By: H.D. Joshi, D.H. Joshi, M.G. Patel and S.R. Naik



'Application of Cationic Dyes to Anionically Modified Nylon and their Performance Evaluation with Cationic Dyeable Polyester with Special Reference to Fastness Properties'


Introduction


The production of multi-colour effects has been done by the help of differential-dyeing systems. The term "differential-dyeing" is applied to fibres which are of the same basic type, e.g., nylon but with different dyeing properties. To vary the dyeing properties of the fibre (nylon), chemical modifications are employed.


In one case the substantivity of the fibre for anionic dyes is modified by altering the amine end-group content.


This can be done by using a stabilizer during polymerisation which has one or two carboxyl groups that can react with the amino end groups of nylon polymer. The stabilizer also has one or two sulphonate groups which make the polymer anionic.


An example of such a stabilizer is disodium 3,5- disulphobenzoic acid- C6H3 (S03Na)2 COOH, i.e., Na2DSBA. The reaction of the nylon polymer with Na2DSBA is as follows:-


HOOC-Nylon Polymer-NH2 + HOOC C6H3(S03Na)2 ------->


HOOC-Nylon Polymer-NHCQ-C6H3 {S03Na)2 + H20

(Cationic dye dyeable nylon)


Other alkali metal salts, e.g., lithium salt can also be used. 5-sodium sulphoisophthalic acid is also used to introduce sulphonate groups in nylon 6 polymer. The intrOduction of the sulphonate group increases the affinity for basic dyes while the affinity for acid dyes is very low.


In another modification, the amine endgroup content is varied which gives a differential dye pick-up of acid dyes on nylon making it regular, light-dyeable and deep-dyeable. The amine end group content has a predominant effect on dye pick-up when dyed with acid dyes. The amino end groups are the functional sites in nylon for the adsorption of anionic dyes in acidic solution; the polymer and acid dyes are ionically bonded in the acidic dyebath.



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About the Authors:


The authors are associated with Man-Made Textiles Research Association (MANTRA), Surat.