Biocomposites for a circular economy

This study systematically investigates the effects of brewer’s spent grain (BSG) particle size and filler loading on the mechanical, thermal, morphological, and degradation behavior of polybutylene succinate (PBS) composites. Optimized formulations with BSG particles below 100 µm and loadings of 25–30 wt.% demonstrate enhanced stiffness while maintaining processability, without using any chemical treatments due to synergistic interfacial interactions. Biodegradation tests in soil reveal that higher BSG content accelerates degradation rates by up to 2.4 times compared to neat PBS, driven by the hydrophilic, amorphous lignocellulosic structures in BSG that promote water absorption, microbial colonization, and matrix erosion evidenced by reduced surface hardness, lower contact angles, and increased roughness. Tensile tests show that PBS-BSG30 demonstrates strong mechanical properties, with tensile strength (32.91 MPa) and stiffness (Young’s modulus: 264.10 MPa) surpassing recycled HDPE and approaching PP. However, its elongation at break (21.76%) is lower than both PP and HDPE, reflecting reduced flexibility. This makes PBS-BSG30 suitable for applications like underground planters, where high tolerance to deformation stress is more critical than flexibility. Under accelerated UV-B/humidity weathering, PBS-BSG30 composites exhibit improved resistance to degradation compared to neat PBS, leveraging BSG’s inherent UV-absorbing and moisture-buffering properties. Thermal analysis uncovers a crystallinity increase over time due to chain scission and molecular rearrangement, a process delayed by antioxidant additives for up to 600 hours. Complementary UVC exposure tests further highlight the stabilizing role of carbon black (CB) in mitigating rapid surface and bulk degradation observed in unfilled PBS. This work advances bio-based materials by establishing critical structure-property-degradation relationships and offering resource-efficient design strategies for circular economy integration.