Design and mechanistic understanding of graphene oxide reinforced zein nanocomposites with improved mechanical, barrier and thermal properties

Graphene oxide (GO)-based zein nanocomposite films with superior mechanical, barrier and thermal properties were fabricated by incorporating GO nanoparticles into corn protein zein (Z), through the solvent casting process. The study offers a mechanistic understanding of the effect of graphene oxide nanofiller on the physicochemical properties of zein. TEM of the zein-graphene oxide (Z-GO) nanocomposites showed uniform dispersion of GO sheets up to 1%GO loading. Mechanisms for Z-GO nanocomposite formation through covalent and noncovalent bonding are developed based on FTIR, FT-Raman and DSC results. At only 3% loading, the Young's modulus of a nanocomposite film increased by 300% and tensile strength increased by 80%. The increases in mechanical property improvements are accompanied by surface roughness increases as indicated by AFM studies. Even though GO is hydrophilic, the Z-GO nanocomposite films showed hydrophobic tendencies. The amount and degree of exfoliation of GO as well as the relative orientation of GO nanoparticles within the zein film all play an important role in the physical property changes of the film. The films became less permeable with increasing amounts of GO addition, as shown by water vapor permeability tests. GO increased thermal stability as shown by TGA.