Measurement of uni-axial fiber angle in non-woven fibrous media

Abstract

Fiber packing structure is known to affect properties of non-woven fibrous media such as paper and filter media. For a thin medium, such as paper, the fibers lay predominantly in a two-dimensional plane and angles are easily measured visually when viewed perpendicular to this plane. This two-dimensional plane is referred here as the X– Y plane. In thicker media, the fibers can have a three-dimensional orientation with a characteristic uni-axial angle measured relative to the Z-axis, where the Z-axis is perpendicular to the X– Y plane. A number of methods exist for measuring the three-dimensional structure of fibers in a non-woven medium. Many of the methods require expensive equipment. In this paper, a simple, relatively inexpensive visual method requiring moderate effort is presented that provides information on the distribution of fiber angles and the average fiber angle relative to the Z-axis. In the filtration industry extensive testing is done to characterize filter media and filter cakes. However, very few data are reported on the effect of fiber angle on filtration properties such as particle capture efficiency and permeability of filter media and filter cakes. In this work a method is developed to extend two-dimensional orientation data to obtain the three-dimensional fiber orientations. The method is used to characterize the average fiber angles of two filters formed of glass fibers with the only difference between the filters being the fiber structure. Filtration tests show significant differences in permeability and particle capture efficiency between the media of an average angle of 48° compared to the media of an average angle of 68°.