Effect of Co-Rotation and Counter-Rotation Extrusion Processing on the Thermal and Mechanical Properties, and Morphology of Plasticized Soy Protein Isolate and Poly(butylene succinate) Blends

Blends of plasticized soy protein isolate (PSPI) and poly(butylenes succinate) (PBS) were prepared in a 70:30 wt.-% ratio via co-rotation (CR) and counter-rotation (CTR) twin-screw extrusion. The novelty in this research suggests that CTR extrusion provides enhanced interfacial adhesion, tensile elongation and prolonged onset (T-onset) and end (T-end) thermal degradation temperatures. The average tensile strain at break showed to be approximate to 40% higher for PSPI-CTR material and approximate to 55% higher for PBS:PSPI-CTR (70:30) blends. Both T-onset and T-end for CTR processed PBS:PSPI(70:30) and PSPI were approximate to 10 degrees C greater than those of CR. These results suggest that the enhanced shear rate and radial motion associated with CTR allows for better destructurization and blending of PSPI within the PBS matrix, resulting in enhanced structural integrity due to the formation of possible amide and ester linkages. Scanning electron microscopy (SEM) provides further support based on evidence of reduced voids on the surface of all CTR blends