Primary recycling of anhydride‐cured engineering epoxy using alcohol solvent

Recycling of engineering thermosets is extremely difficult for conventional techniques due to their crosslinked networks. In this study, we demonstrated a new recycling approach for anhydride‐cured engineering epoxy. After soaking the epoxy networks in alcohol solvent mixed with transesterification catalyst, both solvent and catalyst molecules diffused inside, broke the ester bonds on the chain backbone through bond exchange reactions, and eventually decomposed the networks. The ester covalent bonds would be reformed as evaporating the solvent, and the dissolved polymer solution was re‐polymerized into near‐identical networks. When compared with existing recycling approaches, the proposed one is advantageous for its low cost, zero pollution, low temperature (160°C), and ambient pressure during operation. Epoxy networks with different amount of anhydride cross‐linkers were synthesized, and the influences of solvent choice, network stoichiometry, and crosslinking density on the recycling rate were studied. Specifically, the dissolution rate of epoxy samples was evaluated by their weight loss in two types of alcohol solvents, and the re‐polymerization rate was evaluated by the increment of solution viscosity and network modulus. Thermomechanical properties of recycled epoxy were compared with those of native samples. Finally, the dissolution and re‐polymerization cycles were performed for multiple times to investigate the repeatability. POLYM. ENG. SCI., 59:E111–E119, 2019. © 2018 Society of Plastics Engineers