Closed-Loop Recycling of Tough and Flame-Retardant Epoxy Resins

Abstract

Large-scale applications of flame-retardant epoxy resins have caused sustainability concerns on the use of renewable resources and end-of-life wastes. New strategies are required to address chemical recycling of fire-safe epoxy resins. Here, we demonstrated recyclable flame-retardant epoxy resins (FREPs) using itaconic acid-derived hyperbranched epoxy resin (IA-EHBP) and (1,3,5-hexahydro-s-triazine-1,3,5-triyl) benzyl mercaptan (HT-BM). The unique structure enabled a closed-loop chemical recyclable network that can be degraded into monomers with up to 86% yield of recovered monomers. The hyperbranched topological structure of IA-EHBP also contributed to a significant improvement in the strength and toughness of the FREPs. By using positron annihilation lifetime spectroscopy, the effects of free-volume hole size and relative fractional free-volume on the mechanical performance and dynamic mechanical properties of FREPs were studied, and the function relations were therefore established based on the Williams–Landel–Ferry equation. The incorporation of IA-EHBP effectively promoted the formation of char residue and produced phosphorus- and sulfur-containing free radicals to prevent the generation of combustible volatiles, thus enhancing the flame retardancy. The FREPs can be recycled and reused multiple times without loss of performance. The method reported here provides a facile and closed-loop approach for high-efficiency chemical recycling and reuse of end-of-life flame-retardant materials.

Bio-based hyperbranched epoxy resins: synthesis and recycling

“…28, itaconic acid-derived hyperbranched epoxy resin (IA-EHBP) was firstly synthesized by polyaddition between DOPO (9,10-dihydro-9-oxa-10-phosphaphenan-threne-10-oxide)-containing diepoxide and TMP, and then mixed with DGEBA to be cured by (1,3,5-hexahydro- s -triazine-1,3,5-triyl) benzylmercaptan (HT-BM) to give FREPs. 175 Fig. 29a–c displays the o -P s lifetime τ 3 , free-volume hole size V f , and relative fractional free-volume f r of FREPs under the combined effect of free-volume holes and hydrogen bonding, showing minimum values at a 10 phr IA-EHBP loading.…”

Natural halloysite nanotubes decorated with organophosphorous for highly flame‐resistant epoxy composites

“…Among them, P O can be attributed to the phosphate structure, like aluminum phosphate. 61,62 It originates from the reaction of the phosphoric acid from the decomposition of DOPO and the Al element in HNTs, which has great stability and promotes the production of barrier. The P O structure is mainly a stable carbon layer of P O C structure formed by the reaction of phosphoric acid with the material matrix, which can be proved by C 1 s spectra.…”

Microcage flame retardants with complete recyclability and durability via reversible interfacial locking engineering

“…15–17 These materials have demonstrated the ability to depolymerize into their original flame-retardant molecules through stimulus-triggered reversibility, employing dynamic Diels–Alder adducts and disulfide, imine, and acetal bonds. 18–20 However, the widespread adoption of these materials faces challenges due to the expense and complexity of their designs, coupled with limitations imposed by finite functional groups. This particularly impacts the universal applicability of flame-retardant material fabrication methods, especially for conventional polymers.…”