Cotton is the world’s most widely used fiber. Its popularity stems from both its relative ease of production and its applicability to a wide variety of textile products. The price of cotton yarn, however, is strongly dependent upon the cost of labor, so that in the industrialized nations, where labor is expensive, cotton yarns may be relatively high priced.
Until relatively recent times, however, cotton was not as widely used as wool and linen. This was because it was easier to spin wool or flax into yam because of their greater length. In addition, cotton fibers have to be separated from the seeds to which they cling. This procedure was very tedious and time-consuming when done by hand. Early machinery could be used on only the longest staple cotton. So labor costs tended to be very high.
The invention of the saw-type cotton gin made possible the exploitation of the short staple fiber, which thrived in the Carolinas and Virginia of the United States. The dramatic increase in productivity, coupled with the low cost of labor in the southern United States, gave cotton a continually expanding portion of the world textile market. Increasing mechanization of fiber and yarn production helped keep the cost of cotton goods low. The, development of the textile machinery enlarged the production base.
Cotton cultivation requires warm climates with a high level of moisture or irrigation. The growing season is from six to seven months long. During this period the seeds sprout and grow, producing a white blossom in about 100 days. The blossom produces a seed pod, which matures during the next two months. When the pod bursts, the cotton fibers are ready for picking.
Before yam manufacture, cotton is graded, sorted, and blended to insure uniform yam quality. Cotton is graded on the basis of color, staple length, fineness, and freedom from foreign matter. In the United States, cottons are divided into grades according to length of staple, uniformity, strength, color, cleanness and flexibility. These are compared with a standard supplied by the United States Department of Agriculture. The standard provides 6 grades above and 6 grades below the Middling grade.
The most common grades are:
- Strict good middling.
- Good middling.
- Strict middling.
- Strict low middling
- Low middling.
- Strict good ordinary.
The cotton fiber may be from 0.3 to 5.5 cm long. Under the microscope it appears as a ribbon like structure that is twisted at irregular intervals along its length. The twists, called convolutions, increase the fiber-to-fiber friction necessary to secure a strong spun yarn. The fiber ranges in color from a yellowish to pure white, and may be very lustrous. However, most cotton dull.
A cross-sectional view reveals that the fiber is kidney-shaped with central hollow core known as the lumen. The lumen provides a channel for nutrients while the plant is growing. The fiber consists of an outer shell, or cuticle, which surrounds the primary wall. The primary wall, in turn, covers the secondary wall surrounding the lumen. The cuticle is a thin, hard shell which protects the fiber from bruising and damage during growth. In use as a textile fiber, the cuticle provides abrasion resistance to cotton.