Introduction:
cotton is a natural seed hair fiber and it is natural cellulose fiber. This is called the king of fibers. The botanical name of cotton is Gossypium. In India, the first cotton evidence was found in 6,000 B.C in Indus Delta. India is found to be the 2nd largest cotton exporting country in the world. It is estimated that about 354.50 (each of 170 Kg) lakh bales of cotton are produced during 2019-2020.
Cotton is produced from the cotton plant, which is planted in spring. Generally, the cotton plant produces cotton fiber within 5.5 to 6.5 months after harvesting. It is assumed that about 20,000 liters of water required to produce 1kg of cotton.
Classification of cotton fiber:
Classification based on Species:
Gossypium hirsutum: It is endemic to Central America, Mexico, west indies, Caribbean and southern Florida. It is also known as upland cotton which comprises about 90% production in the word. It grows about 2 meters tall which consists of short fibers when compared to other species. It is used in nonwoven products in the feminine hygiene and baby care categories.
Gossypium barbadense: It is endemic to tropical South America, Egypt. It is an extra-long-staple fiber commonly known as Pima cotton which Comprises about 8% production in the world. It grows about 3 meters tall. Used for apparel and bedding applications.
Gossypium arboreum: It is endemic to India and Pakistan. It is also known as tree cotton which comprises less than 2% production in the world. It grows about 5 meters tall It is used for clothing, making twine and ropes, stuffing material for pillows.
Gossypium herbaceum: It is endemic to southern Africa. It is also known as Levant cotton which comprises less than 2% production in the world. It grows about 1.5 meters tall. It is used for clothing and medical purposes.
Classification based on staple length:
Very short-staple cotton: ≤21 mm
Short staple cotton: >22mm and ˂25 mm
Medium Staple cotton: >26 mm and ˂ 28 mm
Ordinary long staple cotton: >29mm and ˂ 34 mm
Extra-long staple cotton: ≥34 mm
Commercial classification:
Sea Island Cotton:
Originally from Barbados.
Grown in the USA, Carolina, Georgia, Florida.
Fine, long, soft, and silky fiber.
Light cream, tint color.
Staple length- 5cm and more.
Egyptian cotton:
Origin- Egypt and middle east countries.
Fine, long, soft, and silky fiber.
Staple length- 3.7-4.5 cm.
Brazilian Cotton:
Origin- Peru
It is also called Peruvian cotton.
color- Dull white to cream.
harsh, wiry to touch but elastic.
Staple length- 3cm to 4cm.
American cotton:
Origin- America
Staple length- 2.5cm to 3.5cm.
Indian cotton:
Origin- India
Poor quality with lower staple length and coarser diameter.
Color- White
Staple length: 2cm to 3cm.
China Cotton:
Origin- China
Poorest quality
Staple length- 1.5cm to 2cm.
Grading of cotton:
Grading of cotton is done based on
Color
Trash content
Ginning quality
Color:
Best quality of cotton will be white color
Different shades of cotton are found due to continuous exposure to atmosphere and micro-organisms.
Different colors of cotton are.
White
Light spotted (Lt Sp)
Spotted (Sp)
Tinged (Tg)
Yellow stained (Ys)
Light grey (Lt Gy)
Grey (Gy)
Trash content:
Trash includes Leaf, Stems, Huns, Barks, Seeds, Shale, Motes, Grass, sand, Oil, and Dust. Cotton with Minimum trash content has a good spinning value. Based on trash content cotton Is graded into
Strict Good Middling (SGM)
Good Middling (GM)
Strict Middling (SM)
Middling (M)
Strict Low Middling (SLM)
Low Middling (LM)
Strict Good Ordinary (SGO)
Good Ordinary (GO)
Quality of Ginning:
The presence of nips and naps are two important factors to determine the quality of cotton.
Neps are the small tangled knots of fibers that are visible as dots (Neppy cotton)
Naps are Large clumps or matted masses of fibers that contribute to the rough appearance (Nappy cotton).
Morphological structure of cotton: cotton contains
Cuticle
Primary wall
Secondary wall
Lumen
Cuticle:
Thin layer attached to the outside of the primary wall.
The cuticle protects the fiber from mechanical and chemical damage.
The cuticle consists of a waxy mixture of fats and oils.
Cuticle becomes hard like a varnish.
Primary wall:
It is built up of Cellulose and Pectineus substances.
Cellulose present in the primary wall is in the form of fine threads (or) Fibrils.
Fibrils are at 70 degrees to the fiber axis.
The thickness of the primary cell wall is 0.1-0.2 microns.
Secondary Wall:
It is composed of cellulose.
The weight of the fiber is due to the secondary cell wall.
The secondary wall is of different layers.
Fibrils present at the layer which is near to primary wall are at an angle of 20-30o
Fibrils in inner layers are at an angle 20-45o
Lumen:
At the center of the growing fiber, there is a lumen, which remains a cylindrical void at maturity.
It occupies a 30-35% area.
After drying the volume of lumen reduced to 5%.
Chemical composition of Cotton:
Physical properties:
Chemical properties:
Effect of Acid:
Cotton dissolves in cold concentrated Sulphuric acid and forms cellulose hydrate.
Cotton shrinks if it is in Nitric Acid for a short time.
If cotton is in Nitric acid for a longer time it oxidizes the cotton and forms oxycellulose and finally it breakdowns to oxalic acid.
The action of Alkalis:
cotton is resistant to alkalies, cotton swells in alkalies like NaOH but it will not damage.
Effect of Organic Solvents:
cotton has good resistance to normal organic solvents, but it dissolves in some of the copper complexes like cuprammonium hydroxide, cupriethylene diamine, and 70% H2SO4
Effect of Insects:
cotton is resistant to moth-grubs or beetles.
Effect of micro-organisms:
cotton is affected by micro-organisms like fungi, bacteria, mildews.