Fabric whitener

It has also been reported that spent dyebath water can be re-used by decolouri-sation with ozone. Such decolourised liquors could be successfully used in the dyeing of polyester. The dyeing of cotton fabric with reactive dyes can be carried out using a modified dyeing method. Ozonated dyebaths can be re-used for the bleaching of cotton fabric and even for fabric whitening and rinsing, provided the effluent is extensively decolourised. 

Whitening in combination with the finishing process is used primarily for woven fabrics of ceUulosic fibers and their blends with synthetic fibers. 

Detergent Applications. The primary function of FWAs in the laundry process is to whiten fabric load and maintain the original appearance of the white, laundered articles. Laundering is characterized by repeated appHcation to the same item. Fluorescent whiteners used in this repetitive process have to compensate for the reduction in whiteness and contribute toward prolongation of the usefiil life of the textile material. 

An alternative approach is to physicaUy separate the FWA from the wool fiber by incorporating the whitener into a suitable surface polymer treatment for wool fabric (119). The photostabUity of these fabrics is significantly better than conventional FWA treatments, being similar to bleached wool. 

Synthetic Fibers. Most synthetic fibers are sufficientiy white and do not requite bleaching. For white fabrics, unbleached synthetic fibers with duorescent whitening agents are usually used. When needed, synthetic fibers and many of theit blends are bleached with sodium chlorite solutions at pH 2.5—4.5 for 30—90 min at concentrations and temperatures that depend on the type of fiber. Solutions of 0.1% peracetic acid are also used at pH 6—7 for 1 h at 80—85°C to bleach nylon. 

Blueing agents, which are dyes, provide another approach to maintaining fabric whiteness by a mechanism in which a yellow cast of washed fabrics is covered by the blue dye. Since this approach reduces reflectance, it is less desirable than the use of fluorescent whitening agents that increase reflectance. 

Fluorescent whitening agents (LD) Create a brightening effect Substantivity on fabrics Compatibility with other ingredients like bleaches Bistriazinyl derivatives of 4,4 -diamino-stilbene-2,2 -disulfonic acid 0.1-0.5%... 

The other ingredients, the surfactants, the dirt solubilisers, the dye stabilisers, the whitening agents, the fabric... 

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