Poly(vinyl alcohol)/Polypyrrole@Cellulose\nNanocrystal-Based\nHydrogels for Wearable Sensors

Poor dispersibility of pure polypyrrole in the hydrophilic\nmatrixes\nhas limited its application in wearable sensors. Fortunately, the\nin situ polymerization of Py adsorbed on the CNC surface resulted\nin polypyrrole@cellulose nanocrystal (PPy@CNC) with excellent dispersibility\nand electrochemical properties. It was found that the pyrrole (Py)\nwas adsorbed on the CNC surface through the H-bonds. The adsorption\ncapacity of the CNCs for Py was 1006.7 mg·g<sup>–1</sup>. The PPy grew along the CNC surface during the in situ polymerization.\nThe PPy@CNC achieved a capacitance of more than 150.15 F·g<sup>–1</sup>. Even after 1000 CV testing cycles, nearly 98% of\nthe capacitance was preserved. Incorporating 3% PPy@CNC yielded, by\nrepeated freezing–thawing, a conductive PVA hydrogel with an\noptimal conductivity of 1.43 S·m<sup>–1</sup>, stress\nstrength of 0.23 MPa, and toughness of 265.2 kJ·m<sup>–3</sup>. As a strain sensor, its gauge factor reached up to 2.28 at the\nstrain of 100%. The test results on the human body also showed that\nthis hydrogel was an ideal material for a wearable sensor. Therefore,\nthe in situ polymerization of the Py confined to the CNC surface is\nan effective method for creating PPy@CNC-based conductive filler.\nThe green conductive hydrogel with good conductivity and mechanical\nperformance could be fabricated only by physical cross-linkage after\nincorporating this filler in PVA. As a result, the PPy@CNC has the\npotential to be applied to wearable sensors.