- Dyeing is the permanent application of a colourant to a fibre to give a uniform colour
- The colourant must be able to be absorbed by, or react with, the textile fibre
- Must be soluble so it can get into the spaces between the fibre molecules
Direct Dyes
- soluble in water
- used for viscose, cotton and modal fibres
- moderate light fastness
- poor wash fastness
- salt can be added to help fibres absorb the dye
Reactive Dyes
- soluble in water
- forms a strong chemical bond with cellulosic and protein fibres
- produces bright colours that have good wash fastness
Vat Dyes
- not soluble in water
- excellent wash and light fastness
- can produce indigo dye
- a lot of indigo dye sits on top of the fibre rather than being absorbed into it, causing it to rub off onto other fabrics and lose some colour when washed
- to get the dye into the fabric, it has to be converted into a soluble form by removing oxygen
- once the dye is in the fibre it’s converted back into its insoluble form by oxidation, making the molecules too big to get out of the fibre
Disperse Dyes
- used to dye fibres with hydrophobic properties
- almost insoluble in water
- applied to fibre in the form of a fine aqueous dispersion
- held inside fibres by chemical bonds
Acid Dyes
- soluble in water
- applied to fabric in an acidic dye bath
- good light fastness
- wash fastness varies
Solvent Dyes
- were created as water usage and disposal of dyes in an environmentally friendly way is expensive
- uses organic solvents instead of water
- however, solvent dyes are very expensive and there is cost involved in recovering the organic solvent to use again
- equipment can be expensive
- not very economical
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