Cellulose Chromophoric groups

Heat catalyzes free radical formation in cellulose. Aldehydes form from C2 and C3 hydroxyls. Aldehydes oxidize to carboxyls, and with dehydration, carbon monoxide (CO) and carbon dioxide (C02) form as well as conjugated carbonyl-ethylenic chromophoric groups that selectively absorb blue light and impart yellowness (35). During the induction stage of cellulose oxidation, yellowness may increase steadily with selective carbonyl and ethylene group formation. By artificially aging... 

Figure 3. Generation of chromophoric groups from cellulose structure of the linen of the Shroud.

These contain the acrylamide residue D.NH.CO.CH2 CH2 as the reactive component, D representing the chromophore-containing portion of the dye molecule. In the presence of alkali the reaction between a cellulosic hydroxyl group and the terminal CH is similar to that which has been described for the Remazol dyes... 

Another important commercial utilization of cotton etherification is in coloration of fabrics with reactive dyes [338 340]. Reactive dyes contain chromophoric groups attached to moieties that have functions capable of reaction with cotton cellulose by nucleophilic addition or nucleophilic substitution to form covalent bonds. In the nucleophilic addition reaction, an alkaline media transforms the reactive dye to an active species by converting the sulfatoethyl-... 

A process which is important for the dyeing of cotton and for histological staining procedures is the addition of what are known as direct dyes to cellulose. There are various theories about the type of bonding [53, 54]. Obviously hydrogen bonds and hydrophobic interactions are important here, but in view of what has already been said, even these weak interactions should prove capable of influencing the chromophoric groups dissymmetrically. 

Anthraquinone leuco dyes are widely known as vat dyes.10 Vat dyes possess extensively conjugated aromatic systems containing two or more carbonyl groups, e.g., anthraquinone, indigoid chromophores. The colored form of vat dyes are insoluble in water. The dyes are applied by a process whereby the dye is converted to the reduced form (leuco dye) which is soluble in water and can penetrate into a cellulosic fiber. On exposure to the atmosphere the leuco form is oxidized to the original quinoid form which then precipitates as an aggregate. Vat dyes generally have excellent chemical and photochemical stability. 

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