PP), using dynamic vulcanization to combine elastomeric flexibility with thermoplastic processability. To model swelling and phase behavior of TPVs and natural rubber (NR) in various solvent environments, an extended Flory–Huggins model was modified. This model introduces an interaction parameter, χKB, accounting for both composition and temperature, enabling accurate predictions of polymer-solvent interactions across different conditions. The model includes two approaches: Case I, which incorporates χKB into the traditional Flory–Huggins framework to predict temperature- and composition-dependent swelling and phase behaviors for polymer/solvent systems, and Case II, which adds specific interaction terms for more detailed polymer-solvent orientation. The model accurately predicted swelling behavior in polar and nonpolar solvents, closely aligning with experimental data. Results also showed that higher crosslink density restricts solvent uptake, especially in polar environments. Moreover, Case II successfully predicted upper critical solution temperature (UCST) and lower critical solution temperature (LCST) phenomena, validated experimentally for UCST in polyisobutylene (PIB)/diisobutyl ketone (DIBK) systems and LCST in polystyrene (PS)/ethyl acetate (EA) systems. This adaptable model holds promise for industrial and environmental polymer applications requiring precise control of swelling and phase transitions.