Recycling of Pultruded Vinyl Ester Thermoset Scraps into Polyethylene Composites: Toward Circular Composite Manufacturing

Thermoset pultrusion waste was mechanically recycled as vinyl ester–glass (RVC) filler and compounded—without compatibilizers—into LDPE and HDPE (10–50 wt.%) by single-screw extrusion and compression molding. In LDPE, flexural strength increased from 15 MPa to over 30 MPa, and the modulus rose more than fourfold, with the 30 wt.% composition showing the best strength-stiffness balance. For HDPE, tensile modulus improved by more than 300%, and flexural strength reached about 36 MPa at 20–30 wt.% loading. Impact toughness also improved markedly, particularly for LDPE, where the absorbed energy more than doubled. SEM and optical analyses linked optimum performance to 20–30 wt.% filler content, while higher loadings caused agglomeration and void formation. The study demonstrates a scalable route to valorize thermoset waste into functional polyolefin composites for circular material design.