Microwave-Assisted Degradation of Unsaturated Polyester Resin into HDPE-Modified Aerogels for Oil Adsorption and Oil/Water Separation

Thermosetting unsaturated polyester resin (UPR) is difficult to reprocess because curing generates an irreversible three-dimensional network. Here, cured UPR was treated in a microwave-assisted hydrazine hydrate/NaOH medium at 70 °C for 30 min to produce a water-swellable UPR-derived product (NUPR). NUPR was combined with glutaraldehyde, subjected to freeze–thaw processing and freeze-drying, and subsequently modified with high-density polyethylene (HDPE) to fabricate porous aerogels. FTIR results were consistent with partial cleavage of ester-containing structures, while TGA and SEM revealed changes in thermal behavior and morphology. Among the tested aerogels, AAS-6 exhibited a density of approximately 0.036 g cm−3 and a porosity of 96.6%. After HDPE treatment, the aerogel exhibited a water contact angle of 135.2° while maintaining rapid oil wetting. Its 5 min liquid uptake for the tested oils and organic solvents ranged from 20.14 to 38.31 g g−1. After ten adsorption–regeneration cycles, 89–96% of the initial oil uptake was retained, depending on the oil, whereas uptake of the tested volatile solvents remained comparatively unchanged under the respective regeneration conditions. H-6 also enabled free-oil uptake from water and gravity-driven treatment of surfactant-stabilized water-in-oil (W/O) emulsions, yielding high separation efficiencies and markedly reduced dispersed-droplet signals after filtration. These results demonstrate a route for coupling the chemical conversion of cured UPR with fabrication of porous materials for oil uptake and W/O emulsion separation.