Printable cellulose-based electroconductive composites for sensing elements in paper electronics

Conductive flexible hydrogel composites were printed on paper substrates using a functional ink, whichwas designed and formulated for screen-printing. The inkswere prepared using abundant and eco-friendlymaterials by blending carbon fibers into thematrix of a water-soluble cellulose derivative, carboxymethyl cellulose. For an optimal concentration of carbon fibers (10wt.%), the printed patterns exhibit a sheet resistance of around 300Ω/sqwithout any post-printing annealing process. The resistance of the screen-printed hydrogel patterns is sensitive to variations of relative air humidity throughmoisture adsorption and swelling of the cellulosicmatrix surrounding the carbonfibers. It was found that the sensitivity to temperature and humidity can be triggered by drying the printed patterns at 120 °C.Anegative temperature coefficient thermistor with a sensitivity of 0.079 °C at 25 °Cand a hygristor, where a variation in the RH from10% to 60% increases the resistance by 15 times, were screen-printed on paper using the formulated cellulose/carbonfibers based ink.