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Cotton^[1] is a soft, staple fiber that grows around the seeds of the cotton plant, a shrub native to tropical and subtropical regions around the world, including the India and Africa. Cotton fiber, once it has been processed to remove seeds (ginning) and traces of honeydew, protein, vegetable matter, and other impurities, consists of nearly pure cellulose, a natural polymer. Cotton production is very efficient, in the sense that only ten percent or less of the weight is lost in subsequent processing to convert the raw cotton bolls into pure fiber. The cellulose is arranged in a way that gives cotton fibers a high degree of strength, durability, and absorbency. Each fiber is made up of twenty to thirty layers of cellulose coiled in a neat series of natural springs. When the cotton boll is opened, the fibers dry into flat, twisted, ribbon-like shapes and become kinked together and interlocked. This interlocked form is ideal for spinning into a fine yarn.

No one knows exactly how old cotton is. Scientists searching caves in Mexico found bits of cotton bolls and pieces of cotton cloth that proved to be at least 7,000 years old. They also found that the cotton itself was much like that grown in America today. Arab merchants brought cotton cloth to Europe about 800 A.D. When Columbus discovered America in 1492, he found cotton growing in the Bahama Islands. By 1500, cotton was known generally throughout the world.

Cotton grows in warm climates and most of the world’s cotton is grown in the U.S., Uzbekistan, the People’s Republic of China and India. Other leading cotton-growing countries are Brazil, Pakistan and Turkey.

Cotton was first spun by machinery in England in 1730. Today, the world uses more cotton than any other fiber. Cotton is a part of our daily lives from the time we dry our faces on a soft cotton towel in the morning until we slide between fresh cotton sheets at night. It has hundreds of uses, from blue jeans to shoe strings. Clothing and household items are the largest uses, but industrial products account from many thousands of bales.

All parts of the cotton plant are useful. The most important is the fiber or lint, which is used in making cotton cloth. Linters – the short fuzz on the seed – provide cellulose for making plastics, explosives and other products. Linters also are incorporated into high quality paper products and processed into batting for padding mattresses, furniture and automobile cushions.

The cottonseed is crushed in order to separate its three products – oil, meal and hulls. Cottonseed oil is used primarily for shortening, cooking oil and salad dressing. The meal and hulls that remain are used either separately or in combination as livestock, poultry and fish feed and as fertilizer. The stalks and leaves of the cotton plant are plowed under to enrich the soil.

In the spring, farmers prepare for planting in several ways. Producers who plant using no-till or conservation tillage methods, use special equipment designed to plant the seed through the litter that covers the soil surface. Producers, who employ conventional tillage practices, plow or “list” the land into rows forming firm seed-beds for planting. Producers in south Texas plant cotton as early as February. In Missouri and other northern parts of the Cotton Belt, they plant as late as June.

About two months after planting, flower buds called squares appear on the cotton plants. In another three weeks, the blossoms open. Their petals change from creamy white to yellow, then pink and finally, dark red. After three days, they wither and fall, leaving green pods which are called cotton bolls.

Inside the boll, which is shaped like a tiny football, moist fibers grow and push out from the newly formed seeds. As the boll ripens, it turns brown. The fibers continue to expand under the warm sun. Finally, they split the boll apart and the fluffy cotton bursts forth. It looks like white cotton candy.

The crop is harvested by machines, either a picker or a stripper. Cotton picking machines have spindles that pick (twist) the seed cotton from the burrs that are attached to plants’ stems. Doffers then remove the seed cotton from the spindles and knock the seed cotton into the conveying system.

After cotton has been harvested, producers who use conventional tillage practices cut down and chop the cotton stalks. The next step is to turn the remaining residue underneath the soil surface. Producers who practice a style of farming called conservation tillage often choose to leave their stalks standing and leave the plant residue on the surface of the soil.

Nearly all cotton is stored in modules, which look like giant loaves of bread. Modules allow the cotton to be stored without loosing yield or quality prior to ginning. Specially designed trucks pick up modules of seed cotton from the field and move them to the gin. Modern gins place modules in front of machines called module feeders. Some module feeders have stationary heads, in which case, giant conveyors move the modules into the module feeder. Other module feeders are self-propelled and move down a track that along side the modules. The module feeders literally break the modules apart and “feed” the seed cotton into the gin. Other gins use powerful pipes to suck the cotton into the gin building. Once in the cotton gin, the seed cotton moves through dryers and through cleaning machines that remove the gin waste such as burs, dirt, stems and leaf material from the cotton. Then it goes to the gin stand where circular saws with small, sharp teeth pluck the fiber from the seed. From the gin, fiber and seed go different ways. The ginned fiber, now called lint, is pressed together and made into dense bales weighting about 500 pounds.

The seed usually is sold by the producer to the gin. The ginner either sells for feed or to oil mills where the linters (downy fuzz) are removed in an operation very much like ginning. Linters are baled and sold to the paper, batting and plastics industries, while the seed is processed into cottonseed oil, meal and hulls.

Spinning is the process of making yarn from unbundled fibers. It includes the following operations. Upon arrival at the spinning mill, cotton bales are sampled according to lint quality and origin to ensure yarn homogeneity. They are then opened to make the lint fluffy by passage though bale-openers. The following important step in the spinning process is cleaning. Bale fibres are usually fed to air-jet (vortex) cleaners to remove extraneous matter from cotton lint (which may hamper further cotton processing and affect lint quality). At this stage loose fibres are not aligned and parallel in a single continuous strand. Carding is the process of straightening or paralleling the fibres. Carding separates fibres from each other, straightens fibres, aligns and condenses them into a single continuous strand, and removes impurities. A sliver of approximately one-meter width is then obtained. Cotton that has already been carded may be combed. Combining is an optional step in the ginning process. This process is only used to produce superior quality yarn and long- or extra long-staple fibres. As a result of drawing (or doubling) the sliver is condensed into a thinner strand and becomes more uniform. The sliver is fed to several rubber rollers rotating at increasingly higher speed. Cotton bleaching (using either hypochlorite or peroxide) and dying often occur at this stage. Eventually, several slivers are drawn and twisted together to form the final yarn. Twisting is made by two mechanical actions. First, a drawing frame condenses slivers into a thinner strand (slubbing) and winds it on a bobbin. A spinning frame then reduces roving to required size of single yarn (fine spinning). A suitable amount of twist is introduced according to the intended use of the fibre.

The cotton industry relies heavily on chemicals such as fertilizers and insecticides, although a very small number of farmers are moving toward an organic model of production and organic cotton products are now available for purchase at limited locations. These are popular for baby clothes and diapers.

Cotton is used to make a number of textile products. These include terrycloth, used to make highly absorbent bath towels and robes; denim, used to make blue jeans; chambray, popularly used in the manufacture of blue work shirts; and corduroy, seersucker, and cotton twill. Socks, underwear, and most T-shirts are made from cotton. Bed sheets often are made from cotton. Cotton also is used to make yarn used in crochet and knitting. Fabric also can be made from recycled or recovered cotton that otherwise would be thrown away during the spinning, weaving, or cutting process. While many fabrics are made completely of cotton, some materials blend cotton with other fibres, including rayon and synthetic fibres such as polyester.

In addition to the textile industry, cotton is used in fishnets, coffee filters, tents, gunpowder, cotton paper, and in bookbinding. The first Chinese paper was made of cotton fibre. Fire hoses were once made of cotton.

The cottonseed which remains after the cotton is ginned is used to produce cottonseed oil, which, after refining, can be consumed by humans like any other vegetable oil. The cottonseed meal that is left generally is fed to livestock. In the past, cotton seeds were used as an abortifacient, that is, a folk remedy to provoke abortion.

Cotton linters are fine, silky fibres which adhere to the seeds of the cotton plant after ginning. These curly fibres typically are less than 1/8 in, 3mm, long. The term also may apply to the longer textile fibre staple lint as well as the shorter fuzzy fibres from some upland species. Linters are traditionally used in the manufacture of paper and as a raw material in the manufacture of cellulose.

Shiny cotton is a processed version of the fibre that can be made into cloth resembling satin for shirts and suits. However, its hydrophobic property of not easily taking up water makes it unfit for the purpose of bath and dish towels (although examples of these made from shiny cotton are seen).

Organic cotton is cotton that is grown without insecticide or pesticide. Worldwide, cotton is a pesticide-intensive crop, using approximately 25% of the world's insecticides and 10% of the world's pesticides. According to the World Health Organization (WHO), 20,000 deaths occur each year from pesticide poisoning in developing countries, many of these from cotton farming. Organic agriculture uses methods that are ecological, economical, and socially sustainable and denies the use of agrochemicals and artificial fertilizers. Instead, organic agriculture uses crop rotation, the growing of different crops than cotton in alternative years. The use of insecticides is prohibited; organic agriculture uses natural enemies to suppress harmful insects. The production of organic cotton is more expensive than the production of conventional cotton. Although toxic pollution from synthetic chemicals is eliminated, other pollution-like problems may remain, particularly run-off. Organic cotton is produced in organic agricultural systems that produce food and fibre according to clearly established standards. Organic agriculture prohibits the use of toxic and persistent chemical pesticides and fertilizers, as well as genetically modified organisms. It seeks to build biologically diverse agricultural systems, replenish and maintain soil fertility, and promote a healthy environment.

Fibre length is described as "the average length of the longer one-half of the fibres (upper half mean length)" This measure is taken by scanning a "beard” of parallel fibres through a sensing region. The beard is formed from the fibres taken from the sample, clasped in a holding clamp and combed to align the fibres.

Length uniformity or uniformity ratio is determined as “a ratio between the mean length and the upper half mean length of the fibres and is expressed as a percentage".

Fibre strength is measured in grams per denier (g/d) or centi-newton per tex cN/tex. It is determined as the force necessary to break the beard of fibres, clamped in two sets of jaws, (1/8 inch apart). The breaking strength of cotton is about 3.0~4.9 g/denier, and the breaking elongation is about 8~10%.

Micronaire measurements reflect fiber fineness and maturity. A constant mass (2.34 grams) of cotton fibers is compressed into a space of known volume and air permeability measurements of this compressed sample are taken. These, when converted to appropriate number, denote micronaire values.

The color of cotton samples is determined from two parameters: degree of reflectance (Rd) and yellowness (+b). Degree of reflectance shows the brightness of the sample and yellowness depicts the degree of cotton pigmentation. The color of the fibers is affected by climatic conditions, impact of insects and fungi, type of soil, storage conditions etc. There are five recognized groups of color: white, gray, spotted, tinged, and yellow stained. As the color of cotton deteriorates, the processability of the fibers decreases.

A trash measurement describes the amount of non-lint materials (such as parts of cotton plant) in the fiber. Trash content is assessed from scanning the cotton sample surface with a video-camera and calculating the percentage of the surface area occupied by trash particles. The values of trash content should be within the range from 0 to 1.6%. Trash content is highly correlated to leaf grade of the sample.

Leaf grade is provided visually as the amount of cotton plant particles within the sample. There are seven leaf grades (#1-#7) and one below grade (#8).

Preparation is the classer's interpretation of fiber processability in terms of degree of roughness or smoothness of ginned cotton.

Extraneous matter is all the material in the sample other than fiber and leaf. The degree of extraneous matter is determined by the classer either as "light” or "heavy".

A nep is a small tangled fiber knot often caused by processing. Neps can be measured by a nep tester and reported as the total number of neps per 0.5 grams of the fiber and average size in millimeters. Nep formation reflects the mechanical processing stage, especially from the point of view of the quality and condition of the machinery used.

Cotton swells in a high humidity environment, in water and in concentrated solutions of certain acids, salts and bases. The swelling effect is usually attributed to the sorption of highly hydrated ions. The moisture regain for cotton is about 7.1~8.5% and the moisture absorption is 7~8%.

Cotton degradation is usually attributed to oxidation, hydrolysis or both. Oxidation of cellulose can lead to two types of so-called oxy-cellulose, depending on the environment, in which the oxidation takes place. Cotton can also degrade by exposure to visible and ultraviolet light, especially in the presence of high temperatures around 250~397° C and humidity. Cotton fibers are extremely susceptible to any biological degradation (microorganisms, fungi etc.).

Cotton fibers show double refraction when observed in polarized light. Even though various effects can be observed, second order yellow and second order blue is characteristic colors of cellulose fibers.

NOTES: 1) Cotton gin, machine for separating cotton fibers from the seeds. The charkha, used in India from antiquity, consists of two revolving wooden rollers through which the fibers are drawn, leaving the seeds. A similar gin was early used in the S United States for long-staple cotton. In the modern roller gin, rollers covered with rough leather draw out the fibers, which are cut off by a fixed knife pressed against the rollers. This type of gin cleans only about two bales per day, but it does not snarl or break the fibers. The saw gin, invented by the American inventor Eli Whitney in 1793 and patented in 1794, consisted of a toothed cylinder revolving against a grate that enclosed the seed cotton. The teeth caught the fibers, pulling them from the seeds; the fibers were then removed from the cylinder by a revolving brush. This device, especially suited to short- and medium-staple cotton, has been mechanized and is used in commercial plants that are also called gins, where the fiber is conveyed from farm wagon to baler by air suction. Such plants have one or more gin stands, each with a series of from 70 to 80 circular saws set on a shaft. The fibers, freed from dirt and hulls, are pulled through a grid by the saw teeth to remove the seeds. The fibers are removed from the saw teeth by a revolving brush or by a blast of air (in more modern plants) and are then carried by air blast or suction to a condenser and finally to the baling apparatus.