Recent Developments in Thermo-Mechanical Processing of Proteinous Bioplastics

Proteinous bioplastics have received renewed interest over the last decade due to an awareness of the environmental impact of conventional plastics. In the second half of the previous century, further development of proteinous bioplastics was overshadowed by the fast growth in synthetic polymer technology. Today, proteins are considered a sustainable source for producing biodegradable alternatives to conventional plastics. Proteins are complex hetero-polymers, offering a number of different functional side groups capable of forming strong intermolecular bonds. Denaturing, cross-linking and plasticization are the most important aspects of protein processing. Typically, proteins and plasticizers are blended prior to thermo-processing, during which a highly viscous melt should be formed. The softening temperature of proteins is often above their decomposition temperatures, thereby making processability dependant on the type and amount of plasticizer. Generally, increasing the amount of plasticizer will lower the softening temperature and viscosity of the blend. Extrusion is particularly suitable for processing proteins, but excessive aggregation should be avoided by judicial use of chemicals, such as denaturants, plasticizers and reducing agents. Current technology described in recent patents mostly involves chemical modification of protein structures, incorporation of novel plasticizers and developing new process and specialized equipment. These are discussed further in the text.