FWAs Polyamides

Dyes, application and evaluation). Foi dyeing fibei blends such as viscose—polyamide, polyamide—Spandex, oi polyestei—cotton, only compatible FWAs may be used that do not inteifeie with one another oi have any detrimental effect on fastness properties. 

Synthetic Fiber and Plastics Industries. In the synthetic fibers and plastics industries, the substrate itself serves as the solvent, and the whitener is not appHed from solutions as in textiles. Table 6 Hsts the types of FWAs used in the synthetic fibers and plastic industries. In the case of synthetic fibers, such as polyamide and polyester produced by the melt-spinning process, FWAs can be added at the start or during the course of polymerization or polycondensation. However, FWAs can also be powdered onto the polymer chips prior to spinning. The above types of appHcation place severe thermal and chemical demands on FWAs. They must not interfere with the polymerization reaction and must remain stable under spinning conditions. 

Polyamides. Batch brightening usually takes place in combination with reductive bleaching (dithionite). Continuous processes (padding) are followed by steam, heat, or acid treatment (acid shock) [129], Anionic FWAs are absorbed similarly to acid dyes, or insoluble dispersion brighteners are suitable. Examples of products listed in order of increasing fastness are diaminostilbenes (14 and 19) pyra-zolines (50 and 54) distyrylbiphenyls (10) and bis(triazolyl)stilbenes (32). 

Furans and benzo[b]furans are further building blocks of FWAs. They are used, for example, in combination with benzimidazoles and benzo[b]furans as biphenyl end groups. The 4,4 -bis (benzo[b]furan-2-yl)biphenyls can be regarded as distyrylbiphenyls that have their rings closed and are thus fixed in the Zi-confignration. Sulfonated derivatives are readily water-soluble and are used as lightfast brighteners for polyamides and cellulosic fibers. ... 

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