Wheat gluten, a set of proteins from the wheat kernel, is commonly used to process polymeric materials, usually in the presence of glycerol as a plasticizer. Its use is however limited, because of its high sensitivity to water and relatively poor mechanical properties when compared to synthetic polymers. The influence of the glycerol content on the water absorbance, the phase separation and their glass transition were first studied.
Then, another biopolymer, wood lignin, has been incorporated into the materials in order to enhance their properties. The influence of different types of lignin from the paper pulp industry, Kraft lignin and lignosulfonates, have been investigated. Kraft lignin addition enhances materials rigidity and thermal properties, and reduces the water sensitivity, whereas lignosulfonates allow to decrease the glycerol content, resulting in better mechanical properties and reduced water sensitivity.
To gain insights into the interactions between gluten and lignins, several fractionation procedures have then been carried out. The influence of the protein type and lignin molecular mass could be pointed out, and were correlated to the materials macroscopic properties.