Enhanced Conductivity of Chitosan Composite Membranes With Fractionated Kraft and Organosolv Lignin

ABSTRACT Different bio‐based chitosan composites containing kraft or organosolv lignin submitted to successive extraction steps (ethyl acetate and then ethanol) are modified by immersion in a sulfuric acid solution to prepare membranes with suitable conductive properties. Characterization with Fourier‐transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), oxidative stability, water uptake studies, electron and proton conductivity assessments, and fuel cell performance tests contribute to understanding the relationship between the composite's structure and their properties. Immersion of the biocomposites in sulfuric acid solution incorporates sulfate groups, which form ionic interactions between the polymer chains. The stability of the modified biocomposites against radical oxidative degradation is improved. The dry biocomposites exhibit low electron conductivities 10 −14 and 10 −10 S cm −1 between −10°C and 60°C and show their potential to be used as electrical insulators. The sulfuric acid modification also disrupts the crystalline structure and renders the composites more hydrophilic, allowing for greater water absorption. As a result, the proton transport is facilitated, resulting in increased proton conductivity and power output in an H 2 /O 2 fuel cell. Due to the increased affinity between the sulfate groups and the composites containing organosolv lignin fractions, they exhibit better oxidative stability, higher water uptake, and proton conductivity.