Dielectric characterisation of chitosan-based composite membranes containing fractionated kraft and organosolv lignin

Abstract

Chitosan-based composite membranes with fractionated kraft and organosolv lignin were prepared by solvent casting. A small lignin fraction (1%) was added to the neat chitosan to obtain a good distribution. The influence of lignin extraction with ethyl acetate and consequently ethanol on the dielectric and conductive properties of the composites was investigated by dielectric thermal analysis (DETA). Overall, the chitosan-lignin composites exhibit three relaxation mechanisms (β, βwet, and α) and two conductivity phenomena (σ and MWS). FTIR analysis showed that the composites with organosolv lignin fractions have fewer hydroxyl groups than those with kraft lignin, which decreases slightly further for both after ethanol extraction. The lignin fractions with lower molecular weight and higher OH content show stronger interactions with chitosan, due to hydrogen bonding. These interactions affect the thermal activation and cooperativity of the β-, βwet, and α-relaxation. Furthermore, the kraft lignin fractions with many polar groups are very compatible with the chitosan matrix, resulting in a more compact structure and higher fragility. The membranes CS OLEA and CS KLE have a lower electron conductivity and a higher proton conductivity. Thus, they have promising conductivity properties for fuel cell applications.