Plastic pollution, largely driven by packaging waste, calls for sustainable alternatives. This study investigates biodegradable thermoplastic biocomposites based on PLA, PBS, and PBAT, incorporating 10 wt.% of agro-industrial filler-brewers’ spent grain (BSG) and orange peel (OP) without compatibilization. The biocomposites were produced by melt extrusion followed by thermo-compression. A full factorial design was implemented to assess matrix–filler interactions and compare biocomposites to pure polymer fragments. OP particles, smaller and rougher than BSG, exhibited a higher specific surface area, influencing composite morphology and behavior. The OP slightly plasticized PLA, possibly due to volatile release during processing, whereas BSG increased stiffness in PBS and PBAT. Both fillers reduced mechanical strength, especially in PLA, due to limited interfacial adhesion, and significantly decreased PLA’s thermal stability. The addition of fillers also increased water sorption and modified the sorption kinetics of the three main modes (Langmuir-type, Henry’s law sorption, and water molecule clustering), as well as the values of the half-sorption diffusion coefficients (D₁ and D₂), with notable differences between the OP and BSG linked to their structure and composition. These findings provide a better understanding of structure–property relationships in biodegradable composites and highlight their potential for sustainable packaging and other industrial applications.

CO₂ evolution is the standard endpoint for assessing aerobic biodegradation, but it does not resolve the fate of non-mineralized carbon. Here, a non-isotopic carbon-partitioning framework was developed in carbon-free activated vermiculite to evaluate the mesophilic biodegradation of poly(butylene succinate) (PBS) and PBS/orange peel (PBS/OP) biocomposites under composting-like conditions. Two inoculation strategies were compared: a mature compost extract and the same extract bioaugmented with a PBS-degrading bacterial consortium. The framework combined cumulative CO₂ respirometry, matrix-matched GC–MS quantification of residual PBS-derived carbon after acid methanolysis, and total organic carbon analysis of post-biodegradation vermiculite. Matrix-matched calibration revealed a 27% decrease in GC–MS sensitivity in vermiculite, confirming the need to account for matrix effects. After 133 days at 28 °C, residual PBS-derived carbon remained low in neat PBS but increased in PBS/OP, indicating enhanced fragmentation and dispersion of PBS-rich residues. TOC-based partitioning showed that the non-mineralized fraction was not exclusively residual polymer. Biomass-associated carbon represented 2.8, 7.6, 9.1 and 12.3% of the initial PBS carbon in PBS, PBS+, PBS/OP and PBS/OP+, respectively. Including this fraction increased total PBS carbon conversion to 46.4, 81.0, 89.0 and 90.0%, respectively. These results show that incomplete CO₂ evolution does not necessarily indicate persistent polymer, as part of the non-mineralized carbon may be biologically assimilated.

Polylactic acid (PLA) remains poorly mineralized under mesophilic conditions relevant to home and decentralized composting. This study assessed whether bioaugmentation with Amycolatopsis orientalis, protein-based biostimulation with skimmed milk powder, or their combined application could enhance the mineralization of compression-molded amorphous PLA fragments at 28 °C in activated vermiculite. Closed respirometric bioreactors were monitored for 90 days, and the PLA mineralization extent was calculated from the cumulative CO₂ evolution after correction using treatment-specific blanks. The recovered PLA fragments were further analyzed by FTIR-ATR and DSC to provide complementary physicochemical monitoring. The final mineralization remained low, reaching 1.19 ± 1.88% for bioaugmentation, 3.49 ± 1.82% for biostimulation, and 8.75 ± 4.31% for the combined treatment. The combined treatment gave the highest mean value, which was significantly higher than bioaugmentation alone, but the individual biological replicates followed heterogeneous trajectories. In particular, BABS-3 reached 13.19% mineralization, indicating that higher responses can occur at the individual bioreactor level, although they were not consistently reproduced. FTIR-ATR and DSC revealed treatment- and replicate-dependent physicochemical changes but did not provide evidence of extensive bulk PLA transformation. These results contrast those of previous reports of higher PLA mineralization under warmer, mature compost conditions, emphasizing the complexity of the combined influence of temperature and matrix. Overall, the tested strategies were insufficient to achieve effective home compostability of PLA at 28 °C.

La pollution plastique constitue un enjeu majeur de la transition écologique. Légers, résistants et économiques, lesplastiques fossiles, encore faiblement recyclés, s’accumulent dans la biosphère et génèrent des micro- et nanoplastiques auxeffets délétères sur les écosystèmes et la santé humaine. Dans ce contexte, des polymères biodégradables tels que le PLA, lePBS et le PBAT apparaissent comme des alternatives prometteuses, à condition que leurs filières de fin de vie soient adaptées.Le compostage domestique, encouragé par la loi AGEC (2020), représente une option décentralisée de valorisation organiquedes biodéchets, mais ses conditions mésophiles (20–45 °C) limitent la biodégradation par rapport au compostage industriel.Cette thèse évalue différentes stratégies pour améliorer la compostabilité domestique de ces polymères selon trois axes : (i)la formulation de biocomposites avec des charges organiques issues de coproduits agro-industriels (peaux d’orange : OP,drêches de brasserie : BSG), (ii) la bioaugmentation par inoculation de souches bactériennes, et (iii) la biostimulation parajout d’un inducteur protéique, seules ou combinées. Les expérimentations ont reposé sur le suivi respirométrique (CO₂), descaractérisations multi-échelles des matériaux (ATG, DSC, SEC, FTIR, MEB, sorption en vapeur d’eau), l’analyse descomposts, ainsi que l’isolement et l’identification de souches bactériennes et de leurs profils métaboliques. Les résultatsmontrent que l’interaction matrice–charge influe fortement sur la biodégradabilité. Le PLA demeure récalcitrant, tandis quele PBS et le PBAT présentent une minéralisation accrue avec charges. Le PBS/OP a atteint 82.4 % après 200 jours, avec unseuil de 90 % prédit avant 260 jours, contrairement au PBS pur. La bioaugmentation autochtone a augmenté la minéralisationdu PBS de +68.3 %, sans effet sur le PBS/OP. Le PBAT reste peu biodégradable malgré les traitements. Pour le PLA, lesstratégies de bioaugmentation et biostimulation n’ont entraîné que des gains marginaux (<10 %). Ce travail montre quel’amélioration de la compostabilité domestique du PLA, du PBS et du PBAT demeure un défi nécessitant une approcheintégrée associant ingénierie des matériaux et ingénierie microbienne. Il souligne enfin les limites des normes actuelles et lanécessité d’essais incluant variabilité climatique, pratiques domestiques et biodéchets frais.