Tensile Properties of Extruded Zein Sheets and Extrusion Blown Films

Zein-based plastic sheets and films were formed by extrusion through a slit-die or blowing head. Zein was plasticized with oleic acid and formed into a wet moldable mass (resin) to feed the extruders. Both single- and twin-screw extruded sheets showed higher elongation at break, lower tensile strength, and lower Young's Modulus than non-extruded samples. Stress-strain plots for extruded samples showed evidence of plastic behavior. Observed necking of samples under tensile stress was also taken as evidence of plastic behavior. Small differences in tensile strength and elongation at break between single- and twin-screw extruded samples were attributed to the effect of small voids observed by SEM in single-screw extruded samples. Blown film extrusion was affected by feed moisture content and barrel temperatures. Optimal moisture content was determined at 14-15% while temperature at the three extruder zones was maintained at 20-25, 20-25, and 35 °C, respectively. Temperature at the blowing head was 45 °C. Film samples blown after either single- or twin-screw extrusion showed similar tensile properties to those of slit die extruded samples.