Thermoplastic Processing of Blue Maize and White Sorghum Flours to Produce Bioplastics

In this study, we evaluated the feasibility of producing bioplastics from blue maize (BM) and white sorghum (WS) flours by thermoplasticization using sorbitol and glycerol as plasticizers and by using extrusion and compression molding. The analyzed variables were screw speed rotation (50-70 rpm), extrusion temperature (100-140 °C), number of extrusion passes (1 or 2), and chemical modification of the flours with maleic anhydride. Mechanical characterization revealed a major effect of the extrusion temperature among the processing variables studied, and the microstructure and slab color varied significantly with temperature. Chemical modification also had a major effect on the properties of the produced materials. Slabs made with chemically modified flours showed increases in their mechanical properties compared to their native counterparts. Consistently, scanning electronic microscopy revealed a more uniform microstructure in slabs made with chemically modified flours, and dynamic mechanical analysis indicated a better matrix-plasticizer interaction in these slabs when compared to slabs made with native flours. The BM and WS flours were determined to be suitable raw materials for producing thermoplastic materials.