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Preparation and characterization of corn zein nanocomposite coated polypropylene films for food packaging applications
Feasibility of prepared novel corn zein nanocomposite (CZNC) coated polypropylene (PP) film (CZNC-PP) structures for food packaging applications was investigated. Excellent barrier properties of corn zein nanocomposites were successfully combined with mechanically strong PP as an eco-friendly promising alternative to conventional barrier packaging systems. In this study, the effect of nano-sized layered silicate amount, type and processing of CZNC layer on the barrier, mechanical, optical and surface properties of the CZNC-PP films were investigated. Incorporation of organomodified montmorillonite (OMMT) by solution intercalation into zein coating matrix improved barrier and mechanical properties of PP films. The properties of single CZNC layers and interactions between layered silicates and zein matrix were also investigated. Fine delamination of OMMT in zein coating was found to be responsible for the improvements in oxygen and water vapor barrier of single corn zein layers due to more tortuous path formed for permeation of oxygen and water vapor. Prepared CZNC-PP films achieved nearly 4 times reduced oxygen permeability while WVP of the films were reduced by 30% with 5 wt% OMMT content in 5.9 m corn zein coating. Meanwhile, improvements were less significant for unmodified nanoclay loadings due to the incompatibility between unmodified MMT and corn zein. Hydrophobicity of CZNC surface increased with increasing OMMT loading in accordance with WVP results. Permeation data was fitted to various phenomenological models predicting the permeability of polymer nanocomposites as a function of clay concentration and aspect ratio of nanoplatelets. While significant improvements in mechanical properties including doubled elastic modulus and 75% higher yield strength of PP films were obtained, incorporation of OMMT in CZNC layer did not change the color of CZNC-PP films significantly.