Effect of adding a reactive plasticizer on the mechanical, thermal, and morphology properties of nylon toughened wheat gluten materials

Blends of wheat gluten (WG) with up to 30% aliphatic nylon were prepared by mixing in 70% aqueous ethanol solution at 110 degrees C in a sealed reactor. After solvent removal and mechanical milling, rigid plaques were compression molded from the powdered blends. The microstructure of the molded plaques was studied via scanning electron microscopy. All compositions showed a phase separated morphology with seemingly poor compatibility between the two components. Up to 10% addition, the nylon was dispersed within the gluten matrix as discrete particles with an average diameter >10 mu m. At higher nylon volume fractions there was evidence for the presence of gluten sub-inclusions within the nylon phases. The dispersion of particles in a blend containing 10% nylon was improved and the particle size was decreased to roughly 5 mu m by addition of an epoxy functionalized ethylene glycol oligomer. The additive simultaneously lowered the modulus of the WG matrix and appeared to improve the interfacial bonding between the gluten and the nylon. In cross-sections of the ternary blends, fine filaments were observed spanning the gluten/nylon phases at the phase boundary. The compression molded plaques continued to exhibit brittle failure in mechanical bending tests characteristic of glassy gluten materials, however, the mechanical toughness was boosted to almost three times that of reference gluten plaques by the combined addition of the nylon and reactive plasticizer. (C) 2017 Wiley Periodicals, Inc.