Preparation, physicochemical characterization, and ammonia-responsive behavior of poly(lactic acid) / polypyrrole / oxidized multi-walled carbon nanotube composite films with synergistically enhanced electrical conductivity

This study reports the development of high-conductivity composites based on a biodegradable polylactide (PLA) matrix reinforced with polypyrrole (PPy) and oxidized multiwall carbon nanotubes (OMCNTs). Quantum-chemical modeling using density functional theory (DFT; B3LYP/MidiX, n = 100) established the electronic baseline of the neutral polymer chain (Eg = 2.932 eV). Synthesis parameters, including low temperature (~ 0 °C) and the addition of cetyltrimethylammonium bromide (CTAB) surfactant, were optimized to produce a more ordered PPy structure with a maximum conductivity of 6.50 S/cm. Ultraviolet-visible (UV-Vis) spectroscopy confirmed a transition from the theoretical neutral state to an experimental doped state, characterized by broad polaron-band absorption in the NIR region. Unlike conventional binary blends, the ternary PLA/PPy/OMCNT architecture, prepared via a straightforward solution blending process, exhibits a co-supporting effect of the two fillers. The combination of components yields a maximum electrical conductivity of 2.04 S/cm, showing a nearly 10.7-fold synergistic enhancement compared to binary counterparts at identical total filler loadings. The resulting material demonstrates a pronounced electrical response to ammonia vapor, highlighting its potential as a dosimetric-type ammonia indicator. With a 255-fold decrease in specific conductivity upon exposure, these findings offer a practical pathway for the creation of eco-friendly, low-cost chemiresistive materials for environmental monitoring.