Phytic acid extracted cellulose nanocrystals for designing self-healing and anti-freezing hydrogels’ flexible sensor

Phytic acid (PA), a naturally occurring organic acid, has been extensively researched in various fields such as flame retardants, electroactive materials, metal coatings and flexible sensors. This study proposes a method for extracting cellulose nanocrystals (CNCs) utilizing PA and ingeniously applies them to hydrogels, endowing the hydrogels with exceptional mechanical properties, anti-freezing capabilities and high electrical conductivity. First of all, the CNCs@PA and PA were integrated into a multi-component network consisting of hyperbranched polyethyleneimine (HPEI), polyvinyl alcohol (PVA), and zinc chloride (ZnCl2), and their complex interactions resulted in the formation of a robust three-dimensional structure. Consequently, the hydrogels formed after just a single freeze–thaw cycle exhibited exceptional mechanical properties (2.6 MPa) and a significant self-healing ability (92.3 %). Moreover, the strategic addition of PA to the hydrogels effectively immobilizes H2O, providing anti-freeze properties and enabling the hydrogels to maintain their structure and performance even at −20.0 ℃. Notably, following hydrolysis, PA generates a substantial number of hydrogen ions, markedly enhancing the conductivity (2.3 S/m) and a sensitivity gauge factor (GF = 2.5) of the hydrogels. This work offers a cost-effective, eco-friendly, and scalable method for the manufacturing of nanomaterials, and opens new avenues for creating anti-freeze wearable flexible sensors.