Polyvinyl alcohol-enhanced intelligent films for the accurate monitoring of pH via anthocyanin-induced color changes

In this paper, an intelligent film was developed using the cast film process, with acetylated distarch phosphate (ADSP) and polyvinyl alcohol (PVA) as substrates. Red cabbage anthocyanin extracts (RCAE) were incorporated as visual indicators of pH changes. This study aimed to enhance the mechanical strength and barrier properties of ADSP-based films by introducing PVA. The impacts of the ADSP/PVA ration on the film’s microstructure, physical, optical and mechanical properties were evaluated. In addition, the pH responsiveness of the intelligent film and the sensitivity to ammonia were investigated. Scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) showed that adding PVA improved the density of films by forming hydrogen bonds. X-ray diffraction (XRD) results showed that the diffraction peak intensity of the intelligent films increased with the increase of PVA content. When the volume ratio of PVA to the ADSP solution was 5:5, the water resistance, oxygen barrier, and tensile strength increased by 43.41%, 36.30%, and 50.00%, respectively, compared with pure ADSP films. Moreover, the light-blocking ability of films was enhanced by adding anthocyanins. The anthocyanin-rich films were proved to exhibit an obvious color response to pH. The sensitivity test of volatile ammonia showed that the color of intelligent films had different reactions with the increase in ammonia concentration. Notably, the detection limit of the prepared intelligent films for volatile ammonia was 1 ppm. This study proposed a promising avenue for the development of intelligent packaging materials. The practical application of these materials in the field of packaging needs to be further explored.