Catalytic pyrolysis upcycling of waste thermosetting epoxy resin into fire-retardant additive

Abstract

This research introduces a low-temperature catalytic-assisted pyrolysis method for recycling waste thermosetting epoxy resins, transforming them into an efficient fire-retardant additive for new epoxy resin formulations. In this study, we demonstrate that boric acid (BA) can significantly reduce the temperature required for epoxy resin (EP) pyrolysis, resulting in degradation products containing boron atoms that can act as a fire-retardant additive. The impact of 5%–20% content of recycled EP (R-EP) on the curing process, thermal stability, fire retardancy, and mechanical properties of the new EP was comprehensively investigated. The TGA results show that adding BA to epoxy resin at a 1:4 BA:EP ratio significantly reduces pyrolysis temperature. Neat EP degrades in two stages in 341°C and 557°C, while EP with BA degrades in three stages, starting below 120°C and peaking around 142°C. The results demonstrated an outstanding effect of incorporating 20% R-EP on the char formation and fire retardancy of the new EP, surpassing the performance of 20% triphenyl phosphate (TPP), a commercially available fire retardant. The storage modulus for neat EP is 1510 MPa, increasing to 2280 MPa with EP/R-EP 20%, indicating enhanced rigidity. Addition of R-EP raised glass transition temperature (T_g) of the epoxy resin up to 38°C, indicating highly cross-linked structures compared to TPP-modified EP, which shows lower T_g values.