Phase separation of plasticizers in thermally aggregated protein-based thermoplastics

Blood meal-based thermoplastic protein (Novatein) was plasticized with up to 40 parts ethylene glycol, glycerol, propylene glycol, or tri(ethylene glycol) per hundred parts blood meal. The effect of plasticizers was investigated by relating the effect of equilibrium moisture content, phase separation, and protein secondary structure to the glass transition temperature and the mechanical properties. Plasticizers can diffuse through the polymer network and either be part of a protein-rich phase where primary plasticization dominates or a plasticizer-rich phase where secondary plasticization dominates. Equilibrium moisture content and added theoretical hydrogen bonding sites had the strongest correlation with the results. The point at which the equilibrium moisture content reached an equivalent moisture content (POE) to that of compositions without a plasticizer was found to be a critical point at which plasticization changes from primary to secondary, with a corresponding change in mechanical properties from brittle to ductile.