Design and Development of Advanced Thermosetting and Vitrimeric Materials Based on Sustainable Polymers

The growing accumulation of fossil-derived plastic waste represents one of the major environmental challenges of nowadays. Although thermoplastics can be recycled with relative ease, thermosets remain difficult to reprocess due to their permanent cross-linked networks, despite offering excellent mechanical and chemical performance. This limitation underscores the need to redesign such materials to better align with circular economy principles. This PhD work focuses on these issues by developing new sustainable dynamic polymer systems based on aliphatic polyesters, incorporating dynamic covalent bonds to try to obtain reprocessability, repairability, and extended material lifetimes while maintaining comparable mechanical and thermal performances to commercial systems. Branched poly lactic acid (PLA) prepolymers were chosen for this work precisely because of their renewable origin, established scalability, and intrinsic recyclability. They were synthesized by ring-opening polymerization of L-lactide using multifunctional bio-derived polyols as initiators and extensively characterized by NMR and GPC. Their potential for nontoxic, bio-based crosslinking was investigated using a set of bifunctional reagents, including diethyl malonate, citric acid, erythritol biscarbonate, and isosorbide diglycidyl ether, under various catalytic and thermal conditions. To address their limited reactivity, the PLA prepolymers were then functionalized with carboxylic acid end groups and successfully crosslinked with isosorbide diglycidyl ether. The optimized formulations yielded highly crosslinked, insoluble materials with high gel fractions, which were analyzed by DSC, TGA, rheological and mechanical testing, SEM, and water contact angle measurements. These analyses confirmed the formation of a crosslinked network exhibiting vitrimer-like behavior. To explore their potential in a circular economy, preliminary depolymerization tests were carried out in mildly basic aqueous conditions, giving early insights into how these materials might be recycled at the end of their life. Complementary research carried out at École Supérieure de Physique et de Chimie Industrielles de la Ville de Paris (ESPCI Paris) focused on incorporating various bio-based fillers into high-density polyethylene (HDPE) to make conventional thermoplastics more sustainable. By using reactive extrusion with both established and newly developed grafting agents, the compatibility between the fillers and the polymer was improved, leading to better mechanical performance. These improvements were confirmed through DMA, tensile testing and DSC, highlighting the potential of bio-based additives to enhance traditional plastics. Overall, this work represents an advance in more sustainable polymeric materials by combining renewable feedstocks, dynamic covalent chemistry, and compatibilization strategies. The resulting materials contribute to the development of high-performance thermosets and thermoplastics with improved circularity, reduced environmental impact, and viable pathways toward recyclable and responsible polymer networks.