Author:

Abstract:

Various characteristics of wheat gluten proteins, such as availability, unique intrinsic properties and biodegradability, make them attractive candidates for designing sustainable materials. The unique functionality of wheat gluten stems from its very high molar mass and the presence of cysteine amino acid residues, which upon heating provide the polymeric system with intermolecular disulfide crosslinks. Here, we demonstrate that with the use of proper additives one can obtain gluten based materials with properties that range from stiff to rubbery. A stiff material was produced by compression molding gluten with low levels of plasticizer. Routes for improving the ductility of the stiff material by manipulating the native protein structure were explored. In contrast, a rubbery thermoplastic vulcanizate (TPV) material was produced by extruding a gluten rubber precursor with a thermoplastic polymer, and subsequently injection molding to give a final product. Adhesion between the two phases was optimized by reactive compatibilization. The mechanical performance of stiff gluten materials was significantly improved by processing the proteins in denaturing conditions prior to molding. Molecular entanglements and polymer secondary interactions appeared to be increased and the material exhibited strain hardening under compressive loads. The TPV material had a finely dispersed particle morphology and showed excellent elongation in tensile tests as well as good mechanical recovery. Proteins are complex macromolecules with inherent folded structures, a diverse mix of functional monomers and a vulnerability towards degradation at high temperatures. With this in mind, polymer processing approaches need to be adapted and tailored in order to realize the potential of protein based materials. We have shown that high modulus materials approaching engineering polystyrene, as well as elastomers for the ‘soft touch’ industry, can be produced from a common protein feedstock. End of life options for both classes of materials have also been considered.