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 H 2 O 2 before undergoing carboxymethylation. The bleached coconut husks were converted into CMC through alkalization, followed by etherification with NaOH and ClCH 2 COOH 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.