“Wetting Enhancer” Pullulan Coating for Antifog Packaging Applications

Abstract

A new antifog coating made of pullulan is described in this work. The antifog properties are discussed in terms of wettability, surface chemistry/morphology, and by quantitative assessment of the optical properties (haze and transparency) before and after fog formation. The work also presents the results of antifog tests simulating the typical storage conditions of fresh foods. In these tests, the antifog efficiency of the pullulan coating was compared with that of two commercial antifog films, whereas an untreated low-density polyethylene (LDPE) film was used as a reference. The obtained results revealed that the pullulan coating behaved as a "wetting enhancer", mainly due to the low water contact angle (∼24°), which in turn can be ascribed to the inherent hydrophilic nature of this polysaccharide, as also suggested by the X-ray photoelectron spectroscopy experiments. Unlike the case of untreated LDPE and commercial antifog samples, no discrete water formations (i.e., droplets or stains) were observed on the antifog pullulan coating on refrigeration during testing. Rather, an invisible, continuous and thin layer of water occurred on the biopolymer surface, which was the reason for the unaltered haze and increased transparency, with the layer of water possibly behaving as an antireflection layer. As confirmed by atomic force microscopy analysis, the even deposition of the coating on the plastic substrate compared to the patchy surfacing of the antifog additives in the commercial films is another important factor dictating the best performance of the antifog pullulan coating.

Characterization of PLA-limonene blends for food packaging applications

“…7-a). PLA-Lim15 ( This result suggested high transparency for films containing limonene and the possibility to see through the film is one of the most important requirements for consumers [41]. Negative values obtained for a* coordinate are indicative of a deviation towards green.…”

“…This behavior could be attributed to the limonene hydrophobic character. It has been reported that modifying the physicochemical properties of the material surface can control the water adsorption [41]. Therefore, PLA films containing limonene are also expected to have higher resistance to water adsorption than neat PLA film.…”

Engineering of New Proteinoids and Proteinoid Nanoparticles of Narrow Size Distribution for Anti-fog Applications

“…The manipulation of surface wettability through a combination of chemical and structural modifications has been of recent interest for a variety of applications such as anti-fog surfaces [8][9][10]. The "fog phenomenon" describes the condensation of water vapor to small drops that are dispersed on a solid surface.…”

“…In all examples mentioned, fog causes a reduction in the light transmission, hence damaging the visibility of the products. In food packaging, the esthetics of the package is damaged, and the quality of the food may decrease to the point where it can no longer be sold due to the accumulated moisture [8,11]. In agricultural films, the fog droplets reduce light transmission and inhibit the growth of crops.…”

“…Another important property of anti-fog films is the roughness of the film surface. Fog will accumulate on rough surfaces, as the water droplets penetrate the holes in the surface and stay there [8]. The combination of both a smooth surface and a low water contact angle yields a good anti-fog film.…”