Intrinsically flame-retardant epoxy vitrimers with catalyst-free multi-reprocessability towards sustainable carbon fiber composites

An intrinsically flame-retardant epoxy vitrimer with multi-reprocessability was successfully constructed and applied to carbon fiber-reinforced composites with the aim of promoting more economical and sustainable development in the field of fire-safe applications. In this work, a catalyst-free flame-retardant epoxy vitrimer constructed by synthesizing phosphaphenanthrene-derived anhydride (DPI) and using triethanolamine (TEOA) as a multifunctional transesterification modifier was used to solve the two major problems of flame retardancy and recyclability at once. The epoxy resin and its composites exhibit excellent flame retardancy, mechanical properties, and rapid repairability, yet the ability to pass the UL-94 V-0 rating even after reprocessing the epoxy resin five times; while the value of the peak heat release rate (PHRR) and the total heat release (THR) reduced by 58% and 35%, showing great suppression on heat release. In addition, the resin can be completely degraded under mild conditions, enabling 100% recycling of the carbon fibers.