Sustainable PLA- and bio-epoxy-based bio-composites reinforced with sea urchin residues: From waste to worth

• FTIR/XRD confirm sea urchin CaCO₃; favorable PLA-filler interaction. • PLA +5 wt% powder: tensile 44.89 MPa, flexural 52.4 MPa, impact +50%. • PLA +5 wt% powder: compressive strength 111.23 MPa. • Bio-epoxy +3 wt% spines: tensile 23.70 MPa; flexural 49.62 MPa. • DMA (PLA +5 wt%): E′ 5.44 GPa at 35°C; Tg raised to 63.38°C. Transforming marine waste into functional materials offers a sustainable route for next-generation bio-composites. This study investigates the use of sea urchin residues, post-consumer shells and spines as novel fillers for polylactic acid (PLA) and bio-epoxy matrices. Micro- (powder) and macro- (spine) reinforcements were incorporated at 3, 5, and 8 wt.% and systematically evaluated. Chemical and structural analyses (FTIR, XRD, SEM) confirmed the calcitic composition and favorable interfacial interactions in PLA-based systems. Among all bio-composite formulations, the PLA composite with 5 wt.% powder (SU5) exhibited the highest tensile strength (44.89 MPa) and flexural strength (52.4 MPa), along with a 50% increase in impact resistance. In the bio-epoxy system, the bio-composite with 3 wt.% spines achieved the best tensile (23.70 MPa) and flexural (49.62 MPa) strength, despite moderate matrix-filler bonding. Although the unfilled PLA and bio-epoxy matrices displayed higher mechanical properties overall, these formulations represent the most performant bio-composites developed in this study. These findings demonstrate the potential of sea urchin waste as an effective bio-filler for developing sustainable composites, with promising applications in 3D printing, packaging, and biomedical materials.