Cellulose colour fastness

The earliest polymeric cationic aftertreatments stemmed from the development of crease-resist finishes for cellulosic fibres. One such, promoted specifically for its colour fastness improvements when applied as an aftertreatment to direct dyeings, was a condensation product of formaldehyde with dicyandiamide (Scheme 10.82). Many similar compounds followed, such as condensation products of formaldehyde with melamine (10.212), polyethylene imine) with cyanuric chloride (10.213) and alkyl chlorides with polyethylene imine) (10.214 R = alkyl). 

In spite of the anomalous ring-opening decomposition of nicotinotriazine compounds under conditions of alkaline hydrolysis (Scheme 7.34), the product of reaction of a bis(aminonicotinotriazine) dye with cellulose is the same as that from the analogous bis(aminochlorotriazine) dye in terms of hue, colour fastness and stability of the dye-fibre bond. If desired, these bis(aminonicotinotriazine) dyes can be applied satisfactorily at 80 °C and pH 11, as was evident for Cl Reactive Blue 187. They have slightly higher reactivity... 

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]. 

Uncharged styryl (methine) disperse dyes were originally introduced to provide greenish yellow colours on cellulose acetate fibres. One such dye still in use is Cl Disperse Yellow 31 (6.226), which is made by condensing 4-(N-butyl-N-chloroethylamino)benzaldehyde with ethyl cyanoacetate. Suitable compounds for polyester usually contain the electron-accepting dicyanovinyl group, introduced with the aid of malononitrile. An increased molecular size leads to improved fastness to sublimation, as in the case of Cl Disperse Yellow 99 (6.227). A novel polymethine-type structure of great interest is present in Cl Disperse Blue 354 (6.228), which is claimed to be the most brilliant blue disperse dye currently available [85]. 

A relatively uncontrolled attempt to enhance the colour yield and fastness to washing of selected direct dyes involved addition to the dyebath of a colourless reactant that was intended to form covalent attachments between these dyes and hydroxy groups in cellulose [135]. Most of the dyes selected contained at least two primary amino groups in aminonaphthol residues. The reactants evaluated were cyanuric chloride (7.3), N,N-diethyl-3-hydroxyazetidinium chloride (7.124) and 2,4-dichloro-6-(4,-sulphoanilino)-s-triazine (7.125), all of which will indeed react readily with primary arylamines. Some of the dyes selected, however, contained only diphenylurea or salicylic acid residues and these are most unlikely to react efficiently under dyeing conditions. 

CONDENSOL A Is a catalyst which contains ammonium nitrate as active substance and Is used mainly for the resin finishing of regenerated cellulose. It is liable to change the shade of coloured goods, and it may also impair the light fastness of optical brighteners. 

The members of this group are complex organic compounds containing sulphur. They are used to dye cheap shades of high wet-fastness on cellulosic fibres. The colours, however, lack brightness. 

A recent development is based upon the capacity of reactive dyes to combine with resin precondensates during curing conditions. I he advantage is that with those fabrics which are normally resin-finished the conventional dyeing operation is eliminated. The fastness of the colour, in this case, is not governed by the cellulose covalent bond but by the permanence of the polymer finish. 

To dye the wool in a union without staining the cellulose, which may be either regenerated or natural, is comparatively simple. It is not very common for the wool to be dyed and the cellulose to be left white, but it is quite a general practice to incorporate a pattern constructed out of cellulosic yarns dyed in fast colours with an undyed wool background. The problem of dyeing such materials wool way is the same as leaving the other component white, because a non-staining method must be used. 

Imperial Chemical Industries I>td Dyehonse circular No. 576) have described continuous processes for dyeing fast colours on cellulosic and polyester mixtures. Pale shades may be padded with a solution containing Soledon dyes together with ... 

---