Of all the inventions studied by elementary school children, Eli Whitney's cotton gin, which he patented in 1793, stands out as one of the most remembered. This could be because it was given special emphasis because of the way the gin, which is short for engine, revolutionized the cotton manufacturing process. Cotton was a huge U.S. crop grown throughout the South, though these days only 35 percent of the cotton used in American manufacturing is even grown in the country —25 percent of which is grown in Texas. China and India are now the world's major cotton producers.
It's hard to imagine the numerous steps of the manufacturing process ever being done by hand. Early on, slave labor picked and cleaned the cotton. Later, itinerant pickers and sharecroppers handled the tasks. As late as the 1950s, parts of the process were still done by hand, until it became entirely mechanized as it is today.
About three months after planting seeds, the cotton plants flower. They open with white petals that change to yellow, pink and red, and then fall off. What's left is the cotton boll, which looks like a small, green football. Inside are the cotton fibers and seeds. The boll gradually turns brown, and the cotton fibers inside grow and expand until they burst open the pod to expose the fluffy, white cotton.
Different kinds of cotton picking or stripping machines can be used to twist the cotton from the plants. They use forced air to toss the cotton into large baskets which, when full, are stored in trailers until they are ready to be built into modules, which look like huge loaves of bread. The tightly packed modules keep the cotton yield intact so it doesn't deteriorate or break loose while waiting to be ginned.
Giant, specially designed trucks pick up the modules and take them to the cotton gin. There, machines feed the cotton into a cotton gin, which pulls the cotton fibers apart to remove unwanted debris such as dirt, twigs, burs, leaves and other plant material. Then the gin's saws and teeth separate the cotton fiber from the seeds, sending them in different directions. The cotton fibers will be used to make fabric. The seeds will be sold to manufacturers of cottonseed oil, animal feed, paper products and more.
The fiber, which is called lint at this stage, is formed into bales that weigh about 500 pounds each. Samples are taken from each bale and analyzed for properties such as fiber length, strength and color, which determine its class and selling price. Local buyers purchase the bales and sell them to mills that will turn them into a variety of different fabrics.
Mills may have their unique methods of preparing the cotton, but the purpose and end results are the same. Machines pull apart the bales to further rid them of unwanted debris. Smaller, round cakes with a central hole may be made from them. Then a solution of sodium hydroxide is applied which saturates the fibers.
This is often done in a kier, or large vat, which can be heated to very high temperatures. The length of time the cakes stay at the high temperature depends on the type of cotton that is the desired result. This process saponifies the natural waxes on the fiber and the rest of the plant is softened. As these separate, the pectins and other non-cellulosic materials are suspended and washed away.
A hydrogen peroxide solution is then applied to bleach the cotton. Since the fibers have been softened, the bleaching solution is better able to penetrate the fibers. The amount of time it stays in the bleaching process is determined by how white the finished product needs to be.
Some bleached cotton, such as those that are used in pharmaceutical products like swabs and feminine hygiene items can be used at this point. Any clumped or jumbled fibers that remain will not alter the effectiveness of these products.
Other products, though, require finer cotton without any clumps. For these, the fibers go through an added step of careful reopening and further processing. Carding machines pull the clumps apart and lay the fibers straight, side-by-side to dry. They form soft, untwisted ropes called slivers, which will be spun on spinning machines to make various materials and fabrics.
Whether the fibers were reopened or used right after bleaching, both must be finished. With the wax coating washed away, the fibers don't have anything separating them and the resulting friction can hinder further processing. Adding a lubricant at this point enable the fibers to be finished. These lubricating oils are pumped through the cakes until they reach the desired level of finish.
The finished fibers are purchased by different manufacturers to be made into all kinds of fabrics and non-woven materials.