Effect of Formulation and Pressure on Injection Moulded Soy Protein-Based Plastics

The replacement of plastic materials derived from petroleum derivatives by highly biodegradable materials has been pursued to counteract the global environmental damage caused by their accumulated landfilling. In this sense, the feasibility of a soy protein isolate (SPI) to obtain processed materials has been extensively documented. In the present study, the characterization of injection moulded soy protein-based materials with different SPI/glycerol ratios (50/50, 55/45 and 60/40) has been carried out for different processing conditions of pressure (250, 500, 1000 bar) and temperature (80, 100, 120 °C). This characterization was performed in terms of their viscoelastic and tensile properties, water uptake capacity and soluble mater loss. An increase on the mechanical and viscoelastic properties was denoted when the protein content was higher, which could be related to an enhancement of interactions due to a greater proximity between chains. Similar effects were observed when the injection pressure was increased, eventually achieving a remarkable elongation at break value of 2, 7500% when processed at 1000 bar. Moreover, mould temperature was detected to be the most influential parameter on their water uptake capacity, resulting in a hindering of these parameter as higher temperatures were used. The effect of pressure on water uptake of these materials was opposite and milder to that found for temperature.