Rational Integration of Nanomagnetism and Biocatalysis for Sustainable Circular Polymer Systems

The thesis advances a holistic framework for circular polymer processing by integrating enzymatic catalysis, magnetic nanoparticles-based immobilization and functionalized bioplastic interfaces. The resulting approach aspires to contribute to next-generation technologies by developing sustainable and efficient solutions for biocatalytic processes and polymer material management, both during synthesis and in a recycling-oriented perspective, where biocatalysis and nanomagnetism operate in harmony to close the polymer lifecycle within a fully circular bioeconomy. First, a rational Biocatalyst Magnetic Nanoarchitecture (BMN) was designed using spinel iron oxide nanoparticles with optimized morpho structural and textural properties. These tailored nanomaterials served as support for the immobilization of Candida antarctica Lipase B (CaLB), enabling the formation of a stable biocatalyst that could be magnetically recovered for several cycles of reactions. CaLB, immobilized on magnetic nanoparticles, retained high activity in polycondensation reactions using renewable monomers; it exhibited >87% monomer conversion over multiple cycles yielding polyesters with number-average molecular weight (Mn) between 4.2 and 5.6 kDa. The efficient magnetic recycling demonstrated the robustness of the BMN platform. In parallel, the synthetic potential of three novel thermophilic α/β hydrolases, LCC (leaf-branch compost cutinase), its variant form LCCICCG and Thb from Thermoanaerobacterales bacterium, was assessed to widen the range of biocatalysts beyond the well-established use of CaLB. A design of experiments (DoE) approach allowed to precisely evaluate their thermostability and substrate selectivity in esterification and transesterification reactions. By achieving up to 90% of conversion and producing polyesters with molecular weights of ~3.6-3.8 kDa, the study demonstrated the versatility of these thermostable hydrolases as biocatalysts for sustainable polymer synthesis. The concept of magnetically responsive system was further extended to recycling by integrating the concept of nanomagnetism to the end-of-life management of bioplastics. Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) films were functionalized with spinel iron oxide nanoparticles via a Layer-by-Layer (LbL) assembly using bio-derived polymers (i.e., DNA and chitosan) as dispersing agents. This coating imparted magnetic properties without compromising polymer integrity, enabling magnetic separation from mixed plastic waste with potential nanoparticles recovery and reuse after enzymatic degradation.