1.

INTRODUCTION
In textile wet processing the production sequence is pretreatment, dyeing, printing, and finishing. Sometimes
mercerization is done additionally for cotton goods either as pretreatment process for dyed materials or as finishing
process for white goods. Mercerization has great impact on luster, moisture regain, chemical and dye absorbency,
dimensional stability, strength of cotton goods. In this project work, mercerization was done as a finishing process
for white cotton woven fabrics and observed its impact on brightness, moisture absorbency and strength. There are
several factors are involved in mercerization which control the ultimate results of mercerization. During this
experiment, some major mercerization parameters like temperature, alkali concentration and tension were varied,
which play the vital role during mercerization. After mercerization, the brightness, strength and moisture absorbency
of the samples were measured and the results were evaluated in context to the variables. Finally the results obtained
in this project work were graphically represented and the impacts of the variables were observed.

1.1 objectives

 To know the influences of mercerization parameters on mercerization effects.

 To observe the different physical & chemical changes of cotton fabric after mercerization.
 To determine the effect of tension, temperature and alkali conc. on moisture regain, strength, and
brightness of cotton fabric.
 To analyze the different results, compare them graphically & find out some relations among them.

1
THEORETICAL PART

2
2. COTTON FIBRE
Cotton is the most important natural fibre and it accounts for about 50% of the total fibre production of the world.
Cotton fibre is obtained from the seed of the botanical family Gossypium. It is a cellulosic fibre, which is actually
the most pure natural form of cellulose.

2.1 Structure of cotton fibre

Microscopic examination of cotton fibres reveals that they are single cells with a closed up but open at the end
where they were cut from the seed. They have the appearance of flat, twisted ribbons. This characteristic shape
develops as the cotton fibres dry out and collapse in the open boll. The fibre cross-section has a bean shape and
often shows the presence of a central canal or lumen.

The morphology of a cotton fibre is extremely complex. Each fibre is composed of different layers, cuticle, primary
wall, secondary wall and a lumen.

The cuticle, or outer cell wall, is relatively hydrophobic. It contains some cellulose but accompanied by fats and
waxes. It will be broken and more or less removed during processing to render the fibres more water absorbent.

Beneath the cuticle is the primary cell wall composed of criss-crossed fibrils of cellulose and containing some
pectin.

The next layer inside this, the secondary wall, constitutes the bulk of the fibre. It is built up of successive layers of
fibrils. These are long structures, in each growth layer, that spiral around the fibre in a helical manner. From time to
time, the spirals reverse direction and are responsible for the characteristic convolutions of the cotton fibre that
develop on first drying. The fibrils, in turn, are composed of smaller micro fibrils, the smallest being a combination
of cellulose molecules.The lumen, the cavity that may remain after the protoplasm in the cell interior has
evaporated, has proteins, coloring matter and minerals deposited on its walls

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2.2 Chemical composition of cotton

Table: Chemical composition of cotton fibre

Component Main location Relative amount (%)

Cellulose Secondary wall 86.8
Oils, waxes Cuticle 0.7
Pectin Primary wall 1.0
Carbohydrates Primary wall 0.5
Proteins Lumen 1.2
Salts Lumen 1.0
Water 6.8
Other 2.0

2.3 Chemical Structure of Cotton

The chemical composition of cotton, when picked, is about 94% cellulose; in finished fabrics is it 99 percent
cellulose. Cotton contains carbon, hydrogen, and oxygen with reactive hydroxyl groups. Glucose is the basic unit of
the cellulose molecule. Cotton may have as many as 10,000 glucose monomers per molecule. The molecular chains
are arranged in long spiral linear chains within the fiber. The strength of a fiber is directly related to chain length.

Fig: chemical structure of cellulose.

Hydrogen bonding occurs between cellulose chains in a cotton fiber. There are three hydroxyl groups that protrude
from the ring formed by one oxygen and five carbon atoms. These groups are polar meaning the electrons
surrounding the atoms are not evenly distributed. The hydrogen atoms of the hydroxyl group are attracted to many
of the oxygen atoms of the cellulose. This attraction is called hydrogen bonding. The bonding of hydrogen's within
the ordered regions of the fibrils causes the molecules to draw closer to each other which increases the strength of
the fiber. Hydrogen bonding also aids in moisture absorption. Cotton ranks among the most absorbent fibers because
of Hydrogen bonding which contributes to cotton's comfort. These hydrogen bonds also hold several adjacent
cellulose chains in close alignment to form crystalline areas called micro fibrils. Between the crystalline regions
(about 70%) in cotton, disordered amorphous regions are found. Penetration of dyes and chemicals occur more
readily in these amorphous reasons.

The chemical reactivity of cellulose is related to the hydroxyl groups of the glucose unit. Moisture, dyes, and many
finishes cause these groups to readily react. Chemicals like chlorine bleaches attack the oxygen atom between or
within the two ring units breaking the molecular chain of the cellulose.

4
2.4 Important physical properties of cotton

2.4.1 Tensile strength

Cotton is a moderately strong fibre; tenacity is 26.5 - 44.1 cN /tex (3 – 5 g/den) and tensile strength 2800-
8400kg/cm2 (40,000-120,000 lb/in2). A unique property of cotton is that it shows greater strength in the wet state
than dry.

2.4.2 Elongation

Cotton does not stretch easily. It has an elongation at break of 5-10 per cent.

2.4.3 Elastic Properties

Cotton is a relatively inelastic, rigid fibre. At 2 per cent extension it has an elastic recovery of 74 percent, at 5 per
cent extension, the elastic recovery is 45 per cent.

2.4.4 Specific gravity 1.54.

2.4.5 Moisture regain 8.5%

2.4.6 Luster

Cotton fibres have a natural luster which is due, in part, to the natural polish on the surface. The smooth, hard
primary coat of cellulose contains waxes which no doubt contributes to the luster of the fibre. This surface-
smoothness, however, is not the only factor as well; a high luster is provided by fibres of nearly circular cross-
section and with fewer convolutions such as those produced when cotton is mercerized.

3. MERCERIZATION
The treatment of cellulosic textile in yarns or fabric form with a concentrated solution of caustic alkali whereby the
fibers are swollen, the strength & dye affinity of the materials are increased & their handle is modified. The process
takes its name from its discoverer, John Mercer (1844). The additional effect of enhancing the luster by stretching
the swollen materials while wet with caustic alkali & then washing off was discovered by Horace Lowe (1889). The
modern process of mercerization involves both swelling in caustic alkali & stretching to enhance the luster, to
increase color yield & cotton yarn strength.

Mercerization is the process of subjecting a vegetable fiber to the action of a fairly concentrated solution of a strong
base so as to produce great swelling with resultant changes in fine structure, dimensions, morphology and
mechanical properties. Usually cotton goods are treated with 15-25% w/v caustic soda solution (55-65 oTw) at a
temperature of 15-25oC during mercerization.

5
3.1 Changes occur in mercerization

Physical changes

 Lengthwise shrinkage and swelling axially

 Untwisting of fiber
 Fiber cross section becomes circular due to swelling
 Increase the tensile strength
 Decrease the extension at break
 Increase luster and smoothness of fiber

Chemical changes

 Breaks the hydrogen bonds and weak Vander Waals forces

 Formation of soda cellulose
 Increase adsorption of dyestuffs and chemicals
 Increase hygroscopicity

3.1.1 Swelling of cotton during mercerization

Mercerization is based on the swelling action of the concentrated aqueous solutions of sodium hydroxide on cotton.

In cellulose there are three dipolar hydroxyl groups in the molecular chain lying at regular intervals along the chains
on the surface of the molecule. In some places lateral hydrogen bonds are formed between the chains and in other
places, the hydroxyls are non-bonded. In mercerization, cotton yarn or fabric is treated with about 24% caustic soda
solution at about 18C for 30 sec- 2 min. this caustic soda solution contains dissolved sodium hydroxide as Na+ and
OH- ions. When cotton is entered into caustic soda solution, Na+ and OH- ions can easily diffuse into the
amorphous region of the fibre and get hydrogen bonded with the accessible hydroxyl groups of cellulose. Because of
the presence of these ions in the amorphous region, the chain molecules try to vibrate with longer amplitude, when
some of the hydrogen bonds and other weaker bonds between the adjacent chain molecules on the fringe of the
crystalline region are ruptured and the unbound molecular fragments vibrate with still longer amplitude and further
NaOH molecules diffuse and get bound to the liberated hydroxyl groups. In other word, cellulose chain molecules
acquire greater degree of movement. As a result, the fiber swells laterally and shrinks longitudinally.

This swelling action depends on the concentration of caustic soda. As the concentration of alkali increases, the
extent of swelling passes through a maximum and then decreases. Alkali is preferentially absorbed by the cellulose
from the solution when heat is liberated. So the extent of swelling decreases with an increase in the temperature of
the solution.

6
3.2 Types of Mercerization

3.2.1 Cold Mercerization

Cold mercerization process is normally carried out by treating yarn or fabric with 20-25% caustic soda solution for
30-180 sec at a temperature between 15 and 20°C after treatment, the materials is washed to remove excess caustic
soda. The material, which is then in a relaxed state, is further washed and finally washed with dilute acid to remove
the remaining alkali.

The mercerization conditions, i.e. concentration, temperature, dwell time in alkali, etc., are varied in accordance
with the particular effect required on the processed fabric. Althrough normal mercerizing leads to an improvement in
luster, tensile strength, dye absorption, coverage of dead cotton and dimensional stability.

3.2.2 Hot Mercerization

In the hot mercerizing penetration of caustic soda into the textile structure & fiber self is extremely rapid, thorough,
and uniform in effect. The fiber and textile structure become more pliable and less elastic then when saturated with
cold concentrated caustic solution. Shrinkage of the fabric is much less then that occurring in the cold process. If
necessary the fabric can be considerably overstretched to get improved luster, tensile strength, dimensional stability.

Hot mercerizing produces better luster, high tensile strength and improved dimensional stability then cold
mercerization for two main reasons. Firstly owing to thorough of the hot caustic soda into the fabric and fiber
structure a far greater proportion of the cellulose is modified.

Secondly in the presence of concentrated caustic soda solution at an elevated temperature, the fabric becomes highly
plastic and less elastic and so is capable of being readily stretched, leading to improvement of the properties of the
fabric being considered. Extent of the change of these properties depending of the degree of stretch. For example
greater than normal stretch will lower the affinity of dyes, because this is affected by the degree of internal
orientation of molecular structure.

3.3 Yarn mercerization

In yarn mercerization, yarn should be singed to remove those nap hairs which are not twisted into the yarn structure
& hence project from the surface. Mercerization carried out on dry or wet condition. With wet yarns, it is essential
that the greater part of the water be removed evenly before mercerization.

For warp mercerization, there may be 6000 to 10,000 ends parally wound into cylindrical balls. It is important that,
they must be wound at equal tension. Alkali concentration must be constant & high enough to ensure the required
degree of swelling.

Wetting of cotton in grey state is not easy & this may be overcome by wetting the warp in boiling water, cooling &
squeezing prior to mercerization or by wetting agent. After mercerization, yarn is squeezed & passed into warm
water which de-swells cotton. Finally treatment with sulphuric acid (1-3%)is given to remove the last traces of
alkali. Then it is washed & dried.

Sewing threads, embroidery threads may be mercerization in hank form which is cross wound at uniform tension &
spread on to two parallel rollers of the mercerizing machine. The machine give tension by arm, rotate roller in liquor
& raise –lower the yarn into & out of the bath. Yarn is allowed to shrink & tension being applied later

7
3.4 Fabric mercerization

Fabric must be singed, desized to reduce time of wetting, contamination of alkali & raise in temperature. It may be
mercerized before or after scouring. After mercerizing in the grey state, it is not necessary to remove the alkali
completely, since the cloth can go forward into kier where residual alkali is utilized. Howe ever, mercerizing in the
grey state presents some difficulties, namely, slower penetration & contamination of alkali. Before the wet cloth is
immersed into alkali, it must be evenly mangled. Bleached or half bleached cloths usually mercerized dry. It is done
by chain mercerization machine or by chainless mercerization machine.

3.5 Slack mercerization

Slack mercerization is a finishing treatment of cotton. Cotton is treated with cold caustic soda. ‘Slack mercerization’
‘mercerized loose’ and ‘mercerization without tension ‘mean free or complete shrinkage of cotton fibers or textile
structures in sodium hydroxide solutions of sufficiently high concentrations.

Tension normally applied during mercerization restricts shrinkage, swelling and conversion of crystalline areas into
amorphous ones. If no tension is applied, the maximum decrease in the degree of crystallinity and also a decrease in
the orientation of the crystallites would result. Hence the maximum effect of caustic soda would be obtained on
fibers where no restrictions on swelling or shrinkage would be present.

Slack mercerization treatments were carried out using 25% sodium hydroxide solutions containing 1-3% wetting
agent. The duration of immersion and temperature of wash water were varied.

4. MERCERIZATION CHEMICALS

4.1 Sodium hydroxide

Sodium hydroxide (NaOH), is a caustic metallic base. It is used in many industries, mostly as a strong chemical base
in the manufacture of pulp and paper, textiles, drinking water, soaps and detergents and as a drain cleaner.

Pure sodium hydroxide is a white solid available in pellets, flakes, granules, and as a 50% saturated solution. It is
hygroscopic and readily absorbs water from the air, so it should be stored in an airtight container. It is very soluble
in water with liberation of heat. Molten sodium hydroxide is also a strong base, but the high temperature required
limits applications. A sodium hydroxide solution will leave a yellow stain on fabric and paper.

Sodium hydroxide is predominantly ionic, containing sodium cations and hydroxide anions. The hydroxide anion
makes sodium hydroxide a strong base which reacts with acids to form water and the corresponding salts.

Caustic soda plays a vital role in various stages of textile wet processing like scouring, bleaching, mercerizing,
dyeing and printing. It is also used in production of regenerated cellulosic fibre (e.g., viscose rayon).

However mercerization is generally carried out with concentrated solution of NaOH. As it is a secondary standard
material, the purity must be checked before use. There are several ways to express the concentration of NaOH
solution like %w/w, %w/v, g/l, degrees Baume(oBe) and degrees Twaddle (oTw). In mercerization, NaOH acts as a
swelling agent which changes the structure and morphology of cotton fibre.

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4.2 Mercerizing Wetting agents

The use of a suitable wetting agent in the mercerizing solution overcomes many of the difficulties faced in
mercerizing, especially grey mercerizing.

The wetting agent-

 Should have high wetting power.

 Should not be preferentially absorbed by the fiber being treated.
 Should be suitable over a wide range of sodium hydroxide concentration.
 Should be suitable in strong caustic soda solution.
 Should not give rise excessive foaming or turbidity in the solution or deposits on the fiber and
machine parts.
 Should be easily removed completely from the fibers.
 Should not discolor the fibers permanently.
 Should be available at an economical price etc.
There are two types of mercerizing wetting agents,

 Cresylic
 Non -cresylic.
Mixture of o-,m- and p- cresols also called cresylic acid hence the name cresylic type are not soluble in water, but
dissolve in strong caustic soda solutions. These are found to be stable wetting agents in these solutions.

Non-cresylic wetting agent includes sulphated lower aliphatic alcohols such as hexyl alcohol and octyl alcohol
(specifically, 2-ethyl hexyl alcohol).

Commercial cresylic wetting agents are available in the form of dark brown liquid with a strong phenolic odour
while the commercial non-cresylic wetting agent is a clear yellow-brown liquid. These are used in the recommended
range of 10-20 gm/liter for grey cloth and 3-5 gm/liter for bleached cloth.

5. FACTORS AFFECTING MERCERIZATION

 Tension
 Temperature
 Caustic soda concentration
 Time of treatment
 Washing condition
 Use of wetting agent
 Rate of drying
 Construction of yarn

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6. EFFECT OF MERCERIZATION ON MOISTURE REGAIN

6.1 Moisture regain

Moisture regain is defined as the ratio of weight of water present in a material to the oven dry weight of the material.
The ratio is usually expressed as a percentage.
Let
Oven dry weight =D
Weight of water= W
Moisture regain= R
So, R= W/D x 100%
The regain of textile materials appears to depend upon the relative humidity rather than the actual amount of water
vapour present, so it is convenient to describe a given atmosphere in terms of relative humidity rather than absolute
humidity. Since the relative humidity affects the regain of a textile material, and since the properties of the material
are influenced by the regain, it is necessary to specify the atmospheric conditions in which testing should be carried
out.

6.2 Reasons for increasing moisture regain

The moisture regain depends on the change of the molecular orientation in the interior of the fiber. It is well known
that during the mercerizing process molecular structure tends to become decrystallized and the canals or spaces
within the cellulose structure become more uniform. It is the reason that mercerized fabric take on more water, have
higher regains and are more easily wet out then those are non mercerized cotton.

Table: Moisture regain values of cotton yarn mercerizes at different temperatures & concentrations.

Concentration of NaOH. Moisture regain%

%(W/V) o
10 C o
18 C 31oC
5 6.97 6.79 6.80
10.04 7.09 7.11 7.12
16 7.65 7.54 7.56
25.10 8.73 8.72 8.68
29.75 8.83 8.78 8.70
33.47 8.93 8.82 8.71

Due to caustic soda penetration, many hydrogen bonds are broken and it is estimated that that the number of
available hydroxyl groups (-OH) are increased by about 25%. Mercerization thus decreases the crystalline part or
increases the amorphous region of the fiber. Thus in the amorphous part of the fiber is directly related to moisture
sorption. Moisture is assumed to be absorbed by suitable groups in the amorphous region & on the surface of
crystallites. When mercerization is carried out under tension, the change in the crystalline portion is comparatively
lower than that without tension. Standard cotton have moisture content about 7%, mercerized cotton with tension
has about 9% and that without tension about 11%.

Higher concentration of alkali produce better swelling resulting greater amorphousness that’s why moisture regain
of mercerized cotton increases with increase of sodium hydroxide concentration.

The moisture also increases with decrease in the temperature of mercerization at a given sodium hydroxide
concentration as higher temperature causes lower swelling.

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6.3 Measurement of moisture regain

First the sample has to be weighted in its original condition, to dry it, and then weight it again the oven dry weight,
is defined as the constant weight, obtained by drying at temperature of 105+/-3oC, in B.S 1051:1964. The drying
condition specified a recommendation to use a ventilated drying oven with a positively induced air current when
successive weighting at 20 min differ by less than 0.05 %, it may be assumed that the constant weight has been
reached.

To prevent moisture absorption during the transfer from the oven to the balance the weighting should be done with
the samples remaining in the balance or the material is weighted in tared stopped containers.

6.4 Moisture testing oven

The manufacturer of testing instrument offers moisture testing ovens which conforms standard set out in B.S
1051:1964 and at the same time simplifies the work. The major specifications of moisture testing oven are given
below:

1) Forced hot air thermostatically controlled.

2) Automatic balancing.
3) Weighting is carried out inside the heated chamber.
4) Preheating unit for partially drying before transferring to the main oven.

7. EFFECT OF MERCERIZATION ON LUSTER (BRIGHTNESS)

7.1 Lustre & Brightness

Lustre is the visual property of something that shines with reflected light. If a beam of light falls on a surface, it may
be reflected specularly or diffusely or in a combination of both. The total visual appearance resulting from these
reflections determines the luster of the material.

Brightness is the intensity of light reflected or emitted by something. Brightness is an attribute of visual perception
in which a source appears to be radiating or reflecting light. The brightness of an object is the amount of light it
reflects, the more it reflects the brighter it will be.

7.2 Reasons for increasing luster during mercerization

When cotton is viewed using optical microscope, it is found that three forms, unmercerized, mercerized without
tension and mercerized with tension are vastly different. Unmercerized cotton has a general appearance of being a
flat ribbon with spiral twists; its surface is rough and non uniform. Its cross section is irregular and ear shaped while
the lumen, the central canal, is broad, irregular and resembles a collapsed tube. With such a twisted structure, the
light falling on cotton fibers gets reflected irregularly & as a result there is no luster in cotton fibers

11
 A B

Fig: Electron microscope image of cotton fibre (x2200) A. natural B.mercerized cotton

when cotton is mercerized without tension its general appearance is observed to be much rounder with little or no
twist, and its surface is much smoother then to compared with that of an unmercerized fiber fibers are more uniform
with high magnification, approximately 500X,they appear to be creased and wrinkled. A mercerized cotton fiber
cross section is oval and the lumen is contracted but not collapsed.

When mercerized with tension, the general appearance of cotton changes and similar to that of cylindrical glass rod.
Its surface is very smooth and is completely free from folds and creases and its cross section is circular with the
lumen being contracted or compressed to a slit. The smooth & more regular surface structure enables it to reflect
incident light more evenly. This results in increasing the luster of the fibre.

7.3 Factors that affect lustre

The lustre of mercerized cotton depends on various factors:

 Cross-section of fibre

 Staple length of the fibre

 Wall thickness of the fibre

 Concentration of alkali (sodium hydroxide)

 Temperature

 Percent stretch

 Yarn construction

 Yarn twist

 Doubling of yarn

 Degree of singeing

 Application of tension

 Rate of drying

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7.3.1 Cross-section

Lustre of the fabric is due to the regular reflection of light incident on the fibre surface, which depends on the cross-
section of the fibre.

7.3.2 Staple length of cotton fibre

It has been found that long staple length cotton produces better lustre than short staple length cotton after
mercerization under identical conditions. In the raw state, long staple length cotton has a cross-section more
approaching a circle than in the case of short staple length cotton.

7.3.3 Temperature of mercerizing solution

Lustre values produced after mercerization at different temperature are given below:

Temperature (oC) Lustre

7.5 76
17.0 71
25.0 57
35.0 40

It is seen that if mercerization is carried out at 7.5oC using refrigeration, it is costlier than when it is carried out at
17oC which results in very little change in lustre. Most economical mercerization may b carried out at 17 oC. In
countries like Bangladesh, the average room temperature is 30-35oC, the use of refrigeration is essential.

Lower temperature cause better swelling which further provide better smoothness & better surface structure. As a
result better luster is found.

7.3.4 Concentration of alkali

Lower the temperature, lower the alkali concentration needed to produce maximum lustre. Thus if mercerization is
carried out at 0oC a saving of sodium hydroxide may be achieved. However, the cost of refrigeration has to be met
with.

Lustre values obtained when the alkali concentration was varied at 15oC are given below:-

Alkali concentration(Tw) Lustre value

0 26

20 28

25 44

45 70

52 76

58 64

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It is seen that the lustre produced increases with increasing alkali concentrations, reached maximum at 52 oTw & then
decreases with further increase in alkali concentration.

Higher concentration will cause better swelling of fibre which further provide better smoothness & better surface
structure. As a result better luster is found.

7.3.5 Percent stretch

Percent stretch affects lustre. When a cotton hank is mercerized in an unrestricted state & then stretched to different
extents, the resulting lustre values are given below:-

Stretch% Lustre value

0 35

40 57

70 65

100 71

It is seen that maximum lustre is obtained when the hank is stretched 100%.

7.3.6 Yarn construction

Lustre produced by mercerization depends on the construction of the yarn. Single yarn cannot be successfully
mercerized, while doubled yarn can be. Keeping the fibre staple length & fibre wall thickness constant, lower the
twist per inch, higher the lustre because of the greater penetration of sodium hydroxide into the fibre. In the doubled
yarn, the twist must be in the same direction (either S-twist or Z-twist).

7.3.7 Singeing

Yarn to be mercerized is always gassed (singed) to produce maximum lustre. The yarn should be gassed when it is
to be used as sewing thread or for making organdie fabric. The presence of short fibre on the surface decreases lustre
& is removed during singeing.

7.3.8 Tension

Maximum lustre is obtained when the tension is sufficient to bring the material back to its original state & any
increase in tension above this does not increase lustre. The lustre obtained by impregnating & washing under tension
is the same as impregnating loose & washing under tension, but more force is required in the second case. Greater
lustre is produced by the maximum tension, but this high tension reduces the dye affinity & elasticity of the
mercerized sample. It is seen that maximum lustre is obtained when the hank is stretched 100%.

As a caustic solution of sufficient concentration to cause mercerization to take place enters the fiber, the fiber swells.
As the fiber swells, the fiber shrinks in length. Because of the fact that there is no tension, fiber surfaces, and while
much smoother, still show residual creases and wrinkles. The creases and wrinkles scatter light as it falls on the fiber
surface and, therefore, luster does not occur to the same degree as when tension is applied .

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7.3.9 Rate of drying

Lustre produced also depends on the rate of drying after mercerizing & washing. Thus when cotton yarn is
mercerized, washed, hydro-extracted & dried slowly; it acquires a higher lustre value than when it is dried rapidly.

7.4 Measurement of brightness

Brightness can be measured by Spectrophotometer.

7.4.1 Spectrophotometer

A spectrophotometer is an instrument which is used to measure the intensity of electromagnetic radiation at different
wavelengths. Important features of spectrophotometers are spectral band width and the range of absorption or
reflectance measurement. Spectrophotometers are generally used for the measurement of transmittance or
reflectance of solutions, transparent or opaque solids such as polished gases or glass. They can also be designed to
measure the diffusivity on any of the listed light ranges in electromagnetic radiation spectrum that usually covers
around 200 nm-2500 nm using different controls and calibrations

7.4.1.1 Working principle of spectrophotometer

Light source, diffraction grating, filter, photo detector, signal processor and display are the various parts of the
spectrophotometer. The light source provides all the wavelengths of visible light while also providing wavelengths
in ultraviolet and infra red range. The filters and diffraction grating separate the light into its component
wavelengths so that very small range of wavelength can be directed through the sample. The sample compartment
permits the entry of no stray light while at the same time without blocking any light from the source. The photo
detector converts the amount of light which it had received into a current which is then sent to the signal processor
which is the soul of the machine. The signal processor converts the simple current it receives into absorbance,
transmittance and concentration values which are then sent to the display.

8. EFFECT OF MERCERIZATION ON TENSILE STRENGTH

8.1 Tensile Strength

The maximum tensile force recorded in extending a test piece to breaking point. This is the load at which the
specimen break, usually expressed in grams weight or pounds weight.

8.2 Reasons for increasing tensile strength during mercerization

During mercerization of cotton fibers, swelling occurs to a much greater extent & it’s molecular structure become
decrystallized & the canals or spaces within the cellulosic structure become more uniform. Cotton fiber allign
themselves in a regular way leading to an increase in the hydrogen bond formation. The major reason can be an
alleviation of internal stresses and the deconvoluting of the fibers in the fabric during swelling process. Tensile
strength increases with the increase in swelling. Mercerization increases cohesion between individual cotton hairs &
this closer embedding of the hair in the yarn not only increase the strength but makes it more uniform in strength.
Because of the longitudinal shrinkage & lateral swelling of yarn, fabric shrunk & the yarn appeared closer together
with an increased thickness, polymer chain minimizes the weak link in the fiber which helps to increase strength.

15
8.3 Factors affecting tensile strength

When cotton fiber, yarn, cloth is mercerized its strength increases by 10-50%. The tensile strength increases depends
on –

 Alkali concentration

 Temperature of impregnation

 Tension in the fabric

 Time of impregnation

 Construction of yarn

8.3.1 Alkali concentration

It is seen that as the alkali concentration increases, the tensile strength also increases, reaches a maximum value at
52 0Tw & then decreases with further increase in alkali concentration

Dependence of tensile strength (breaking load) on the alkali concentration:

Alkali concentration , 0Tw Tensile strength, gm

25 247

35 287

45 288

52 302

60 282

Swelling depends on hydration of alkali ion. Greater degree of hydration will give greater increase in swelling.
Degree of hydration increase with concentration of alkali but decrease with temperature. Thus degree of hydration
influences swelling which further influence tensile strength.

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8.3.2 Temperature of impregnation

Again, lower the temperature of mercerization, greater is the tensile strength (breaking load of the yarn) as seen
from the table:

Dependence of tensile strength (breaking load) on the temperature:

Temperature,oC Tensile strength , gm

7 302

17 276

30 253

Primary & secondary hydroxyl group in cellulose are the basis for the high hydrogen bonding & orientation found in
cotton fibers. During mercerization, hydroxyl groups independently dissociate to the extent of alkali sorption. The
result is that there is an osmotic pressure increase which causes water to enter the fiber until such time as the
osmotic pressure is in balance with the restraining or elastic force of the swollen fiber. If the osmotic pressure has
increased to the maximum which can be contained by the primary wall of the fiber, the resultant pressure can realign
the fibrillar structure & cause the orientation of fiber to be changed permanently. Experiments have shown that
mercerization causes the osmotic pressure to increase when mercerization is carried out at any temperature. If
temperature of mercerizing media decreases, osmotic pressure increases.

So , it is clear that lower temperature will cause higher osmotic pressure & higher osmotic pressure will give higher
swelling. Higher swelling will convert crystallign region into amorphous region where molecular alignment will be
more uniform which produce better strength.

8.3.3 Tension in the fabric

Mercerization, both slack & with tension , increase strength uniformity along the fiber length , but mercerized fiber
with tension shows greater gain in strength than that of without tension.

Internal pressures caused by the swelling, are much less during tensionless processing than when cotton is processed
using high tension. Changes in the interior portions of the fiber are the direct result of internal osmotic pressure
causing changes in the molecular configuration of the cotton fiber. When warp and filling tensions are applied,
shrinkage tends to be reduced, internal pressures are increased causing the changes to be more profound both on the
morphological structure.

8.3.4 Time of impregnation

Provided minimum time for maximum swelling to take place is given, the increase in time of contact of material
with alkali does not seem to effect the tensile strength. Usually, cloth is treated for 30 sec & yarn for 50 sec.

8.3.5 Construction of yarn

For long staple fiber yarn, greater the twist, greater is the tensile strength of the mercerized material. Grey yarn with
soft doubling twist gives stronger yarn.

17
8.4 Methods of determining tensile strength

Basically, two methods are used to observe the effect of tensile forces on textile specimen-

 Constant rate of loading (C.R.L.)

 Constant rate of extension (C.R.E.)

8.4.1 Constant rate of extension (C.R.E.)

In this principle the top jaw is not fixed but needs a certain amount of movement in order to operate the load
indicating mechanism. The movement relative to the bottom jaw prevents extension of specimen at an absolutely
constant rate. Nevertheless bottom jaw traverse downward at a constant rate.

8.4.2 Tests

 Grab test

 Strip test

8.4.2.1 Grab test.

A tensile test in which only the central portion of the width specimen is held in jaws.

8.4.2.2 Strip test.

Laboratory method where the strip of the fabric cut along the yarn to a specific width. Here strip size is equal to the
width of the clamp.

18
EXPERIMENTAL PART

19
9. MACHINES & INSTRUMENTS

9.1 Band
A wooden circular band of diameter 9 inch

Fig: Circular Band Fig: Fabric attached with band

9.2 Tensile tester

Name: Universal strength tester (Titan)
Origin: England
Company: James H. heal & Company Ltd
Standard: EN ISO 13934-1(100mm 100mmmin)
Software: Version 6.1.4

Fig: Universal strength tester (Titan)

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9.3 Spectrophotometer
Name: Dual Beam Spectrophotometer
Instrument: Data color 650
Software: USA
Manufacture: China

Fig: Dual Beam Spectrophotometer

9.4 Oven
Name : Binder
Nenntemperature : 300oC
Manufacturer : Germany

Fig: Binder

21
10. RAW MATERIALS
10.1 Fabric specification
Fibre type : Cotton
Fabric weaves : Plain
Fabric construction : 60×60/110×70
GSM : 75

10.2 Chemical specifications

Sodium hydroxide:
Purity : 98 %( Lab standard)
Physical form : solid flakes

Mercerizing oil:
Name : NANOWET MRO
Chemical composition : Sulphated alcohol
Stability : Stable to conc. alkali (up to 32°Be´)
Ionic nature : anionic
Manufacture : Jrk colour & chemicals ind. (bd) ltd.

11. MERCERIZATION

11.1 Sample preparation

We have cut our required number of samples (12inch x 12inch) from fabric by scissor & scale.

11.2 Mercerization liquor preparation

We have prepared required concentration of liquor according to the recipe:

NaOH : 13% /18% /25%

Mercerizing oil : 4 g/l

Water : 650ml

Time : 1 min

Temp : 10oC/ 17oC/ 27oC

22
11.3 Mercerization parameters

We performed the experiment using the following parameters are given below:

No Concentration Temperature Tension

1 13% 10oC With tension

17oC With tension
o
27 C With tension
Without tension
o
2 18% 10 C With tension
o
17 C With tension
o
27 C With tension
Without tension
o
3 25% 10 C With tension
o
17 C With tension
27oC With tension
Without tension

11.4 Tension adjustment

Tension was applied to the fabric by attaching the fabric with a wooden circular band. Here tension was applied
manually.

11.5 Temperature adjustment

We have maintained 10oC by using ice & performed mercerization immediately. Then we waited until the liquor
temperature becomes 17oC & performed mercerization & again we waited until it becomes 27oC & done the same.

11.6 Mercerization procedure

Mercerization was performed within required temperature, time, and concentration with constant tension. Then
fabrics were rinsed with cold water to remove traces of alkali completely. Any remaining alkali was neutralized with
dilute acetic acid solution, followed by washing with cold water. Then fabrics were dried in oven at 95 oC for 16 min.

23
12. TESTING PROCEDURE
The following tests were done:

 Determination of moisture regain %

 Determination of Brightness values
 Measurement of Tensile strength

12.1 .Determination of moisture regain%

12.1.1 Atmospheric condition

Dry bulb temperature : 30oC

Wet bulb temperature : 29oC

Difference : 01

Relative humidity % : 93

12.1.2 Procedure

At first, we cut sample from both mercerized & unmercerized fabrics of same size. Then we weighted them
by electric balance. Then we took oven dry weight of these samples. Then we calculated M.R. %. By using the
following formula:

R= W/D x 100%

Here,
Oven dry weight = D
Weight of water = W
Moisture regain = R

12.2 Determination of brightness values

Samples are prepared in 4 fold & set it in the measuring port of spectrophotometer. Then we evaluated brightness
value of samples by using “Data Color Tools” software.

24
12.3 Measurement of tensile strength

12.3.1 Atmospheric condition

Dry bulb temperature: 26oC

Wet bulb temperature: 24oC

Difference: 02

Relative humidity %: 84

12.3.2 Sample size. (18cm x 5cm)

Rectangular, both in warp & weft direction.

12.3.3 Procedure

At first, we cut the fabric according to the size. Then we ensure proper gripping of samples in machine manually.
We gave command via computer to the machine. We have measured both warp & weft strength in same manner by
strip method.

25
RESULT & DISCUSSION

26
13. DATA ANALYSIS

13.1 Effects of alkali concentration on moisture regain

Concentration of NaOH (%) Moisture regain (%)

0* 6.66

13 7.02

18 7.46

25 8.47
*unmercerized

13.1.1 Dependence of moisture regain (%) on Conc. of NaOH

9
8 8.47
moisture regain (%)

7 7.46
7.02
6 6.66
5
4
3
2
1
0
0 13 18 25
conc. of NaOH(%)

Comment

From the above graph, we found that moisture regain increases with the increase of concentration of NaOH. The
increase in moisture regain is concerned with the decrystallization in the molecular structure of the fibre. As the
concentration of alkali increases, the amorphousness of the fibre also increases and the canals or spaces within the
cellulose structure become more uniform which causes more moisture absorption.

27
 13.2 Effects of temperature on tensile strength

The tensile strength of the unmercerized sample was: warp 420.36 N & weft 211.41 N

13.2.1 For 13% alkali concentration

Temperature Tensile strength (N)

Warp Weft
o
10 c 456.98 232.36

17oc 451.03 226.32

27oc 448.28 219.55

13.2.1.1 Dependence of tensile strength on temperature

458 235
456.98 232.36
456
230
454
tensile strength(N)
tensile strength(N)

452 225 226.32

450 451.03
448 220
448.28 219.55
446
215
444
442 210
10 17 27 10 17 27
tem perature ( oc) tem perature ( oc)

A) Warp B) Weft

28
 13.2.2 For 18% alkali concentration

Temperature Tensile strength (N)

Warp Weft
10oC 478.31 237.57

17oC 473.09 231.02

27oC 461.55 227.63

13.2.2.1 Dependence of tensile strength on temperature

485 240

480 238
478.31 237.57
475 236
tensile strength(N)

tensile strength(N)

470 473.09 234

465 232

460 230
461.55 231.02
455 228

450 226 227.63

445 224

440 222
10 17 27 10 17 27
temperature (oc) temperature (oc)

A) Warp B) Weft

29
 13.2.3 For 25% alkali concentration

Temperature Tensile strength (N)

Warp Weft

10oc 520.32 255.14

17oc 495.12 246.4

27oc 467.31 240.25

13.2.3.1 Dependence of tensile strength on temperature

530 260

520 520.32
255 255.14
510
tensile strength(N)

tensile strength(N)

500 250

490 495.12
245
480 246.4

470 240

460 240.25
467.31
235
450

440 230
10 17 27 10 17 27
o
tem perature ( c) o
tem perature ( c)

A) Warp B) Weft

Comment

From the above graphs, we can say that the tensile strength decreases at both warp and weft direction with the
increase of temperature within same alkali concentration (13%/18%/25%). Due to increasing temperature, less
swelling occurs inside the fibre within same caustic soda concentration. As a result less hydrogen bonds is formed
which causes lower tensile strength.

30
 13.3 Effects of conc. on tensile strength

13.3.1 Dependence of Tensile strength (warp) on concentration of NaOH (%)

530

520.32
tensile strength(N)

510
495.12
490 478.31 10
473.09 467.31 17
470 456.98 27
451.03 461.55
450
448.28
430
13 18 25
conc. of NaOH(%)
13.3.2 Dependence of Tensile strength (weft) on concentration of NaOH (%)

260
255.14
250
tensile strength(N)

246.4
237.57
240 240.25
10
232.36 231.02
230 17
226.32 227.63
220 219.55 27

210

200
13 18 25
conc. of NaOH(%)

Comment

From the above graphs, we can say that the tensile strength increases at both warp and weft direction with the
increase of concentration of NaOH within same temperature (10 C/17 C/27 C). As the concentration of alkali
increases, more swelling takes place which results molecular alignment in more regular way leading to an increase
in hydrogen bond formation. So tensile strength increases with the alkali concentration.

31
13.4 Effects of tension on tensile strength

13.4.1 for warp

Conc. of NaOH (%) Tensile strength(N)

With tension Without tension

13 448.28 441.6

18 461.55 460.27

25 467.31 465.4

13.4.1.1 Dependence of tensile strength (warp) on tension.

500
490
tensile strength(N)

480
470 461.55 467.31
465.4 with tension
460 460.27
without tension
450 448.28
440 441.6
430
420
13 18 25
conc. of NaOH(% )

32
13.4.2 For weft

Conc. of NaOH (%) Tensile strength(N)

With tension Without tension

13 219.55 215

18 227.63 221.27

25 240.25 226.33

13.4.2.1 Dependence of tensile strength (weft) on tension

260

250
tensile strength(N)

240 240.25

227.63 with tension

230
226.33 without tension
220 219.55 221.27
215
210

200
13 18 25
conc. of NaOH(%)

Comment

From the above graphs, we found that mercerization with tension shows slightly better tensile strength, for both
warp & weft, than mercerization without tension. Tension increases molecular orientation in the amorphous region
which provides additional strength.

33
13.5 Effects of temperature and conc. on brightness values

The brightness value of unmercerized sample was 63.65

Brightness values at different conc. of NaOH (%)

Temperature
13% 18% 25%

10oC 70.22 71.24 72.46

17oC 68.85 70.21 71.31

27oC 67.09 68.72 70.67

27oC* 65.64 67.8 69.28

*Mercerization
13.5.1 Effects of temperature on brightness values without tension
.
13.5.1.1 Dependence of brightness on temperature (for 13% concentration)

70.5
70.22
70

69.5

69
brightness

68.5 68.85
68

67.5

67
67.09
66.5

66

65.5
10 17 27

temperature (oc)

34
13.5.1.2 Dependence of brightness on temperature (for 18% concentration)

71.5
71.24
71

70.5

70
70.21
brightness

69.5

69

68.5
68.72
68

67.5

67
10 17 27
o
temperature ( c)

13.5.1.3 Dependence of Brightness on temperature (for 25% concentration)

73

72.5 72.46

72
ss
e
71.5
n
t
h
g
ir 71 71.31
b
70.5 70.67

70

69.5
10 17 27
temperature (oc)

Comment

From the above graphs, we found that the brightness value decreases with the increase of temperature within same alkali
concentration (13%/18%/25%). This fact can be clarified with the extent of swelling which decreases with the increase of
temperature. So the cross section of the fibre becomes less circular and the surface structure becomes less smooth and regular
when temperature of the alkali solution is increased. As a result brightness is decreased.

35
 13.5.2 Effects of concentration on brightness values

13.5.2.1 Dependence of Brightness on conc. of NaOH (%)

75
74
73 72.46
72 71.24
Brightness

71 71.31 10
70 70.22 70.21 17
70.67
69 68.85 68.72 27
68
67 67.09
66
65
13 18 25
conc. of NaOH(% )

Comment

From the above graph, we can say that the brightness value increases with the increase of concentration of alkali
within same temperature (10 C/17 C/27 C). When the concentration of alkali increases, more swelling takes place
in the fibre. As a result the cross section becomes more circular and the surface structure becomes more smooth and
regular enabling it to reflect incident light more evenly. So brightness is increased

36
13.6 Effects of tension on brightness value

Conc. of NaOH (%) Brightness value

With tension Without tension

13 67.09 65.64

18 68.72 67.8

25 70.67 69.28

13.6.1 Dependence of brightness on concentration of NaOH (%)

75
74
73
72
Brightness

71 70.67
with tension
70
68.72 69.28 without tension
69
68 67.8
67 67.09
66 65.64
65
13 18 25
conc. of NaOH(%)

Comment

From the graph, we found that mercerization with tension shows greater brightness values than mercerization
without tension. Because of the fact that there is no tension, fiber surfaces, and while much smoother, still show
residual creases and wrinkles. The creases and wrinkles scatter light as it falls on the fiber surface and, therefore,
luster does not occur to the same degree as when tension is applied.

37
14. LIMITATIONS
There are few limitations in this project. Such as:

 There was no tensioning device to control the fabric tension precisely over the whole process.
 We could not do enough tests due to lack of same construction fabric.
 Uniformity of the strength of the supplied fabric was not good. We found strength variation in different
parts of the fabric.
 We could not maintain standard atmospheric condition.
 We were not able to maintain the mercerizing temperature perfectly.
 Fabric properties & construction were not well known.
 We were not able to control the liquor pickup of fabric.
 We were not able to determine the oven dry weight accurately.

15. SUGGESTIONS
This project could have been better if we had a tensioning device & moisture testing oven. More number of tests
would give us more accurate results. Fabric of known properties like construction, strength, count and TPI for both
warp and weft may help for better evaluation of the results. Standard atmospheric condition & liquor pick up control
must be ensured for accurate result. Similar project work can be done for further investigation on the effects of
mercerization parameters on dye absorbency and the brightness after dyeing.

16. CONCLUSION
In this project, we have learned about mercerization & its effect. We found effect of mercerization parameters
variation over its performance. We have also learned about important cotton properties & there change after
mercerization. We have learned about a project presentation, writing sequence, team work. This will enrich our
analytical ability. All these will be very helpful for our knowledge; will increase our experience, skill & above all
our future industrial job life.

38