Extrusion Processing and Properties of Protein‐Based Thermoplastics

Abstract

Increasing interest in competitive, sustainable, and biodegradable alternatives to petroleum‐based plastics has encouraged the developmentof protein‐based plastics. The formation of a homogeneous protein melt during extrusion occurs through: denaturation, dissociation, unraveling, and alignment of polymer chains. The presence of covalent cross‐links is unfavorable, decreasing chain mobility, increasing viscosity and preventing homogenization. Proteins have high softening temperatures, often above their decomposition temperatures. To avoid degradation, the required chain mobility is achieved by plasticizers. By understanding a protein's physiochemical nature, additives can be selected that lead to a bioplastic with good processability. The final structural and functional properties are highly dependent on the protein and processing conditions.

Improvement of Food Packaging-Related Properties of Whey Protein Isolate-Based Nanocomposite Films and Coatings by Addition of Montmorillonite Nanoplatelets

“…This is achieved by reducing protein-protein interactions as highly polar plasticizer molecules interfere with other polar-binding sites, e.g., polar amino acids or water molecules (Cuq et al, 1997). In addition, due to their relative high hygroscopicity (and relative differences in hygroscopicity between glycerol and sorbitol) (Shaw et al, 2002;Verbeek and van den Berg, 2010), polyol plasticizers cause increased sorption of water molecules from the surrounding environment which leads to an increased free-volume and consequently further increased protein chain mobility (Lieberman and Gilbert, 1973). Thus, the mechanical properties of WPI-based nanocomposite films may be further improved by the choice of a more compatible plasticizer type (or mixture) and concentration (McHugh and Krochta, 1994).…”

“…And on the other hand, the strong influence of the plasticizer type may be explained by the molecular structure of the plasticizer molecules. Glycerol and sorbitol both are highly polar molecules consisting of 55.4% hydrophilic groups in case of glycerol, and 56.0% hydrophilic groups in case of sorbitol (Verbeek and van den Berg, 2010). However, at equal mass fractions of the plasticizing molecules, glycerol could be responsible for an increased polar fraction and consequently an increased SFE as due to its lower molecular weight of 92 g mol…”

Production and applications of crude polyhydroxyalkanoate-containing bioplastic from the organic fraction of municipal solid waste

“…Natural antioxidants, which present in biomass, can reduce the rate of thermal destruction of biopolymers (Giner et al 2012). Protein itself can be considered as the thermoplastic material but with addition of plasticizers, which inhibit the formation of cross-linking that can result in the formation of the thermoset material from extruded protein (Verbeek and van den Berg 2009). Therefore, the molding of composite crude PHA-containing bioplastic must be as short as possible to diminish the thermal decomposition of PHAs and other biopolymers of bacterial biomass.…”

Influence of sorbitol on mechanical and physico-chemical properties of soy protein-based bioplastics processed by injection molding

“…These tend to form three-dimensional macromolecular networks, which are stabilized by hydrogen bonds, hydrophobic interactions, and disulfide bonds [5] . The diversity in protein availability, as well as in their assembling, a big amount of biodegradable materials can be obtained, offering a wide range of techno-functional properties [6] .…”