Humidity sensing performance of polyaniline-grafted pullulan/PVA blend

This work reports the synthesis, characterization, and humidity sensing performance of a polyaniline (PANI)-grafted pullulan/polyvinyl alcohol (PULL/PVA) blend prepared via chemical oxidative polymerization. Structural and thermal analyses using FTIR, UV–Vis, DSC, XRD, and TGA confirm successful grafting and enhanced thermal stability of the composite films, which is further supported by HF–DFT calculations through agreement between experimental and calculated vibrational features. The fabricated sensors exhibit a nearly linear resistance response over a wide humidity range of 8–97% RH, with low hysteresis. The optimized composition shows fast response and recovery times of 17 s and 14 s , respectively, and stable performance over repeated humidity cycling. Measurements performed at a low bias voltage of 1 V indicate that humidity sensing is governed predominantly by electronic charge transport, with water-induced protonation modulating carrier density. The novelty of this work lies in combining PANI grafting with a PULL/PVA biopolymer matrix to achieve wide-range, fast, and stable humidity sensing while maintaining good film integrity and mechanical robustness. These results demonstrate the potential of PANI-grafted biopolymer blends for sustainable resistive-type humidity sensor applications.