Flexible capacitive pressure sensor with high sensitivity and wide detection range applying solvent-exchanged porous lignin-cellulose hydrogel as the dielectric layer

Recently, the application of flexible sensors for wearable devices has attracted much attention from researchers. This study reports a capacitive pressure sensor with a solvent-exchanged porous lignin-cellulose hydrogel as the dielectric layer (SPLCH). The detection range and sensitivity of the sensor were modulated by adjusting the ratio of alkaline lignin(AL) and sodium lignosulfonate(SL). The existence of the porous structure and the ester bonds generated by cross-linking were demonstrated by material characterization experiments. The compression modulus of SPLCH is in the range of 310-320 kPa. The capacitive pressure sensing prepared in this way has a sensitivity of 5.18kPa-1 and 2.87kPa-1, a wide detection range (0-185.22 kPa), a short response-recovery time (25-50 ms), a low detection limit (1.875 Pa), and a good stability of repetitive loading (20,000 cycles) within two phases, respectively, which is finally applied practically in the detection of breathing, swallowing, human motion signals, speech recognition, pedometers, and Morse code information transmission scenarios. It provides a new idea for future porous structure fabrication processes and utilization of lignin to prepare flexible capacitive pressure sensors with high detection range and high sensitivity.