Long-chain amino acids and hydrogen bonding enhanced epoxy thermosets: High latency, thermal and mechanical properties, and its application in recyclable carbon fiber composites

Thermoset carbon fiber reinforced polymer (CFRP) composites are widely used and in increasing demand in composites industries. Among them, CFRP with one-component epoxy matrix can optimize the preparation process. However, high-value carbon fiber (CF) is difficult to recover and no cases of latent CFRP with CF recyclability have been reported. In this study, long aliphatic chains were innovatively introduced into amino acid type latent curing agents to improve the latent performance and the solubility in organic solvents. The latent performance of curing agents improved with the increase of chain length due to the difficulty in proton transfer of ammonium ions along to the long chain. The latent curing agent derived from 1,10-diaminodecane exhibited good solubility in ethanol and good compatibility with epoxy monomers, making it had the potential for industrial use in the preparation of CFRP. Moreover, amide bonds in the synthetic amino acid were prone to form hydrogen bonds to improve the thermal and mechanical properties of cured resin, while ester bonds in the amino acids imparted the resin with degradability in alkaline environments, thereby endowing CFRP with CF recyclability without damaging surface morphology and chemical structure. This work will open a door for the recycling research of latent CFRP.