Readily recyclable carbon fiber reinforced composites based on degradable thermosets: a review

A carbon fiber reinforced polymer (CFRP) is a structural composite widely used in automobiles, the aerospace industry, sporting goods, etc. because of its high strength-to-weight ratio, excellent fatigue and corrosion resistances. However, it is difficult to recycle mainly due to the permanent cross-linked thermosetting matrices. Recent years have witnessed the development of a new generation of CFRPs based on degradable thermosets which can depolymerize on demand under mild conditions. Carbon fibers (CFs) can be reclaimed readily and their original high performance and value can be retained, and the degraded thermosetting matrices can also be reused. In this tutorial review, the necessities of recycling CFRPs and developing readily recyclable CFRPs are presented. Critical differences between traditional and readily recyclable CFRPs are introduced. The readily recyclable CFRPs based on degradable thermosets are divided into several categories based on different degradable thermosets with various controlled-cleavable linkages such as ester bonds, acetal linkages, Schiff base bonds, disulfide bonds, hexahydrotriazine structure, boronic ester bonds and di-N-benzylaniline linkages. The recycling mechanisms and synthetic routes of the degradable thermosets, and the recovery and reuse process of CFs and resins are illustrated. The research progress of each recyclable CFRP is described separately. Finally, conclusions and prospects are provided.