Page 33 - Basic Principles of Textile Coloration

22 FIBRES AND TEXTILES: PROPERTIES AND PROCESSING

Table 2.1 Regain values of fibres obtained by
water absorption at 65% relative humidity and
20 °C

Fibre Regain

Wool 13.0–15.0
Viscose 13.0
Cotton
Cellulose diacetate 7.0–8.0
Nylons 6.0–6.5
Cellulose triacetate 4.0–4.5
Acrylics 2.5–3.0
Polyester 1.0–2.5
0.4

regain is higher. The swollen wet fibres are more accessible to water so they retain
more of it at equilibrium (Figure 2.1).

For hydrophilic fibres such as wool, cotton and viscose, the relatively high
regain values significantly influence the gross weight of a given amount of fibre.
This has consequences in buying and selling, and is also significant in dyeing.
Amounts of dyes used are usually expressed as a percentage of the weight of
material to be coloured. Thus, a 1.00% dyeing corresponds to 1.00 g of dye for
every 100 g of fibre, usually weighed under ambient conditions. For hydrophilic
fibres, the variation of fibre weight with varying atmospheric conditions is
therefore an important factor influencing colour reproducibility in repeat dyeings.
For example, the weight of 100 g of dry cotton varies from about 103 g to 108 g
as the relative humidity of the air changes from 20% to 80% at room temperature.

The mechanical properties of fibres, such as tensile strength, flexibility and
elasticity, are important in determining the behaviour of a fabric. Some fibres have
quite remarkable physical and chemical properties, such as high heat or chemical
resistance, or high elasticity with good recovery. Although a detailed discussion of
these is beyond the scope of this book, the important physical and chemical
properties of the major fibres are discussed in subsequent chapters, particularly in
relation to dyeing [2,3].

2.2 PRODUCTION AND PROPERTIES OF YARNS

Natural staple fibres arrive at the spinning mill in large bales. A number of