Sustainable bioproducts through thermoplastic processing of wheat gluten and its blends

Proteins are unique biopolymers extensively used for food and non-food applications. In addition to animal proteins such as poultry feathers that are generated as byproducts, plant proteins such as wheat gluten and soy proteins are also available in large quantities at reasonable cost. Since proteins are inherently non-thermoplastic, they cannot generally be processed by thermal treatments. Further, most proteins do not dissolve in common solvents either. Hence, most of the non-food applications of plant proteins require extensive chemical and physical modifications which increases cost and also reduces the biodegradability of the products developed. However, studies have shown that proteins including wheat gluten and keratin can become thermoplastic under specific conditions, when adequate pressure, heat and moisture are applied. Similarly, proteins can be made thermoplastic after physical or chemical modifications or by using plasticizers and compatibilizers. Based on such modifications, completely biodegradable composites with proteins as matrix and natural fibers as reinforcement and even all protein composites have been developed. Proteins as matrix offer new avenues to obtain sustainable, green composites with unique properties. Wheat gluten is a novel protein that has many distinct properties and characteristic behavior. Wheat gluten has been used for several non-food applications mostly by dissolving and solution casting which is a cumbersome process and restricted to only a few types of materials that can be developed. Alternatively, wheat gluten has been made thermoplastic using chemical, physical modifications or a combination of both. Several organic and inorganic additives, crosslinkers and plasticizers have also been added to ensure thermoplastic processing of wheat gluten and to obtain products with properties suitable for commodity applications. In this review, we discuss the processes and possibility of converting wheat proteins into thermoplastic products and as matrix for composites and the properties and applications of the wheat gluten based thermoplastics.