Static and Dynamic Aspects of Liquid Capillary Flow in Thermally Bonded Polyester Nonwoven Fabrics

Abstract

The weight gain method is employed to study the vertical capillary flow of wetting liquids in polyester nonwoven fabrics with different basis weights. The quantity of liquid absorbed by capillarity in the nonwoven is recorded as a function of time, until saturation. The liquid retention capacity of the nonwovens has been studied from their “saturation level”, i.e. the fraction of pore volume effectively filled with liquid. It is found that this saturation level varies greatly with the type of nonwoven, and generally decreases with nonwoven thickness. Moreover, the expected 100% value is rarely attained even when the sample height is smaller than the Jurin equilibrium height. These observations are attributed to the more heterogeneous pore sizes in very thin nonwovens, where the interconnection of large and small pores inhibits the continued capillary rise of liquid front. The other part of the study concerns the kinetics of liquid capillary flow which has been analyzed by taking into account the contribution of the meniscus in filling the pores. By subtracting this contribution from the mass of liquid absorbed, the new absorption mass is found to vary linearly with the square root of time, in agreement with the Washburn theory. For the thinnest nonwovens, the very small and unrealistic values of Washburn radii deduced from the experimental results do not correspond to the real physical pore sizes, but reflect slow capillary kinetics. This phenomenon is, however, less important when the thickness of the sample increases.