Crosslinked SPEEK membranes: Mechanical, thermal, and hydrothermal properties
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Brunella Maranesi Laboratoire Chimie Provence (UMR 6264), Centre St Jérôme, Aix-Marseille Univ - CNRS, 13397 Marseille, France; and Dip. Scienze e Tecnologie Chimiche, Univ Roma Tor Vergata, 00133 Roma, Italy
Jean-François Chailan Univ Sud Toulon-Var, MAPIEM (EA 3834), 83402 La Garde, France
Mustapha Khadhraoui Laboratoire Chimie Provence (UMR 6264), Centre St Jérôme, Aix-Marseille Univ - CNRS, 13397 Marseille, France
Riccardo Polini and Maria Luisa Di Vonaa) Dip. Scienze e Tecnologie Chimiche, Univ Roma Tor Vergata, 00133 Roma, Italy
Philippe Knautha), b) Laboratoire Chimie Provence (UMR 6264), Centre St Jérôme, Aix-Marseille Univ - CNRS, 13397 Marseille, France (Received 11 January 2012; accepted 30 April 2012)
The thermal and mechanical behavior, the water uptake (WU), and water diffusion coefficient of sulfonated poly(ether ether ketone) (SPEEK) membranes annealed at 180 °C for different times were explored by high-resolution thermogravimetric analysis, mechanical tensile tests, dynamic mechanical analysis, and WU measurements. The mechanical and thermal stability increased with the thermal treatment time, i.e., with the degree of crosslinking. The effect of residual casting solvent, dimethyl sulfoxide (DMSO), on the WU within SPEEK was probed. In presence of residual DMSO, crosslinked SPEEK exhibited higher water sorption at low and medium relative humidity (RH), and lower water sorption at high RH. These membranes have properties well adapted to fuel cell applications.
These authors were editors of this focus issue during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs. org/jmr-editor-manuscripts/ b) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.151
of sulfonation (DS).8 In addition, the rather harsh environment during PEMFC operation, combining strong acid and strong oxidizing or reducing conditions, and cyclic variations of temperature and humidity, can aggravate the degradation.9–12 How to achieve a better compromise among the proton conductivity, mechanical and thermal stability remains therefore a big challenge. Different strategies have been developed to solve this problem. First, reinforced materials, such as polytetrafluorethylene,13,14 inorganic carbon fibers,15 ceramic oxides,16 or silanol moieties,17 were introduced into the polymer matrix to improve its mechanical, thermal, and structural stability. The stabilization effect can be owed to the reinforcement by additives and intermolecular interactions between the polymer and other components. Inter/intramolecular crosslinking of macromolecular chains is an alternative strategy.18 The studies include ionic,19,20 covalent,21–24 or mixed ionic and covalent crosslinks.25–28 The formation of covalent crosslinks (XL) between macromolecular chains allows improving the resistance to solvents, the dimensional stability, and the mechanical strength, while maintaining a locally high density of functional group
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