A manufactured fiber is a long, thin strand of material created through industrial chemical and mechanical processes, as it is not found naturally in a continuous filament form. Manufactured fibers are broadly categorized into two main groups: regenerated fibers, which start from natural polymers, and synthetic fibers, which are built entirely from chemical compounds. These fibers are engineered to possess specific properties such as strength, elasticity, and resistance to heat.
Regenerated Fibers: Sourced from Natural Polymers
Regenerated fibers are sourced from natural polymers, primarily cellulose, which is extracted from plant-based materials. Common sources for this cellulose include wood pulp from fast-growing trees like eucalyptus and beech, as well as cotton linters.
Viscose rayon is one of the oldest and most widely produced regenerated fibers, created by chemically treating cellulose pulp with sodium hydroxide and carbon disulfide to form a thick, viscous solution. This solution is then extruded to regenerate the cellulose into a solid filament.
Lyocell, a more modern example, is often considered more environmentally sound due to its closed-loop system, which uses a non-toxic organic solvent to dissolve the wood pulp. Modal is another cellulose-based fiber that uses beechwood pulp and is known for its high wet strength and softness.
Synthetic Fibers: Derived from Petrochemicals
Synthetic fibers are produced entirely from polymers that are chemically synthesized in a laboratory or industrial plant. The raw materials for these fibers are overwhelmingly derived from petrochemicals, which are compounds extracted from crude oil and natural gas. These substances provide the small chemical building blocks, known as monomers, needed to construct the long chain-like molecules of the finished fiber.
The process of joining these small molecules together is called polymerization, which forms the large polymers that constitute the fiber. Polyester, the most commonly used synthetic fiber globally, is a polymer called polyethylene terephthalate (PET). It is synthesized through a chemical reaction between ethylene glycol and terephthalic acid, both of which trace their origins back to petroleum products.
Nylon, a type of polyamide, was the first truly synthetic fiber and is typically manufactured from compounds like hexamethylenediamine and adipic acid for Nylon 6,6. Acrylic fibers, conversely, are built from the polymerization of acrylonitrile monomers.
The Mechanical Process of Fiber Creation
Regardless of whether the polymer is regenerated or synthetic, the final step in creating a usable textile material involves a mechanical process called spinning. The polymer must first be converted into a viscous liquid, either by being dissolved in a solvent or by being melted at high temperatures. This molten or dissolved polymer is then forced through a device called a spinneret, which is a small metal plate containing numerous microscopic holes, similar to a showerhead. As the liquid polymer is pushed through these tiny openings, continuous streams, or filaments, are formed. The method used to solidify these filaments depends on the specific polymer’s properties.
Melt Spinning
In melt spinning, used for materials like polyester and nylon, the molten polymer solidifies simply by cooling in a stream of air.
Dry Spinning
Dry spinning, used for acetate and some acrylics, involves evaporating a volatile solvent by exposing the extruded filaments to warm air.
Wet Spinning
Wet spinning, necessary for polymers that cannot be melted or dissolved in volatile solvents, involves extruding the liquid polymer into a chemical coagulation bath where it precipitates as a solid fiber.