Saville Physical Testing of Textiles

1. Auflage 1999
ISBN: 978-1-84569-015-1
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 336 Seiten

Reihe: Woodhead Publishing Series in Textiles

This book examines the physical testing of textiles in the form of fibre, yarn and fabric, the emphasis throughout eing on standard and reproducible tests. After an introductory explanation of sampling and measurement, the author explores the effects of moisture on textiles, then goes on to discuss fibre dimension, yarn tests for linear density, twist, evenness and hairiness, tensile strength, and dimensional stability and serviceability. Also covered are aspects of comfort and fabric handle, colour fastness and quality assurance. The book's comprehensive coverage of the physical properties of textiles makes it an essential reference for managers in the textiles industry concerned with quality assurance, garment and fabric technologists, and students of textile science and engineering.

Autoren/Hrsg.

Saville, B P

Inhaltsverzeichnis

1;Front Cover;1
2;Physical Testing of Textiles;2
3;Copyright Page;3
4;Table of Contents;4
5;Preface;11
6;Acknowledgements;12
7;Chapter 1. Introduction;13
7.1;1.1 Reasons for textile testing;13
7.2;1.2 Standardisation of testing;15
7.3;1.3 Sampling;16
7.4;1.4 Measurement;27
7.5;General reading;36
7.6;References;37
8;Chapter 2. Textiles and moisture;38
8.1;2.1 Introduction;38
8.2;2.2 Effect of moisture on physical properties;38
8.3;2.3 Atmospheric moisture;41
8.4;2.4 Regain and moisture content;45
8.5;2.5 Correct invoice weight;52
8.6;2.6 Control of testing room atmosphere;54
8.7;References;55
9;Chapter 3. Fibre dimensions;56
9.1;3.1 Fibre fineness;56
9.2;3.2 Fineness measurement;57
9.3;3.3 Fibre length;71
9.4;3.4 Methods of measurement: direct methods;74
9.5;3.5 Methods of measurement: tuft methods;76
9.6;3.6 High-volume instruments;86
9.7;General reading;87
9.8;References;87
10;Chapter 4. Yam tests;89
10.1;4.1 Linear density;89
10.2;4.2 Twist;97
10.3;4.3 Yarn evenness;106
10.4;4.4 Hairiness;116
10.5;4.5 Yarn bulk;120
10.6;4.6 Friction;122
10.7;References;126
11;Chapter 5. Strength and elongation tests;127
11.1;5.1 Introduction;127
11.2;5.2 Definitions;127
11.3;5.3 Force elongation curve;130
11.4;5.4 Factors affecting tensile testing;144
11.5;5.5 Fibre strength;150
11.6;5.6 Yarn strength;154
11.7;5.7 Fabric strength;157
11.8;5.8 Tear tests;159
11.9;5.9 Bursting strength;166
11.10;5.10 Stretch and recovery properties;168
11.11;5.11 Seam strength;172
11.12;General reading;177
11.13;References;178
12;Chapter 6. Dimensional stability;180
12.1;6.1 Introduction;180
12.2;6.2 Methods of measuring dimensional stability;186
12.3;General reading;194
12.4;References;194
13;Chapter 7. Serviceability;196
13.1;7.1 Introduction;196
13.2;7.2 Snagging;197
13.3;7.3 Pilling;198
13.4;7.4 Abrasion resistance;207
13.5;7.5 Wearer trials;216
13.6;References;219
14;Chapter 8. Comfort;221
14.1;8.1 Introduction;221
14.2;8.2 Thermal comfort;221
14.3;8.3 Moisture transport;239
14.4;8.4 Sensorial comfort;244
14.5;8.5 Water absorption;245
14.6;8.6 Water repellency;247
14.7;References;254
15;Chapter 9. Colour fastness testing;256
15.1;9.1 Introduction;256
15.2;9.2 Outline of colour fastness tests;258
15.3;References;267
16;Chapter 10. Objective evaluation of fabric handle;268
16.1;10.1 Handle;268
16.2;10.2 Kawabata system;291
16.3;10.3 FAST: Fabric Assurance by Simple Testing;300
16.4;General reading;306
16.5;References;306
17;Chapter 11. Quality;308
17.1;11.1 Definitions of quality;308
17.2;11.2 Types of quality;309
17.3;11.3 Quality control;310
17.4;11.4 Quality assurance;310
17.5;11.5 ISO 9000;310
17.6;11.6 Textile product labelling;314
17.7;References;317
18;Appendix: Conversion factors;318
19;Index;319

Leseproben

2 Textiles and moisture
2.1 Introduction
The properties of textile fibres are in many cases strongly affected by the atmospheric moisture content. Many fibres, particularly the natural ones, are hygroscopic in that they are able to absorb water vapour from a moist atmosphere and to give up water to a dry atmosphere. If sufficient time is allowed, equilibrium will be reached. The amount of moisture that such fibres contain strongly affects many of their most important physical properties. The consequence of this is that the moisture content of all textile products has to be taken into account when these properties are being measured. Furthermore because the percentage of moisture that can be retained by fibres is quite high (up to 40% with some fibres), the moisture content can have a significant effect on the mass of the material. This factor has a commercial importance in cases where material such as yarns and fibres is bought and sold by weight. 2.2 Effect of moisture on physical properties
The physical properties of fibres can be affected by their moisture content. In general the fibres that absorb the greatest amount of moisture are the ones whose properties change the most. Three main types of properties are affected. 2.2.1 Dimensional
The mass of the fibres is simply the sum of the mass of the dry fibre plus the mass of the water. The absorption of moisture by fibres causes them to swell, because of the insertion of water molecules between the previously tightly packed fibre molecules. Because the fibre molecules are long and narrow most of the available intermolecular spaces are along the length of the molecules rather than at the ends, so that the swelling takes place mainly in the fibre width as shown in Table 2.1. Nylon is a notable exception to this Table 2.1 is a summary of measurements made by different workers so that there is a certain amount of discrepancy among them. Because of the noncircular cross-section of a number of fibres, most notably cotton, the percentage change in cross-sectional area is a better measure than change in diameter. The change in volume of a fibre is linked to the changes in its length and cross-sectional area by simple geometry. The change in volume is also linked to the amount of water that has been absorbed. The swelling of fibres is a continuous process which takes place in step with their increasing moisture content. From this it follows that the swelling increases with the relative humidity of the atmosphere, the shape of the curve linking swelling to relative humidity being similar to that linking fibre regain with relative humidity [1]. Table 2.1 The swelling of fibres due to moisture absorption [2] Cotton 20, 23, 7 40, 42, 21 42, 44 Mercerised cotton 17 46, 24 0.1 Viscose 25, 35, 52 50, 65, 67, 66, 113, 114 3.7, 4.8 109, 117, 115, 119, 123, 126, 74, 122, 127 Acetate 9, 11, 14, 0.6 6, 8 0.1, 0.3 Wool 14.8–17 25, 26 36, 37, 41 Silk 16.5, 16.3–18.7 19 1.3, 1.6 30, 32 Nylon 1.9–2.6 1.6, 3.2 2.7–6.9 8.1–11.0 Fabrics made from fibres that absorb large amounts of water are affected by the swelling. When such a fabric is soaked in water the increase in width of the fibres leads to an increase in diameter of the constituent yarns. Depending on the closeness of spacing of the yarns this can lead to a change in dimensions of the fabric. However, on subsequent drying out the structure does not necessarily revert to its original state. This behaviour is responsible for the dimensional stability problems of certain fabrics. Advantage is taken of fibre swelling in the construction of some types of waterproof fabrics whose structures are designed to close up when wetted, so making them more impermeable to water. 2.2.2 Mechanical
Some fibres, such as wool and viscose, lose strength when they absorb water and some, such as cotton, flax, hemp and jute, increase in strength. Furthermore the extensibility, that is the extension at a given load, can increase for some fibres when they are wet. Figure 2.1 shows the loss in strength and the gain in elongation of a sample of wool tested when wet compared with a similar sample tested when dry. These changes in strength and extension have consequences for many other textile properties besides tensile strength. Some properties such as fabric tearing strength are ones that are obviously likely to be affected by fibre strength, but for other ones such as crease resistance or abrasion resistance the connection between them and changes in fibre tensile properties is less apparent. It is because of these changes in properties that textile tests should be carried out in a controlled atmosphere. 2.1 The strength of wet and dry wool. 2.2.3 Electrical
The moisture content of fibres also has an important effect on their electrical properties. The main change is to their electrical resistance. The resistance decreases with increasing moisture content. For fibres that absorb water the following approximate relation between the electrical resistance and the moisture content holds for relative humidities between 30% and 90% [3, 4]: Mn=k where R = resistance, M = moisture content (%), and n and k are constants. The changes in resistance are large: there is approximately a tenfold decrease in resistance for every 13% increase in the relative humidity. Figure 2.2 shows the change in resistance with relative humidity for a sample of nylon [4], This fall in resistance with increasing moisture content means that static electrical charges are more readily dissipated when the atmospheric relative humidity is high. 2.2 The change in resistance of nylon with relative humidity. The relative permittivity (dielectric constant) of fibres increases with increasing moisture content in those fibres that absorb moisture [1]. Water itself has a much higher permittivity than the material making up the fibre and so as moisture is absorbed by the fibre the overall value is influenced by this, which will therefore affect any capacitance measurements, such as for evenness, which are made on textile materials. 2.3 Atmospheric moisture
The moisture content of textile materials when they are in equilibrium with their surroundings is determined by the amount of moisture in the air. Therefore the moisture content of those materials that absorb water can vary from day to day or from room to room. The atmospheric moisture level is normally expressed in terms of relative humidity and not absolute water content. 2.3.1 Vapour pressure
Water molecules evaporate from the bulk at a rate determined by the exposed surface area and the temperature. Eventually the space above the surface reaches a stage when as many molecules are condensing back onto the surface as are evaporating from it. The space is then saturated with vapour. The amount of water held at saturation depends only on the temperature of the air and its value increases with increasing temperature as shown in Fig. 2.3. The pressure exerted by the water vapour is known as the saturated vapour pressure and is independent of the volume of space existing above the surface. If the vapour pressure in the space is kept higher than the saturated vapour pressure, water will condense back into the bulk. If, however, the vapour pressure is kept lower than the saturated vapour pressure, water will continue to evaporate from the surface until all the water has gone or the vapour pressures are equal. The total pressure above a surface is the pressure of the air plus the saturated vapour pressure. For example at 20°C the saturated vapour pressure of water is 17.5 mm Hg, if the atmospheric pressure is 760 mm Hg then the pressure of the air above a water surface is 742.5 mm Hg (Dalton’s law of partial pressures). 2.3 The mass of water vapour in the atmosphere (RH = relative humidity). 2.3.2 Relative humidity
The amount of moisture that the atmosphere can hold increases with its temperature so that warmer air can hold more water than cold air. The converse of this is that when air containing moisture is cooled, a temperature is reached at which the air becomes saturated. At this point moisture will condense out from the atmosphere as a liquid: this temperature is known as the dew point. When considering the effects of atmospheric moisture on textile materials the important quantity is not how much moisture the air already holds, but how much more it is capable of holding. This factor governs whether fibres will lose moisture to or gain moisture from the atmosphere. The capacity of the atmosphere to hold further moisture is calculated by taking the maximum possible atmospheric moisture content at a particular...