Poly (vinyl alcohol)/carboxylated cellulose nanofibers composite hydrogel flexible strain sensors.

This study introduces a method for constructing a dual cross-linked hydrogel network via combined chemical and physical processes. Carboxylated cellulose nanofibers (CNF-C) and tannic acid (TA) were integrated into a borax-polyvinyl alcohol (PVA) matrix, followed by the incorporation of metal cations (Al) to fabricate PVA/CNF-C composite hydrogels. The PVA-TA@CNF-C-Borax-Al hydrogel forms a multi-crosslinked 3D network through dynamic borate ester bonds between PVA and borax, coordination bonds between TA and Al, and hydrogen bonds from CNF, endowing the hydrogel with excellent mechanical properties. The PTCB(PVA-TA@CNF-Borax) hydrogel, with a TA to CNF-C mass ratio of 1:4, exhibits superior mechanical strength(1.6 MPa), robust conductivity(1.7 × 10 S/cm), and stable thermal properties(95 % at 60 °C). Furthermore, the influence of different valence ions on the hydrogel's properties was systematically investigated through the introduction of Na, Zn, and Al cations. It was found that Al can effectively enhance the tension and elasticity of the crosslinked network, improving the mechanical adaptability and sensitivity of the hydrogel. Additionally, this hydrogel system exhibits excellent strain-sensing capabilities. When employed as a self-powered triboelectric nanogenerator sensor, it can generate a stable open-circuit voltage of 2 V.