CELLULOSIC FIBRES

CELLULOSIC FIBRES

Cotton, linen, viscose and polynosic fibres all consist of the same natural polymer, but differ in the chain length and orientation of their molecules and in their morphology. Natural and regenerated cellulosic fibres differ from one another not only in their degree of polymerisation, strength and elasticity but also in their impurities, the packing density of the molecules and their regain, their degree of crystallinity, and, above all, their capacity for dye sorption. The fastness properties of a dye differ on different substrates.

Pretreatment of fibres depends on the nature of the fibre concerned. Some foreign substances do not absorb the dye (cotton wax is an example) or are dyed a different colour from the fibre (pectin) or impair the clarity of the colour and the stability of the material (lignin). In fabrics which have poor wetting properties or tend to retain sizing agents, the absorption of the dye is considerably impaired. In the descriptions that follow it has been assumed that the goods to be processed have been pretreated, and are ready for printing.