TEXTILE CHEMICAL
PROCESSING: PREPARATORY
PROCESSES
PREPARATORY OPERATIONS
Main Objectives
•Removal of all impurities from fiber, both natural and / or
those added during production that may interfere in
subsequent dyeing and / or finishing process.
•Improve the ability of the fibers to absorb water solutions
of dyes and chemicals.
•Impart proper brightness or whiteness to fabrics according
to need, especially when brilliant or certain pastel shades
are desired.
Rashmi Thakur- DT, NIFT BLR
DESIZING
Types of Desizing
Rot Steeping
Acid Steeping
Oxidative Desizing
Enzymatic Desizing
Rashmi Thakur- DT, NIFT BLR
DESIZING
Rot Steeping
oldest and economical method
no chemical are used in this treatment.
fabric is soaked in warm water at 35 – 40°C temperature
passed through a padding mangle and squeezed.
allowed to stand for 24 hrs.
Acid Steeping
• dilute hydrochloric acid or sulphuric acid or a mixture of both are used for
hydrolysis
Rashmi Thakur- DT, NIFT BLR
DESIZING
Oxidative Desizing
• starch is oxidized
• commonly used oxidative desizing agents are:
• Hydrogen per oxide
• Sodium bromide
• Ammonium per sulphate.
Enzymatic Desizing
• Enzymes are proteins of high molecular weights
• Amylase is the enzymes used in desizing
• Enzymes can be derived from sources like animal (pancreatic) and
vegetable (malt and bacterial)
Rashmi Thakur- DT, NIFT BLR
SINGEING
The process of removal of protruding short fibres from the
surface of fabric (sometimes yarns also) by burning them with
the help of flame or hot plate.
• Gas Singeing
• Hot Plate Singeing
Before After
Rashmi Thakur- DT, NIFT BLR
SCOURING
Removal of natural oil substances like waxes, fats and pectins
as well as added impurities like lubricating oil, dust, dirt and
residual starch (in cotton materials).
• Oils, waxes and free fatty acids are emulsified by the
soaps
• Pectins are converted into soluble salts
• Proteins are degraded to simple soluble amino acids
and mineral matter is dissolved.
Rashmi Thakur- DT, NIFT BLR
BLEACHING
To remove the natural coloring matters and prepare the fabric with
required whiteness.
Full-Bleach
• When highest degree of whiteness is required
• Achieved by bleaching with hypochlorite, followed by hydrogen
peroxide bleach.
Half-Bleach
• Fabrics meant for dyeing and printing, where less degree of
whiteness is required
• Done by bleaching with hypochlorite or hydrogen peroxide of
adequate concentration.
Rashmi Thakur- DT, NIFT BLR
BLEACHING
Oxidizing Bleaching agents
Sodium hypochlorite, Sodium chlorite, sodium perborate, sodium per
carbonate
Hydrogen peroxide. “Universal bleaching agent”
Continuous bleaching process
In this process desizing, scouring and bleaching are
combined together. These are very popular practice since
savings in terms of time, energy and labor are possible.
However, combined operations are not always sufficient for
preparation of certain cotton fabrics for dyeing and
finishing.
Rashmi Thakur- DT, NIFT BLR
OPTICAL BRIGHTENERS- fluorescent whiteners
The purpose is to obtain extraordinary brilliant
whiteness to cotton materials.
Optical brighteners acts as fluorescent dyes and they
are colorless
They absorb light near to ultraviolet region ( below
400nm) and reemit the light in the violet blue visible
region.
Rashmi Thakur- DT, NIFT BLR
MERCERIZATION
Treatment of cotton fabrics or yarns with a cold
concentrated solution of sodium hydroxide (NaOH)
solution for one minute or less is called mercerization.
Cotton fibers swell, untwist and their bean shaped cross
section changes into round form.
Rashmi Thakur- DT, NIFT BLR
CLEANING OF WOOL
Carbonizing
CLEANING OF SILK
Degumming
Rashmi Thakur- DT, NIFT BLR
SELECTION OF PROCESS SEQUENCE
The fabric preparation depend on type of fibre and blend
composition, yarns, fabric quality parameters, colour
fastness requirement and end use.
• Cotton knitted fabrics are subjected to a modified routine in
which singeing and desizing stages are some times omitted.
• Whereas for woven fabrics desizing can not be omitted.
• Preparation of fabric also depends on the end requirement.
Rashmi Thakur- DT, NIFT BLR
COLOURING MATERIALS
Colour is one of the most important
characteristics of apparel and home furnishing
products.
It is a significant factor for adding aesthetic
value to textile products.
Curretly dyes and pigments are used to impart
color to the textile materials.
Rashmi Thakur- DT, NIFT BLR
IMPORTANT PROCESS PARAMETERS OF
DYEING
Dye bath
•For reproducibility, all the amount of dyes and dyeing
assistants and the liquor ratio used should be measured
and recorded accurately, in order to be followed precisely
in future runs.
•All dyeing assistants in any dye bath should be used only
if necessary.
•Using excessive amounts (larger than recommended) of
any additive should be avoided.
Rashmi Thakur- DT, NIFT BLR
IMPORTANT PROCESS PARAMETERS OF
DYEING
Concentrated Dye solution
• To insure uniformity throughout the dyeing bath, initially a
small solution or dispersion of the dye is prepared.
• Undissolved or undispersed dye particles, may cause unlevel
dyeing or form specks on the goods.
• The dye solution is filtered through a coarse filter before the
preparation of solution.
• While preparing concentrated solutions, dyes and dyeing
assistants should not be mixed together in their concentrated
form unless specifically required.
Rashmi Thakur- DT, NIFT BLR
IMPORTANT PROCESS PARAMETERS OF
DYEING
Material to liquor ratio (MLR)
• Ratio indicates how much liquor is to be taken for dyeing a
given weight of the material.
• The total quantity of water to be taken for dyeing depend
upon the weight of the material to be dyed and is expressed
in terms of MLR.
• Thus a Material : Liquor ratio of 1: 20 means that the weight
of the liquor to be taken should be 20 times the weight of the
material to be dyed.
Rashmi Thakur- DT, NIFT BLR
IMPORTANT PROCESS PARAMETERS OF
DYEING
Percentage of shade
• It is based on the weight of the material taken for dyeing.
• Thus when a 2% shade is to be produced on the cloth,
then 2gm of dye is taken for every 100gm of cloth for
dyeing.
• The dyeing so produced gives a 2% shade.
• It does not mean that the cloth contains 2gm of dye per
100gm of cloth after
Rashmidyeing.
Thakur- DT, NIFT BLR
IMPORTANT PROCESS PARAMETERS OF
DYEING
Wash cycles
• This treatment removes unbonded dyes and dyeing
assistants from the fabric.
• Procedure varies from a mild rinse with warm water to
the use of a detergent solution at or near the boil.
• With certain groups of dyes, a slight change of shade
occurs at this stage, yielding the true color.
Rashmi Thakur- DT, NIFT BLR
Dye Selection Factors
• Suitability of dye for a particular type of fabric
• Fiber Content and fabric structure
• Required color fastness
• Penetration and absorption of dyes
• Cost of dye stuff
• Method of application
Rashmi Thakur- DT, NIFT BLR
