Natural vegetable fiber
Cotton (Gossypium )
The cotton fiber is a natural fiber from the seed hairs of cotton plants of the genus (Gossypium ) is obtained. In the scheme of natural fibers cotton, therefore, belongs to the seed fibers. The seeds of the cotton forms as an extension of his longer hair epidermis, called lint, and 3-5 days after flowering very short hair, called linters. Only the long fibers, usually spun into yarn or thread and used for textiles, while the Linter are only suitable for cellulose products.
Development and construction
The cotton fiber is a single cell whose primary wall first grows out of the seed of the cotton to the final expansion of the fiber. This is then filled by a secondary wall. At this, a tertiary wall closes and eventually a cavity, the lumen. In the cytoplasm cellulose is synthesized by the concatenation of glucose into an enzymatic complex. Approximately 40-100 cellulose molecules combine to form elementary fibrils. In these, the cellulose is present in highly ordered crystal lattices. Several elementary fibrils, also called micelles, combine to form microfibrils, and these in turn to macrofibrils.
The structure of primary, secondary and tertiary wall is very different. In the secondary wall of the cellulose content is highest, while they are in the primary wall, which is a few tens of microns thick, only about 5 % of the total cellulose content of the fiber. It consists mainly of cellulose in addition to pectin and waxes. In the tertiary wall, there is little cellulose and many impurities. It fulfills the function of a practical " filter " of the fiber.
The chemical composition of the primary wall, the entire fiber and occurring contaminants such as vegetable impurities, v. a seed husks, the table shows.
The arrangement of the fibrils in the three walls is very different. While the fibril present in the primary cell wall arranged very irregularly, they are in the secondary wall crossbred arranged strictly parallel to the fiber axis in the manner of helical structure and in the tertiary wall.
The figure shows a schematic cross section through a cotton fiber. The surface structure of the cotton fiber is flat, twisted and loop similar. The color of the fibers varies from creamy white to dirty gray, depending on the manufacturing or treatment process. Unlike many other natural fibers cotton has extremely low lignin or Pektinbestandteile, and only a very small amount of hemicellulose of about 5.7 %. Thus, there is the cotton fiber, next to the wax layer of the cuticle, almost exclusively of highly crystalline cellulose.
In the workup of cotton only about 10% of the gross weight will be lost. When the wax, protein and other crop residues are removed, a natural polymer of cellulose remains. The particular arrangement of cellulose are of cotton, high tensile strength. Each fiber consists of 20-30 layers of cellulose in a rotated structure. If the cotton ball - the fruit of the cotton plant stand - opens dry the fibers and entangled with each other. This form is used for spinning at a very fine yarn.
Cotton is very absorbent and can absorb up to 32 % of their weight in water. However, Are Woven fabrics of cotton once wet, they dry slowly. Moreover, cotton also has a high dirt and oil absorption capacity, but is also able to give it off again. Cotton fabrics are considered very skin-friendly ( they " scratch " is not ) and have an extremely low allergy potential. These properties makes them interesting for the textile industry.
Cotton is not soluble in water and in damp or wet tear-resistant than in dry. The strength and stiffness of the cotton fiber are less than the fiber obtained, the elongation is significantly higher. The fibers are alkaline but not acid resistant. Cotton is susceptible to attack by microorganisms, however, the resistance to moths and other insects is quite high. Cotton is highly flammable, but can be boiled and sterilized.
Auxins play an important role in cotton fiber development. Researchers at the Southwest University (Chongqing) was accomplished by genetic engineering an increase in IAA production in the epidermis of the plant at the beginning of fiber growth. This leads to an increase in the number and length of useful fibers ( lint ), and a decrease in the number of non- textiles can be processed to fibers ( linter ). Field trials of four years showed that the linter support in the transgenic plants was consistently higher by more than 15 % than that of the conventional controls. In addition, the fineness of the fibers improved.