Mechanical Behaviors of Alginate/Chitosan Polyelectrolyte Complex Film with Water Content, Temperature, and Ionic Strength Change

Alginate/chitosan (ALG/CHI) polyelectrolyte complex films are widely used across multiple disciplines. However, they typically exhibit weak mechanical behavior in hydrated form or salty environment due to water affinity and ion sensitivity. In this work, we modulated interpolymer interactions through salt and fabricated a ALG/CHI complex film with an equimolar ratio and then systematically investigated the mechanical behaviors of the film with temperature, water content, and ionic strength changes. The initial modulus of the dry ALG/CHI film at room temperature is 600 MPa and remains largely stable across 25–120 °C. When water uptake reaches equilibrium in aqueous solution, the initial modulus decreases to 25 MPa, exhibiting ductile behavior. In a 1 M salt solution, it maintains a modulus of 14 MPa, showing excellent salt-resistance behavior. The prepared ALG/CHI film is demonstrated to have a robust mechanical performance in salt solution at 37 °C and remains stable in artificial sweat and simulated body fluid for 1 week, implying its applications in physiological environments.