ACID DYES
Introduction:
Textile dyes are classified according to the textile material going to be dyed or colored.Say, cotton fiber,the garment or the fabric or the yarn made of cotton are dyed with Direct dyes or Reactive dyes.Polyester materials dyed with Dispersed dyes.Nylon materials are dyed with Acid dyes.Like that,textile materials made of different substances are required different chemical bondable or chemical structure dyes.The textile dyes selection are based on the textile fibers to be dyed. In this article,we tried to brief on acid dyes.What are acid dyes ?.Acid dyes are used to dye colour the textile material contain protein or polyamide.Examples of protein natural fibers are wool and silk.Wool contains protein substance called Keratin.Silk contain protein fiber Fibroin .And synthetic fiber nylon contains chemical substance Polyamide.
Wool dyeing or nylon dyeing takesplace based on the affinity mechanism between acid dye and protein substance of wool fiber or polyamide substance of nylon fiber.Basically,acid dyes are of anionic electro charging in nature.They have the chemical sites of anion.As we studied in your previous academy,specially in high school level or 11th standard or 12th standard in chemistry.Anion and cation are the charged electronic sites.They are charged negative and positive respectively.These anion and cation are attracted to each other like north and south poles of the magnets.How the two opposite poles if two magnets attracts,like that anions and cations are attracted to each other.
Anions of acid dyes are attracted towards the cationic sites of the protein fiber wool(or silk) or polyamide fiber nylon.The poly molecules of the wool is having cationic sites in its polymer structure.That is morphology, whatever the polymer chain is there,that is containing cationic sites attracted by the anionic sites of the acidic dyes.When the wool fiber is dyed with or the nylon is dyed with the acid dye in acidic concentration,then both the affinity that attraction takesplace between the anion or cations and form an electrovalent bond.
The base of the acid dyes is the mechanism involved in acid dyes.That is mode of attachment of acid dyes to protein or polyamide fibers.
Types of Acid dyes:
Acid dyes are divided into two groups.1.Molecularly split acid dyes and 2.Aggregated acid dyes.
Molecularly split acid dyes:
When these dyes are dissolved in water, individual molecules of the dyestuff are sepersted,followed by ionisation.
Aggregated acid dyes:
These dyes do not split into individual molecules when dissolved in water.Many molecules cluster together into bigger particles.Some of the molecules ionise,giving electrically charged aggregates.
Other method of classification of acid dyes are divided as below.And will be briefed in separate articles.
1.Levelling dyes
2.Milling dyes
3.Super Milling dyes
The dyes used for the particular textile material,it depends upon the class of dyes,which are selected depends upon the efficiency of the fastness rating.What fastness is required ? What efficiency is required ? Main mechanism involved basically,the acid dyes are called salt called sodium salt produce coloured negative ions anions when dissolved in water.They soluble in water.
Properties:
Everybody expects good fastness from applied dyes or shades. Rubbing fastness,Light fastness, Washing fastness are the three major fastness considered to judge quality of dyes.
Shade creations that is possibility of shades produced by dyes.Those are Light shade,Medium shade and Dark shade.
The properties of acid dyes will be briefed in separate articles.
Source:
1.Ref: Chemistry of Dyes and Principles of Dyeing by V A Shenai.
2.Educational qualification and industrial experience of the author/blogger.
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