Bio-based conductive composites: Preparation and properties of polypyrrole (PPy)-coated silk fabrics

Silk fabrics were coated with electrically conducting doped polypyrrole (PPy) by in situ oxidative polymerisation from an aqueous solution of pyrrole (Py) at room temperature, by using FeCl3 as catalyst. The amount of polymer deposited on the fabrics increased with increasing the reaction time or the concentration of Py in the reaction system. PPy-coated silk fabrics were characterized by optical microscopy (OM) and scanning electron microscopy (SEM), Fourier transform-infrared (FT-IR) spectroscopy, and thermal analysis (differential scanning calorimetry (DSC), thermogravimetric (TG)). OM and SEM showed that PPy completely coated the surface of individual silk fibres and that the polymerisation process occurred only at the fibre surface and not in the bulk. FT-IR (attenuated total reflectance (ATR) mode) showed a mixed spectral pattern with bands typical of silk and PPy overlapping over the entire wavenumbers range. The intrinsic crystalline structure and the molecular conformation of silk were not affected by the polymerisation. PPy-coated silk fabrics attained a significantly higher thermal stability than untreated ones, owing to the protective effect of the PPy layer against thermal degradation. PPy-coated silk fabrics displayed excellent electrical properties. Current versus voltage curves showed a linear fit, with higher current increments at higher PPy amount. The resistance of PPy-coated silk fabrics decreased exponentially with increasing the reaction time or the concentration of Py in the reaction system. Due to the Joule effect, the temperature of PPy-coated silk fabrics increased as a function of the electrical potential applied and of the amount of PPy. The encouraging results reported in this study open new perspectives for future application of PPy-coated silk fabrics, from interactive and smart textiles to innovative bio-based conductive composites for biomedical end-uses.