Influence of colloidal silica nanoparticles on pullulan-coated BOPP film

The influence of two different types of colloidal silica (CS) nanoparticles in a main pullulan coating on bi-oriented polypropylene (BOPP) was evaluated in this work with the goal of exploring new and more advantageous applications in the food packaging sector. It was observed that the addition of the nanoparticles did not affect the friction properties of the pristine pullulan coating, with the static and kinetic coefficient mean values being 0.35 and 0.22, respectively. An improvement in the barrier properties against O2 and CO2 was observed for all the tested nanocomposite coatings. The best performance was provided by the particles with the highest surface area (750 m2 g-1) (O2TR ~30 mL m-2 24 h-1 and CO2TR ~80 mL m-2 24 h-1 at 23 °C under dry conditions) compared to the pristine pullulan-coated BOPP (O2TR ~480 mL m-2 24 h-1 and CO2TR ~1245 mL m-2 24 h-1). Noteworthy, the change in the permeability properties ultimately yielded a decrease of the CO2/O2 selectivity towards 1. The addition of CS nanoparticles did not modify the optical attributes of the pullulan coating, with the final haze values being approximately 1.5% for all nanocomposite layers. The wettability of the final coatings was influenced by the addition of the CS nanoparticles, with a remarkable decrease of the water contact angle to ~19° for the formulation loaded with the lowest concentration of silica nanoparticles that have the smallest size and the highest surface area. The potential application of the pullulan-CS coatings for MAP-packaged fruit and vegetables is suggested.