Extrusion Processing and Properties of Protein-Based Thermoplastics

Increasing interest in competitive, sustainable, and biodegradable alternatives to petroleum‐based plastics has encouraged the developmentof protein‐based plastics. The formation of a homogeneous protein melt during extrusion occurs through: denaturation, dissociation, unraveling, and alignment of polymer chains. The presence of covalent cross‐links is unfavorable, decreasing chain mobility, increasing viscosity and preventing homogenization. Proteins have high softening temperatures, often above their decomposition temperatures. To avoid degradation, the required chain mobility is achieved by plasticizers. By understanding a protein's physiochemical nature, additives can be selected that lead to a bioplastic with good processability. The final structural and functional properties are highly dependent on the protein and processing conditions. Thermoplastic protein‐based polymers are gaining interest, mainly supported by increased environmental awareness. Proteins can be extruded like synthetic thermoplastics, given that the strong intermolecular forces present between protein molecules are overcome. This can be achieved during extrusion by the addition of water, plasticizers, and other additives, such as reducing agents.