Pore Size Distribution Measurements of Nonwoven Fibrous Filter by Differential Flow Method

Abstract

The differential flow method (DFM) test equipment was newly developed to measure the pore size distribution (PSD) of filter having relatively large pore size like nonwoven fibrous filter. The applicability of this equipment was investigated by using the Nuclepore membrane filters (PC membranes) having different pore size of 0.4, 0.8, 1.2 and 2.0μm and the stainless steel nonwoven fibrous filter having different fiber diameter and filter porosity. The fiber diameters of stainless steel were 2, 4 and 8μm and the range of filter porosity was 0.6-0.85. The PSD of PC membranes measured by DFM almost agreed with that measured by SEM observation and the mean flow pore size measured by DFM also agreed with the nominal one. The PSD was not influenced by the kind of wetting liquids used here, i.e. ethylene glycol, IPA and PorofilTM. The PSD of nonwoven fibrous filter depended on the kind of wetting liquids, although the maximum pore size evaluated by the bubble point was not influenced by them. The mean flow pore size measured by DFM in the nonwoven fibrous filter almost agreed with the mean pore size measured by liquid permeation method.