Barrier and structural properties of polyethylene terephthalate film coated with poly(acrylic acid)/montmorillonite nanocomposites

Food packaging is one of the most important parts of the food industry, and polyethylene-based polymers have been widely used as food packaging films. In this study, corona-treated polyethylene terephthalate (PET) films were used to increase adhesion to the barrier coating solution for multilayered film formation and various concentrations of montmorillonite (MMT; 0, 1, 3, and 5 wt.%) were used to improve the barrier properties of PET films for food packaging after different treatments of MMT including ultrasonication with bath or probe and 100-W or 300-W microwave to evenly disperse MMT. Among them, a 300-W microwave treatment was most effective for size reduction of MMT particles. Even though 5 wt.% MMT was used to coat PET films with polyacrylic acid (PAA), good transmittance in the visible region (500 nm) was obtained, with a value similar to that of the neat PET film. The dispersion of MMT and binding of PAA/MMT nanocomposites were confirmed by field-emission scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy analyses. The water vapor and oxygen barrier properties of PET films were enhanced by PAA coating. Moreover, the oxygen permeability of PET films decreased via coating by PAA blended with 1 and 3 wt.% MMT. Based on these results, the PET film coated with PAA/MMT nanocomposites could be applied as food packaging films that require high gas barrier properties for oxygen-sensitive food.