Construction of zinc bromide/cellulose-reinforced high-performance antifreezing conductive poly(vinyl alcohol) hydrogels for flexible sensing applications

Objective The mechanical flexibility and low temperature adaptability of hydrogels are crucial for their application in flexible sensors. However, the existing poly(vinyl alcohol) (PVA) hydrogels are prone to freezing and failure at low temperatures, and it remains difficult to simultaneously improve their mechanical properties, conductivity, and environmental stability, which restrict their practical use under complex deformation and extreme environmental conditions. Therefore, this study aimed to develop a composite hydrogel with anti-freezing capability, high conductivity, and excellent mechanical performance to meet the requirements of flexible electronic devices in variable environments.

Methods In this study, bamboo dissolving pulp cellulose (BDP) was used as the raw material, and a zinc bromide (ZnBr₂) solvent system was employed to dissolve BDP and construct a rigid conductive BDP/Zn²⁺ network. This network was then incorporated into a flexible poly(vinyl alcohol) (PVA/GA) network through glutaraldehyde (GA) chemical crosslinking combined with freeze–thaw cycling, thereby preparing a composite hydrogel (BZPG) with excellent overall performance.

Results (1) The incorporation of BDP significantly enhanced the mechanical properties of the BZPG hydrogels. When the mass ratio of BDP/ZnBr₂ solution to PVA solution was 1.5∶1 and the GA content was 2.0%, the tensile strength and elongation at break of the obtained BZ_1.5PG_2.0 were increased by 75.7% and 330.2%, respectively, compared with the PVA hydrogel (H_1.5PG_2.0). (2) BZ_1.5PG_2.0 exhibited excellent ionic conductivity and freeze resistance. Under –20 ℃ conditions, its conductivity remained as high as 5.1 S/m, while the hydrogel still maintained good flexibility and could be bent freely without fracture. (3) BZ_1.5PG_2.0 demonstrated long-term stability and water retention. When stored at room temperature for 40 days, its mass loss rate was only 22.4%, which is significantly lower than that of the H_1.5PG_2.0 hydrogel. (4) The flexible strain sensors assembled from the BZ_1.5PG_2.0 hydrogel showed sensitive and stable signal responses to external stimuli, enabling reliable monitoring of human motion.

Conclusion A biomass-based composite hydrogel with high mechanical strength, high conductivity, and excellent freeze resistance was successfully developed by integrating a rigid BDP/Zn²⁺ conductive network with a flexible PVA/GA network. Owing to its simple fabrication process, renewable raw material, and outstanding comprehensive performance, this hydrogel showed great potential for application in wearable flexible sensors.