Turning unsorted stranded seaweeds into biocomposites

The valorisation of stranded seaweeds (SW) represents a promising strategy to transform an environmental burden into a renewable resource for sustainable materials. In this work, SW collected from coastal areas were tested as bio-fillers for the production of polybutylene succinate based biocomposites. Composites containing 10, 20, and 30 wt% SW were prepared by melt mixing and injection moulding. The effect of epoxidized soybean oil (EP, 2-6 wt%) as a bio-based compatibilizer/plasticizer was also evaluated. Thermal (DSC, TGA), mechanical (tensile strength, elongation at break, Young's modulus), morphological (SEM), surface (contact angle), colorimetric, and ATR-FTIR analyses were performed. Results showed that SW acts as a nucleating agent, increasing the crystallization temperature and slightly enhancing the crystallinity degree of polybutylene succinate, while maintaining a melting temperature comparable to the neat polymer (similar to 114 degrees C). Although tensile strength decreased with increasing filler content, the addition of 6 wt% EP significantly improved elongation at break and interfacial adhesion, as confirmed by SEM and ATR-FTIR analyses. Thermal stability remained suitable for conventional processing. Soil burial tests showed enhanced biofragmentation of SW-containing composites, with the highest weight loss (similar to 58% after 183 days) observed for P-SW20-EP6 and P-SW30-EP6. Overall, P-SW20-EP6 emerged as the best compromise between mechanical performance, thermal stability, and sustainability. This study demonstrates the feasibility of directly employing unsorted stranded seaweeds as fillers in PBS biocomposites, offering a scalable and environmentally sound valorisation route.