Porosity of microporous polyethylene membranes modified with polypyrrole and their diffusion permeability to low-molecular weight substances

Abstract

Diffusion permeability of the composite polypyrrole/polyethylene (PPy/PE) membranes in relation to various low-molecular weight electrolytes (hydrochloric acid, potassium chloride or sodium hydroxide) was studied. PPy/PE membranes were prepared by oxidative polymerization of pyrrole in the presence of FeCl 3. They differed in the thickness of PPy layers deposited on both the membrane and pore surfaces and in porosity. It was shown that changes of porous, hydrophilic and ion exchange properties of the membranes affect their diffusion permeability to electrolytes in the same way as was demonstrated earlier for diffusion permeability of microporous ion exchange Neosepta membranes in relation to proteins [M. Bleha, G. Tishchenko, Y. Mizutani, N. Ohmura, in: A. Dyer, M.J. Hudson, P.A. Williams (Eds.), Progress in Ion Exchange. Advances and Applications, Cambridge, 1997, pp. 211–218]. It means that there is an optimum combination of PPy content and membrane porosity ensuring the maximum fluxes of electrolytes through the membranes. At low (<2 h) and high (>6 h) duration of pyrrole polymerization the diffusion permeability of PPy/PE membranes is low. In the first case, PPy covers mainly the outer membrane surfaces; the surface of pores remain hydrophobic because pyrrole has no time for penetrating into them. In the second case, PPy forms thick layers on both the membrane and pore surfaces resulting in their blocking. It was found that the diffusion transport of acid and alkali accompanied with removing of Fe from the PPy/PE membranes. The influence of Fe-containing compounds presenting in the PPy/PE membranes on their diffusion permeability in alkaline or acidic conditions is discussed.