Reduced graphene oxide/polyurethane coatings for wash-durable wearable piezoresistive sensors

Graphene-based functional coatings for cotton textiles were realized through an easy dip-coating procedure. Cotton fabrics were coated with a reduced graphene oxide (rGO) layer and then protected with a very thin polyurethane (PU) layer that does not affect the flexibility and the hand of the pristine cotton. The application of the rGO coating induces electrical conductivity to the fabric and the application of the PU phase increases the durability of the coatings, that show very stable surface resistivity after 10 washing cycles performed at temperatures up to 40 °C. Furthermore, the rGO and rGO/PU coated fabrics show good comfort properties, increased thermal conductivity and breathability with respect to cotton. In particular, the realized coatings allow to confine the heat transfer in correspondence of a localized heating source, which is very interesting for thermal therapy applications. Finally, the rGO/PU coated fabrics present a piezoresistive behaviour characterized by very stable electrical response to applied stretching up to 50% deformation, high sensitivity especially at low deformations with gauge factor values up to 11.7 and fast response time down to 500 ms when stretched at 100 mm/min rate at 2.5% strain. Overall, the results demonstrate that rGO/PU coated fabrics are very promising wash-durable electrically conductive e-textiles with improved comfort, enhanced thermal conductivity for possible thermal therapy applications, and piezoresistive properties for sensing applications as human motion monitoring.