Protein thermoplastics, like Novatein, typically comprise a polymer, additives, and plasticizers. During foaming, the plasticizers performed different functions; triethylene glycol (TEG) affected the Tg of the polymer, while water altered the shear viscosity and urea the extensional viscosity. Water and urea also functioned as blowing agents; increasing urea increased the expansion ratio, while an increase in TEG and water decreased it. It was concluded that at this level of plasticization, phase separation occurred and that the plasticizers are most influential during late bubble growth and stabilization. Contrary to previous thought, increasing water had no effect on the Tg, but did lower the shear viscosity, while increasing TEG had the opposite effect. This enables the properties of protein thermoplastics to be tailored during development. During foaming, lower viscosity allows more time for gases to diffuse before the viscosity in the surrounding polymer increases, restricting bubble growth. At higher TEG content, the material is processed further above its Tg, slowing down stabilization and decreasing expansion. This study clarified the role of plasticizers during foaming and showed a decrease in random coils and β‐turns (measured by FT‐IR) with increasing expansion ratio. Knowledge of these mechanisms enables tailoring properties of protein thermoplastics foams during development. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47781.

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Novatein is a biopolymer produced from blood meal and can be foamed for use as a packaging material. The effect of foaming on protein ordered structures such as a-helices and b-sheets was investigated using synchrotron Fourier transform infrared (FTIR). Foaming caused a reduction in ordered structures due to an increase in random coils. FTIR also revealed a higher proportion of plasticizer (triethylene glycol, TEG) and b-sheets toward the surface of enclosed bubbles. Increased TEG will assist foaming with greater plasticization aiding nucleation, while b-sheets contribute to bubble stabilization. These structural changes occur as foaming takes place close to the degradation temperature of Novatein, and coincide with melting of a-helices and/or b-sheets. A more amorphous polymer is therefore produced which is subsequently easier to foam due to its increased elasticity. V C 2017 Wiley Periodicals, Inc. J.Appl. Polym. Sci. 2018, 135, 46005.Normal limits as defined in literature were redefined due to the shape of the second derivative.

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