Cellulose fibres/molecules

In all other dyeing systems, however, the charge (if any) on the dye ion or molecule does not enhance affinity. A cellulosic fibre, for example, normally carries a negative charge like that of an approaching dye anion and measures must be taken to minimise the forces of... 

Although many types of dye contain sulphur other than in sulphonic acid groups, sulphur dyes are usually considered to be those dyes that are best applied from a sodium sulphide dyebath. Like vat dyes, sulphur dyes are water-insoluble before and after application to cellulosic fibres. Disulphide linkages in the dye molecules are readily reduced by sodium... 

It is possible to tailor dyes, by use of the stepwise reactivity of the chlorine atoms in cyanuric chloride (B-59MI11200), to a variety of applications. For example, in structure (16), two molecules of cyanuric chloride may be reacted with one molecule of a suitable diamine, such as 4,4 -diaminostilbene-2,2 -disulfonic acid, at 0-5 °C and then the subsequent bis-dichlorotriazinyl product condensed with two molecules of an azo dye with a primary amino group at 35-40 °C. The resultant dyes are applied very efficiently to cellulosic fibres at 85-90 °C with very little dye remaining in the dyebath. The same molecule may also be prepared by condensation of the dye with cyanuric chloride at 0-5 °C and then with the diamine at higher temperature. Dyes more suitable for printing application may be prepared by condensation of a dye-amino group with cyanuric chloride followed by a diamine and then a further molecule of cyanuric chloride. The various applications are manifested in the various ranges of ICI s Procion dyes. 

Related to ionic liquids are substances known as deep eutectic solvents or mixtures. A series of these materials based on choline chloride (HOCH2CH2NMe3Cl) and either zinc chloride or urea have been reported (Abbott et al., 2002 2003). The urea/choline chloride material has many of the advantages of more well-known ionic liquids (e.g. low volatility), but can be sourced from renewable feedstocks, is non-toxic and is readily biodegradable. However, it is not an inert solvent and this has been exploited in the functionalisation of the surface of cellulose fibres in cotton wool (Abbott et al, 2006). Undoubtedly, this could be extended to other cellulose-based materials, biopolymers, synthetic polymers and possibly even small molecules. 

Reactive dyes typically contain the chlorotriazinyl group. The chloro substituent can be displaced by hydroxy functional groups from cellulosic fibres thereby incorporating the dye molecule into the fabric. Bright and lightfast colors are obtained by this approach. Reactive dyes for cotton generally contain a number of sulfonic groups to provide the water solubility which is required to apply the dyes from aqueous solutions. 

The swelling of cellulosic fibres by moisture can be reduced by the application of self crosslinking urea or melamine products as well as by products that mainly crosslink with cellulose molecules. Without such a crosslinking finish, cellulose fibres can take up more than 10 % of their weight in water. As the fibres swell, the fabric must crease and shrink to relieve the internal stresses caused by the swelling. 

Two different chemical approaches have been used commercially to produce non-swelfing or durable press cellulose fabrics. The original approach is the incorporation of a polymerised finish in the pores of the fibres, so that water molecules cannot easily penetrate the fibre. The newer approach is the reaction of multifunctional crosslinking agents with the hydroxyl groups of adjacent cellulose molecules that hinder the swelfing of the cellulose fibre. 

Deactivation of cellulases after the desired effects have been achieved is very important. If the enzyme is not completely removed from the fabric, or is not effectively deactivated, the hydrolysis reaction will continue, although at a slower rate. As very large molecules, cellulases cannot diffuse into the crystalline parts of the cellulose fibres. They react on the fibre surface, so fibre damage takes time. But eventually enough hydrolysis will have taken place to weaken the affected fabrics or garments, leading to customer complaints and returns. 

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