Fiber

Or fibre is a class of materials that are continuous filaments or are in discrete elongated pieces, similar to lengths of thread. Fibers are of great importance in the biology of both plants and animals, for holding tissues together. Human uses for fibers are diverse. They can be spun into filaments, thread, string or rope. They can be used as a component of composite materials. They can also be matted into sheets to make products such as paper or felt. Fibers are often used in the manufacture of other materials.

Fibers used by man come from a wide variety of sources.

• Natural fibers include those produced by plants, animals, and geological processes. They can be classified according to their origin:
• Vegetable fibers are generally based on arrangements of cellulose, often with lignin: examples include cotton, linen, hemp jute, flax, ramie, and sisal. Plant fibers serve in the manufacture of paper and cloth.
• wood fiber, distinguished from vegetable fiber, is from tree sources. Forms include ground wood, thermo mechanical pulp (TMP) and bleached or unbleached kraft or sulfite pulps. Kraft and sulfite, also called sulphite, refer to the type of pulping process used to remove the lignin bonding the original wood structure, thus freeing the fibers.
• Animal fibers consist largely of particular proteins. Instances are spider silk, sinew, catgut and hair (including wool). Polar bear fibers are noted for being hollow.

• Mineral fibers comprise asbestos. Asbestos is the only naturally occurring long mineral fiber. Short, fiber-like minerals include wollastinite, attapulgite and halloysite.

• Man-made fibers may come from natural raw materials or from synthetic chemicals.
• Many types of fiber are manufactured from natural cellulose, including rayon, modal, and the more recently developed Lyocell. Cellulose-based fibers are of two types, regenerated or pure cellulose such as from the cupro-ammonium process and modified or derivitized cellulose such as the cellulose acetates. Fiberglass made from specific glass formulas and optical fiber, made from purified natural quartz, are also man-made fibers that come from natural raw materials. Metallic fibers can be drawn from ductile metals such as copper, gold or silver and extruded or deposited from more brittle ones such as nickel, aluminum or iron.

   Synthetic fibers are a subset of man-made fibers, which are based on synthetic chemicals (often from petrochemical sources) rather than arising from natural materials by a purely physical process. Such fibers are made from polyamide nylon, PET or PBT polyester, phenol-formaldehyde (PF),polyvinyl alcohol fiber (PVOH), polyvinyl chloride fiber (PVC), polyolefins (PP and PE), or acrylic polymers, although pure polyacrylonitrile PAN fibers are used to make carbon fiber by roasting them in a low oxygen environment. Traditional acrylic fiber is used more often as a synthetic replacement for wool. Carbon fibers and PF fibers are noted as two resin-based fibers that are not thermoplastic, most others can be melted. Aromatic nylons such as Kevlar and Nomex thermally degrade at high temperatures and do not melt. More exotic fibers have strong bonding between polymer chains (e.g. aramids), or extremely long chains (e.g. Dyneema or Spectra). Elastomers can even be used, e.g. spandex although urethane fibers are starting to replace spandex technology.

Coextruded fibers have two distinct polymers forming the fiber, usually as a core-sheath or side-by-side. Coated fibers exist such as nickel-coated to provide static elimination, silver-coated to provide anti-bacterial properties and aluminum-coated to provide radar chaff. Radar chaff is actually a spool of continuous glass tow that has been aluminum coated. An aircraft-mounted high speed cutter chops it up as it spews from a moving aircraft to foil radar signals.

Micro fibers in textiles refer to sub-denier fiber (such as polyester drawn to 0.5 dn). Denier and Detex are two measurements of fiber yield based on weight and length. If the fiber density is known you also have a fiber diameter, otherwise it is simpler to measure diameters in micro metres. Microfibers in technical fibers refer to ultrafine fibers (glass or meltblown thermoplastics)often used in filtration. Newer fiber designs include extruding fiber that splits into multiple finer fibers. Most synthetic fibers are round in cross-section, but special designs can be hollow, oval, star-shaped or trilobal. The latter design provides more optically reflective properties. Synthetic textile fibers are often crimped to provide bulk in a woven, non woven or knitted stucture. Fiber surfaces can also be dull or bright. Dull surfaces reflect more light while bright tends to transmit light and make the fiber more transparent.

Very short and/or irregular fibers have been called fibrils. Natural cellulose, such as cotton or bleached kraft show smaller fibrils jutting out and away from the main fiber structure.

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