Home compostability of PLA, PBS, and PBAT biocomposites incorporating orange peel and brewer’s spent grain: Mineralization kinetics, structural evolution, phytotoxicity, and bacterial isolation

This study investigates the home compostability of biocomposites based on polylactic acid (PLA), poly (butylene succinate) (PBS), and poly (butylene adipate-co-terephthalate) (PBAT) under mesophilic conditions (28 °C), building on previous work on their fabrication and physicochemical properties. Biocomposites containing 10 wt % agro-industrial fillers, namely orange peel (OP) and brewer’s spent grain (BSG), were compared with their corresponding neat polymers. Ultimate aerobic biodegradation was monitored over 200 days in respirometric chambers using a protocol adapted from NF T51–800. Mineralization remained negligible for PLA-based materials, whereas PBS and PBAT reached 72.3 % and 7.2 %, respectively. Filler incorporation significantly enhanced biodegradation, particularly for PBS/OP (82.4 %) and PBAT/BSG (24.6 %). Kinetic modelling using Hill and Weibull functions indicated that PBS/OP could reach the 90 % mineralization threshold within approximately 260 days, whereas neat PBS would require longer. Structural evolution during composting was characterized using scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic vapor sorption (DVS). Sorption behaviour was analysed using the Park model and mean cluster size (MCS). BSG-based biocomposites exhibited earlier fragmentation and increased porosity, promoting water uptake and microbial accessibility. Selective enrichment enabled the isolation of eight bacterial strains capable of utilizing polymer-derived carbon. Phytotoxicity assays performed on Sinapis alba and Hordeum vulgare showed no significant adverse effects, supporting the environmental safety of the resulting composts. Overall, this work provides a comprehensive multiscale assessment of biodegradable biocomposites under laboratory-simulated home composting conditions and highlights the key role of matrix–filler interactions in controlling biodegradation.