Page 81 - Basic Principles of Textile Coloration

70 NATURAL CELLULOSIC FIBRES

CHAPTER 5

Natural cellulosic fibres

5.1 INTRODUCTION
Cotton is, by far, the most important textile fibre. This chapter discusses the
chemical and physical properties of cotton, related to the preparation, dyeing and
finishing of fabrics containing this fibre. In Sections 1.1.2 and 3.1, we saw that
cotton consists of cellulose, a polymer of glucose. Cellulose is the basic building
material of all types of vegetation and many different plants are sources of
cellulose fibres. Linen and ramie are cellulosic fibres of lesser importance than
cotton. Purified cotton consists almost exclusively of cellulose, whereas fibres such
as linen and ramie contain other materials besides this polymer. Other types of
cellulosic fibres, such as hemp and jute, are used for sacks and cord but these are
not usually dyed.

Chapter 6 deals with regenerated cellulose (viscose) and cellulose acetate,
mentioned in Section 1.1.2. Although cotton and viscose are almost pure
cellulose, they have quite different physical properties because of their distinctive
morphologies and molecular arrangements. Even though cotton and viscose fibres
can be dyed with the same types of dyes, using similar methods, their dyeing
characteristics are different.

5.2 COTTON [1,2]

5.2.1 Production of cotton
Cotton comes from the seed pod of plants in the Gossypium family cultivated in a
number of subtropical climates. The fibres grow out of the seeds in the closed pod.
In the initial phase, they form long, thin-walled cells filled with protoplasm. Later,
as the growth in length ends, the cell walls increase in thickness as rings of
cellulose are deposited on the inner surface of the cell wall. When the pod or boll
bursts, the cotton fibres, whose function is to aid seed transport in the wind, dry
out. Once the remaining protoplasm has evaporated, the cotton bolls are
harvested mechanically and the fibres removed from the seeds by a process called
ginning. This must be carefully controlled to avoid over-cutting of the fibres.
Cotton ‘linters’, the short lint hairs not removed from the seeds by ginning, are

70