CMC and CNF-based alizarin incorporated reversible pH-responsive color indicator films

•Smart color indicator films were prepared using CMC, CNF, and alizarin.•The indicator films showed UV–vis light barrier and antioxidant properties.•Alizarin showed pH-responsive color changing from yellow to purple in the pH 2−12.•The films showed stable and reversible color changes during repeated use in acid and base conditions. Smart color-changing indicator films were prepared using two different types of cellulose (CMC and CNF) and pH-sensitive dye, alizarin. pH-responsive color indicator films were produced by ionization and deprotonation of hydroxyl groups of alizarin phenolic compounds. The X-ray diffraction pattern of the color indicator film showed a new weak diffraction peak at 2θ = 13°, indicating the semi-crystalline character of alizarin. The indicator film showed UV–vis light screening properties and radical scavenging activity with enhanced thermal stability. The indicator film showed a distinct color change of alizarin from yellow to purple in the pH range of 2−12. In addition, the color indicator film showed stable and reversible color changes even after repeated changes in environmental pH. The pH-responsive color indicator films are likely to be used as an acid or base gas sensor due to the rapid response and reversible color change to the pH change in the packaging environment.