Page 37 - Curriculum Visions Dynamic Book

they can all be lined up and brought close together, they will be much stronger. So, after the fibre has been spun, it is often pulled, or drawn. This causes the molecules in it to line up and move closer. Some fibres become several times their spun length during this process. Once they have all closed up, the fibre will not draw out any further. Fibre for tyre cord is made this way.
Giving a synthetic fibre a texture
Synthetic fibres are long filaments. But they can be given quite different feels by processing further. For example, a fibre that will be spun into yarn and used as a substitute for wool needs to look as wavy as wool. This waviness is called crimping. Crimping is produced by passing the fibre through intermeshing wheels like gear wheels. Crimping can also be produced during spinning by extruding together two different polymers so they join as they leave the spinneret and before they solidify. Then, when the fibre is drawn, one polymer will pull out more than the one it is joined to, and this will make the fibre form into a spiral.
Yet another way is to twist two fibres together as they come from the spinneret, wait for them to cool so the twist is set in the fibre, then untwist them.
Dyeing artificial fibres
For natural fibres the dyeing process is all very straightforward. However, synthetic fibres tend to be
more difficult to dye with natural dyes than natural fibres because they naturally repel water. This is
especially the case with rayon, PET, and acrylics.
(Left) Fibres are widely used in tyre manufacture to support the rubber and help give the tyre its strength. Different fibres are used in the tread (where considerable elasticity is needed) and
in the walls (where the amount of elasticity required is much smaller). Rayon and nylon are common tyre fibres.
See Vol. 6: Dyes, paints, and adhesives to find out more about the dyeing process.
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