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 (CSH) and low (CSL) 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. CSH composites exhibit stronger ionic interactions with sulfate groups compared to CSL 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.