Smart packaging in the sustainability challenge : eumelanin as a UV-absorption enhancer of polymers

Abstract

The black-brown biopigment eumelanin screens the harmful ultraviolet (UV) radiation in the human skin. In industry, the absorption of plastics in the UV range is improved by the inclusion of additives. Our work reports an evaluation of the biopigment eumelanin as a nature-inspired additive for polymers to improve their UV-absorption. Eumelanin, being non-toxic and produced by natural sources, represents an interesting candidate for sustainable plastic additives. We fabricated eumelanin-including films of commercial linear low-density polyethylene (LLDPE), a plastic ubiquitous in packaging applications. The films were obtained by melt-compounding and compression molding. The melanin free acid treatment (MFA) was used to enhance the biopigment dispersion in the films. We observed that amounts of eumelanin as low as 0.8% wt. bring about an increase of the UV absorption up to one order of magnitude in the UVA range. We also assessed the effect of eumelanin on the film stability under prolonged UV irradiation: the biopigment proved to work both as UV-absorption enhancer but also as a photo-prooxidant, as inferred by thermogravimetric analysis (TGA) and infrared (IR) spectroscopy.