Effect of fiber count and knit structure on intra- and inter-yarn transport of liquid water

The moisture transport in fabrics determines its cooling effect and therefore the wearing comfort during sudorific activities. When liquid sweat is present, the moisture absorption by a fabric is characterized by the in-plane and transplanar wicking. We investigated the effect of fabric structure and fiber count on wicking by X-ray projection images using four different polyester knit structures (rib, eyelet, interlock and modified interlock, all hydrophilic), as well as five rib knits with different fiber counts per yarn (24-192, all quasi-hydrophobic with water contact angles 89 +/- 1). Experiments were conducted with two-layer samples of the same fabric exposed to different external pressures. The liquid was transported in recognizable waterfronts, which can be interpreted as distinct intra-yarn and inter-yarn in-plane wicking fronts. For layer-to-layer wicking in hydrophilic samples, pressure-dependent time delays were observed; the delays correlated negatively with the relative void area at the interface, and were shortest for the rib knits. For the quasi-hydrophobic samples, however, the liquid wicked up to the upper layer without time delays, which was due to the liquid being pressed into the fabric, that is, due to the supply-driven flow. We distinguish this from the supply-limited flow, which is driven by capillary forces. The presented results have implications for the design of clothing systems for sudorific activities.