Page 34 - Curriculum Visions Dynamic Book

(Left) This is a strip of Kevlar.
(Right) The manufacture of nylon uses melt spinning. Nylon pellets are heated to 265°C
to form a molten polymer solution. This molten solution is forced – extruded – through tiny holes in a spinneret. The solid filaments of nylon produced are treated in a cooling bath and spun into a long yarn of thread and wound onto a reel. Polyester fibre is produced using a similar melt spinning process.
In a few cases very high melting point polymers can have advantages that outweigh their difficulty in manufacture. That is the case with the ring-shaped molecules that are made into materials known under such trade names as Kevlar®. They are used as fire- resistant and bulletproof fabrics as well as stiffening materials in boats and aircraft.
Spinning
The most common way of producing fibres from artificial polymers is to force them in liquid form through the small holes of a metal object that works rather like a showerhead and is known as a spinneret. This is a process of extrusion, and it produces a continuous fibre, or filament.
Liquids are a form of matter in which the molecules can slip easily past one another and so
can readily take on new shapes. In an artificial fibre factory this process is known as spinning. However, it is not at all like the process of spinning natural fibres, in which many short fibres are twisted together to make a yarn.
There are four methods of spinning filaments from manufactured fibres: wet, dry, melt, and gel spinning. More than one process can be used for many polymers. In wet and dry spinning the polymer is dissolved in a liquid solvent, so the solvent has to be removed as soon as it passes through the spinneret. How this is done depends on the solvent. In some cases the solvent has to be reacted with another chemical in order to precipitate the polymer. This is
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