Mechanical properties of proton-conducting sulfonated aromatic polymer membranes: Stress–strain tests and dynamical analysis

Abstract

a b s t r a c tThe mechanical properties of sulfonated aromatic polymers (SAPs: SPEEK and SPPSU) are studied by tensile stress-strain tests and dynamic mechanical analysis (DMA). The elastic moduli are generally above 1 GPa with tensile strength between 25 and 80 MPa and elongation at rupture between 7 and 50%. These properties are consistent with polymers below their glass transition temperature. The glass transition and elastic moduli are strongly increased by thermal treatments of the SAP membranes, due to formation of cross-links between macromolecules. The cross-linking is observed "in situ" during DMA experiments on thermally untreated SPPSU. These data show that previously neglected SAPs might become very interesting PEM fuel cell membranes, if previously thermally treated.

Composite polymer electrolytes of sulfonated poly-ether-ether-ketone (SPEEK) with organically functionalized TiO2

“…8. The static mechanical properties of SPEEK [38] and SPEEK with hydrophobic TiO 2 are very reproducible, which is in accordance with a very homogeneous membrane. In contrast, the mechanical properties determined for the membrane with hydrophilic TiO 2 show a large scatter, probably related to the inhomogeneous nature of the membrane, as shown in the SEM image.…”

“…SPEEK/THP-TiO2 1400 ± 500 41 ± 13 7 ± 4 200 ± 5 SPEEK [38] 1240 ± 120 43 ± 4 2 9± 13 190 ± 10 SPEEK/Soil-TiO2 880 ± 20 27 ± 2 8 ± 2 185 ± 5 removal of residual solvent which has a plasticising effect and morphological stabilization as reported for PEEK [39]. However, one can note that modulus increase is more pronounced for SPEEK/THP-TiO 2 composite than for SPEEK/Soil-TiO 2 composite.…”

Proton Mobility in Sulfonated PolyEtherEtherKetone (SPEEK): Influence of Thermal Crosslinking and Annealing

“…For example, it is well-known that the water solubility of the polymer increases with the content of sulfonic acid groups (expressed, e.g., as degree of sulfonation (DS) or ionic exchange capacity IEC in mmol g -1 ) [15][16][17]. For a large acidic content, the polymer membranes lose their mechanical strength and swell in water; at even higher sulfonic acid group density, the polymers become water-soluble [18][19][20]. Nevertheless, the presence of water is essential for a good ionic conductivity of the membranes: water allows the full dissociation of sulfonic acid groups, according to the equilibrium:…”

“…The reticulation is followed by important changes of mechanical properties and a reduced solubility in various solvents [18,33]. This strategy has been followed in previous investigations to improve the stiffness and mechanical strength of the polymer, but the influence on the proton conductivity was only marginally studied.…”

Cross‐Linking of Sulfonated Poly(ether ether ketone) by Thermal Treatment: How Does the Reaction Occur?

“…For example thermally treated SPEEK membranes can resist in water also at 145°C without significant swelling, having a Young higher modulus than untreated SPEEK, with interesting proton conductivity [27][28][29]. These improved functional properties are of great interest in electrochemical applications (i.e., PEMFCs) and, according to our preliminary hypotheses, are related to the formation of covalent cross-links between macromolecular chains.…”