Using mathematical models to predict and control the dimensional properties of plain knitted wool fabrics

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Using mathematical models to predict and control the dimensional properties of plain knitted wool fabrics

 

Author: Chen, Qihong
Title: Using mathematical models to predict and control the dimensional properties of plain knitted wool fabrics
Degree: Ph.D.
Year: 2002
Subject: Hong Kong Polytechnic University -- Dissertations
Wool -- Measurement -- Mathematical models
Department: Institute of Textiles and Clothing
Pages: xxx, 281 leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1676090
URI: http://theses.lib.polyu.edu.hk/handle/200/2214
Abstract: Plain knitting has taken up about 90% of all knitted fabric consumption, thus the dimensional stability of plain knitted wool fabrics has been one of the most widely investigated projects for many years. However, early investigations have not been able to develop a mathematical model for effectively predicting and controlling the dimensional properties of plain knitted wool fabric due to various reasons. In this research project, the effects of different loop lengths, yarn linear densities, twist factors, machine gauges and anti-felting treatment levels on the dimensional properties of the plain knitted wool fabrics in various relaxed states were investigated. Further multiple regression analyses on the variables have enabled mathematical models to be developed. These models can be used to predict the linear dimensions, namely courses per unit length (CPU) and wales per unit width (WPU) respectively, of plain knitted wool fabrics in the commercially stable state under the prescribed nominal knitting parameters and conditions. The results of analyses confirmed that, of all the parameters being studied, loop length is the most important or decisive factor affecting the CPU and WPU of both the untreated and DC 109 treated plain knitted wool fabrics. Other variables such as tightness factor, gauge factor, twist factor of ply yarn and anti-felting treatment level only have a slight influence on both CPU and WPU. The experimental results also showed that it was practically difficult to obtain the perfectly stable state for knitted wool fabrics. This was not only because the knitted structure could not be fully relaxed due to high internal restrictive forces caused by inter-yarn friction, but also due to the fact that different drying processes and conditions would result in different fabric dimensions. For the plain knitted fabrics, after they have been washed in water, the size of tumble-dried fabrics is always smaller than that of the flat-dried ones. Furthermore, owing to the fact that the knitted loop is easily distorted, the knitted fabrics in the perfectly relaxed state may also exhibit instability. Hence, in the present project, two reference states used for the measurement of knitted fabric dimensions have been proposed. The first one is the 'washing plus tumble drying' (WTD) state. The developed mathematical models of this state are used for predicting the dimensional properties of knitwear with the IWS 'Machine Wash & Tumble Dry' care claim. The second one is 'washing plus flat drying' (WFD) state. The derived mathematical models of this state are intended for predicting the dimensional properties of products with the IWS 'Machine Wash' care claim. The WTD state is achieved after the fabrics have been washed in water and then tumble-dried, whilst the WFD state is obtained after the WTD relaxation followed by the IWS 1 x 7A washing plus flat drying. The present investigation also demonstrated the correlation of the thickness and the spirality of plain knitted wool fabrics in various relaxed states with the prescribed variables. The experimental results showed that yarn linear density was the most important variable affecting fabric thickness in all relaxed states. The second important parameter was tightness factor while twist factor of ply yarn had only little effect on fabric thickness. Although anti-felting treatment demonstrated a great influence on fabric thickness, varying the treatment level only had a slight effect. For the spirality of plain knitted wool fabrics, the results of the investigation also showed that higher twist factor of ply yarn, loop length or fibre diameter would lead to an increase in the angle of spirality. Relaxation treatment in water would result in a decrease of the angle of spirality. This study also identified the characteristics in relaxation shrinkage of the plain knitted wool fabrics changing from the dry relaxed state to the WFD state. The experimental results showed that the length, width and area relaxation shrinkages of both the untreated and DC 109 treated plain knitted wool fabrics were influenced by loop length, tightness factor, gauge factor, twist factor of ply yarn, anti-felting treatment as well as treatment level. Furthermore, the felting shrinkages of plain knitted wool fabrics were also monitored at different washing stages. The standard laundering cycle, IWS 5A wash cycle, was employed for testing the felting shrinkage of wool in the present project. The effects of knitting parameters such as fibre diameter, loop length, yam linear density, twist of ply yarn, tightness factor, anti-felting treatment level as well as the number of standard laundering cycles, on the felting shrinkages of plain knitted wool fabrics were investigated. The experimental results demonstrated that regardless of the linear densities of yarn and knitting parameters being used, all the untreated plain knitted wool fabrics were commercially unacceptable with respect to the IWS 'Machine Wash' care claim as they exhibited more than 8% area shrinkages after undergoing the IWS 2 x 5A wash cycles. For plain knitted wool fabrics subjected to the anti-felting treatments using 2.5%, 4% and 5.5% DC 109 resin respectively, the felting shrinkage was greatly reduced. As the anti-felting treatment using DC 109 resin is a polymer-deposition process, the evenness and effectiveness of treatment are influenced by resin concentration and fabric structure. It was identified that the treatment process using 4% DC 109 resin would render better anti-felting properties of fabrics knitted from fine wool yarn. Results of the multiple regression analysis also indicated that the major factors affecting the felting properties were tightness factor and loop length, whereas fibre diameter and twist of ply yarn were secondary with regard to their effects on felting properties.

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