Preparation and characterization of corn zein coated polypropylene (PP) films for food packaging applications
The plasticized corn-zein coatings on polypropylene (PP) films as an alternative to multilayer packaging films consisting of non-degradable polymers were prepared to evaluate barrier, mechanical, thermal, surface and optical properties of the resulting coated film, as affected by coating formulation (solvent, corn-zein, plasticizer concentration, and plasticizer type). PP films coated with corn zein were obtained through a simple solvent casting method. Corn-zein with different amounts (5% and 15%) was dissolved in 70% and 95% aqueous ethanol solution at 50oC, respectively. Solutions of corn-zein plasticized by polyethylene glycol (PEG) and glycerol (GLY) with various levels (20% and 50%) were applied on corona-discharged-treated PP film. The resulting corn-zein coated PP films showed good appearance, flexibility and adhesion between the coating and the base film. The coated PP films showed a significant (P<0.05) increase in barrier (water and oxygen) properties and improvement in mechanical properties when coating formulation consisted of higher corn-zein content and lower amount of GLY as plasticizer. Furthermore, zein coating increased the service temperature range of the PP films, and promised good printability on the surface due to contact angle results. The statistical analysis defined that the key parameters of coating formulation that had major effect on the final properties of coated PP films as corn-zein concentration, plasticizer concentration, and plasticizer type while ethanol concentration was found to be as less effective parameter compared to others. In conclusion, corn zein coatings with appropriate formulation on PP films could have potential as an alternative to conventional synthetic coatings for food packaging applications.