Effect of extrusion processing on properties of zein-fatty acids sheets

The feasibility of applying extrusion technology to the processing of zein-fatty acids resins was investigated. Zein resins were prepared in the laboratory by mixing zein and fatty acids (1:0.75 w/w) in an aqueous ethanol solution followed by the recovering and drying of plasticized zein into a granular solid. Granular resins were melted in a twin-screw extruder and collected as large pellets, which were immediately rolled into sheets. A response surface experimental design was followed to investigate the effect of three extrusion parameters (barrel temperature, screw speed, and amount of solvent added during extrusion) on mechanical properties of the resulting sheets. Zein resins were uniformly melted and flowed smoothly through the extruder barrel. Mechanical properties of sheets prepared by extrusion were comparable to those of samples prepared by a previously described bench-top method, indicating the feasibility of extrusion for processing of zein resins. Extrusion temperatures included in the experiment affected mechanical properties and water resistance of zein sheets. High temperatures increased tensile strength but decreased elongation at break of resulting sheets. The storage stability of zein sheets was also investigated. Zein sheets maintained their mechanical properties after three months of storage at room temperature, indicating their stability in storage. SEM images of sheet external and cross-section surfaces seemed to show an entanglement of fiber-like structures. Further research is needed to determine sheet morphology.