History Of Cotton
Archaeological findings in Mohenjo-Daro, in modern Pakistan, and in the Tehuacán valley in Mexico, both dating from about 3000 BC, suggest that the cotton plant was already domesticated and being used for making textiles over 5000 years ago.
Cotton fabrics from India, of outstanding fineness and quality, were traded in the Mediterranean area from the time of Alexander, who had established the trade routes to the East. Alexandria became the major dispersal point for these goods. Later the rise to power of the city-state of Venice is said to have been built largely on trade in Indian cotton cloth.
In the 8th century, cotton growing and fabric manufacture were introduced into Spain by the Moors, where it thrived until the expulsion of Islam in the 15th century. Thereafter, the opening of the sea route to India promoted Portugal to the prime source of cotton fabrics.
During the 17th-century textile manufacturing expertise and sea, power began to concentrate in England which then became the dominant centre of textile manufacture.
Meanwhile, cotton growing was expanded in North America and the Caribbean. These trends were reinforced in the late 18th century by the invention of the cotton gin in America, and by the development of spinning and weaving machinery, plus the harnessing of water and steam power, in Britain.
Cotton Production & It’s Sources
By 1930 cotton accounted for 85% of the world consumption of textile fibers but, during the last half of the twentieth century, its market share fell to about 40% due to the introduction of synthetic fibers. Current annual production (2010-12) is about 26 million tonnes.
Although cotton production has tripled in recent decades, the amount of land utilized has not increased. This is a result of constant improvements in cotton varieties and farming techniques. Cotton is grown in about 80 different countries worldwide.
The Cotton Plant
Cotton is a member of the Mallow family. Its height ranges from 25 cm to over 2 m, depending on variety, climate, and agronomy. It is normally grown as an annual shrub but, in parts of South America and the Caribbean, it is cultivated as a perennial shrub (tree cotton).
From planting to maturity takes between 175 and 225 days. At planting and during its growth, cotton needs plenty of water. For ripening, it needs heat. Therefore, the world’s cotton belt is located mainly in the tropics and sub-tropics. After flowering, the fruit nodes, located in the calyx (bracts), grow into capsules (bolls) which eventually crack open to reveal the seed hairs. In each ball, there are about 30 seeds.
The number of hairs on each seed ranges from less than 1000 to more than 10000, depending on the variety. Like any agricultural product, the way that cotton is grown in different countries varies widely, depending on the level of development: in the USA, Australia, Brazil, Uzbekistan and Israel large machines are utilized; in poorer countries, oxen or buffalo may be used for traction, and manual labor is the rule.
Harvesting of Cotton
Harvesting is either by hand or by picking machines. Hand picking extends over several weeks. In principle, it has the advantage that only the fully ripened bolls are collected and no leaves are included.
A picking machine will usually harvest the whole crop in one passage. It has a tendency to include some unripe bolls, together with various quantities of dead leaves and other plant parts.
Drying of Cotton
If the newly-harvested seed-cotton is wet, then it may have to be dried using warm air before it can be stored in large piles to await ginning. In many countries, drying is an integral part of the ginning process.
Ginning of Cotton
Ginning is the separation of the fibers from the seeds using special machines. The separated fibers, called lint, have a staple length of between 15 and 50 mm, depending on the cotton variety. On many types of seed, there are some very short fibers, called linters.
They are made of cellulose and they find many uses, including the production of man-made fibers. The seeds can also be utilized for the production of edible oil and as cattle feed. 100 kg of clean seed cotton yields about 35 kg of fiber, 62 kg of seed and 3 kg of waste.
Processing Into Yarn
Cotton fibers are made into staple fiber yarns predominantly by ring spinning or OE rotor spinning.
Commercially, cotton is usually designated according to its variety and origin. Different varieties are grown in different countries – about 40 in the USA alone. Thus the country of origin is only a partial guide to quality. The high-quality, long-staple cotton, such as the Giza’s of Egypt and the Pimas of the USA, Peru, and Israel, account for less than 10% of total production.
Sea Island cotton, from the West Indies, is a very high-quality type produced in vanishingly small quantities. The most common type worldwide is the American Upland cotton, with about 85%.Naturally coloured cotton, mostly in brown shades, have been adapted for commercial production on a very limited scale.
|Staple length||This is the most important aspect of quality. It generally lies between 20 mm and 40 mm. Spinnable fibers have a staple
length greater than about 16 mm. Sea Island cotton can be as long as 50 mm. Giza and Pima are about 36 mm, Upland
Is about 28 mm.
|Fineness, Handle||Cotton fibers are fine. Their weight per unit length is Between 1 and 4 dtex. Generally, the longer the fiber, the Finer it is and the softer its handle.|
|Large amounts of contaminants, such as leaf or seed fragments, or of very short fibers, or of immature and “dead”
Fibers are severely detrimental to quality.
|Strength||High-quality cotton will have a high strength relative to its fineness.|
|Color and Luster||The color of cotton varies, according to the variety, from white (Upland) through creamy (Giza, Pima) to light yellow or brown. The luster is usually subdued. High-quality types, such as Giza and Pima have a silky luster.|
Construction of Cotton Fibres
Cotton is composed of cellulose, the foundation of all plants. Whilst it is growing inside the boll, the fiber is circular (annular) in section. When the boll opens, the fiber begins to dry and it collapses to a kidney-shaped cross-section. At very strong magnification in the electron microscope, a suitably prepared cross-section shows daily growth rings, comparable with the annual rings in wood.
These are the result of daily deposits of layer upon layer of fresh cellulose, proceeding from the outside inwards. The first-formed outer layer is composed of an especially tough kind of cellulose. At the end of the growth period, a cavity remains at the centre. This is called the Lumen. During drying the fiber twists along its length axis and looks like a flattened, twisted tube. A layer of natural wax coats the surface.
Each cellulose layer is formed from fibrillar bundles composed of individual fibrils (fibril = tiny fiber). The fibrils are made of cellulose macromolecules. The fibrillar bundles of succeeding cellulose layers are inclined at an angle to the length axis of the fiber.
Spaces between the ordered lattice of the fibrillar structure, as well as the hollow fiber centre, are easily penetrated by water. Moisture can be stored in the cavities. Sweat can be absorbed and will be removed during subsequent washing.
Cotton is stronger when it is swollen by water. This is because the presence of water promotes a more uniform distribution of stresses across and along the cellulose layers. The high strength of the cotton fiber is a consequence of its construction from highly organized cellulose chain molecules in the fiber interior (crystalline regions). Its low elasticity is due to slippage between the crystalline regions.
Cotton fibers are single cells that extend from the seed coat epidermis. Their dimensions depend on the cotton species and variety. Thus the superfine Sea Island cotton (Gossypium barbadense) have a length of up to 5 cm and a linear density of 1 dtex, while the coarse Asiatic cotton (Gossypium herbaceum, Gossypium arboreum) have a length of about 1.5 cm and a linear density of 3 dtex.