The role of water in plasticizing thermally aggregated protein-based thermoplastics

摘要

Blood meal-based thermoplastic protein (Novatein) is made from a highly aggregated protein network, and as a result, water plays a significant role during plasticization. Novatein was plasticized with up to 40 parts tri(ethylene glycol) or glycerol and equilibrated at different relative humidities. The equilibrium moisture content (EMC) was the dominant factor determining mechanical properties, with a brittle to ductile transformation observed at 8% EMC. However, EMC was not sufficient to explain this behavior and the point of equivalence (POE) was introduced to differentiate between primary and secondary plasticization. It was shown that the constraint theory, which relates to hydrogen bonding plasticizers, was more applicable below the POE whereas the free volume theory, and the formation of the microscale phase separation, described material behavior above the POE. Water played a critical role improving ideal mixing conditions in the material and was also related to the brittle-to-ductile transition. (c) 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46746.