Photoreactivity and Enhanced Mechanical Properties and Water Stability in Polysaccharide-Based Films Using Vanadium Ion Coordination

Different strategies have been employed to improve the physicochemical and mechanical properties of soft polysaccharide-based materials. Some of these strategies include covalent cross-linking or chemical modification and blending of polymers. In an alternative approach, we used vanadium ion coordination to create dynamic covalent bonds and obtain films with enhanced properties. We prepared bio-based films using pectin and chitosan, two naturally occurring polysaccharides, with glycerol added as a plasticizer to increase the flexibility and elasticity of the material. We incorporated the vanadium ion into the films via soaking in V(V) solutions. Films were characterized through FT-IR to examine the different interactions inside the films. Scanning electron microscopy showed laminated sheets separated by ∼0.16 μm in the V(V)-containing films as compared to ∼0.75 μm in the films without V(V). Rheological studies showed that V(V)-coordinated films possessed better mechanical properties (higher storage modulus) and water stability than films without vanadium. Upon irradiation with blue light, diffuse reflectance spectroscopy and color analysis showed the changes in the color of the film with irradiation from yellow to blue, consistent with the photochemical reduction of V(V) to V(IV). A small change in modulus was observed during light irradiation without significant structural changes observed within the film in scanning electron microscopy. These results show that it is possible to create robust and water-stable polysaccharide-based materials through coordination of the functional groups of polysaccharides with metal ions.