Materials Chemistry and Physics, Vol.163, 54-62, 2015
PVDF-HFP/silica-SH nanocomposite synthesis for PEMFC membranes through simultaneous one-step sol-gel reaction and reactive extrusion
In this study, synthesis of thiol-functionalized silica/PVDF-HFP [poly(vinylidene fluoridehexafluoropropylene)] nanocomposite materials was carried out by reactive extrusion through in situ sol-gel reactions of an alkoxysilane inorganic precursor solution composed of polydimethoxysiloxane (PDMOS) and mercaptopropyltriethoxysilane (MPTES). Successful introduction of the functional MPTES and structural PDMOS alkoxysilanes, and subsequent condensation reactions in the PVDF-HFP, were obtained through pre-hydrolysis reactions of the precursors. Si-29-Nuclear magnetic resonance was used to assess the hydrolysis level of the inorganic precursor solution and condensation state in the resulting PVDF-HFP/functionalized silica nanocomposites, while the morphology was observed using scanning electron microscopy (SEM). The hydrolysis-condensation reactions resulting in the inorganic phase were optimized by setting an appropriate R-0 molar ratio (H2O/alkoxy function), R-1 molar ratio (MPTES/ PDMOS) and pH of the solution. Increasing the R-0 ratio barely affected the hydrolysis kinetics. However, a higher R-1 ratio led to a decrease in the inorganic precursors condensation state and consequently to an increase in the reaction time in the extruder to reach the subsequent condensation state. Hence the morphology of the obtained nanocomposites was finer for the highest R-1 ratio and in agreement with the evolution of the solubility parameters. Promising ionic exchange capacity (IEC) and conductivity values were obtained for these innovative nanocomposite materials thanks to a controlled oxidation reaction of the thiol groups into sulfonic acid functions. This original approach demonstrated the possibility of incorporating in situ functionalized silica into a molten fluorinated polymer matrix in a unique reactive extrusion procedure. (C) 2015 Elsevier B.V. All rights reserved.