Room-temperature and recyclable preparation of cellulose nanofibers using deep eutectic solvents for multifunctional sensor applications.

Cellulose nanofibers (CNFs) have gained increasing attention due to their robust mechanical properties, favorable biocompatibility, and facile surface modification. However, green and recyclable CNF production remains challenging. Herein, a green, low-cost and room-temperature strategy was developed to exfoliate CNFs using deep eutectic solvents. A high average yield (~90 %) of CNFs was achieved during the recycling process. The resultant CNFs delivered favorable dispersion in water with an average length of ~5.3 μm and an average diameter of ~44 nm. The application of the resultant CNFs for multifunctional sensors was explored by fabricating the composite films of poly(vinyl alcohol) (PVA), tannic acid-decorated CNFs (CNF@TA) and Ag nanoparticles (AgNPs). As a stretchable strain sensor, the PVA/CNF@TA/AgNPs sample exhibited superior sensitivity (GF = 46.42), low detection limit (<1 %) and fast response (80 ms). This sensor possessed excellent temperature sensing performance with good accuracy (0.1 °C), high TCR (29.84/°C) in the body temperature region of 34-42 °C and desirable linearity (R = 0.981). In addition, the sensor could be used to monitor real-time skin moisture information. This simple and economical preparation strategy may facilitate potential applications of CNFs in the development of multifunctional sensors for wearable electronic devices.