Degradable Semi-Cycloaliphatic Epoxy Resin for Recyclable Carbon Fiber-Reinforced Composite Materials

The development of an energy-saving method to recycle expensive carbon fibers (CFs) from the end-of-life thermosetting resin-based CF-reinforced composites (CFRCs) is strongly desired taking account of the environmental and economic issues. The replacement of traditional thermosetting matrixes with controllably degradable epoxy resins provides a promising solution to this challenging task. In this work, a liquid acetal-containing semi-cycloaliphatic epoxy resin (H-ER) is designed and synthesized. After curing, compared with the commercial cycloaliphatic epoxy ERL-4221, H-ER shows simultaneously increased thermal stability, shearing strength, flexural strength, strain at break and critical stress intensity factor by 126%, 26.5%, 17.0% and 29.5%, respectively. Particularly, the cured H-ER is sufficiently resistant to organic solvents, bases and weak acids, but degrades rapidly in a modestly strong acidic aqueous solution, and the rate of degradation is controllable by modulating the acidity. GC-MS and FTIR spectra demonstrate that the degradation is indeed due to the cleavage of acetal linkages in the network, and the degradation-generated benzaldehyde may be reused as the raw material for the synthesis of the H-ER resin. More importantly, for the CFRCs using H-ER as a matrix, the CFs are readily recovered without detectable damage and are able to be recycled for the CFRCs fabrication.