Effect of blend mixing and formulation on thermophysical properties of gluten-based plastics

Gluten-based plastics represent an interesting biodegradable alternative to conventional plastics, due to their greater mechanical properties when compared to other protein-based materials. In this manuscript, the effect that both blend mixing and the presence of sugars exerts on the gluten-based material properties was evaluated through rheological assays, water immersion tests, and microscopy. Thus, two different mixing procedures were performed (extrusion and internal mixing) for gluten samples plasticized by water and glycerol that were eventually injection moulded. The effect of trehalose and sucrose was studied including a 20 wt% content in the material formulation. It was observed that, even if no great differences were noticed when using different mixing processes, extruded blends, as well as the resulting bioplastics, displayed higher viscoelastic moduli than those mixed using an internal mixer. For both mixing procedures, bioplastics displayed a much more pronounced thermoplastic behaviour when compared to blends. The plasticizing effect of the sugar in the gluten-based plastics was apparent, denoted by a decrease in the viscoelastic properties, together with an increase in the water uptake capacity and their porosity. Interestingly, a superabsorbent material could be obtained when including trehalose in extruded samples, showing the feasibility of using gluten plastics in this field.