Modeling Of The Capillary Effect Of Shaped Fibre And Characterization Of Absorbency Textile Material

As one important heading developing direction, modifications of chemical fibres by physical or chemical methods to endow with extra-value have been investigated by many researchers. However, it has too limited fundamental systematically theory to support the new shaped fibre development, understanding of the application mechanism of shaped chemical fibres as well as the characterization of wicking properties. Focusing on the problems about the shaped fibres and corresponding fabrics, this thesis is mainly evolved into the following several parts.Firstly, some basic conceptions about the phenomenon and principles of wicking in textiles are explained separately like wetting, wicking, contact angle and etc. According to the way that the fibre assembly contacts with liquid, normally the wicking can be divided into two categories: finite liquid wicking and infinite liquid wicking. The exploring of mechanism and characterization of wicking in shaped fiber assembly will be based on these two categories subsequently. It emphasizes that wicking is the liquid transporting in textile by large scale, which is also the consequential phenomena after wetting. And wetting is the necessary pre-stage of wicking, which means that the fiber without wetting property will not be wicked either.On the basis of comprehension of wicking in textile, the factors affecting the capillary effect of shaped polyester fibres such as the geometric size and distribution of capillary space formed between fibres, cross sectional shape of fibres, surface area and morphology of fibre, moisture absorbency of fibre material and liquid properties are lucubrated logically. The affections of geometric size and distribution of capillary space formed between fibres, fibre radius, number of fibres and capillaries on wicking in shaped fibre assembly are analysed and discussed by simulation and prediction of the Model of Fibre Bundle （MFB）, which is realized by the computer programme （Shape-Generator） to model the stochastic alignment of fibres in the cross section of bundle systematically. According to the results of modelling and simulation, the effect of single fibre morphology on the wicking in textiles is predicted theoretically to compare the capillary effect difference caused by cross sectional shape of fibre. Therefore, the capillary effect of fibre assembly will be anticipated when the fibre shape is given. The result of prediction is instructional for the development of new shaped chemical fibre.The works about the fundamental theory of capillary effect mechanism in textile are investigated profoundly. Comparing the critical spreading coefficient of normal round and shaped fibre bundle, it is certificated that the shaped fibre is easier to be wetted when the fibre material and liquid are given. The forces in the dynamic wicking behaviour for fibre bundle in infinite liquid are balanced by vertical wicking model. And the mechanical relationship between wicking height, wicking time and wicking velocity are deduced and the wicking behaviour are predicted from the result of MFB accordingly. The critical efficient geometric size of capillary space is discussed to present that there is size limitation of the space formed between fibres to be capillary. The function of meniscus shape is putted forward to characterize the wicking in fibre bundle vertically and to obtain the dynamic contact angle indirectly.Shaped fibers are mainly applied in functional moisture absorbency and liquid transporting fabric. It is necessary to build up a standardized selecting theory for choosing the applicable measurement equipment and method for characterization of the functional fabric. Normal common used devices and measurement method are introduced simply. Experimental methods can be divided into static and dynamic mainly; horizontal and vertical by sample placement; finite and infinite liquid reservoir by the quantity of liquid. It is the reasonable characterization method only when it is selected according to sample material and structure, liquid as well as the end use of fabric and etc. In this work, OCA40 Micro-Optical Contact Angle Equipment is chosen to measure the liquid drop on the fabric; 3S Balance Capillary Instrument is taken to investigate the dynamic wicking behavior vertically; Demand Absorbency Self-made Device is used to test the horizontal wicking property of fabric in the infinite liquid reservoir. These three equipments and measurement methods can present the typical wicking actions in textiles basically.OCA40 Micro-Optical Contact Angle Equipment can be used to measure the geometric size of liquid drop microcosmically as the experiment condition is finite liquid reservoir. According to the linear relationship between wicking height and wicking time, the procedure of liquid drop absorbed by fabric can be defined as two parts: preparing wicking and main wicking. Cross and flat shape fiber assemblies are found to be quicker in main wicking process by comparing the preparing wicking and main wicking time and their distribution. Although six kinds of typical shaped hydrophobic polyester fiber assembly （even in fabric blended with cotton） all showed pretty good linear dynamic relationship between main wicking time and height, the capillary effect of cross shaped fiber assembly is prior to others obviously.The experiments of wicking in fabric vertically on 3S Balance Capillary Instrument took three kinds nonwoven fabric as objective examples to investigate the dynamic relationship between wicked liquid weight and time. By measuring the meniscus weight and liquid trapped by fabric, the dynamic contact angles on the surface of fabric and inside of fabric are obtained on the base of Washburn principle. The wicked liquid weight and the square root of time have a good agreement with linear relationship. The equivalent radius of capillary pores in the fabric are acquired from the results of dynamic wicking behavior, which are all about 10^-6m agreed to the value from simulation. The hydrophilic property of fibre in the fabric also does an important role in swelling, capillary space changing and the dynamic contact angle. Besides the chemical agent like hydrophilic or hydrophobic finishing agent affect the wicking significantly. It will be helpful for liquid transporting in textile dyeing or finishing process to mix some organic surfactant into the liquid.Demand Absorbency Self-made Device also took the same tree nonwoven fabric as experimental example in this work. The experimental method is modified by discussion the results and exploration of the measurements time and again repetitiously and circumspectly before acquiring the stable and regular laboratorial data. The results illustrate that the absorbency weight is linear to the square root of time under the limited pressure, which is also followed by Washburn principle. Unlike normally assumed, not all of the capillary spaces are filled with liquid when the wicking action reaches the saturation. The wicking velocity is influenced by how the fabric contact with the liquid principally, namely the osculatory area.The vertical wicking and horizontal wicking both agree with Washburn except they have some difference in the individual characters. Since the capillary sizes in fabric are almost in the microscopic grade of 10^-6m, the effect of 3D existing state of capillary on the large scale wicking in textile is exiguous, which is supposed to be the mode of liquid contact with textile. It is recommended to take the vertical wicking mode for investigation of micro-capillary effect and the horizontal wicking mode for characterization of liquid transporting by large scale separately. The appropriate and reasonable measurement methods should be chosen according to the end use of fabric, the liquid contacting way and so on.This work supports the development of new fibbers by simulation of shaped fiber bundles; demonstrates the principles of liquid transporting in the capillary space in textile; presents a series of exemplifications for the standard measurement and characterization of liquid absorbing fabric.