Curing-Agent Chemistry Controls Epoxy Resin Degradation and Bisphenol a Recovery

Bisphenol A (BPA) epoxy resins are widely used because of their excellent thermal and mechanical properties but are difficult to recycle owing to their highly crosslinked network. This study investigated the effect of curing-agent chemistry on epoxy resin degradation and BPA recovery, with emphasis on chemical recycling of legacy thermoset waste. Three amine curing agents, ethylenediamine (EDA), 1,2-diaminocyclohexane (DCH), and p-phenylenediamine (PPD), together with methyl tetrahydrophthalic anhydride (MTHPA), were evaluated, and a commercial wind blade epoxy resin was used as a representative waste material. Ethanol was selected as the degradation solvent because it combined effective degradation under the tested conditions with lower toxicity than several screened alternatives. The highest BPA recovery from the wind blade resin reached 31.79% at 170 °C after 24 h. MTHPA- and DCH-cured resins achieved BPA recoveries of 45.38% and 44.38%, respectively, whereas EDA and PPD exhibited lower degradability because of network and bond-stability effects. By linking curing-agent structure to depolymerization and monomer recovery, the study supports waste prevention and resource circularity objectives relevant to Sustainable Development Goal 12.