Smart sensing film developed by polyvinyl alcohol/carboxymethyl cellulose doped with anthocyanin extract as a natural pH indicator

Abstract This research focused on developing a pH-responsive film based on a poly(vinyl alcohol)/carboxymethyl cellulose (PVA/CMC) composite combined with anthocyanin, a natural pH indicator extracted from butterfly pea flower (ABA). Coconut husks were treated and bleached with NaOH and H2O2 before undergoing carboxymethylation. The bleached coconut husks were converted into CMC through alkalization, followed by etherification with NaOH and ClCH2COOH in an alcoholic medium. The CMC/PVA film, incorporating ABA as a natural pH indicator, was prepared via casting with varying anthocyanin contents. The PVA-to-CMC ratio and ABA content significantly influenced the mechanical properties and pH sensitivity of the ABA-PVA/CMC films. Notably, films with a PVA/CMC ratio of 4:1 exhibited the highest tensile strength and uniform dispersion. Additionally, ABA-PVA/CMC films displayed strong pH sensitivity, changing color distinctly at different pH levels.