Lots of experimentation with the many natural fibers available, cotton, wool, jute, flax, and silk became recognized as the most satisfactory. The commercial development of man-made fibers began late in the 19th century, experienced much growth during the 1940s, expanded rapidly after World War II, and is still the subject of investigation.
The animal fibers consist exclusively of proteins and, with the exception of silk, constitute the fur or hair that serves as the protective epidermal covering of animals. Silk filaments are extruded by the larvae of moths and are used to spin their cocoons.
With the exception of mineral fibers, all natural fibers have an affinity for water in both liquid and vapor form. This strong affinity produces swelling of the fibers connected with the uptake of water, which facilitates dyeing in watery solutions.
Unlike most synthetic fibers, all natural fibers are nonthermoplastic; that is, they do not soften when heat is applied. At temperatures below the point at which they will decompose, they show little sensitivity to dry heat, and there is no shrinkage or high extensibility upon heating, nor do they become brittle if cooled to below freezing. Natural fibers tend to yellow upon exposure to sunlight and moisture, and extended exposure results in loss of strength.
All natural fibers are particularly susceptible to microbial decomposition, including mildew and rot. Cellulosic fibers are decomposed by aerobic bacteria (those that live only in oxygen) and fungi. Cellulose mildews and decomposes rapidly at high humidity and high temperatures, especially in the absence of light. Wool and silk are also subject to microbial decomposition by bacteria and molds. Animal fibers are also subject to damage by moths and carpet beetles. Termites and silverfish attack cellulose fibers. Protection against both microbial damage and insect attacks can be obtained by chemical modification of the fiber substrate; modern developments allow treatment of natural fibers to make them essentially immune to such damage.
- The Editors of Encyclopedia Britannica.