Fibres bonding

It is not economical to use expensive woven material for long lines, which can be, and normally are, coated by mechanical means. For such lines the most commonly used material nowadays is a glass-fibre tissue of a nominal 0-5 mm thickness, consisting of glass fibres bonded together with a phenolic resin or starch. 

There is no doubt that the major weakness of the reactive dyeing process is the hydrolysis reaction and the consequent need for a wash-off" process. The extent to which dye hydrolysis takes place in competition with dye-fibre reaction varies quite markedly within the range 10 40% depending upon the system in question. A considerable amount of research has therefore been devoted to the search for reactive dyes with improved fixation. The most successful approach to addressing this issue has involved the development of dyes with more than one fibre-reactive group in the molecule, which statistically improves the chances of dye fibre bond formation. Examples of products of this type are the Procion H-E... 

The work with Cl Acid Yellow 129 used only unilamellar vesicles. The liposomes again suppressed exhaustion but increased dye-fibre bonding, leading to better fastness properties. It is claimed that liposomes can be used to control the rate of exhaustion. 

Bond stability - the dye-fibre bonds must be reasonably stable to a range of relatively severe fastness tests. 

An alternative mechanism [8] entails reaction of cyanamide (or dicyandiamide) with the dye phosphonate to give an O-acylisourea derivative (7.47). This is able to react directly with cellulose to form dye-fibre bonds, urea being released as the anticipated by-product (Scheme 7.31). In support of this mechanism, it is known that O-acylisourea derivatives of arylcarboxylic acids react readily with alcohols and this constitutes an efficient route for the preparation of carboxylic esters [44]. 

Interest in acid-fixing reactive dyes has remained active because of their environmentally attractive features (section 1.7). The freedom from competing hydrolytic reactions potentially offers exceptionally high fixation, extreme stability of the dye-fibre bonds and complete suitability of the unfixed dyes for recycling. In contrast to conventional reactive dyes, sensitisation problems arising from reaction with skin proteins are not anticipated. Unlike the haloheterocyclic reactive dyes, there is no risk of release of AOX compounds to waste waters. Heavy metals are not involved in the application of acid-fixing reactive dyes, nor are the electrolytes or alkalis that normally contaminate effluents from conventional reactive dyeing. 

In the case of quaternary derivatives made from the non-planar aliphatic amines 7.64, 7.65 and 7.66, steric strains further destabilise the C-N+ bond so that reaction with cellulose occurs under alkaline conditions at 30 °C, whereas temperatures of about 40-50 °C are required for the pyridinium derivatives 7.67. The quaternisation approach appeared to offer the opportunity to prepare dyes yielding reactivity levels intermediate between those of aminochloro- and dichlorotriazine dyes without loss of the desirable stability of the dye-fibre bond to acidic conditions that is characteristic of aminohalotriazine dyes. Unfortunately, this ideal was not attainable because of the objectionable odours of the tertiary amines liberated by the fixation reaction and the sensitivity of the reactivity behaviour of the quaternised derivatives to the nature of the chromogen attached to the triazine ring, making it difficult to select compatible combinations of dyes. 

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... 

The hydroxide ion is not the most active nucleophile with which the dye-fibre bonds in reactive dyeings have to contend. Many commercial detergent formulations contain sodium... 

Surprisingly, however, dyes of the chlorodifluoropyrimidine type readily form a perhydroxide derivative that leads to cumulative damaging effects on dye-fibre bond stability. A comparison between seven different haloheterocyclic systems each attached to the same chromogen (phenylazo H acid) demonstrated several important conclusions [89] ... 

Only dye-fibre linkages that carry on the heterocyclic ring an electronegative substituent that is ortho (or para) to the dye-fibre bond show both peroxidation (Schemes 7-41 to 7.43) and bond breakage (Scheme 7.44). 

An amine aftertreatment has been developed recently to protect haloheterocyclic dyes with substituents vulnerable to attack by perborates or other peroxy compounds in detergents. This product displaces such substituents, deactivating the dye-fibre bond system and rendering it resistant to peroxidic attack [90]. 

The relationship between dye-fibre bonding and light fastness was examined for ten sulphatoethylsulphone reactive dyes on cellulose and it was shown that the stronger the bonding between dye and substrate, the more stable was the dyeing when exposed to light... 

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