Reuse of beer spent grain for the industrial production of biodegradable bio-composites

Brewer’s grains (BSG), the main by-product of beer production, are an underutilized, free and widely available resource for biorefinery. Our research group has explored the use of BSG as a bio-filler (BSGF) with polybutylene succinate (PBS) to develop novel bio-composites (PBS-BSGF), reducing the dependence on virgin biomass and fossil-based polymers. This study demonstrates the potential of BSG as a valuable feedstock for bio-composite production at industrial-scale. The PBS-BSGF bio-composites (from 5 to 45 wt% BSGF) were characterized for rheological, chemical, physical and morphological properties, as well as evaluations of processability, biodegradability in soil and production scale-up. The results indicate that the optimal blend can contain up to 30 wt% BSGF, with particle sizes below 100 μm, ensuring melt processability. Proteins in BSGF, especially melanoidins, act as natural compatibilizers between PBS and BSGF, eliminating the need for toxic additives. These biocomposites exhibit superior toughness, with 9–21 times higher deformability and 3–7 times lower stiffness than comparable natural bio-filler blends. Thermal stability is maintained up to 230 ◦C, enabling processing with conventional thermoplastic polymer technologies. BSGF increases surface roughness and hydrophilicity, accelerating the rate of soil degradation by approximately ~ 2.4 times compared to pure PBS. As a practical demonstration of circular economy principles, we have produced plant pots made of PBS-BSGF, demonstrating their feasibility for sustainable industrial production.