Reprocessable 3D-Printed Conductive Elastomeric Composite Foams for Strain and Gas Sensing

Mechanically robust, highly compressible, and conductive thermoplastic polyurethane/carbon black foams were successfully fabricated via 3D printing. Thixotropic inks were formulated by dispersing nanoclay, carbon black, and polymer in an organic solvent, and then 3D multifunctional sensors were prepared by direct ink writing (DIN). Sequential removal of solvent and nanoclay yielded a porous polymer/carbon black structure, which maintained excellent elasticity and compression cyclability. The presence of carbon black in the foams led to good electrical conductivity and stable piezoresistive sensing signals at a strain of up to 80%, including the ability to distinguish human motions. Complementary to a decrease in resistance upon compression, the foam can be used as a gas sensor device, as exposure to volatile organic compounds causes the polymer to swell and an increase in resistance. The printed conductive foams can be easily recycled and reprocessed by dissolution in an organic solvent and subsequent re-3D printing, with little detriment to performance.