Page 422 - Basic Principles of Textile Coloration

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CHAPTER 20

Union dyeing

20.1 FIBRE BLENDS

For the seven major types of textile fibre (wool, cotton, viscose, acetate, nylon,
polyester and acrylic – given in bold face in Table 1.1, Section 1.2.1), there are 21
possible blends, or combinations, of two different components. This number
excludes any blends of fibres of the same generic type such as two different nylons.
For each binary mixture, there is obviously a vast choice of the proportions of the
two component fibres. For combinations of three fibres, the number of possibilities
is very much larger. The major commercial blend by far is cotton/polyester,
estimated to consume about 15% of world fibre production. Other important
combinations include cotton/nylon and wool/polyester. In addition, the dyeing of
blends of nylon or polyester variants is becoming more popular, especially in the
USA.

At one time, wool/cotton fabrics were called unions and the dyeing of fibre
blends became known as union dyeing. This chapter only covers dyeing of the
most important blends. The dyeing of cotton/polyester blends, and of one or two
other types, will serve to illustrate the principles of union dyeing. In general, the
methods used for union dyeing are similar to those used for dyeing the individual
component fibres with the particular types of dyes selected. This is so because
many binary blends are mixtures of a synthetic and a natural fibre. In such cases,
the type of dye selected to dye one fibre in the blend often does not significantly
colour the other component. In other words, there is minimal cross-staining.

The actual distribution of the different fibres is an important characteristic of a
fibre blend. For example, a woven cotton/polyester fabric may consist of a polyester
filament warp and a spun cotton filling, or of yarns spun from intimate blends of
staple polyester and cotton fibres. Many speciality yarns of complex construction,
such as core spun yarns, are also blends of fibres. Different fibres are combined and
assembled into a fabric for both aesthetic and functional effects. The blending of
expensive fibres with cheaper ones often has economic advantages. Many blends
provide fabrics with superior performance. This is particularly true for materials
containing a mixture of natural and synthetic fibres where the desirable properties
of both types of fibre contribute to the quality. For example, the polyester in a

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