2. Mercerization
Mercerization, in textiles, a chemical treatment applied to cotton fibres
or fabrics to permanently impart a greater affinity for dyes and various
chemical finishes.
Mercerizing is a pre-treatment or finishing treatment for cotton articles
and/or natural fibres composed by cellulose in a higher concentrated
solution of caustic soda (300 g/l), under tension and ambient
temperature
3. Cont…
Typically cotton (or cotton-covered thread with a polyester core) but hemp
and linen can be mercerized also – to increase luster.
It is done after weaving (in the case of fabrics) or spinning (for yarns or
threads).
But early on it was found that the process also had secondary benefits as the
mercerized fibers were able to absorb more water, and therefore absorb more
dye, making the color of the dyed cloth brighter and deeper.
The difference is dramatic. As mercerization increases the absorption of
dyestuffs by as much as 25%
4. History
. • The process goes back to the 1880’s. The effect of caustic
soda on cotton was discovered in 1844 by John Mercer, an
English calico printer, who received a patent for it in 1850.
• John Mercer was granted a British Patent for his discovery
that cotton and other fibers changed character when subjected
to caustic soda (NaOH, also known as sodium hydroxide or
lye), sulfuric acid, and/or other chemicals.
• One of the changes was that caustic soda caused the fiber to
swell, become round and straighten out. But so what – these
changes didn’t impart any luster to the fibers, so his patent was
largely ignored.
5. H. A. Lowe
Then in 1890 Horace Lowe found that by applying Mercer’s caustic soda process to cotton yarn or
fabric under tension,
By holding the cotton during treatment to prevent it from shrinking
The fabric gained a high luster as a result of the light reflection off the smooth, round surface
created by the NaOH.
It became an overnight success and revolutionized the cotton industry.
By applying this Lowe found that the fibre gained a lustrous appearance
6. To improve the luster
To improve the strength
To improve the dye uptake and
To improve water absorbency
Purpose
7. Internal hydrogen bonds are broken
Native cellulose (Cellulose I) forms alkali cellulose I with concentrated sodium
hydroxide.
On washing and neutralization cellulose II is formed
In Cellulose II, the number of available hydroxyl groups (-OH) is increased by
25%.
Mercerised cotton has an increased affinity for reactive, direct cotton dyes, water
and an increased strength
As a result of the penetration of the alkali into the lattice
thus lustre is increased.
8. Change due to mercerization
Round surface can reflect the light better than a rough surface. Due to mercerization cotton shape
become round.
Luster is a result of light reflection off a surface. The more glass like the surface, the better the luster
Yarn has a very fine covering of tiny fiber ends (fuzz). This fuzz is removed by passing the yarn (or fabric)
through a controlled heated atmosphere termed singeing (gas fired in the past, electric more currently)
resulting in a cleaner surface.
(
9. What happens to cotton during
Mercerization
Swelling of the fibre takes
place.
the cross section ,like
kidney shaped becomes
circular or oval-shaped,
thus enhancing the luster
Shrinkage of length wise.
Strength improved
Cellulosic chains gets
rearranged .
11. WHAT HAPPENS INSIDE COTTON
After swelling NaOH thoroughly penetrates amorphous phase
of the fibre,
reaction between the alkali and the micelle occurs
completing the generation of alkali cellulose I.
At higher concentrations, the hydrate volume is smaller.
Hydrates cause lower swelling but able to penetrate the
crystalline phase and change the crystal structure.
Such changes are capable of inducing important structural
modifications in fibre structure.
12. Cellulose-I to cellulose-II
• The native form of cellulose which occurs in cotton and other natural cellulosic fibres,
is known as cellulose I.
• It has it unique crystal diffraction pattern (monoclinic). It is a thermodynamically less
stable form of cellulose.
• When cellulose in converted to regenerated cellulosic fibres like viscose, dissolution
of cellulose is an intermediate step.
• During regeneration, it gets converted to a different crystalline form, known as
Cellulose II.
15. Change due to mercerization
A. Fiber level
1. Swelling
2. Cross sectional morphology changes from beam shape to round shape.
3. Shrinkage along with longitudinal direction.
B. Molecular level
1. Hydrogen bond readjustment
2. Orientation (parallelization) of molecular chains in amorphous region along the direction of fiber
length.
3. Orientation of the crystallinity in the direction of the fiber length.
4. Increased crystallinity
C. Chemical Changes
1. Increased rate of reaction on hydrolysis and oxidation
2. Liberation of heat during the caustic treatment.(heat of sorption and heat of reaction)
3. Increase in the alkali absorption.
4. Increase in the absorption of iodine. Changes during mercerizing process
19. How it is done
To get the desired luster and tensile strength, cotton is held under specified tension for about
10 minutes with an application of between 21-23% caustic soda (NaOH) and wetting agents
(used to facilitate the transfer of the NaOH into the fibers), at room temperature. Then the
fabric is neutralized in an acid bath.
The material is then treated with water or acid to neutralize the sodium hydroxide.
If the material is held under tension during this stage, it is kept from shrinking appreciably;
if no tension is applied, the material may shrink by as much as 25%. Higher-quality cotton
goods are usually mercerized; cloths so treated take brighter, longer-lasting colors from
less dye.
20. Cont…
The process, done in a continuous way, involves 4 subsequent steps:
a. Impregnation of the material in relaxed state, cold caustic solution of
required strength and wettability.
b. Stretching while the material is still impregnated in the caustic solution.
c. Washing off the caustic soda from the material while keeping the
material still in the stretch state.
d. Neutralizing with acids and rinsing.
21.
22. According to the form of the tension
A. tension mercerization
slack mercerization
Mercerization are Two Types:
23. 1) Tension Mercerization
• The purpose of mercerization is to increase luster of Cotton fibers
• The fiber untwists and swells, lumen becomes rounder in cross-section and it gains luster.
• Dye affinity and chemical reactivity increase. Fabric becomes stronger and smoother.
1) Slack Mercerization
• Not as lustrous as tension method
• Elongation and recovery properties improve and thus have been used to produce comfort
• stretch garments and fabric bandages, which need to conform to body shapes.
24.
25. Form of mercerization
B. On basis of product:
a) Yarn mercerization
1.Batch
Hank mercerization
Cheese mercerization
2.Continuous
Single end mercerization
Tow mercerization
Warp mercerization
34. Fabric Passing Speed:
Fabric Type Speed (m/min)
Grey Fabric Single Mercerizing 12
Grey Fabric Double Mercerizing 15
Yarn Dyed Double Mercerizing 15
Nip pressure:
Position
For yarn dyed fabric in
Bar
For gray fabric in Bar
After NaOH bath 1.5 1.5
Before acid bath 1.0 1.0
After acid bath 1.0 1.0
After washing 1.0 1.0
36. Time: The time of the mercerization is 30 to 60 seconds. If the
mercerization takes longer time it will not improve the quality but if
the time is limited to 30 s the good quality in appearance can be
achieved .
Temperature: The optimum temperature of mercerization ranges
between 18 -20°c
Twaddle (conc. of NaOH) :the concentration of NaOH is 48° Tw
to 54° Tw
Tension: Tension will be applied both in warp and weft of the fabric
41. Mercerization is possible
- on greige goods
- after desizing
- after desizing and scouring
- after bleaching
- after dyeing.
At which stage mercerization can be
done?
43. Test For Mercerization :
AATCC test method 89 is the most common test for quantifying
the degree of mercerization. It is based on the fabric’s ability to
absorb barium hydroxide. It is also called Barium No test.
Ba No=
𝑎𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝐵𝑎𝑟𝑖𝑢𝑚 ℎ𝑦𝑑𝑟𝑜𝑥𝑖𝑑𝑒 𝑎𝑏𝑠𝑜𝑟𝑏𝑒𝑑 𝑏𝑦 𝑚𝑒𝑟𝑐𝑒𝑟𝑖𝑧𝑒𝑑
𝑎𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑏𝑎𝑟𝑖𝑢𝑚 ℎ𝑦𝑟𝑜𝑥𝑖𝑑𝑒 𝑎𝑏𝑠𝑜𝑟𝑏𝑒𝑑 𝑏𝑦 𝑢𝑛𝑚𝑒𝑟𝑐𝑒𝑟𝑖𝑧𝑒𝑑
×100
Generally mercerized cotton has Ba No 115 t0 130
44. Test For Mercerization :
Mercerized and un-mercerized cotton samples (2 gm each) are treated with 30 ml
of N/4 Barium hydroxide for two hours in conical flasks at room temperature.
Preferential absorption of barium hydroxide by cotton samples reduces the
strength of Barium Hydroxide solutions.
The amount of Ba(OH)2 absorbed can be determined by taking 10 ml of
Ba(OH)2 solution from each of the flasks and titrating it with N/10 HCl,
phenolphthalein being used as an indicator. Fresh Ba(OH)2 is also titrated (blank
titration) to accurately assess the actual Ba(OH)2 in solution.
45. 1. Larger dyeing affinity
2. Larger dimensional stability of the articles
3. Increasing of the lustre
4. Increasing of the tensile strength
5. Better covering of dead and/or mossy cotton
6. Improving to the touch
THE ADVANTAGES OF THIS PROCESS ARE:
46. Environmental effect
We know about the toxicity profile of sodium hydroxide, which is considered
one of the building blocks of chemistry. It’s a very powerful alkali. It’s used in
industry in a broad range of categories: chemical manufacturing; pulp and paper
manufacturing; cleaning products such as drains, pipe lines and oven cleaners ;
petroleum and natural gas; cellulose film; and water treatment as well as textiles.
The US Food and Drug Administration (FDA) considers sodium hydroxide to
be generally safe, and recognizes it as not being found to pose unacceptable
dietary risks, though it is generally only used on food contact surfaces rather than
in foodstuffs.
47. Cont…
The Barium Activity Number is given as:
BAN = (B-M) / (B-C)*100
Where B = Volume of HCl (ml) required for blank titration
M = Volume of HCl (ml) required with mercerized cotton
C= Volume of HCl (ml) required with un-mercerized cotton
For completely mercerized cotton the value of BAN is around 155 and for semi
mercerized cotton it varies in between 115 and 130.
48. The chemical is toxic to wildlife, and the EPA requires that effluent containing
NaOH not be discharged into groundwater.
Because sodium hydroxide falls in the group of chemicals (salts) which are by far
the most often used in textile processing, the sheer volume of NaOH used by the
textile industry is important to recognize. Usual salt concentrations in cotton mill
wastewater can be 2,000 – 3,000 ppm, far in excess of Federal guidelines for in-
stream salt concentrations of 230 ppm.
So treatment of effluent is very important, as prevention is the only reasonable
alternative to solve the environmental problems associated with this hard-to-treat,
high volume waste.
