Cure kinetics of aromatic disulfide epoxy vitrimer: influence of epoxy/amine stoichiometry

Disposal of End-of-Life (EoL) thermoset composites, difficult to recycle due to polymer crosslinked structure, presents a significant challenge. Development of thermoset polymers with increased recyclability, self-healing, and reprocessability offers a promising solution for managing composite waste and extending component lifetime. Vitrimers, based on covalent adaptable networks (CANs) that rearrange their topology via reversible exchange reactions, are particularly promising. Recent research has shown that varying vitrimers stoichiometry can impact properties such as dissolution capability, potentially enhancing recyclability. This study explores the effects of stoichiometry variation on the thermomechanical properties and cure kinetics of epoxy vitrimers incorporating 4-aminophenyl disulfide (4-AFD) as hardener. Knowledge regarding the progression of crosslinking for both stoichiometric and non-stoichiometric mixtures is critical for optimizing processes and predicting behaviour at different curing temperatures. Vyazovkin's approach emerged as the most suitable for analysing cure kinetics among the different methods. It revealed that the non-stoichiometric formulation with hardener excess maintained nearly constant activation energy, suggesting that the cure mechanism is primarily driven by interactions between primary amines and epoxy groups. This reduces the availability of epoxy groups for tertiary amine formation, resulting in a less dense network, lower storage modulus, and decreased Tg, as confirmed by DMA and DSC results.