Fibrous Structures with Designed Wicking Properties

Fibrous structures have been designed and tested to achieve anisotropic flow properties. A structure that transports liquid in one specific in-plane direction as fast as possible was formed by parallel arrangement of continuous filament yarns in the middle layer of a three-layer structure. The top and bottom layers consisted of low areal density nonwoven fabrics. Tests showed that flow was faster in the middle layer, yielding a nonuniform flow front among the layers. Structures with larger pores in the middle layer wicked faster, as anticipated from the Washburn equation. Although we maximized the in-plane orientation to increase the flow anisotropy of the structures, the flow anisotropy was only approximately 3, which can be usefully compared to a mechanical anisotropy of the structure of perhaps 50 or higher. A mathematical expression derived from combining the continuity equation with Darcy's Law was used to model the flow behavior in these structures. The predicted values of the flow front were within 20% of the experimental values. Another structure was designed to maximize liquid transport through the thickness of a fabric. It contained flocked fibers in the middle layer oriented parallel to the direction of flow. Structures with single and double layers of flocked fibers with varying fiber denier and flock density were made and tested. The number of layers, the fiber denier and the interaction between the number of layers and flock density influenced the transverse flow behavior of these structures. Single layer samples with high-flock density and high fiber denier promoted transverse flow best. Double layer high-flock density samples hindered the transverse flow, retaining the liquid in the middle region where the layers met to produce smaller pores.