Optical and thermal properties of intelligent pH indicator films based on chitosan/PVA and a new xanthylium dye

Abstract

Intelligent food packaging systems register and monitor food quality through data carriers, sensors or indicators. Food spoilage often leads to pH variations which can be easily evidenced through a colorimetric pH indicator. The objective of this study was to obtain and characterize intelligent pH indicator films based on biopolymers, namely chitosan and polyvinyl alcohol, doped with a new bio-inspired synthetic dye. UV–Vis, FTIR and 1D and 2D NMR techniques were used to characterize the xanthylium dye. The pH-dependent photochromic properties of the synthesized compound were confirmed through a UV–Vis spectroscopy study. The indicator films were obtained by using the solvent casting technique, and their optical and thermal properties were evaluated. When subjected to pH variations in aqueous solutions and in milk stored at improper temperatures, the films showed color changes. The thermal properties of the dye-containing films were evaluated through TG/DTG analysis. It was found that the inclusion of the dye does not change the thermal behavior of the films compared with that of the dye-free chitosan, PVA and chitosan/PVA blended films.