Preparation And Characterization Of Spunlaced Nonwovens Having Unidirectional Water-transfer Properties

Unidirectional water-transfer textile materials are mainly processed through the addition of chemical additives to create a hydrophilicity/hydrophobicity difference between fabric sides. Currently, the unidirectional water-transfer of textiles is confined to the vertical direction, and cannot be simultaneously achieved in the horizontal plane. Therefore, this thesis managed to develop unidirectional water-transfer nonwovens without applying and chemicals. By using water-repellent polyester fiber and hydrophilic viscose fiber as raw materials, spulanced composited nonwovens were prepared using a typical carding and spunlacing method. The nonwoven showed unidirectional water-transfer in both vertical and horizontal directions. The principle of unidirectional water-transfer was explored and attributed to the differential capillary effect formed by the hygroscopic difference between the two layers. Fibers were further arranged along the machine direction(MD), to form continuous diversion channel along MD, thus unidirectional water transfer in the horizontal plane was realized.The influence of web surface density, polyester fiber crimpness and fiber length on the unidirectional water transfer along vertical direction was analyzed. Meanwhile, the impact of fiber arrangement, polyester fiber crimpness and fiber length on the unidirectional water transfer along horizontal direction. The conclusion as follows:(1) With the increase of polyester proportion, liquid penetration time was longer, unidirectional water-transfer ability in vertical plane became less apparent. Two dimensional crimping polyester fibers were found to entangle loosely, but viscose fiber entangled tightly. As the result, the difference in capillary equivalent radius was increased. Such difference helped raise additional pressure difference and improved differential capillary effect, which is conducive to the unidirectional water-transfer ability in vertical plane. With the increase of fiber length, entanglement coefficient of the fibers increased, and the number of capillaries inside the spunlaced nonwovens decreased. Therefore, the additional pressure reduced and the capillary effects became weak, causing a weaker unidirectional water-transfer ability in vertical plane.(2) The orientation of fibers directly affects unidirectional water-transfer ability in horizontal plane, and viscose fibers were found to play a bigger role than polyester fibers. As a hydrophilic fiber having surface grooves, viscose fibers helped the liquid diversion. Through controlling the arrangement of viscose fibers in the web, unidirectional water-transfer could be realized in horizontal plane. After spunlace, the fibers were tightly packed, which blocked some of the capillary pores, and the capillary effect decreased. Consequently, unidirectional water-transfer in horizontal plane was less apparent. The longer the fiber length, the closer the fibers were entangled after spunlace. Fibers formed continuous diversion channels along MD. The number of capillaries was larger and capillary effect was enhanced, thus unidirectional water-transfer in the horizontal plane was ideal.(3) After considering the unidirectional water-transfer ability in both directions, optimal samples were used to replace commercialized product, which is …. We found that the liquid retention rate, fluid absorption rate, moisture permeability, gas permeability and other ability could well meet the requirement of diversion layer in diapers.