Scouring synthetic fibres

When scouring synthetic fibres that are to be dyed with disperse dyes, nonionic scouring agents are best avoided unless they are formulated to have a high cloud point and are known not to adversely affect the dispersion properties of the dyes. Conversely, when scouring acrylic fibres, anionic surfactants should be avoided [156] because they are liable to interfere with the subsequent application of basic dyes. These fibres are usually scoured with an ethoxylated alcohol, either alone or with a mild alkali such as sodium carbonate or a phosphate. 

The purpose of scouring is to reduce to an acceptable level the amounts of fats, waxes, oils and dirt present. Apart from the aesthetic benefits of a clean substrate, the major technical reason for scouring is to improve the extent and uniformity of absorbency for subsequent processes, especially coloration. Usually the objective is the complete removal of all extraneous matter but on occasion only partial removal is the aim, since a certain residue of oils, for example, will aid such processes as spinning, weaving or knitting. Scouring is particularly important with natural fibres, which obviously contain much more extraneous matter than do synthetic fibres. 

Compared with wool and cotton, the scouring procedures for synthetic fibres are relatively simple since these fibres contain fewer impurities. Most of these have at least some degree of water solubility the most important are sizes and lubricants. The major sizes used are poly (vinyl alcohol), carboxymethylcellulose and poly (acrylic acid), all of which are completely or partially water-soluble. Sometimes aliphatic polyesters are used. 

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