Titre de la dissertation: Control of PLA Crystallization

Promoteur de thèse: Monsieur Jean-Marie Raquez

Co-promoteur: Monsieur Jérémy Odent

Résumé de la dissertation: Poly(lactic acid) (PLA) has emerged as one of the most promising bio-based polymers in response to increasing environmental concerns and strict regulations aimed at reducing carbon emissions and the dependence on fossil-derived, non-degradable plastics. Despite its favorable attributes, including high stiffness comparable to petrochemical polymers, bio‑based origin, compostability, and compatibility with chemical recycling, PLA remains limited by its intrinsically low thermal resistance, modest barrier performance, and slow crystallization kinetics ; all of which restrict its implementation in advanced engineering applications. This doctoral research addresses these limitations towards enhancing PLA crystallization and molecular organization during processing, thereby improving its thermo‑mechanical performance and expanding its industrial perspectives. Under the guidance of Futerro, a Belgian PLA producer with an annual PLA production capacity of 100,000 tonnes, and NOOSA, a Belgian manufacturer of PLA-based textile fibres and fabrics, the research combines two complementary approaches: (i) polymer additivation to develop advanced PLA formulations with tailored crystallization kinetics, and (ii) innovative processing methods capable of inducing controlled shear and extensional flows to promote chain alignment and orientation. The first approach investigates two novel hydrazide‑based nucleating agents, decanedioic acid 1,10-bis(2-benzoylhydrazide) (TMC-300) and hexanedioic acid 1,6‑bis(2-benzylhydrazide) (TMC-306) to significantly improved heat deflection temperature, barrier performance, and toughness at loadings below 1 wt.%, outperforming commercially established ethylene bis stearamide (EBS). The second approach focus on designing a novel extensional layer‑multiplying element (XME) capable of generating strong shear and elongational stresses during melt-processing, enabling the formation of highly oriented crystalline networks including hybrid shish-kebab superstructures and imparting superior thermal and mechanical properties. Finally, the combination of hydrazide‑based additives with XME‑induced extensional flow produced synergistic effects, dramatically accelerating PLA crystallization to levels unprecedented in the literature while simultaneously improving functional properties. Overall, the proposed approaches enable the production of PLA materials with markedly enhanced crystallization kinetics, improved thermo-structural stability, and superior mechanical and barrier performance, without affecting the polymer’s bio‑based and recyclable nature. Beyond expanding the fundamental understanding of structure-property relationships in PLA in presence of TMC-300 and TMC-306, and under complex flow, this work delivers scalable, industry‑compatible solutions supporting the development of high-performance, sustainable PLA-based products. These results bridge academic insights with industrial implementation and consolidate PLA’s position as a viable alternative for demanding applications across packaging, automotive, textile, and related sectors.