Measurement and improvement of water transport properties of apparel fabrics

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Measurement and improvement of water transport properties of apparel fabrics


Author: Tang, Ka Po Maggie
Title: Measurement and improvement of water transport properties of apparel fabrics
Degree: Ph.D.
Year: 2015
Subject: Textile fabrics -- Testing
Moisture in textiles
Hong Kong Polytechnic University -- Dissertations
Department: Institute of Textiles and Clothing
Pages: xxxi, 287 pages : illustrations (some color) ; 30 cm
Language: English
InnoPac Record:
Abstract: Liquid water absorption and transport properties of fabrics are critical not only to the success of wet processes such as dyeing, printing and finishing, but also to the performance of textile product. In order to characterise the water transport properties and maximize the comfort of wearer, it is essential to choose the appropriate measurement method. Since perception of wetness is a complex process involving multiple human sensory receptors, subjective assessment with realistic representation of the actual wear situation is preferred. Various subjective assessment methods have been developed in the past. In the present study, those subjective assessment methods were reviewed with respect to the technique for setting the experimental condition, its reliability and sensitivity. Based on this critical review, two subjective assessment methods, viz. the psychological scaling method using forefinger and the psychophysical threshold method performing on inner forearm, were developed in the present study to evaluate the wetness discomfort of a range of apparel fabrics. Each of these two methods has advantages and disadvantages in differentiating the wet sensation of apparel fabrics. For the psychological assessment method, it is easy to use by the assessors. Forefinger was utilised to glide and sweep around the wetted portion of fabric (active touch) and the intensity of wet discomfort was assessed. Human perception regarding dryness of fabrics is emphasised but it might have limited implication about the sensation during wear. With just circling a number on the wetness rating scale for the psychological method, the assessor involvement level is low. Besides, end-of-scale problem and error of central tendency might reduce the accuracy and sensitivity of the test. In general, this method might be suitable for fabrics with relatively large difference in terms of hydrophilicity. For the psychophysical threshold experiment, the relation of stimulus and sensation could be quantified. Fabrics with increasing wetness were moved across the inner forearm (passive touch) and the absolute threshold for wet and clingy sensation of fabric was assessed. Compared with the first method, the experimental setting of this forearm method may be closer to actual wear condition. Water was applied to the fabric continuously simulating the sweating process and sweat rate is adjustable. This method emphasised the initial wetness discomfort during wear where effect of body movement was also considered. However, due to differing wetting phenomenon of hydrophilic (water spreads on both sides of fabrics) and hydrophobic (water aggregates only at the back of fabric and may roll away from skin) fabrics, receptors from our skin cannot differentiate these two fabric types in the current set up. Notwithstanding, this method could successfully differentiate the wetness intensity of hydrophilic fabrics in a reproducible manner suggesting reliable and sensitive measures.
Subjective assessment tends to better represent the actual wear conditions, but less accurate and reproducible compared to objective measurements. Good objective measurement methods should at least simulate some aspects of actual wear conditions and at the same time give accurate and reproducible measurements. In this study, some most common objective measurement methods were for the first time systematically compared in terms of reproducibility and relevance to subjective wet and clingy sensation through testing a range of apparel fabrics. It is apparent that conventional objective measurement methods fail to accurately characterize the transplanar wicking property of fabric, which is of great importance in removing liquid perspiration from the skin. Therefore, in this research two novel instruments were developed to measure the in-plane as well as the transplanar wicking property of fabric. The first instrument, called Spontaneous Uptake Water Transport Tester (SUWTT), measures the water absorption rate, in-plane and transplanar wicking properties of fabrics under zero hydrostatic head. The amount of water applied is fabric absorbency dependent and is governed by material property. This tester enables real-time and direct measurement of the amount of water absorbed by the sample (initial period of sweating) automatically to minimise errors caused by manual operation. Another instrument, called Forced Flow Water Transport Tester (FFWTT), can measure the direction of water flow in fabric under adjustable rate of water supply depending on the physiological condition and activity level to be simulated. While the former instrument is more related to wear comfort since it is capable of measuring initial and prolonged sweating condition, the latter instrument better simulates human physiology since the metabolic rate is assumed to be constant and independent of fabric types. Both instruments are versatile for single layer or multiple layers of fabrics with varying geometrical properties, and give accurate measurements at a relatively low cost. It was found that (1) the water absorption rate by 1-layer SUWTT test; (2) water content of fabric by 1-layer SUWTT test; (3) water absorption by bottom filter paper in 3-layer SUWTT test; (4) fraction of water absorbed by the fabric in FFWTT test; and (5) fraction of water absorbed by the bottom filter paper in FFWTT test are strongly related to the subjective wet and clingy sensations, suggesting their capability to simulate the actual wear condition. Besides, the correlation analysis suggests that transplanar and in-plane wicking property of fabric are not related to the subjective assessment result. The main cause of this is that the subjective tests developed focus on the initial wetness discomfort, instead the wetness comfort after prolonged wear is not considered while transplanar and in-plane wicking property may affect wear comfort in long run.

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