Enhancement in hydrolytic stability and proton conductivity of optimised chitosan/sulfonated poly(vinyl alcohol) composite membrane with inorganic fillers

The study aimed to obtain a chitosan/sulfonated poly(vinyl alcohol) (CS/SPVA) membrane with optimised hydrolytic stability and ion conduction properties by using the Taguchi method. Three factor variables including concentration of glutaraldehyde (GA), crosslinking temperature and crosslinking time were considered. An L18 orthogonal array along with the approach of larger-the-better was selected for the optimisation. The highest value in S/N ratio of -19.9947 was observed on sample set 9 without GA involvement, crosslinking temperature of 110 degrees C and time of 90 minutes. The ionic conductivity and water uptake were 8.21 mS/cm and 82.05%, respectively, compared to 7.34 mS/cm and 215.9% of the nonoptimised CS/SPVA15. Further inspection with the incorporation of inorganic fillers (titanium dioxide (TiO2), silicon dioxide (SiO2) and sulfonated graphene oxide (SGO)) was conducted on the optimised CS/SPVA15. The thermomechanical properties of CS/SPVA15 composite membrane was improved with inorganic fillers. In terms of electrochemical properties, ionic conductivity was reduced because of the enhancement in thermal stability. The inorganic filler inhibits the accessible functional groups and increase the ionic resistance of CS/SPVA15 composite membrane. Amongst all samples, CS/SPVA15-SGO is the most optimised with a minor trade-off in ionic conductivity (6.82 mS/cm) and IEC (0.8866 mequiv/g) compared with CS/SPVA15, whilst delivering an exceptional hydrolytic stability (76.41%).

Automated summary

This study aimed to optimize the hydrolytic stability and ion conduction properties of a CS/SPVA membrane using the Taguchi method. The optimal conditions were found, and it was observed that incorporating inorganic fillers improved the thermomechanical properties while slightly reducing ionic conductivity. The CS/SPVA15-SGO sample showed the most optimized performance with a trade-off in ionic conductivity but exceptional hydrolytic stability.