Curcumin-Activated Copolymer Coatings for Barrier Enhancement and Antioxidant Activity in Recycled Polypropylene

The recycling of postindustrial flexible polypropylene into flexible food packaging is industrially limited due to drastic deterioration in the polymer properties, as well as a concerning increase in overall migration of the polymer to food, even when this rPP is not of the postconsumer or household source. Active polymer coatings have been proposed as an alternative to functionalize and improve the properties of packaging films; however, there is a research gap regarding the effect of the polymer coating’s chemical structure on the activity and properties of the packaging. This work investigated the tuning of the properties and antioxidant activity of postindustrial recycled flexible polypropylene (rPP)-based films by developing and applying curcumin-activated coatings. Curcumin-activated ethylene and acrylic copolymer coatings were developed, and their effect on the properties of cast-extruded rPP was systematically and comprehensively compared. The polymer materials were characterized using ATR-FTIR, optical microscopy, SEM, DSC, TGA, tensile testing, water vapor and oxygen permeability, overall migration, curcumin release measurements, and antioxidant activity assessed by the ABTS method to evaluate their potential for packaging applications in preserving oxygen-sensitive foods. The curcumin-activated ethylene copolymer-based coating increased Young’s modulus by 44% and tensile strength by 47% of rPP. Meanwhile, the curcumin-activated acrylic coating increased stiffness by 28%. The active copolymer solutions, incorporated by coating onto the corona-treated rPP, reduced its oxygen permeability by factors of 5.4 and 1484 for the acrylic and ethylenic types, respectively. The developed bilayer composites exhibited high antioxidant activity in a fatty food simulant, indicating the potential to prevent food oxidation, regardless of the type of activated copolymer. Nonetheless, only the ethylene-vinyl alcohol-based copolymer was within the overall migration limit for food contact in isooctane.