Modifications induced by the addition of a nanoclay in the functional and active properties of an EVOH film containing carvacrol for food packaging

A nanoclay/EVOH composite has been developed to retard the release of a volatile antimicrobial from an EVOH film with application in active packaging. Concretely, 2% of bentonite nanoclay was added to the EVOH-29 matrix to modify its mass transport properties and consequently the activity of the antimicrobial film. The nanocomposite obtained, containing 5% of carvacrol as antimicrobial compound, is characterized in terms of antimicrobial solubility and release, water vapor solubility and permeability, oxygen and carbon dioxide permeability, diffusivity and solubility, thermal properties, and microstructural morphology. The clay-filled EVOH-29 film had a similar macroscopic appearance to the unfilled film, thanks to the excellent dispersion of bentonite nanoparticles as revealed by TEM images. Glass transition temperature was higher in the modified material, whereas fusion temperature was slightly lower, although the differences found were not significant. Water vapor, oxygen, carbon dioxide, and carvacrol solubilities were found to be higher for the modified polymer, whereas water vapor permeability, carvacrol diffusivity, and oxygen and carbon dioxide permeabilities and diffusivities were found to be lower for the nanocomposite. All parameters, with the exception of water vapor permeability, increased with the water concentration in the polymeric matrix. Therefore, the incorporation of 2% bentonite nanoclay in EVOH-29 provides a significant improvement in the controlled release of the antimicrobial agent with no relevant drawbacks.