MERCERIZATION
DEFINATION OF MERCERIZATION:
Mercerization is a physio-chemical process where cotton / yarn or fabric is treated with
15-22% caustic soda solution at a temperature at 70-80°C. It is necessary to hold the fabric under
tension and wash thoroughly.
Mercerization, in textiles, a chemical treatment applied to cotton fibers or fabrics to
permanently impart a greater affinity for dyes and various chemical finishes. Mercerizing also
gives cotton cloth increased tensile strength, greater absorptive properties, and, usually, a high
degree of luster, depending on the method used.
OBJECTS /BENEFIT OBTAINED BY MERCERIZATION:
To improve the luster.
Improve smoothness.
To improve the tensile strength.
To improve the dye uptake and moister regain.
Improve hygroscopicity.
Improve physical compactness & dimensional stability.
Mechanism:
When cotton fiber is brought into aqueous solution of sodium hydroxide of (18%), the
cellulose begins to swell immediately and in a few seconds the fiber is elliptical in X-
section. On further swelling, the section rounds off the major axis of the ellipse is at least
25-30% greater than the fiber width oh the wall and swells inwards until the lumen is
practically eliminated. These changes are shown in the following figure:
When the fiber is transferred to water and washed shrinkage begins (stage 6) and on
drying at room temp a further and final shrinkage occurs (stage 7). During the last three
stages shrinkage proceeds uniformly towards the centre and the lumen does not recover
its original size.
1. Higher strength is obtain after the process sequence due to:
Molecular orientation increase.
Length wise shrinkage of fabric occurs which minimize the
weak links of the fiber.
Fiber become more elastic thus strength increases.
2. Higher absorbency obtained due to:
NaOH acts as decrystalline agent which causes increasing
amorphous region.
Crystal lattice is altered and tends to increase absorbency.
3. Dye affinity increase due to:
Increase amorphous region.
Crystal lattice is altered.
Available –OH group increase which contribute dye affinity.
4. Luster increase due to:
Kidney shaped becomes almost circular (Oval shape) in X-
section.
Deconvolution occurs or convolution twist becomes less.
Increase transparency and reduce surface roughness
Considerable points for mercerization:
1) Temperature.
2) Concentration of caustic soda solution.
3) Time
4) Tension.
5) Wash thoroughly.
5. Temperature:
Normally/commercially mercerization is carried out at a temp range of 30-
45°C
We may found that the higher the temperature-
Lower concentration of caustic soda need.
Greater tension necessary to prevent shrinkage.
Greater dye affinity.
Slightly higher tensile strength.
Higher luster.
Caustic recovery easy.
Different temp affects on luster.
6. Concentration of caustic soda solution:
Dye absorption increases with increasing caustic soda concentration from
13 to 26% .
Tensile strength increases steadily with increasing caustic soda
concentration up to 13% to 21% and on further increases of caustic soda
strength decrease slightly
If caustic conc. Increase above 27%, tensile strength falls rapidly.
Most commonly used concentration is 21-22%.
Less than 13% generally not used
7. Time:
Ideal time of mercerization is 30 sec to 90 sec
But more time than ideal time is required for mercerizing, Oxycellulose
will be produced which will damage the mercerized.
30-60s times is enough for mercerizing in 22% caustic conc. or more.
When caustic concentration is less, temp is increased, and then time is
increased.
8. Tension:
Mercerization without tension gives no luster a causes a considerable
shrinkage.
Maximum luster is obtained when the tension is just sufficient to bring the
material back to its original dimension.
Further increment of tension causes-
No benefit.
May be harmful.
Fabric damage.
9. Washing thoroughly:
Washing under stretched condition after mercerization is very important..
After washing, caustic soda concentration in the fabric must be less than
8%, otherwise shrinkage may occur or cellulose may degrade due to
excess alkali
0.1-0.5% HCL may used to neutralize caustic soda.
Efficiency of Mercerization:
The Degree of mercerization is expressed in terms of moisture regain and barium activity
number/ ( BAN ) number.
BAN: It means barium activity number; it is a ratio by which we can determine the result of
mercerization.
If BAN is less than 116 then No mercerized , if BAN is 117-129 mercerization is average, if
BAN is 130-157 it may call good mercerized and if BAN is more than 157 then it is over
mercerized.
Pad chain mercerization m/c:
m/c description:
A high speed pad-chain mercerizing machine capable of handling different fabric at
the same time producing a high degree of luster.
This Machine comprises two powerful 2-bowl mangles followed by a heavy pattern
clip stentor machine fitted with washing and caustic recovery arrangement
The mangles are of open type, enabling the bowls to be easily changed.
Each mangle is arranged to provide either a single or double immersion in the caustic
liquor or two squeezes.
Hot wash Cold wash
To stenter
Padding mangle Acid bath
Fig: Typical Mercerization Process
