Dielectric Characterization of Protonated Chitosan-Lignin Biocomposite Membranes: Influence of Chitosan and Lignin Types

Biobased chitosan-lignin composite membranes with tailored dielectric and conductive properties were developed using chitosan of high (CS_H) and low (CS_L) molecular weight and degree of deacetylation, combined with kraft (KL) and organosolv lignin (OL) as fillers. The membranes were protonated by immersion in 1.0 M sulfuric acid. CS_H composites exhibit stronger ionic interactions with sulfate groups compared to CS_L composites, resulting in a dense structure that hinders water absorption and increases fragility. Chitosan interactions with sulfuric acid and lignin restrict the mobility of dielectric relaxations, with KL having a more pronounced effect than OL due to its smaller size and higher phenolic OH content. The membranes act as electrical insulators, exhibiting electron conductivities ranging from 10^–15 to 10^–8 S/cm between −10 and 170 °C, and proton conductivities between 2.9 × 10^–3 and 4.4 × 10^–3 S/cm at 60 °C. These properties make them promising candidates for use as biobased electrolytes in fuel cell applications.