Reactive dyes fastness

The dyes used on wool can be divided into the following groups acid dyes, chrome dyes, premetallized dyes and reactive dyes (88,89,92—94,97—99). Strictly speaking, all types of wool dyestuffs can be described as acid dyes, but in practice this term is confined to leveling acid dyes, half-milling dyes, milling dyes, and supermilling dyes (94,97). This subclassification of acid dyes arises out of the methods used for their appHcation and their fastness properties on wool. 

Dyes for cellulose fiber include the direct, sulfur, vat, a2oic, and reactive dyes. R D activities of world dye manufacturers have been focused on the area of reactive dyes, because reactive dyes offer brighter shades and excellent wet-fastness and have been increasingly used for dyeing cotton. 

In one study [90], enzyme pretreatment increased colour yield without affecting fastness properties. However, pretreatment of cellulosic fibres with cellulase lowered the subsequent fixation of homobifunctional triazine reactive dyes but did not impair the fixation of other types of reactive dyes [91]. Another study suggested that the enhanced brightness of reactive dyeings was greater with triazine dyes than with vinylsulphone types when cotton was pretreated or aftertreated with cellulase [92]. 

Enhanced dyeability with anionic and reactive dyes, the latter applied under neutral or slightly acidic conditions. Reduced light fastness and marked dulling with some dyes... 

Dyeable neutral without salt good results with some high-reactivity dyes (dichlorotriazine and difluoropyrimidine) but not with some other types (monochlorotriazine and dichloroquinoxaline). Washing fastness very good but light fastness lower... 

Ethylenediamine derivative of Hercosett Scheme 10.64 About 95% fixation of low- or high-reactivity dyes under slightly acidic conditions without salt, but light fastness still inferior... 

Polyepichlorohydrin and dimethylamine Polymerisation of epichlorohydrin in carbon tetrachloride with boron trifluoride/ether catalyst, then reaction with dimethylamine. Applied to cotton by exhaust method or pad-dry. Scheme 10.65 Good yields with direct dyes using only 2 g/l salt. Excellent build-up with most reactive dyes only 10% of normal salt usage needed for low-reactivity dyes and none for highly reactive types. Washing fastness very good but light fastness impaired. 

As already mentioned, some lubricants can be difficult to remove by washing and surfactants are often added to overcome this problem [463]. Lubricants can impair fastness properties, particularly those of disperse dyes. They may influence the uptake of dyes either positively or negatively, although seldom seriously except where it results in unlevelness. For example, knitting oils can increase the yield of relatively oleophilic reactive dyes on cotton and yet with highly hydrophilic types they may cause dye-resist effects [467]. 

Heavy metals are widely used as catalysts in the manufacture of anthraquinonoid dyes. Mercury is used when sulphonating anthraquinones and copper when reacting arylamines with bromoanthraquinones. Much effort has been devoted to minimising the trace metal content of such colorants and in effluents from dyemaking plants. Metal salts are used as reactants in dye synthesis, particularly in the ranges of premetallised acid, direct or reactive dyes, which usually contain copper, chromium, nickel or cobalt. These structures are described in detail in Chapter 5, where the implications in terms of environmental problems are also discussed. Certain basic dyes and stabilised azoic diazo components (Fast Salts) are marketed in the form of tetrachlorozincate complex salts. The environmental impact of the heavy metal salts used in dye application processes is dealt with in Volume 2. 

Table 3.34 Perspiration and light fastness of various azo reactive dyes [150]...

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