Characterization of polymeric nonwovens using porosimetry, porometry and X-ray computed tomography

Removal of particles from gas and liquid streams is becoming increasingly important as a drive toward greater sustainability, the promise of resources recovery, and the regulatory environment create economic incentives to control water and air emissions. Membranes, and more specifically nonwovens, are commonly used for this purpose. Performance of nonwovens as filters is dependent on their pore structure (i.e. pore diameter, constricted pore size, and porosity). However, the characterization tools available for determining these structural metrics are underdeveloped for soft materials. In this study, several methods for evaluating pore size, pore diameter distribution, and porosity using polymeric nonwovens are investigated. Using both commercial polyester (PET) nonwovens and electrospun nanofibers, pore diameter distributions of nonwovens have been determined using two porosimetry techniques: mercury intrusion porosimetry (MIP) and liquid extrusion porosimetry (LEP). Analytical results from porosimetry were compared to porosity estimates obtained from X-ray computed tomography (XCT) images. The constricted pore size, or pore throat diameter, was also measured using porometry. In general, LEP resulted in higher measured porosities than MIP, likely due to compaction of the nonwoven in the latter. Electrospun materials exhibited similar or slightly lower porosities when compared to PET nonwovens, but their constricted pore diameters were orders of magnitude smaller due to smaller fiber sizes. The use of XCT was limited to the PET nonwovens due to limited resolution but it was shown to have potential for visualizing the 3-D structures of nonwovens and other polymeric materials.

► Different techniques are used to measuring pore size and volume of various nonwovens.
► Both commercial polyester and electrospun nonwovens were evaluated.
► High pressure intrusion porosimetry compacted samples and resulted in lower measured porosity.
► Pore throat size is proportional to fiber size, but is not related to porosity.
► X-ray tomography can calculate porosity but it has limited resolution.