Preparation of high-strength and low-temperature-resistant nanocellulose/polyvinyl alcohol conductive composite hydrogel and its application in flexible sensing

Nanocellulose is an excellent nano-reinforcing material with large aspect ratio, high elastic modulus and specific surface area, and abundant surface functional groups. Nanocellulose (cellulose nanofibers, CNFs) was first used as the dispersion medium to disperse the MXene nanosheets for preparing the nanocellulose/MXene nanocomposites, and the interaction between nanocellulose and MXene was characterized and analyzed by FTIR and XPS. Then the CNF-MXene/PVA composite hydrogel was prepared by using the CNF-MXene nanocomposites as the reinforcing filler and polyvinyl alcohol (PVA) as the matrix, which was further treated with KOH solution to improve the mechanical properties of the composite hydrogel and endow the composite hydrogel with excellent ionic conductivity. The composite hydrogel exhibites excellent mechanical properties, the tensile strength and elongation at break were 22.5 kPa and 1098.2%, respectively. The hydrogel also possesses high conductivity (2.38 S/m), anti-freezing, and excellent strain/pressure responsive properties. Thanks to the extremely low detection limit (100 mg) and extremely fast response time (225 ms), the hydrogel-based strain/pressure sensor could monitor the pressure changes causes by pulse beating and small vibration of throat. Therefore, the composite hydrogel-based flexible sensor showes great promising applications in the next-generation wearable electronics and human-machine interaction.