Thermal stability of ion-exchange Nafion N117CS membranes

• Published in: Polymer degradation and stability Vol. 94; no. 4; pp. 679 - 687
• Main Authors: Iwai, Yasunori, Yamanishi, Toshihiko
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.04.2009; Elsevier
• Subjects: Applied sciences; Differential scanning calorimetry; Exact sciences and technology; Exchange resins and membranes; Forms of application and semi-finished materials; Ionic radii; Nafion; Polymer industry, paints, wood; Technology of polymers; Thermal stability; Thermogravimetric analysis; X-ray photoelectron spectra; Differential scanning calorimetry; Thermogravimetric analysis; Nafion; Ionic radii; Thermal stability; X-ray photoelectron spectra; Cation exchange; Ionomer; Property composition relationship; Experimental study; Alkaline earth metal Ions; Sulfonate copolymer; Thermal properties; Tetrafluoroethylene copolymer; Transition metal Ions; Molecular mobility; Cation exchange membrane; Alkali metal Ions
• ISSN: 0141-3910; 1873-2321
• DOI: 10.1016/j.polymdegradstab.2008.12.020

The effect of exchanged ions on the thermal stability of Nafion N117CS membranes was investigated by X-ray photoelectron spectra (XPS), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and ion exchange capacity determinations. The ion exchange of alkaline metal ions was effective in improving the thermal stability of the Nafion N117CS membrane. Findings reveal that when Nafion was exchanged for cations with a larger ionic radius, the membrane attained superior thermal stability. On the other hand, we confirmed that the Na-exchange Nafion N117CS membrane possessed a distinctive degree of thermal stability among the alkaline ion-exchange Nafions, although the order of ionic radii is K > Na > Li. Thermal stability improved the most when the Nafion membrane was exchanged for alkaline ions, followed by divalent ions, then trivalent ions. As for the Nafion membrane when it was exchanged for divalent ions or trivalent ions, Nafion following the ion exchange had a thermal stability proportional to an increase in the ionic radius of the cation. This stability may be explained by the reduction of water content and a greater interaction between the sulfonate groups and the cations with larger ionic radii. Since the Al cations acted as a Lewis acid center, the decomposition of the ether bonds of the perfluoroalkylether pendant-chains of the Nafion membrane was observed for the Nafion N117CS membrane that had been exchanged for Al ions. The activation of molecular mobility in Nafion was observed between the decomposition stages of the loss of water and the loss of sulfonic groups. The temperature of activation of cation-exchange Nafion became much higher than that of Nafion in an acid form.