Upcycling epoxy-glass thermoset waste into high-performance polyethylene composites

The growing demand for sustainable material management highlights the challenge of recycling thermoset composites. This study explores the upcycling of epoxy-glass fiber pultrusion wastes through mechanical shredding and dual-acid (acetic-citric) surface treatment, enabling their direct use as functional fillers in lowdensity (LDPE) and high-density (HDPE) polyethylene matrices without compatibilizers. Recycled fillers were compounded via single-screw extrusion and characterized in terms of morphology, water absorption, and mechanical performance. Results showed substantial improvements: in LDPE, tensile modulus increased by 286-589 % and strength by 40-47 %; in HDPE, modulus increased by 347 % and strength by 23.6 %. Flexural properties also improved markedly, though tensile strength declined at filler loadings above 30 wt% due to fiber clustering and interfacial voids. Impact strength decreased with higher filler content, while water absorption remained low (0.09-0.13 % after 60 days). Surface treatment reduced water absorbtion by 5-10 % and enhanced interfacial bonding, as confirmed by optical and SEM analyses. Optimum performance was observed at 20-30 wt % loading in LDPE and 30-40 wt% in HDPE. Overall, the study demonstrates a scalable and cost-effective strategy to valorize thermoset composite waste into high-performance thermoplastic systems, supporting circular economy goals.