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.

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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. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46746.

Bioplastic materials have been developed in response to environmental concerns regarding the widespread use of conventional polymers. It is one of the cornerstones in the circular economy approach that is expected to change the way materials and energy are produced and consumed. However, bioplastics still cover less than 1% of total market, and the industry is still in its early stages. A holistic sustainability assessment takes into account the origin of a material, its end‐of‐life destination, as well as social and economic effects; new materials in the market need to improve sustainability but also be cost‐ and performance‐competitive. Biobased polymers have taken the leading role in the market, largely because of total production of bioplastics is expected to increase almost fivefold over the next 5 years. This article provides an up‐to‐date definition of bioplastics, their environmental profile, and contribution to the global economy.

Novatein is a thermoplastic produced from blood meal and is used in different agricultural applications. Novatein has some unique processing challenges and its rheology was studied using screw‐driven capillary rheometry, with a particular focus on sheet extrusion using ethylene glycol, glycerol, propylene glycol (PG), or triethylene glycol (TEG) as plasticizers. The entrance pressure drop contributed up to 44% of the total pressure drop (entrance and capillary pressure drop), but this was significantly reduced by plasticization or increased temperature. Polyol addition led to higher shear viscosities in comparison to no polyol plasticization, most likely due to improved chain mobility resulting in orientation effects. Elongational flow was dominated by primary plasticization of the protein‐rich phase and changes in secondary structure, whereas secondary plasticization (phase separation into a polyol‐rich phase) played a significant role in the reduction of the shear viscosity. Of the selected plasticizers, PG showed the most efficient plasticization in both shear and elongational flow. When combined with the beneficial secondary structural changes brought about by TEG, the sheet forming ability of Novatein was drastically improved.