Supercritical CO2 impregnation of α-tocopherol into PET/PP films for active packaging applications

Abstract

Supercritical carbon dioxide impregnation technique was used to adsorb α-tocopherol (TOC), a natural antioxidant, on monolayer and multilayer polyethylene terephthalate (PET)/polypropylene (PP) films to obtain active packaging. Supercritical impregnation experiments were performed at 17 MPa and 40 °C using different supports: PP films, PET films (ut-PET), corona discharge treated PET surface (ct-PET) films, PET/PP films. Supercritical carbon dioxide (SC−CO2) impregnation revealed to be an effective technique in the attainment of active packaging films. Indeed, very high amounts of TOC were impregnated (up to 3.2 mgTOC/cm2film considering a monolayer PP film and up to 2.66 mgTOC/cm2film considering a multilayer film). Field emission scanning electron microscopy (FESEM) showed how the impregnation with TOC modified the film surface (which became heterogeneous). Fourier transform infrared spectroscopy (FT-IR) revealed the presence in the impregnated films of both TOC and polymers characteristic bands. Differential scanning calorimetry (DSC) indicated that the presence of SC-CO2 induced a slight reduction in the crystallinity percentage of the polymers. Moreover, migration of α-tocopherol from the packaging films in a food simulant was studied using UV–vis spectroscopy, and the effectiveness of the supercritical impregnation to obtain the controlled-release of the active agent was verified. Finally, antioxidant activity tests confirmed the preservation of TOC antioxidant power after its impregnation on monolayer and multilayer films.