Mechanochemical characteristics and influence mechanisms of a biomass hydrogel artificial muscle based on different parameters of the sodium alginate adjustment

Biomass hydrogel artificial muscle (BHAM) is a kind of ionic electroactive polymers, such as ionic polymer gels of good biocompatibility and stimulus responsiveness under electric field, which is largely used in the fields of soft robots and electric actuators. In this paper, based on the freeze-drying process, effect and influence mechanisms of sodium alginate (SA) parameters adjustment on the BHAM mechanochemical characteristics were researched extensively, which was verified by a set of perfect characteristic evaluation and experimental test methods, such as the porosity P (v%), water retention rate W_r (w%), mechanochemical property testing and scanning electron microscope shots. The results showed that when the concentration of SA was 20 g l⁻¹, the actuating film of BHAM had suitable thickness and stomata in macroscopic appearance, and its micro pore distribution and size were uniform with the thin pore wall, which resulted in the highest porosity (i.e. ion channel) of 73.5 v%, the largest water retention rate of 76.2 w% and the optimum tensile strength of 0.38 Mpa. Furthermore, calcium chloride (CaCl₂) was adopted as a cross-linking agent to react with the SA to form calcium alginate (CA) by different CaCl₂ cross-linking ratios, that was to modify the three-dimensional microstructure of the BHAM to improve its mechanical properties with the best deflection displacement of 23.9 mm and bending strain of 3.45% under the ideal CaCl₂ cross-linking ratio of 1%. Besides, the diffraction of x-rays analysis and thermal decomposition experiments of the BHAM were performed, which was demonstrated that the thermal stability of the CA-based BHAM was higher than that of the SA-based BHAM.