Dye printing Flashcards
Describe the physical structure of wool fibre.
Outside scales with an inner cortex
What chemicals are wool sensitive to? What are they stable to?
- sensitive to Alkalis
- stable to acids
What process can be carried out on wool to reduce felting?
Chlorination, an oxidation process
How does scouring effect wool?
-removes spinning oils and greases
How does chlorination effect wool?
3
- improves wetting qualities
- improves dye uptake
- provides stronger, brighter colours
What are the three categories of acid dye?
- acid levelling
- acid supermilling
- acid milling
What qualities does acid levelling achieve?
3
- brilliant colours
- good levelness
- fairly weakly attracted to the fibres
What qualities does acid supermilling achieve?
3
- strongly attracted to the fibre
- difficulties obtaining level dyeing
- restricted colour range
What qualities does acid milling achieve?
3
- intermediate properties
- there is a compromise between washfastness and levelling
- commonly used
What is the typical process for acid dye?
3
- print, dry
- steam for 30 mins
- wash off, rinse with cold water, then with hot water
Name 3 types of cellulosic fibres
- cotton
- linen
- flax
What are the effects of singeing on cotton?
- a burn-off of protruding fibres, seed husks, etc, for a cleaner surface
What is the effects of desizing on cottons?
Removal of “sizes”, e.g chemicals added to cotton to protect the yarn during weaving
What are the effects of scoring on cottons?
3
- treatment with hot alkali
- removes fatty materials and waxes
- gives better wetability and absorbency
What are the effects of bleaching on cottons?
- oxidation process using hydrogen peroxide
- removes any natural colour
- improves wetting and swelling ability
- easier penetration for dye, cleaner background
What are 2 pros of direct dyes?
- good solubility
- relatively low cost
What are 3 cons of direct dyes?
- tendency to bleed
- dye fixing agents should be used
- cheap but lower quality
what are vat dyes and how do they work?
- insoluble dyes
- they are converted to a water soluble form by reduction in alkali conditions
- oxidised back to insoluble dye when on the fibre
What are the properties of vat dyes and what are the used for?
(3)
- expensive
- very high wet fastness and light fastness
- used for upholstery, bedding, and curtains
What are the 5 steps of the vat dye process?
- print and dry rapidly, cool
- steam for 15 mins at 103 degrees
- oxidise in a bath containing hydrogen peroxide to get the dye colour back
- add acetic acid to neutralise
- cold rinse, followed by warm rinse, followed by boil wash with detergent
How do reactive dyes attach to cellulosic fibres?
Forms a covalent bond, effectively becoming part of the fibre
Name two pros of reactive dyes
- full range of bright colours available
- excellent wash fastness
Name to cons of reactive dyes
- fairly expensive
- some environmental problems
What conditions must there be for reactive dyes to produce a covalent bond?
Alkaline conditions
