Poly(vinyl alcohol)/Polypyrrole@Cellulose Nanocrystal-Based Hydrogels for Wearable Sensors

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