|Title:||Development of plant structured knitted fabrics|
Hong Kong Polytechnic University -- Dissertations
|Department:||Institute of Textiles and Clothing|
|Pages:||xvii, 194 leaves : ill. (some col.) ; 30 cm.|
|Abstract:||The water and moisture transport properties of textile fabrics are critical to clothing comfort. Clothing should assist the human body to maintain body temperature in a narrow range, and to keep the skin dry under different environmental conditions. Ideal fabrics should therefore prevent the accumulation of sweat on the skin surface by facilitating the transport of sweat away from the skin and evaporation of sweat to the outside environment. Different approaches have been adopted in developing moisture management fabrics, viz. fabrics that facilitate the transport of liquid sweat from the inner surface to the outer surface. One approach is to make fibers to have non-circular cross-sections. When many of such fibers are spun together into yarns, micro-channels are created for wicking. Another way is to modify the molecular composition of fibers by grafting hydrophilic bond in molecule chain, thereby improving fiber hydrophilicity. Blending hydrophilic and hydrophobic fibers into a yarn or to form a composite core and sheath yarn is another way, which can offset the low drying rate of hydrophilic fibers and the poor water absorption of hydrophobic fibers so as to achieve better moisture absorption and release. Fabric structures can also be optimized to improve moisture management properties. For example, double-layered fabrics made of hydrophobic yarns in the inner layer and hydrophilic yarns in the outer layer help to transport sweat to the outer layer for evaporation and to keep the skin dry; hydrophilic and hydrophobic yarns may be knitted alternatively to form strips in a single-layered fabric. Fabric surfaces in contact with the skin are raised to speed up the removal of liquid sweat. Besides, fabric surface may also be modified by chemical treatments to enhance hydrophility so as to improve water absorbency. Recently, the biomimetics of a plants-shaped branching structure in fabrics has been proposed as a potential approach for enhancing the liquid water transport and moisture management properties of fabrics. Woven fabrics mimicking plants-shaped branching structure have been developed and demonstrated improved water absorption and moisture management. Nevertheless, knitted fabrics mimicking plants-shaped branching structure (plant structured knitted fabrics) have yet to be developed. This study therefore aims to explore this novel concept through creative design of knitting structures. In comparison with woven fabrics, plant structured knitted fabrics will have a potential application for sportswear and leisure wear for inherent stretchability as knitted fabrics and enhanced moisture management properties. It was envisaged that the plants-shaped branching network in plants can be emulated in knitting by grouping several yarns together to form multi-yarned loops at the back side of the fabric (mimicking the stem of a plants), splitting yarns into individual ones to form single-yarned loops at the top layer (mimicking the branching).|
With circular knitting technique, the above idea however could not be exactly implemented, since it is not possible to split yarns in multi-yarn loops at the back side into individual ones, and to directly run to the top side to form single-yarned loops due to the inherent working principle of circular weft knitting. A weft plating knitting structure close to the above idea was therefore developed, in which two yarns were bundled together at the back side to act as main stems, with one yarn running to the top side to form loops. Tuck stitches were also used in circular knitting so as to emulate more branching effects. With Raschel warp knitting techniques, the above idea can be fully implemented. The developed plant structured knitted fabrics were evaluated in terms of initial water absorption rate by the transplanar water transport tester, in terms of water content retained at the back and the top side of fabrics by the moisture management tester, in terms of air resistance by KES-F8-AP1 and in terms of vapor permeability in accordance with BS 7209. It was found that both plant structured circular weft knitted and warp knitted fabrics had significantly higher initial water absorption rate and one-way transport property than their corresponding conventional structured knitted fabrics. In other words, the plants-shaped branching network can significantly improve liquid water transport. Additionally, the air resistance values of plant structured knitted fabrics were considerably lower than for those of corresponding control fabrics. The results confirmed that plant structured knitted fabrics can significantly improve liquid water transport and ultimately the comfort properties of fabrics. The enhanced water transport properties of plant structured knitted fabrics could be the combined effects of following possible factors: (a) the yarns at the top side are individual, and therefore more area is exposed to air, it is easier for water in yarns at the top layer to evaporate; (b) the evaporation at the top layer creates the "cohesion-tension mechanism" to pull liquid water underneath; (c) the running of yarns from the bottom layer to the top layer creates a continuous water channel; (d) pores at the bottom layer are larger than those at the top layer, creating a net directional capillary force to drive liquid water from the bottom layer to the top layer; (e) the branching network reduces flow resistance from the bottom layer to the top layer.
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