A study on ionic interactions in chitosan–oxalic acid polymer electrolyte membranes

Solid polymer electrolyte (SPE) membranes consisting of chitosan and oxalic acid (C2O4H2) were prepared by the solution casting method with various amounts of oxalic acid (OA) from 10 wt% to 50 wt%. The ionic interaction between chitosan and oxalic acid in each electrolyte with different OA concentrations is explained using the Fourier Transform Infrared (FTIR) spectroscopy in the wavenumber range between 1400 and 1800 cm−1. The ionic conductivity of the electrolytes is found to increase with OA content up to 40 wt% (OA40 membrane) and decrease on further addition of OA. The increment in conductivity with OA content can be associated with the increase in number of ions. From the study of conductivity variation with frequency, the value of fractional exponent, s is observed to approach 1. X-ray diffraction (XRD) analyses indicate that the OA40 sample is the most amorphous with only 13% degree of crystallinity. Thermogravimetric analyses (TGA) show that membranes with 10–40 wt% OA are stable and preserve their compositions up to 168 °C.