Humectant release from membrane materials

We report the results of membrane filtration studies designed to measure the removal of humectant preservatives (expressed as total organic carbon) from new membrane samples. Membranes with different characteristic properties, that is, relative molecular mass cutoff and material chemistry, were filtered with deionized water under constant flux and feed water temperature (in either dead-end or cross-flow devices) to determine the area-normalized filtrate volume required to remove all of the measurable organic carbon. For specific cases, the effects of changing flux and feed water temperature are also reported. Release of humectants depends on the nominal relative molecular mass cutoff and the thickness (including support) of the membrane—complete removal is not simply predicted by a soaking time or measured volume of deionized water filtered through the membrane without regard to the flux. This report provides general guidance and a suggested measurement technique for monitoring the removal of membrane preservatives prior to membrane application studies.