VOC vapour transport properties of new membranes based on cross-linked fluorinated elastomers

The synthesis of crosslinked fluoroelastomers is described as a new preparation way for composite membranes exhibiting a high volatile organic compounds (VOCs) permeability as well as a good mechanical and solvent stability. The preparation method consists in the synthesis of silicone ter-polymers bearing Si-H reactive groups used for membrane crosslinking and fluoroalkyl side chains as network; filling polymer. The ter-polymers were further used as starling materials to form thin films supported on polyvinylidene fluoride (PVDF) and polyether sulfone (PES) porous supports. Vapour permeation experiments were performed using a home made apparatus producing a constant air/vapour mixture stream. The composite membranes were used first for vapour permeation experiments in relation with the polymer structure in terms of silicon segment length, crosslinking degree, and fluorine content. Then, four different permeants were selected (ethanol, hexane, 1-2 dichloroethane, ethyl acetate) which are representative of the most common VOCs encountered in released air streams. Finally, ethyl acetate/ethanol and ethyl acetate/hexane vapour mixtures were tested with different mole percents in air in order to see the mutual influence of polar and non polar solvent vapours on membrane permeation characteristics. Two independent structural parameters have been considered as important factors influencing vapour permeation: one is the degree of crosslinking of the silicone segments forming the polymer matrix, the other is the fluoroalkyl chain content in the material. (C) 2001 Elsevier Science B.V. All rights reserved.