Vapor Barrier Properties and Mechanical Behaviors of Composite Hydroxypropyl Methylcelluose/Zein Nanoparticle Films

Composite films of hydroxypropyl methylcellulose and zein nanoparticles (ZNP) were prepared to create a biopolymer-based film with reduced vapor permeability and potential for active-packaging applications. Microscopy verified the dispersion of ZNP with diameter of 100 nm throughout the width and depth of the films, with ZNP forming sub-micrometer clusters of nanoparticles at loaded volume fractions > 0.15. Incorporation of non-hygroscopic ZNP increased film-water contact angles to > 70 degrees and decreased water vapor permeability of films by 10-30%. Extensional measurements of films described an increase in tensile strength from 27 kPa to 49 kPA, a decreased capacity to elongate, and an initial increase followed by gradual decrease in Young's moduli with increasing ZNP fractions. Decreased elasticity was observed within microscale regions of the films at higher ZNP volume fractions using dynamic force spectroscopy, and the trends were strongly correlated with bulk Young's moduli of the composite films. A mathematical model rationalized the initially increased and subsequently decreased Young's modulus by the change in ZNP dispersion/clustering combined with a collapse of the interfacial zone surrounding ZNP.