Multiple-reprocessable guaiacol-derived epoxy vitrimer with disulfide crosslinks and closed-loop recycling of carbon fiber-reinforced composites

Developing high-performance bio-based epoxy resin as an alternative to petroleum-derived bisphenol A epoxy resin (DGEBA) for manufacturing recyclable carbon fiber-reinforced polymers (CFRP) presents a formidable challenge. A novel epoxy monomer derived from 4-propyl guaiacol with significantly low viscosity was synthesized via a two-step process, followed by curing with 4,4′-dithiodianiline to yield a bio-based vitrimer featuring only reversible disulfide bonds. In contrast to DGEBA, this vitrimer alleviated concerns regarding the residual presence of bisphenol A and its derivatives while maintaining good thermal and mechanical stabilities. Furthermore, the flexible propyl side chains accelerated chain segment motions and synergistically enhanced the dynamic characteristics of this bio-based vitrimer with dynamic disulfide bonds. It demonstrated a much rapid stress relaxation of 15.8 s at 200 °C, facilitating the complete repair of scratches from epoxy resins and composite materials within 30 min under tiny pressure. The vitrimers could undergo reorganization four times while upholding chemical integrity and was readily achievable for closed-loop recycling. The low viscosity of the epoxy matrix facilitated the molding process of the composites resulting in high performance composites without diluents. The resulted carbon fiber reinforced polymer composite (CFRP) exhibited excellent mechanical characteristics and enabled reprocessing, self-repairing, and high-value, non-invasive fiber recycling. This research expands the dynamic attributes of epoxy vitrimer to CFRP, a pivotal step towards realizing multifunctional bio-based CFRP and facilitating the closed-loop recycling of composite materials.