The production of synthetic man-made fibers is carried out in two sub-steps:
1) Synthesis of reactive precursors. These consist of individual small molecules, the monomers.
Petroleum is the main raw material for their production.
2) Linking thousands of small molecules to form macromolecules. Because macromolecules are formed from many individual molecules, they are called polymers. Three different chemical reactions are distinguished in the polymer formation of synthetic man-made fibers: Polymerization, polyaddition and polycondensation.
3) The spinning mass is produced from the polymers, e.g.in the form of granules or powder.
The spinning mass coming out of the nozzle solidifies to the fiber inside of which the molecular chains are still disordered. Drawing, which is possible during spinning or in a separate process, makes the man-made fibers thinner and aligns the chain molecules in the longitudinal direction of the fiber. In addition to the amorphous areas, crystalline areas are also formed, as well as cross bridges between the individual molecular chains, which provide the necessary strength.
A distinction is made between three different spinning processes to produceman-made fibers: Wet and dry spinning processes -where the starting materials are liquefied by dissolving the spinning mass, and the melt spinning process, where the starting materials are melted. After the filaments have left the spinneret and solidified, drawing takes place by drawing at higher speeds or in a downstream process. The size of the nozzle hole as well as the drawing influence the fineness of the fiber.
The outlet opening of the spinneret can be made round or in other cross-sectional shapes as required. This allows the fiber cross-sections to be designed differently. Depending on the fiber cross-section and possible addition of matting agents such as TiO2, shininess, haptic and strength are influenced. It is also possible to spin two polymers with different properties in one die as bicomponent fibers.
The “endless” long spun man-made fibers are called filaments. If the spinneret has only one orifice, the result is a monofilament. The filaments of a multi-hole nozzle together are called multifilaments. Thermoplastic multifilaments can be textured, i.e.,permanently crimped. Monofilaments processed in filter cloths or belts ensure optimal, quick and easy cake removal. The use of multifilaments increases the filtration efficiency and mechanical resistance. Staple fiber yarns optimize the particle separation, but have a poorer cake release behavior.
According to the formation of macromolecules from small molecules, synthetic man-madefibers can be divided into fibers formed from polymerization, polycondensation and polyaddition products.