A Water-Resistant Poly(Vinyl Alcohol) Film Grafted by Sodium Lignosulfonate for Biocompatible Polymer Actuators

An ionic polymer–metal composite (IPMC) offers advantages of low driving voltage, large strain, and high flexibility, widely used in flexible actuation and sensing. Traditional IPMC actuators use a commercial Nafion film as the electrolyte film and face drawbacks of low water uptake (WU), high modulus, high cost, and poor biocompatibility. This study reports a poly(vinyl alcohol) (PVA) electrolyte film that combines waterproof properties with ion exchange functionality. Glutaraldehyde (GA) serves as a cross-linking agent that connects adjacent PVA molecular chains to form an insoluble network polymer. Sodium lignosulfonate (SLS) is grafted onto PVA chains through GA, creating ion exchange sites. The obtained SLS-PVA film exhibits ideal IPMC-related properties, including high water resistance (no visible dissolution in 90 °C hot water), favorable mechanical properties, (Young’s moduli ranging from 23.21 to 34.84 MPa, elongations at break ranging from 154.89% to 289.39%), 0.99 mS/cm ionic conductivity (exceeding Nafion’s 0.83 mS/cm), and superior WU (over 65.42%, significantly higher than Nafion’s 38.59%). When driven by hydrated Li+ under a 10 V, 0.1 Hz sinusoidal signal, the SLS-PVA film-based IPMC actuator demonstrates stable and symmetrical deflection, with a swinging angle of around 72.9° and a displacement up to 6.83 mm for 1100 s; after rehydration, the actuator remains a repeatable and reliable deflection without an evident displacement decay.