General discussion on how to scour textiles and effect of different scouring agents.

2.  Scouring is basically the removal of inpurities
such as dust particles,waxes,pectins,oils etc
from natural fibers with the help of chemicals or
without chemicals before dyeing or printing.
The process of removing naturals (oil,
wax, fats, gum etc) as well as added
impurities (during fabrication process) to
produce hydrophilic and clean textile

3.  Scouring is a purifying treatment of textiles, the
objective of scouring is to reduce the amount of
impurities sufficiently to obtain level and reproducible
results in dyeing and finishing operations.
 Saponify fats and waxes
 Break down of proteins and pectins
 Complex formation of minerals substances containing
Ca, Mg, Fe, Cu.
 Increase the absorptive capacity
 Improve the degree of whiteness and reduce the seed
husk contents
 Extraction of reactions by-products.

5.  The type of scouring agent generally depends
on the kind of fibers i.e. cotton or wool; fabric
type i.e. woven or knitted, thick or thin;
texturized or non-texturized and the extent
of impurities present in the fiber.
 For example, silk and wool dissolved by alkali,
whereas acetate and triacetate are converted
back to their original cellulose form.
 sodium or ammonium carbonate are
preferred in case of wool.

6.  Fats and waxes are removed by the action of alkali and
surface active agents, in some cases use of solvent and
surfactants mixtures may be necessary.
 Pectins and related substances are solubilized by the
action of alkali, usually NaOH, which also acts as
swelling agent to facilitate removal.
 Minerals and heavy metals are removed by producing
more soluble salts e.g. acids demineralization or by
use of sequestering agents.
 Amino acids or proteins are solubilized by producing
corresponding sodium salt.

7.  Emulsification, forming stable suspensions of the impurities in
water and
 Saponification, Converting the contaminates into water soluble
components
 An emulsion is a dispersion of a liquid in another liquid in which it
is not soluble.
 When two immiscible liquids are mixed and shaken aggressively
one of them break into small droplets and gets dispersed in other,
however, such dispersion is thermodynamically unstable, hence
liquids again go to two distinct continuous phase.
 To stabilize such dispersions, emulsifiers are used. Emulsifier is
surfactants whose molecules cover the surface of two droplets.
One portion of the surfactant molecule becomes compatible with
one phase and other part with second phase.This way of
dispersion of one liquid phase in another becomes stable, which
is known as emulsion.

9. Natural fats, oils and lubricants tallow are mostly esters usually in
the form of triglycerides. After saponification, glycerol is water
soluble and soap is efficient surfactant or emulsifier. If wax is not
removed, non uniform absorption of dyes and finishing agents
will take place. Actually removal of wax determines the
absorbency after scouring. Also alkali removes pectic acid, pectic
acid is insoluble in water but soluble in alkaline solution

10.  Scum formation because of Ca+2, Mg+2, Fe+3 metal ions
 Sequestering agents or chelating agents are
negatively charged and are capable of forming strong
ring structure with the metal ions present in hard
water and in pectins.
 This prevents film and scum formation; precipitation
of hard water. Advantages are better levelness and
more brilliance in dyeing process, lower peroxide
consumption, high degree of whiteness, and no
catalytic damage during peroxide bleaching.
 Mostly used sequestering agent is EDTA.

11.  A surfactant is a substance,
which reduces the surface
tension of the water, e.g.
water surface tension 72
dynes/cm to 30 dynes/cm at
less than 0.1 %
concentration. Only non-
ionic and anionic
surfactants are used in
scouring.This helps in
wetting as well as
dispersion and suspension
of soil and oils.

12.  In this process cotton fabric boiled with a solution of 10 to 20
g/l (3-6 % o.w.f.) caustic soda in kier with a liquor ratio 3:1.
 In continuous scouring about 30 g/l of caustic soda is added
in the pad-bath with a liquor pick-up of about 100 %.
 In continuous processes it is possible to decrease the time of
post impregnation steaming to about 2 min at a
temperature of 130-135 C with NaOH solution of 40-60 g/l.
 The rate of saponification of waxes increase as the
temperature (pressure) of boiling increase, rate of chemical
reaction is doubled with each 10 C rise in temperature and
saponification of oil is increased sixteen times from 60 to 100
C.

13.  With increase in temperature oxycellulose formation is
also increased in presence of oxygen, generally
oxygen is removed from kier before process but a
small amount can cause problems, thus a small
quantity of mild reducing agent such as sodium
bisulphite or hydrosulphite is added, which prevents
oxidation of cellulose during kier boiling.
 Cotton is not degraded by boiling with sodium
hydroxide solution up to a concentration of 20 g/l in
the absence of air.
 If colored yarns are present in fabric, soda ash (sod.
Carbonate) is used because of its low pH.

14.  Synthetic fibers generally do not contain naturally
occurring impurities like natural fibers. However spin
finishes, knitting weaving oils, antistatic agents are
added to improve physical as well as mechanical
properties.Other are dirt etc.
 For polyester weak and low concentration of alkalis
are used at low temperature.
 Special precaution is necessary when polyester is
scoured with strong alkali at higher temperatures and
care has to be taken not to hydrolyze the fiber.
 Nylons are scoured with mild alkali and detergents.
Generally non-ionic detergents are used in scouring of
nylons.

15.  AATCCTest Method No. 79
 Properly scoured fabric should wet out faster and be
more water absorbent.
 AATCCTest Method No. 79 is used to measure fabric
wetting. A drop of water is placed on the fabric and
the time it takes for the drop to penetrate the fabric is
recorded.The faster the wetting time, the more
absorbent the fabric.
 Cuprammonium fluidityTest:
 To check the degree of degradation/polymerization.
 Fibers/fabric is dissolved into Cuprammonium hydroxide.
High viscosity means high degree of polymerization and low
damage