The coronavirus disease (COVID-19) was first identified in China, December 2019. Since then, it has spread the length and breadth of the world at an unprecedented, alarming rate. Severe acute respi... Graphical abstract

There is an increasing demand for sustainable and safe packaging technologies to improve consumer satisfaction, reduce food loss during storage and transportation, and track the quality status of food throughout its distribution. This study reports the fabrication of colorimetric pH-indicative and flame-retardant nanocomposite films (NCFs) based on polyvinyl alcohol (PVA) and nanoclays for smart and safe food packaging applications. Tough, flexible, and transparent NCFs were obtained using 15% nanoclay loading (PVA-15) with superior properties, including low solubility/swelling in water and high thermal stability with flame-retardant behavior. The NCFs showed average mechanical properties that are comparable to commercial films for packaging applications. The color parameters were recorded at different pH values and the prepared NCFs showed distinctive colorimetric pH-responsive behavior during the transition from acidic to alkaline medium with high values for the calculated color difference (∆E ≈ 50). The prepared NCFs provided an effective way to detect the spoilage of the shrimp samples via monitoring the color change of the NCFs during the storage period. The current study proposes the prepared NCFs as renewable candidates for smart food packaging featuring colorimetric pH-sensing for monitoring food freshness as well as a safer alternative choice for applications that demand films with fire-retardant properties.

In this study, a biocompatible and non-toxic pH-responsive composite film was prepared for food packaging application. The films are composed from polyvinyl alcohol as the main polymeric matrix, nanoclay as a reinforcing component, and red cabbage extract as a non-toxic indicator. The prepared films showed lower water uptake values when the amount of nanoclay was increased up to 25%. It was observed that the films become brittle at high loading of nanoclay (40%). The prepared films exhibited color change in alkaline and acidic medium due to the presence of red cabbage extract, which turned pinkish in acidic medium and greenish in an alkaline environment. The prepared films were characterized by FTIR and visible spectroscopy. The maximum absorption in acidic medium was (λ_max = 527 nm), while a red-shift occurred in the alkaline medium (λ_max = 614 nm). Future work will focus on the crosslinking of the prepared films to improve their mechanical properties.