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It was realised long back that the natural fibres consist of polymers held together by various links or forces. The first step in the development of man-made fibre was the manufacture of regenerated fibre using natural fibrous raw materials. For example, cellulosic materials from plants or trees are regenerated into viscose, which can be spun into yarn.
The next step was to produce chemicals, which have the ability to form links giving rise to polymers called synthetic fibres. It must be realised that only a few of organic chemicals can be used in the production of synthetic fibres. The properties of the polymer necessary for fibre formation are as follows:
The next step was to produce chemicals, which have the ability to form links giving rise to polymers called synthetic fibres. It must be realised that only a few of organic chemicals can be used in the production of synthetic fibres. The properties of the polymer necessary for fibre formation are as follows:
Essential Properties Of Textile Fibre
- Molecular weight - a ploymer should have high molecular weight, which consequently results in considerably longer fibre. The length of polymer contributes to the strength of the fibre by holding crystalline region together. To produce fibre of adequate strength, the length of a polymer molecule in the range of 100 nm is required. Many naturally available cellulosic materials can not be used as textile fibres as they are much shorter in length.
- Linearity - only predominantly linear polymers will form sufficient crystalline regions, permitting an adequate number of inter-chain forces of attraction to occur within the polymer system. The molecular chains, which are bulky and / or branched, can not pack closely enough together to form a crystalline region resulting in a week fibre.
- Inter-fibre forces of attraction - there should be a sufficiant degree of inter-molecular links or bonds of one or more of the following types:
- Hydrogen bonds, which occur between positively charged hydrogen atoms in one polymer molecule and negatively charged oxygen, nitrogen or chlorine atoms in an adjacent polymer molecule. Natural fibres are rich in hydrogen bonds.
- Van der waals forces are similar but weaker than hydrogen bonds. They occur when polar groups are absent. The polymers are to be closely packed so that attraction can occur between slight charges of opposite character in the polymer chains. Both the hydrogen bonds and van der waals forces of attraction are weak, but the presence of these forces in large numbers in case of closely packed polymers significantly contributes to its strength.
- Strongest and chemically most stable covalent bonds or corss-links are formed when any two atoms share a pair of electrons . The greater the number of cross-links, the more rigid the fibre becomes. However, a low degree of cross-links, as in case of wool or elastomeric fibres, imparts a good to excellent elasticity.
- Ionic bonds are formed between oppositely charged polar groups in polymers and are stronger than hydrogen bonds and van der waals forces. They occur principally in protein fibres like wool and silk, and polyamide fibres like nylons.
- Orientation - a fibre consists of a large number of individual polymer chains arranged in either highly ordered form called crystalline region or randomly called amorphous region. In afibre, the extent and proportion of crystalline and amorphous regions mayvary- in natural fibres, the variation is created by nature and in case of man-made fibres, the variation can be controlled during production. In some polumers, the crystalline regions are formed during extrusion and subsequent drawing process merely aligns the crystalline regions parallel to the fibre axis; whereas in other systems, the polymers are first formed in amorphous state and become crystalline fibres have harsh handles and poor abrasion resistance, i.e. quickly damaged on rubbing.
- Melting point - when a polymer is highly crystalline or when the intermolecular attraction between the polymer molecules is strong, its resistance to heat will be high. Most textile fibres are subjected to heat treatment during production or during use. Hence the fibres should have high resistance to heat. Synthetic fibres have specific ranges of temperature during which and the degree of crystallinity of the polymer. Natural fibres do not melt as they have storng inter-chain bonding and long chain-length. However, they turn yellow and are damaged above certain temperature depending on the chemical structure of the fibre.
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