Development of a coating technique for the internal structure of polypropylene microfiltration membranes

A novel method of coating hydrophobic polyolefinic microfiltration (MF) membranes to produce a more hydrophilic membrane has been developed. A modified interfacial polymerization technique was used to coat the internal surface of a polypropylene (PP) membrane (about: 1.1μm pore size, 84% void volume, 84μm thick). 1,8-octanediamine (selected from several possible diamines) is dried onto the membrane internal surface from methanol and then reacted with a disulfonyl chloride (plus trisulfonyl chloride crosslinking agent) from a mixed solvent system of CHCl3 and CCl4, forming a polysulfonamide coating. Key polymerization parameters were identified as time and temperature of polymerization, concentrations of the diamine and the sulfonyl chlorides, and the ratio of CHCl3 to CCl4. The coating was uniform and stable. Permeation measurements were performed with various size polystyrene latex spheres and carboxylic modified polystyrene latex spheres in aqueous solution. Coating significantly increased hydrophillicity, and hence flux, and reduced membrane fouling for latex sphere solutions.