PREPARATION OF NEW KERATIN-BASED BIOPLASTICS

Keratin is one of the most abundant structural proteins occurring in nature. The waste stream of low-grade wool from fabric preparation or chicken feathers from the poultry industry are keratin-rich materials currently underused. Hence, appropriate waste management and finding new methods to give value to these wastes are necessary. The transformation of underutilized biomass into high value-added products improves the environmental and economic sustainability of the value chain. Moreover, keratin shows versatile properties, including biocompatibility, biodegradability, and the presence of various functional groups. Keratin-rich waste is available at a low cost, making its use more attractive and advantageous because a waste stream will become a renewable source of materials. Wool and feathers waste comprises more than 90% of keratin proteins by weight with 5-10 mol% cysteine residues. The presence of intra- and intermolecular bonding, including the disulfide bridges formed between cysteine residues, ionic bonds, hydrogen bonds, or hydrophobic bonds, makes the keratin structure strong but, conversely, challenging to extract and reprocess. Consequently, the key to successful keratin extraction is the selection of appropriate chemicals to break these bonds. The initial part of this thesis investigates the efficiency of keratin extraction with the high yield target. Extraction protocols based on sulfitolysis and reduction with cysteine produced keratins that showed a good compromise between the molecular weights (in the range of 10−60 kDa) and yield (63 and 56%, respectively). In addition, the possibilities of keratin particle preparation were explored. Furthermore, this study describes the utilization of micro-contact printing technique to fabricate keratin-based micropatterns and evaluate their role in cellular guidance applications. Leveraging on the presence of the amino acid sequence leucine−aspartic acid−valine (LDV) in keratin, a tripeptide promoting cell adhesion, we showed that the presence of keratin micropatterns supports and facilitates dermal fibroblast cells adhesion and directs their growth orientation and, therefore, could be employed as the tissue regeneration templates. In this work, by adopting the circular economy model, we present a process for the valorization of keratin-rich wastes by converting them into flexible freestanding bioplastics. Reduced keratin was prepared using the sulfitolysis approach and modified with compounds containing carbon-carbon double bonds via the thiol-ene click reaction. For example, it was grafted with poly(ethylene glycol) methyl ether methacrylate (PEG ME MA), poly(ethylene glycol) dimethacrylate (PEG DMA), and epoxidized soybean oil acrylate (ESOA). The grafting efficiency was determined by nuclear magnetic resonance (NMR). Surprisingly, we found that this click chemistry process enables the direct conversion of the brittle keratin films into significantly more flexible, freestanding keratin-based films, which show thermoplasticity and reprocessing. The last part of this work refers to the synthesis of non-isocyanate polyurethanes (NIPUs) that constitute an alternative and environmentally friendly way to substitute polyurethanes. It describes the preparation of novel NIPU self-blown foams containing various proteins: keratin, gelatin, or zein. In this process, gaseous CO2 produced via hydrolysis or decarboxylation of 5-membered cyclic carbonate acts as a blowing agent and expands the polymer matrix. Fine-tuning parameters like temperature, protein loading, and component ratio allowed optimizing conditions to create self-blowing networks with densities as low as 156.7 ± 5.7 kg/m3. In summary, this thesis proposes new possibilities for valorizing protein-rich waste, giving a chance to utilize them for upcycling into value-added products. Moreover, preparing the materials with biomass can significantly reduce fossil fuel-based materials utilization.