Fibers are filiform elements, which present a high length ratio with respect to their maximum transverse dimension. They are characterized by flexibility and fineness.
Fibers are made of macromolecules referred as polymers. In turn, these polymers are composed of a sequence of monomers. Polymers are chemically stable while monomers are chemically unstable, which explains the reaction of the union of monomers in the formation of a polymer.
The polymer length is a very important factor, since almost all fibers have very long polymer chains. Regarding the molecular arrangement, fibers can be highly or slightly oriented. When they are highly oriented, they conform a crystalline region, which means that the polymers are longitudinally aligned and in order, more or less parallel. In the case of fibers being slightly oriented, amorphous regions are formed, where the polymers do not have a defined orientation.
Highly orientated polymers confer fibers high tensile strength, low elongation, heat resistance and chemical resistance. On the contrary, the amorphous areas of slightly oriented polymers give fibers features such as: flexibility, softness and comfort.
Fibers can be classified attending to several aspects:
- With respect to the length, fibers can be classified as discontinuous, when they are limited to a few centimeters length; or continuous, when they have a very high length, which is only limited by technical reasons;
- With respect to its origin, they can be classified as natural or man-made fibers. Within the latter group, artificial, synthetic and inorganic fibers can be found. Natural fibers exist as they are found in nature, and can be of animal, vegetable or mineral nature.