Interfacially polymerized hydrophilic microporous thin film composite membranes on porous polypropylene hollow fibers and flat films

Solvent-stable ultrafiltration (UF) membranes are of significant interest especially if they are also hydrophilic. Porous polypropylene flat films and hollow fibers can provide substantial chemical, pH, and solvent resistance and are therefore suitable as supports for forming appropriate coatings functioning as solvent-stable UF membranes. Flat Celgard 2400 films, Cegard X-10 and X-20 hollow fibers of polypropylene were used as a support for thin film composite (TFC) membranes prepared by interfacial polymerization (IP) technique. Monomer reactants for this reaction were diacyl chlorides such as sebacoyl chloride or iso-phthaloyl dichloride and diamines such as hexanediamine or polyethyleneimine (PEI). These TFC membranes have substantial solvent stability. Their IP layer and the membrane are also hydrophilic. The surface at the internal diameter of the hollow fibers was modified; plasma polymerization, UV techniques are generally not suitable for modification of this surface. The membranes obtained were characterized by the permeance of a gas (N₂), permeability of water and ethanol, scanning electron microscopy (SEM), and ultrafiltration of a protein, zein, from an ethanolic solution. Amongst a number of factors which hold the key to a successful coating/membrane are hydrophilization of the different surfaces of the porous hydrophobic support via acetone and chromic acid oxidizing solution, order of introduction of the monomer-containing solutions, exposure of the nascent film to reduced shear conditions, and heat treatment of the IP layer formed. The hollow fibers membranes developed successfully were capable of 97% zein rejection from an ethanolic solution.