Reuse of beer spent grain for the industrial production of biodegradable bio-composites
Annamaria Visco, Noemi Bardella, Cristina Scolaro, Hossem Belhamdi, Salim Brahimi, Vanessa Gatto, Riccardo Samiolo, Valentina Beghetto
Abstract
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 bio-composites 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.