The work presented here addresses the outer electroding of a fully textile piezoelectric strain sensor, consisting of bi-component fibre yarns of β-crystalline poly(vinylidene fluoride) (PVDF) sheath and conductive high density polyethylene (HDPE)/carbon black (CB) core as insertions in a woven textile, with conductive poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) coatings developed for textile applications. Two coatings, one with a polyurethane binder and one without, were compared for the application and evaluated as electrode material in piezoelectric testing, as well as tested for surface resistivity, tear strength, abrasion resistance and shear flexing. Both coatings served their function as the outer electrodes in the system and no difference in this regard was detected between them. Omission of the binder resulted in a surface resistivity one order of magnitude less, of 12.3 Ω/square, but the surface resistivity of these samples increased more upon abrasion than the samples coated with binder. The tear strength of the textile coated with binder decreased with one third compared to the uncoated substrate, whereas the tear strength of the coated textile without binder increased with the same amount. Surface resistivity measurements and scanning electron microscopy (SEM) images of the samples subjected to shear flexing showed that the coatings without the binder did not withstand this treatment, and that the samples with the binder managed this to a greater extent. In summary, both of the PEDOT:PSS coatings could be used as outer electrodes of the piezoelectric fibres, but inclusion of binder was found necessary for the durability of the coating.

Electrically conductive textile coatings have been prepared by the addition of a dispersion of poly(3,4-ethylenedioxy thiophene)-polystyrene sulfonate (PEDOT-PSS) and ethylene glycol to a polyurethane-based coating formulation. The formulations were designed to have similar viscosities, measured with a rheometer using a cone-and-plate set-up. The formulations were applied to woven poly(ethylene) terephthalate substrates using a direct coating method. The concentration PEDOT-PSS in the finished coatings varied between 0.7 and 6.2 wt%, the coating deposit between 19 and 155 g/m2 and the drying procedure between 4 hours at 20 C and 10 minutes at 150 C. Surface resistivity was measured with a ring probe and surface topology was addressed with scanning electron microscopy (SEM). The PEDOT-PSS concentration had a large effect on the resistivity, which dropped by five orders of magnitude with an increased concentration. The steepest decrease occurred between 1 and 3 wt% PEDOT-PSS, indicating a percolation threshold. An increased coating deposit resulted in a resistivity drop by a factor 10, but no significant effect on the resistivity of the samples could be ascertained by variation of the drying conditions when samples had been subjected to subsequent annealing.

Textile coatings with electrical conductivity were obtained by the addition of poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) and ethylene glycol (EG) to a polyurethane (PU)-based coating formulation. Variations of the coating formulation, the coating amount and the drying conditions, as well as the absence of an annealing step, were investigated. The coated fabrics were evaluated for tear strength and bending rigidity as well as surface resistivity and appearance before and after Martindale abrasion. A high proportion of PEDOT:PSS dispersion in the formulation and the presence of EG provided low surface resistivity. This composition resulted in softer samples with higher tear strength than those containing more PU-binder. All coatings proved to withstand abrasion to a similar extent. The surface resistivity increased gradually with the abrasion, about one half order of magnitude, except for those coatings that had been subjected to a faster drying process, where the surface resistivity increased somewhat faster.