Coupled deep-eutectic-solvent swelling and Fe-assisted pyrolysis of waste wind turbine blade epoxy for selective enrichment of C9-substituted phenols

Selective recovery of phenolics from waste wind-turbine blade epoxy is limited by uncontrolled secondary reactions during pyrolysis. Here, choline chloride–ethylene glycol deep eutectic solvent (DES) swelling was coupled with iron(III) citrate-assisted Fe introduction. Final temperature (400–600 °C) and Fe level were varied to resolve changes in thermal behavior, phase yields, and normalized gas chromatography–mass spectrometry peak areas. Pretreatment retained 81.16–88.81% of the resin, and inductively coupled plasma optical emission spectrometry measured 0.629–1.406 wt% Fe in Fe-containing composites. The main decomposition region shifted to lower temperature, while the full width at half maximum of the main DTG peak narrowed from 42.51 to 35.48 °C. At 500 °C, Fe0.45 (0.45 mol L −1 Fe 3+ in the treatment solution; 0.750 wt% Fe in the composite) gave a C 9 -substituted-phenol normalized peak area of 57.70%, 35.26% higher than that of Raw. These products represented 63.65% of total phenolics. Higher Fe levels or a final temperature of 600 °C increased gas formation and reduced oil recovery, consistent with stronger secondary conversion. Product-distribution, Raman, and textural trends indicate that Fe0.45 at 500 °C provided the most favorable observed balance between precursor conversion and downstream dealkylation and condensation. Coupling DES swelling with controlled Fe introduction therefore offers a tunable route for the relative enrichment of C 9 -substituted phenols during the thermochemical valorization of waste wind-turbine blade epoxy.