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 (Al³⁺) to fabricate PVA/CNF-C composite hydrogels. The PVA-TA@CNF-C-Borax-Al³⁺ hydrogel forms a multi-crosslinked 3D network through dynamic borate ester bonds between PVA and borax, coordination bonds between TA and Al³⁺, 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^-2 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⁺, Zn²⁺, and Al³⁺ cations. It was found that Al³⁺ 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.