Cotton fiber manufacturing, physical and chemical properties
M.Sc (C.T) 3rd sem.
As it is obtained from a plant it is classified as a
natural, cellulose, seed, mono-cellular, staple fiber.
The macro structure of cotton-
Under a microscope, a cotton fiber appears as a
very fine, regular fiber.
. It ranges in length ½” to 2 ¾ “, depending upon
the quality of the fiber.
It is the finest in common use, ranges 11µm to
The fiber length to breadth ratio of cotton ranges from about
6000:1 for the longest and best types, to about 350:1 for the
shortest coarsest cotton type. the greater the ratio, the more
readily can the cotton fibers be spun into yarn.
The color of cotton fibers depends on its type, environment,
soil and climatic conditions under which it is grown.
The microscopic appearance of cotton-
Under the microscope, the cotton fiber looks like a twisted
ribbon or a collapsed and twisted tube. These twists or
convolutions identify the cotton fiber under the
The seed end of the fiber is quite irregular, having been
torn, during ginning, from the epidermis or skin of the
The main part of the fiber, about 3/4th to
5/6th of its length, is regular, with a thick fiber wall,
a canal along the center of the fiber called the
lumen, and about 16 convolutions/cm.
fiber tip is less than 1/4th of the fiber length.
At this end, the fiber tapers to a cylindrical, pointed
tip, and has no convolutions.
The convolutions are formed after the cotton boll
bursts open, the limp, sap-filled cotton seed hairs
begin to dry out, their cell walls collapse inward,
decreasing the size of the lumen. When the cotton
seed hairs cease shrinking, twisting and collapsing
inward, they become the valuable, convoluted
The micro-structure of cotton fiber-
Its cross-section is oval, compared with the normal
hexagonal plant cell. However, like all plant cells, cotton has
a distinct cuticle, well developed primary and secondary
walls, and a lumen.
The cuticle is the’ very-outside’ or ‘skin’ of the cotton
fiber. It is composed of a waxy layer (pectin) only a few
molecules thick. The waxy nature of the cuticle enables
it to adhere tenaciously to the primary wall of the fiber.
The primary cell wall, which is immediately
underneath the cuticle, is about 200nm thick. It is
composed of very fine threads of cellulose, called
These fibrils are about 20nm thick, but length is not
known. The fibrils spiral at about 70° to the fiber axis.
This spiraling imparts strength to the primary cell wall
and hence, to the
Secondary cell wall, which forms the bulk of the fiber. Concentric
layers of spiraling, cellulosic fibrils, not unlike the growth rings of
trees, make up the secondary wall.
The hollow canal, running the length of the fiber, Is called the
The lumen was once the central vacuole of the growing cotton fiber.
It was full of cell sap, which was composed of a dilute, aqueous
solution of proteins, sugars, minerals and cell-waste products.
When the sap evaporated, its constituents remained behind to
contribute to the color of the cotton fiber
This caused the fiber to collapse inward resulting in the
characteristics kidney-shaped cross-section of the cotton fiber.
The polymer system-
The cotton polymer-
The cotton polymer is a linear, cellulose polymer. The
repeating unit in the cotton polymer is cellobiose which
consists of two glucose units.
The cotton polymer consists of about 5000 cellubiose units,
i.e. degree of polymerization.
The most important chemical
groupings on the cotton polymer
are hydroxyl groups(OH) and
The polymer system of cotton-
Cotton is a crystalline fiber. Its polymer system is about
65-70% crystalline and, correspondingly, about 35-30%
cotton polymers are, in the main, well oriented and
probably no further apart then 0.5nm , in the
crystalline regions. This is maximum distance across
which hydrogen bonds can form between polymers.
Hydrogen bonds are the most dominant and most
important forces of attraction present in the polymer
system of cotton. For this reason, Van der Waal’s forces
which are also present have little relevance.
The strength of cotton fibers is attributed to the
good alignment of its long polymers.
And its polymer system is about 70% crystalline, the
countless, regular, hydrogen bond formations between
adjacent polymers, and the spiraling fibrils in the primary and
secondary cell wall.
It is one of the few fibers which gains strength when wet.
this occurs because of a temporary improvement in polymer
alignment in the amorphous regions of the polymer system,
which leads toapproximate 5% increase in fiber tenacity.
Elastic –plastic nature-
The cotton fiber is relatively inelastic because of its
crystalline polymer system, and for this reason cotton
textiles wrinkle and crease readily.
Bending and crushing of cotton textile materials places
considerable strain on fibers polymer system.
These become weak points in the polymer system, and
hence weak areas in the cotton fiber structure.
Causes cotton textile materials to crease and wrinkle
The cotton fiber is very absorbent,
Owing to the countless polar –OH groups in its polymers,
these attract water molecules, which are also polar.
Aqueous swelling of the cotton fiber is due to a separation
or forcing apart of polymers by the water molecules in the
amorphous regions only.
The hygroscopic nature ordinary prevents cotton textile
materials from developing static electricity.
Cotton fibers have the ability to conduct heat
energy, minimizing any destructive heat
accumulation. Thus they can withstand hot
Excessive application of heat energy causes the
cotton fiber to scorch, char and burn. This is an
indication that cotton is not thermoplastic.
Effect of acids
Cotton fibers are weakened and destroyed by acids.
Acidic conditions hydrolyze the cotton polymer at the glycoside
oxygen atom, which links the two glucose units to form the
Mineral or inorganic acids, being stronger that organic acids,
will hydrolyze the cotton polymer more rapidly.
Effect of alkali-
Cotton fibers are resistant to alkalis and are relatively
unaffected by normal laundering. The resistance is attributed
to the lack of attraction between the cotton polymers and
Mercerization without tension, or slack mercerization,
causes the cotton fibers to swell; that is, increase in
thickness, and contract in length.
The swelling is thought to be due to alkali molecules, or
radicals, entering the amorphous regions of the fibers
Mercerization under tension, which can only be
carried out on cotton yarn or fabric, little swelling or
fiber contraction occurs. The fiber emerges with
increased tenacity and with a distinct, though subdued
Mercerizing also causes the fiber surface to become
smooth and more regular, enabling it to reflect incident
light more evenly.
Effect of bleaches-
The most common bleaches used on cotton textile
materials are sodium hypochlorite and sodium per
Sodium hypochlorite bleaches cotton textile materials
at prevailing room temperature. However, bleaching
with sodium per borate is more effective when the
laundry solution exceeds 50°C in temperature.
These two bleaches are examples of oxidizing bleaches,
which is mostly used for cotton textile materials.
Oxidizing bleaches are so called because they liberate
oxygen which does the actual bleaching
Manufacturing of cotton
Introduction- cotton is grown in different parts of
world, where the climate is mild. The most favorable
conditions for cotton belt are North America, Egypt.
The largest cotton growing areas are India, China,
United States, Egypt etc.
Manufacture of cotton-
1. Growing and harvesting- cotton grows on bushes 3-4
feet height, the blossoms or flowers appears, falls off
and the ball begins its growth, inside the ball are the
seeds from which the cotton fibers grow.
• This is also called seed hair. When ball is ripe, it splits
open and the fluffy white cotton stands out from the
The cotton is picked up with the help of machine or
by hand. Cotton gets discolored and dirty if it is kept
on plant for longer duration.
2.Ginning- in this process seeds are removed and fibers are
pressed into bales. This process is carried out by a
machine. Seeds are used for the production of oil, soaps
and cosmetics. The fiber at this stage is called LINT.
3. Bailing- cotton is compressed or pressed into bales. These
are wrapped with jute cocking and cotton is then supplied
to mills in bales.
4.Opening and picking-
opening refers to opening of the bale and loosening and
fluffing of the fiber which have been tightly packed into
Layers of fibers from several bales are fed into an opener.
The fibers emerge from the opener like a fluffy mass, i.e.
10-15 times as bulky as compared to the bale.
The picking machine continues the loosening and
cleaning of the fibers and a thick white sheet is formed
which is called LAP.
In this process the lap passes between two
cylinders covered with clothing, which is a heavy
fabric with many specialty bent wires. Individual
fibers are straightened and made somewhat
In this machine cotton is thoroughly cleaned off all
embedded dirt and foreign matter. There is no
sorting of long and short fibers. The fibers
emerges from the carding rolls as a thin sheet
it removes the short fibers and keeps rest of the
fibers nearly parallel. As much as ¼ of the fiber
may be combed out as waste which are used for
The fibers that remain here are long staple, good
quality fibers. These are used for manufacturing
cotton. Combed fibers are fine, uniform, strong
The thin sheet of fibers laid parallel to each
other after combing. These are given a slight pull
and then twisted into one inch thick, long sliver.
The slivers are collected in a dram
The slivers are fed into the drawing rolls at the same
time. This is a continuation of the blending which started
in the opening process.
The drawing frame consists of four sets of cells, each of
which travels at a faster speed then the previous set. The
difference in the speed causes elongation of the sliver
and reduction in the diameter.
9. Roving- this is similar to drawing but the diameter of
the sliver reduces further and slight twist is given. Then it is
wound on the bobbin.
10.Spinning & weaving- in factories cotton is spun into
yarns on large spinning machines. Afterwards it is fed to
the spools which are sent for weaving to the weaving mills.
11.Dyeing & finishing- the woven fabric is
dyed with different colors and then finishing is
given to the fabric t improve its appearance
and to remove certain drawbacks or
The bobbins are place in the spinning frame, where
these are passed through several sets of rollers
running at successively more speed and finally
drawn out to yarn of the desired size.