Hydrophilic surface modification of microporous poly(tetrafluoroethylene) membranes through defluorination and sulfonation

Poly(tetrafluoroethylene) (PTFE) microfiltration membranes were chemically modified with a two-step chemical reaction. The membranes were defluorinated through controlled etching with sodium-naphthalene solution, and then sulfonated using chlorosulfonic acid. The effects of surface modification on the morphology, pore size and distribution, ion-exchange capacity (IEC), hydrophilicity, pure water flux, and fouling of the membrane were investigated. Using X-ray photoelectron spectroscopy (XPS), the surface composition of the sulfonic acid groups on the modified PEFE membranes was analyzed. As the degree of sulfonation increased, the IEC and hydrophilicity of the membranes increased without any deformation of the morphology or pore size, as observed by scanning electron microscopy (SEM) and capillary flow porometry under controlled reaction conditions. It was also observed that the flux of pure water increased with decreasing intrinsic resistance as the degree of sulfonation increased. Membrane fouling with humic acid was suppressed with an increasing degree of sulfonation, because of enhanced electrostatic repulsion between the negatively charged surface and negative charged humic acid.