Thermal Transitions and Structural Relaxations in Protein-Based Thermoplastics

Protein-based thermoplastics resemble semi-crystalline polymers, suggesting the occurrence of a glass transition (Tg) and melting point. Denaturing a protein's native structure is often called melting, but this does not necessarily imply complete unfolding into a fully amorphous structure as true melting would. Protein secondary structures, such as α-helices and β-sheets, can remain after denaturing, stay intact above the Tg and do not necessarily melt at typical processing temperatures. This implies that consolidation of aggregated protein particles into a macroscopically monolithic material depends on inter-chain interactions in the amorphous phase and on newly formed secondary structures. Structural relaxations and transition temperatures of the amorphous phase are influenced and constrained by the presence of these secondary structures as well as heavily influenced by plasticizers.