Heterogeneous network design strategy toward mechanically robust and recyclable elastomers

It is well-accepted that thermoplastic vulcanizates (TPVs) integrate the fascinating recyclability of thermoplastics and the mechanical robustness comparable to nano-filled elastomers, deriving from the particular heterogeneous network structure. However, the elasticity of TPVs is inferior to covalently cross-linked elastomers, since the irreversible deformation or even collapse of plastic phases of TPVs will certainly give rise to considerable hysteresis loss and therefore deteriorate the elasticity. Herein, we proposed a facile network design strategy toward covalently cross-linked elastomer with mechanical robustness and recyclability by engineering heterogeneous blend networks into diene-rubber system. Specifically, two conventional diene-rubbers, ethylene propylene diene terpolymer (EPDM) and styrene-butadiene rubber (SBR), were adopted as thermodynamic incompatible pair and then directly admixed. Due to the significant difference in the cross-linking reactivity between the pair, the resulting system assembled into a microphase-separated structure with strong interfacial adhesion upon in situ co-cross-linking. Upon deformation, the overall chain orientation of the networks is promoted by the efficient interfacial stress transfer and a striking reinforcement of the networks is achieved accordingly. More importantly, by virtue of the slightly cross-linking attribute of EPDM component, the resulting system featured with desirable recyclability and high elasticity in comparison with conventional TPVs. We envisage that this work will provide important inspiration for the non-filling reinforcement of elastomers and the development of a new generation of thermoplastic vulcanizates with considerably low hysteresis through manipulating the covalent network heterogeneity.