Degradable benzyl cyclic acetal epoxy monomers with low viscosity: Synthesis, structure-property relationships, application in recyclable carbon fiber composite

Degradable thermosets can address the recycle issue of conventional thermosets and downstream materials like carbon fiber composites. Significant advances have been achieved on their recyclability even on high performance, but their processability was neglected. Herein, for the first time, from the processing point of view, degradable epoxy monomers with low viscosity were designed. Ethyl or methyl group was incorporated into the benzyl cyclic acetal structure to obtain three acetal epoxy monomers by the acetalization between p-hydroxybenzaldehyde analogues and triols to achieve diols, followed by reacting with epichlorohydrin. Two benzyl cyclic acetal epoxy monomers with ethyl group are liquid. The viscosity and structure-property relationship of epoxy monomers were systematically investigated from experiments to simulate computation. The cured epoxies possessed favorable thermal properties, mechanical properties and controllable degradability. Furthermore, the epoxy monomer with suitable viscosity was used to prepare carbon fiber composites with excellent performance via vacuum assisted resin transfer molding (VARTM) process. Meanwhile, the non-destructive recovery of carbon fiber was realized by taking advantage of the degradability of the acetal epoxy matrix.