Natural, artificial, and synthetic fibers
Even before building his first cities, his first castles, man made fabrics to cover himself. And he continued to make them for thousands of years using plant or animal fibers as raw material.
In plants, fibers form the skeleton that supports the soft and pulpy parts of leaves, roots, and stems. In animals, fibers are found in meat, skin, muscles, and fur. All these fibers are extremely thin (their length is about two thousand times their thickness) and consist of a long chain of molecules roughly parallel to each other. Plant fibers, such as cotton and linen, are made of cellulose, which is a compound of carbon, hydrogen, and oxygen; animal fibers, such as wool and silk, are made of various types of proteins, compounds of carbon, hydrogen, oxygen, nitrogen, and sometimes also sulfur (in wool).
To meet the demands of current manufacturing methods and modern machinery, fibers must be strong, resistant, flexible, shiny, and of almost uniform size. They should be at least 12 mm long (even better 35 mm or more) and only a few hundredths of a millimeter thick. Furthermore, they should be rough or wrinkled, so that they intertwine securely when twisted to form a yarn, thereby increasing the strength of the fibers and preventing them from sliding over each other when subjected to tension.
Only some of the natural fibers have all or most of these requirements; these include cotton, which is particularly strong and resistant, wool, which is warm and wrinkle-resistant, silk, which is soft and shiny, and linen, which is crisp and lustrous. Bast fibers, which include jute, hemp, sisal, and ramie, are strong and resistant, but too coarse for clothing: they are mainly used for ropes, twine, sacks, and mats.
Since the possibilities of natural fibers are limited, the textile industry fully exploits artificial fibers that have been produced in the last 75 years. Between 1890 and 1920, chemists discovered how to obtain numerous varieties of fibers from cotton and wood pulp. The most successful ones were viscose rayon and cellulose acetate rayon, which are still manufactured on a large scale. Initially, rayon fibers were called artificial silk due to their silky softness and great luster.
Like all natural fibers, rayon absorbs water and thickens when washed, but there is a difference: natural fibers remain strong when wet and swell, cotton even becomes stronger; rayon, on the other hand, when it absorbs an amount of water equal to its weight, loses about a third of its strength. This weakening is only temporary, because once dry, rayon regains all its original properties. It is evident, however, that the quality of a fiber is better if it does not lose its strength when washed.
Carothers' discovery of nylon was particularly important because nylon, which is the first of the so-called synthetic fibers, is at least twice as strong as cotton, absorbs a minimal amount of water, and maintains its shape even when wet. The success of nylon led to the discovery of other synthetic fibers with similar properties.
No fiber presents all the advantages or all the disadvantages we have discussed. Natural fibers and the first rayon fibers are resistant to heat and to those organic solvents sometimes used in dry cleaning. On the other hand, they are attacked by moths and bacteria. The new synthetic fibers, however, are not attacked by insects and bacteria, but they are damaged if ironed with a very hot iron.
Since rayon and natural fibers absorb water quickly, they are particularly suitable for garments that are more likely to come into contact with sweat. For the same reason, they can be dyed and starched with water-soluble substances. However, synthetic fiber fabrics repel water and must therefore be dyed and starched by more complex and expensive processes. Synthetic fibers also require special procedures for spinning and weaving.
