Coupled mechanical and liquid moisture transfer behaviour of textile materials

Abstract

The mechanical properties of yarns have a considerable effect on the processing behavior and performance characteristics of yarns and fabrics. The absorbency and transportation of liquids by textile yarns are important factors in the dyeing and finishing of yams and fabrics. The wicking mechanism in a yarn is coupled with the mechanical behavior of the yarn and constituent fibers with presence of diffusion of the wicking liquid into fibers. Therefore, the mathematical modeling of mechanical behavior of yarn, liquid transport behavior of yarn and the coupled mechanism were the subjects of this research. Knowledge of mechanical and liquid transfer behavior of yarn is fundamental to examine the coupled mechanism. A comprehensive mechanical model of yarn to predict tensile as well as torsional behavior of singles yarn was developed. On the basis of a discrete modeling principle, the yarn was treated as an assembly of discrete fibers whose shapes followed perfect helices. Migration of fibers and interfiber slippage were not investigated in this research. An energy method was employed to calculate applied external forces, and nonlinearities of tensile, bending and torsional behavior of fibrous material were considered in the calculation. Experimental validation showed that the prediction agreed well with the experimental results under limited conditions of small strain. Many textile fibers, especially synthetic fibers, have a circular section. Fibers inside a yarn are more or less parallel to each other. Therefore, an investigation of the wicking mechanism in the gap between cylinders may provide a basic understanding of capillary rise in twisted yarn. A mathematical model to simulate the capillary rise between cylinders was developed for this purpose. Using an interfacial analysis, wicking height of the liquid at equilibrium was derived in terms of interfacial features and characteristics of the liquid. An experimental apparatus was designed and a series of experiments was conducted using this apparatus. On the basis of the model of wicking between cylinders, a mathematical description of the capillary rise in twisted yarn was presented. Uniform packing of fibers was assumed. The governing equation of the wicking liquid was derived from a macroscopic force balance analysis of the liquid, and the wicking time was obtained in the form of the capillary rise by solving the governing equation. Then the theory was extended to investigate non-uniformly packing yarn, and swelling and change of mechanical properties of fibers after absorption were also considered. The wicking mechanism was coupled with the mechanical behavior of yarn and fiber in a manner that absorption of the wicking liquid of fibers during wicking caused the fibers to swell and change their mechanical properties; on the other hand, change of mechanical properties and geometric features of fibers altered pore structures between fibers and capillary pathways, thus affected the wicking process. A mechanical model of yarn and a model of wicking in yarn were combined to study the coupled mechanism, and a basic understanding of the coupled mechanism was developed.