Effect of aqueous and alcoholic shear treatments on the properties of rigid plastics from wheat gluten

• The number of defects in rigid gluten plastics was reduced by shear pre-treatments.
• Strain hardening of gluten plastics can be increased by alcoholic pre-treatments.
• Extrusion and solvent mixing may be suited to blending gluten with other polymers.

Two procedures conducive to blending wheat gluten with other polymers in view of enhancing the mechanical properties of rigid gluten materials, were investigated. Method 1 involved extrusion of an aqueous gluten dough at 30–110 °C. In method 2, gluten was processed in 70% ethanol at temperatures ≤130 °C in a pressurised reactor. After solvent removal, the dried powders were compression moulded into products exhibiting fewer defects than gluten moulded directly without any pre-treatment, suggesting that application of either method improved polymer flow. In temperature regimes where little or no crosslinking occurred during the shear treatments, the mechanical properties of compression moulded samples were also better than those of directly moulded gluten. Further improvements were observed when glutenin aggregates depolymerised via breaking of disulfide bonds. This occurred in method 2 at temperatures exceeding 90 °C. Materials processed via method 2 at 110 °C displayed a high level of strain hardening in compression tests, which suggests an increase in molecular entanglements.

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