From physical blending to polymerization-assisted integration: degradable polyester/keratin biocomposites for functional applications

The growing environmental impact of non-biodegradable plastics derived from fossil fuels has intensified the search for sustainable polymeric materials that combine functional performance, biodegradability, and the valorization of renewable or waste-derived resources. In this context, this doctoral thesis investigates the integration of keratin derived from chicken feathers into degradable polyester matrices, with the aim of developing multifunctional biocomposites for biomedical and functional applications. Keratin was explored as a bioactive, structural, and storage component within systems based on poly(ε-caprolactone) (PCL) and poly(butylene succinate) (PBS). A progressive research strategy was adopted, moving from physical mixing to polymerization- assisted integration. In the first part of the work, PCL/keratin films and three-dimensional porous scaffolds were prepared and characterized in terms of morphology, thermal behavior, surface properties, degradation profile, and biological response. The incorporation of keratin improved the interaction of PCL-based materials with biological environments, supporting the viability and proliferation of HaCaT keratinocytes in film systems and MC3T3-E1 pre-osteoblasts in porous scaffolds, thus highlighting their potential for skin applications and bone tissue engineering. To overcome the limitations commonly associated with physical mixing, keratin was subsequently introduced during the ring-opening polymerization of ε-caprolactone. This in situ polymerization approach enabled the formation of PCL/keratin materials with distinct structural, thermal, and morphological characteristics, demonstrating that keratin can be incorporated during polymer formation without impeding polymerization. The functional potential of these systems was further explored by loading them with thyme essential oil, demonstrating that keratin can act as a reservoir phase capable of modulating the retention and release of volatile bioactive compounds. Antioxidant analyses confirmed the ability of keratin-containing films to prolong functional activity, suggesting potential applications in active packaging and controlled-release systems. Finally, keratin integration during polymerization, was extended to polycondensation-based systems through the synthesis of PBS and unsaturated PBS materials in the presence of keratin. Although keratin incorporation affected molecular weight development, the resulting materials retained the polyester structure and exhibited modified thermal, rheological, morphological, and surface properties. Overall, this thesis demonstrates that feather-derived keratin can be successfully exploited as a multifunctional component in biodegradable polyester systems. Depending on the processing strategy and material architecture, keratin can act as a bioactive surface modifier, structural organizer, and functional reservoir, offering a promising path toward sustainable polymeric materials for functional applications.