Unit 5- part 4- Fibres

Fibres may be defined as any hair-like raw material directly

obtainable from an animal, vegetable, or mineral source and
convertible into nonwoven fabrics such as felt or paper or,
after spinning into yarns, into woven cloth. A natural fibre may
be further defined as an agglomeration of cells in which the
diameter is negligible in comparison with the length. Although
nature abounds in fibrous materials, especially cellulosic types
such as cotton, wood, grains, and straw, only a small number
can be used for textile products or other industrial purposes.
Apart from economic considerations, the usefulness of a fibre
for commercial purposes is determined by such properties as
length, strength, pliability, elasticity, abrasion resistance,
absorbency, and various surface properties. Most textile fibres
are slender, flexible, and relatively strong. They are elastic in
that they stretch when put under tension and then partially or
completely return to their original length when the tension is
removed.
• Natural fibres can be classified according to their
origin.
• 1. The vegetable, or cellulose-base, class includes
such important fibres as cotton, flax, and jute.
• 2. The animal, or protein-base, fibres include wool,
mohair, and silk.
• 3. Regenerated and synthetic fibres include Nylon,
Terylene, Orlon, Viscose, Alginate fibres, etc.
• 4. An important fibre in the mineral class is asbestos.
The vegetable fibres can be divided into smaller groups, based on their
origin within the plant. Cotton, kapok, and coir are examples of fibres
originating as hairs borne on the seeds or inner walls of the fruit,
where each fibre consists of a single, long, narrow cell. Flax, hemp,
jute, and ramie are bast fibres, occurring in the inner bast tissue of
certain plant stems and made up of overlapping cells. Abaca,
henequen, and sisal are fibres occurring as part of the fibrovascular
system of the leaves.
Chemically, all vegetable fibres consist mainly of cellu-lose, although
they also contain varying amounts of such substances as
hemicellulose, lignin, pectins, and waxes that must be removed or
reduced by processing. The animal fibres consist exclusively of proteins
and, with the exception of silk, constitute the fur or hair that serves as
the protective epidermal covering of animals. Silk filaments are
extruded by the larvae of moths and are used to spin their cocoons.
With the exception of mineral fibres, all natural fibres have an
affinity for water in both liquid and vapour form. This strong
affinity produces swelling of the fibres connected with the
uptake of water, which facilitates dyeing in watery solutions.
Unlike most synthetic fibres, all natural fibres are non-
thermoplastic—that is, they do not soften when heat is
applied. At temperatures below the point at which they will
decompose, they show little sensitivity to dry heat, and there
is no shrinkage or high extensibility upon heating, nor do they
become brittle if cooled to below freezing. Natural fibres tend
to yellow upon exposure to sunlight and moisture, and
extended exposure results in loss of strength.
All natural fibres are particularly susceptible to microbial
decomposition, including mildew and rot. Cellulosic fibres are
decomposed by aerobic bacteria (those that live only in
oxygen) and fungi. Cellulose mildews and decomposes rapidly
at high humidity and high temperatures, especially in the
absence of light. Wool and silk are also subject to microbial
decomposition by bacteria and moulds. Animal fibres are also
subject to damage by moths and carpet beetles; termites and
silverfish attack cellulose fibres. Protection against both
microbial damage and insect attacks can be obtained by
chemical modification of the fibre substrate; modern
developments allow treatment of natural fibres to make them
essentially immune to such damage.
 COTTON
• Synonyms
• Raw cotton, purified cotton, absorbent cotton.
• Biological Source
• Epidermal trichomes of the seeds of cultivated
species of the Gossypium herbaceum and other
species of Gossypium (G. hirsutum, G.
barbadense) freed from impurities, fats and
sterilized, belonging to family Malvaceae.
• Cultivation, Collection, and Preparation
• Cotton is cultivated by means of seed sowing method. The seeds
are sown in rows of about 4–5 ft in distance. Proper fertilizers are
provided timely. The cotton plants are shrubs or small trees that
bare fruits (capsules) after flowering. The capsule consists of three
to five seeds and is covered with hairs. The bolls are collected when
ripe, separated from the capsule, dried, and subjected to the
ginning press for processing. In ginning process, hairs and seeds are
put before the roller with a small space, which separates the
trichomes from the seeds. The short and long hair separated by
delinter. Short hairs are known as ‘linters’, which are used in the
manufacturing inferior grade cotton wool, whereas long hairs are
used for preparation of cloth. The seeds remain after the removal
of hair is used for the preparation of cotton seed oil and oil cake for
domestic animal feed. The raw cotton so obtained is full of
impurities like the colouring matter and fatty material. It is then
subjected to further purification by treating it with dilute soda ash
solution under pressure for about 15 hours. It is then bleached and
washed properly, dried, and packed. The packed cotton is then
sterilized using radiations.
 Description

Chemical Constituents
It consists of 90% of cellulose, 7–8% of moisture, wax, fat and oil 0.5% and cell
content about 0.5%. Purified cotton has almost cellulose and 6–7% of moisture.
• Chemical Tests
• 1. On ignition, cotton burns with a flame, gives very little odour or fumes, does not produce a
bead, and leaves a small white ash; distinction from acetate rayon, alginate yarn, wool, silk, and
nylon.
• 2. Dried cotton is moistened with N/50 iodine and 80% w/w sulphuric acid is added. A blue
colour is produced; distinction from acetate rayon, alginate yarn, jute, hemp, wool, silk, and nylon.
• 3. With ammoniacal copper oxide solution, raw cotton dissolves with ballooning, leaving a few
fragments of cuticle. Absorbent cotton dissolves completely with uniform swelling, distinction from
acetate rayon, jute, wool, and nylon.
• 4. In cold sulphuric acid (80% w/w) cotton dissolves; distinction from oxidized cellulose, jute,
hemp, and wool.
• 5. In cold sulphuric acid (60% w/w) cotton, is insoluble; distinction from cellulose wadding and
rayons.
• 6. In warm (40°C) hydrochloric acid it is insoluble; distinction from acetate rayon (also silk,
nylon).
• 7. It is insoluble in 5% potassium hydroxide solution; distinction from oxidized cellulose, wool,
and silk.
• 8. Treat it with cold Shirla stain A for 1 min and wash out. It shows shades of blue, Tilac or
purple; distinction from viscose, acetate rayons, alginate yarn, wool, silk, and nylon.
• 9. Treat it with cold Shirla stain C for 5 min and wash out; raw cotton gives a mauve to reddish-
brown colour and absorbent cotton a pink one; distinction from flax, jute, hemp. The Shirla stains
may be usefully applied to a small piece of the whole fabric under investigation to indicate the
distribution of more than one type of yarn.
• 10. It does not give red stain with phloroglucinol and hydrochloric acid; distinction from jute, hemp,
and kapok.
• Uses
• Cotton is used as a filtering medium and in
surgical dressings. Absorbent cotton absorbs
blood, pus, mucus, and prevents infections in
wounds
 HEMP
• Biological Source
• Hemp is the pericyclic fibre obtained from Cannabis sativa Linn.,
belonging to family Cannabinaceae.
• Chemical Constituents
• Hemp mainly consist of cellulose and lignin.
• Uses
• Hemp is mentioned historically to have more than 25,000 diverse
uses. The historically mentioned uses are printing inks, paints,
varnishes, paper, bibles, bank notes, food, textiles (the original
Levi’s jeans were made from Hemp cloth), canvas and building
materials. Due to its high tensile strength, bast fibres are ideal for
such specialized paper products as: tea bags, industrial filters,
currency paper, or cigarette paper.
 JUTE
• Synonym
• Gunny.
• Biological Source
• It consists of phloem fibres from the stem of various species of the
Corchorus; C. capsularis Linn, C. olitorius Linn, and other species like
C. cunninghamii, C. junodi etc., belonging to family Tiliaceae.
• Description
• They are tall, usually annual herbs, reaching to a height of 2–4 m,
unbranched and if branched it has only a few side branches. The
leaves are alternate, simple, lanceolate, 5–15 cm long and a finely
serrated or lobed margin. The flowers are small (1.5–3 cm in
diameter) and yellow, with five petals; the fruit encloses many
seeds in the capsule.
• Preparation
• Retting is the process for the preparation of bast
fibres. This process is done by three methods, that is,
microbial (or water), steam, and mechanical process.
The microbial or water retting process is the oldest and
the popular method employed for the breaking of
lignin bond present between parenchyma and
sclerenchyma. The breaking of this bond facilitates the
easy procurement of skin from its core. Then the
material is washed dried to release pectin bond which
makes the hard skin to fine thread like fibres. The jute
fibres are graded according to its colour, strength and
fibre length. The fibres are of white to brown and 1–4
m. long.
• Microscopy
• A thin transverse section of the strand when treated with
phuloroglucinol and HCl, stains the strands deep red,
indicating the presence of lignin. Each strand is a collection
of polygonal cells which are surrounded by lumen with
various sizes. These strands can be separated by treating it
with mixture of potassium chloride and nitric acid.
• Chemical Constituents
• Jute fibres are composed primarily of the plant materials
cellulose and lignin. Jute is composed of about 50–53%
cellulose, nearly 20% of hemicellulose and 10–11% of lignin
along with other constituents like moisture not more than
12–13%, fats, wax, and ash contributing to 1% each.
• Uses
• It has a large range of use (about 1,000 uses). It is
listed as the second most important vegetable fibre
after cotton. Jute is used chiefly to make cloth for
wrapping bales of raw cotton, in the preparation of
sacks and coarse cloth. They are also woven into
curtains, chair coverings, carpets, Hessian cloth very
fine threads of jute can be made into imitation silk and
also in the making of paper. It is even used in the
manufacture of tows, padding splints, filtering, and
straining medium. Jute is used for the preparation of
coarse bags.