Effect of different plasticizers on the mechanical and surface properties of wheat gliadin films

Films were prepared by casting alkaline solutions of gliadin, a major wheat storage protein fraction. Their compositions and mechanical and surface properties were analyzed. Five polyols of the ethylene glycol series and glycerol were compared as plasticizers. The plasticized film-forming solutions exhibited viscosities almost independent of shear rate. Glycerol-containing protein solutions had, however, a higher viscosity than others, after drying, concentrations of plasticizers in films were explained mainly, but not uniquely, by their volatility. At equal concentrations in films, glycerol and tetraethylene glycol were more efficient than the other plasticizers studied. A wide range of elongation (10-600%) was obtained when the plasticizer contents were varied, but the tensile strength (2-12 MPa) was always lower than that of usual synthetic polymer films. A negative relationship, independent of the plasticizing molecules used, was found between tensile strength and elongation at break of gliadin films. Surface hydrophobicity of films was high and no influence of plasticizers was observed.