A Comparative Study of Thermoelectric Properties of Various Polypyrrole-Coated Textiles

A polypyrrole (PPy) is an intrinsic conducting polymer, known for its excellent electrical conductivity and found suitable for use in electronic and electrical devices, including sensors, actuators, and conductive coatings. In spite of many advantages polypyrrole (PPy) is not much researched in thermoelectrical applications. This paper presents a comparative analysis of thermoelectric characteristics of polypyrrole-coated cotton, silk, and polyester fabrics. An in-situ chemical polymerization method is used to coat the textile fabrics with PPy in aqueous solution using ferric chloride as oxidant. Thermocouples are developed using PPy-coated textiles as p-type and metallic copper as n-type conductors. Various thermoelectric characteristics of the PPy-coated fabrics, such as electromotive force (emf) vs temperature gradient, power factor, figure of merit, and temperature vs Seebeck coefficient, are plotted and compared. PPy-coated cotton fabric shows the best thermoelectric performance among all thermoelectric fabrics. The electrical conductivity of the PPy-coated cotton, silk, and polyester fabrics are measured as 97.42 S/m, 37.28 S/m, and 66.22 S/m, respectively. Seebeck coefficients of PPy-coated cotton, silk, and polyester thermoelectric fabrics are found to be 16.5 μV/K, 14.14 μV/K, and 12.68 μV/K, respectively. The highest power factors of the PPy-coated cotton, silk, and polyester fabric/copper thermocouple are found to be 16.16 × 10^–3 µWm⁻¹ K ⁻², 3.42 × 10^–3 µWm⁻¹ K ⁻², and 3.51 × 10^–3 µWm⁻¹ K ⁻², respectively. At an absolute temperature of 277 K, the thermoelectric figures of merit for PPy-coated cotton, silk, and polyester/copper thermocouples are found to be 1.31 × 10^–4, 0.315 × 10^–4, and 0.483 × 10^–4, respectively. Field-emission scanning electron microscopy (FE-SEM) study reveals that the coating of PPy over the textile surface is uniform with granular morphology. FTIR study confirms significant intermolecular interaction between the textile fibres and PPy molecules. Differential scanning calorimetry analysis (DSC) and thermogravimetric analysis (TGA) of the PPy-coated textiles are done for comparative analysis of thermal behaviour of the materials. X-ray diffraction (XRD) analysis of PPy-coated textiles denotes the penetration of PPy molecules into the amorphous zone of the fibres.