Long-chain polyamide covalent adaptable networks based on renewable ethylene brassylate and disulfide exchange

Abstract

Conventional thermosets cannot be recycled once they reach their end-of-life creating unavoidable waste. Covalent adaptable networks (CANs) are a promising circular solution as they can be reprocessed by conventional techniques employed for processing thermoplastics. In this work, strong and chemically resistant, long-chain polyamide (PA) CANs were developed by introducing intrinsically reactive disulfides in PA networks. Following a solvent-free strategy and utilizing ethylene brassylate, a renewable cyclic diester, our approach brings together the high strength and chemical resistance of long-chain, crosslinked PAs with the reprocessability of dynamic networks in a sustainable fashion. The structure of the PA CANs was elucidated by X-ray diffraction analysis, and the effect of the disulfides on the thermal, mechanical, viscoelastic and dynamic properties was evaluated. The PA CANs had high gel content (86–98%) and they were reprocessable over three grinding-compression molding cycles, retaining their strength (15–20 MPa), crosslink density and gel content. They exhibited rapid stress relaxation with relaxation times as low as 1.06 s and were healable within 5 min. The long-chain PA CANs are easy to prepare and feature several elements of sustainable materials design, highly valued in plastics’ circular economy.