Page 32 - Curriculum Visions Dynamic Book

There is little or no difference between the chemistry of the materials used to make synthetic fibres and those used to make
any kind of plastic. It is simply that in the case of synthetic fibres, the molecules are made into long, flexible strands without interlinked branches.
Once made into fibre, synthetics can be used in the same way as natural fibres. The big advantage of many synthetic fibres is that they resist the rotting and attack
by insects that beset natural fibres. They can also be designed to have particular characteristics.
Polyester or polyethene terephthalate (PET, PETE) are now the main synthetic fibres, accounting for more than half of worldwide production.
Characteristics of artificial
fibres
All artificial fibres are polymers. The differences between the many kinds of fibres lie in the shape of the polymer chains and the materials from which they are made. For example, some chains remain long and straight, while others develop branches along their length.
Many polymers are unsuitable for making into fibres because they develop interlinked branching networks of molecules that stop them from being strong when made into fibres. That is why, for example, no fibres are made of polystyrene. Only single chain polymers can be used for fibres.
An important property of single-chain synthetic polymers is that on heating, they will soften and eventually become molten.
(Below) Synthetic fibres such as nylon
can be made in a beaker in the laboratory using two chemicals. Hexanedioyl
chloride is poured carefully onto hexamethylenediamine. The chemicals react across the surface where they touch. The white precipitate is the nylon forming.
(Right) The nylon has to be carefully teased from the liquids at a constant rate to produce a filament. Of course, this process can only continue while enough of the chemicals remain to react. This is called batch processing. For industrial use a more continuous way of producing a filament
is used. Solid nylon pellets are melted
and then extruded through a spinneret to produce a controlled filament (see page 35).
See Vol. 1: Plastics to find out more about the chemistry of plastics.
Hexanedioyl chloride
Hexamethylenediamine dissolved in water
Here you can see the nylon forming at the interface between the two liquids.
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