Basics of man-made fibres
Natural and man-made fibres have the following in common:
Natural fibres and man-made fibres are made up of chain molecules. Every molecule in the chain consists of identical chemical elements or combinations of these elements: these are carbon, hydrogen, oxygen and nitrogen.
The starting point is always nature (the sun).
1. Among other substances, sunlight also causes dextrose to be formed in plants, the fundamental building block of the cellulose molecule.
2. Cellulose constitutes the fundamental structure of cotton plants, which are the source of the cotton fibre.
3. Nutrients in food, which are transformed into chemical compounds, are the basis for growth of wool and hair.
4. The silk worm collects a protein depot from its nourishment which is spun to endless threads through its glands.
5. After being treated with chemicals, the short fibres contained in wood are transformed into an aqueous solution and then pressed through spinnerets. After drying, cellulosic fibres are obtained.
6. The raw materials for synthetic fibres generally stem from crude oil, which originates from the transformation of huge quantities of marine organisms.
The main difference between man-made and natural fibres
In contrast to natural fibres, the composition and structure of man-made fibres can be determined by man. This lends man-made fibres special properties and renders them useful for many different purposes.
With the exclusion of ceramic or glass fibers all man-made fibers as well as natural fibers are organic fibers.
Production of spin masses
In order to manufacture man-made fibres, viscous, stringy liquids are needed. The matter that results from dissolving or heating is called the spin mass. Today, three manufacturing processes are primarily used: polymerisation, polycondensation and poly-addition. The resulting spinnable matter from these processes is called a polymer.
Types of man-made fibres
As a rule, a distinction is made between man-made fibres from synthetic polymers and those from cellulosic polymers which both belong to the class of organic fibers. The ACRYLIC-, POLYAMIDE-, POLYESTER- and ELASTANE FIBRES belong to the man-made fibres made from synthetic polymers. In the case of man-made fibres manufactured from cellulosic polymers the distinction is e.g. between the VISCOSE- and the ACETATE FIBRES.
In order to produce filaments (continuous yarns) from the spin mass, various spinning processes are employed: the dry spinning process, the wet spinning process and the melt spinning process. In all cases the spinnable material is pressed through the extremly small openings of a spinneret and upon exiting the spinneret the filaments produced are either gathered to a filament yarn and spooled, or joined to form tows. After spinning the man-made fibres the parallel alignment of the molecules is not yet optimal. Man-made fibres have to be drawn in order to acquire the ultimate properties for the yarns. The extent to which they are drawn depends on their intended use.
Forms of man-made fibres
The spin mass is pressed through the so-called spinnerets. Depending on the number of holes monofilaments (one hole) or multifilaments (several holes) are produced. Depending on the shape of the spinneret holes, different cross section shapes are obtained in the melt spun man-made fibres (from round, multi-lobed, triangular, star shaped to ribbon-shaped). They exert a decisive influence on the properties of the textiles produced from them.
Texturing is a procedure used to increase the volume and the elasticity of a filament yarn. The essential properties of textured yarns and the products made from them are softness, fullness, a high degree of elasticity, thermal insulation and moisture-transporting properties. All yarns which can be shaped by heat are suitable for texturing. The most important texturing processes are FALSE-TWIST TEXTURING, STUFFER-BOX TEXTURING and AIR-JET TEXTURING.
Production of staple fibres
In all spinning processes filaments are formed from the spin mass by the spinnerets. If the production of staple fibres is desired, i. e. short fibre sections for the spinning mill, thousands of filaments are combined to form tow and cut into staple fibres. While during the production of filament yarns each single filament bundle exiting the spinnerets is wound onto a spool, in the production of staple fibres numerous filament bundles are first combined to form a thick filament tow which can be crimped and cut into staple fibres. By cutting the tow, staple fibres are obtained which can be compared in length, e.g. with wool or cotton. Depending on the process used, the tow is either cut directly by the manufacturer and pressed into bales for delivery, or cut or torn into staple fibres using a so-called converter at a later stage by a downstream manufacturer.