POLY(4-VINYLPYRIDINE)-FILLED MICROFILTRATION MEMBRANES - PHYSICOCHEMICAL PROPERTIES AND MORPHOLOGY

The morphology and physicochemical properties of poly(4-vinylpyridine) -filled microfiltration membranes have been examined. These membranes, which were prepared by photoinitiated grafting of up to 125 mass% of 4-vinylpyridine into the pores of polypropylene (PP) microfiltration m embranes, were characterized in terms of the amount of poly(4-vinylpyr idine) incorporated (graft yield), ion-exchange capacity, water conten t, and thickness. The morphology of samples of the grafted membranes d ehydrated by freeze substitution was examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques . While the ion-exchange capacities of the grafted membranes are a fun ction of graft yield, ranging to 4.0 meq/g of dry membrane, the water contents of the grafted membranes in the free base form are essentiall y independent of graft yield. The porosity of the grafted membranes wa s shown to be almost the same as that of the starting base polypropyle ne membranes (60-80%). However, protonation of the grafted poly(4-viny lpyridine) was shown to lead to a further and very substantial increas e of the void volume of the membranes as measured by their water conte nt. The thickness of the grafted membranes was found to increase linea rly with increasing incorporation of polyvinylpyridine. Ionization of the polyelectrolyte was shown to cause a further systematic increase i n thickness which was partly reversible with reversion to the unproton ated form. These changes in thickness are attributed to the stretching of the mesh of the substrate microfiltration membranes.