Poly(chloroethene), commonly referred to as PVC (polyvinylchloride)
has been in commercial production since 1933, and now accounts for about
20% of all plastic made, second only to poly(ethene). World production
is in the region of 30 million tonnes, with UK producing 500,000 tonnes.
Structure
The structure of the polymer molecule is very similar to poly(ethene),
with one hydrogen on alternate carbon atoms substituted by a chlorine
atom. The much higher relative atomic mass of chlorine means that chlorine
makes up 56.8% of the pure polymer mass.
Click to find out more about the structure
of PVC
Additives
Pure poly(chloroethene) is unstable when exposed to visible light or
ultra violet, and also needs its properties modifying to make it suitable
for various different applications. Most polymers will in fact contain
many other materials to modify properties. For PVC these may include:
| Anti-oxidants and other stabilisers |
Slow down the rate at which the polymer will
be degraded by oxygen, heat, visible light or UV radiation |
| Compatibilisers |
Enable PVC to be blended with other plastics
with which it would not normally mix (also used to help mixed plastic
recycling) |
| Flame retardants |
Reduce flammability of plastic |
| Pigments |
Colour the plastic |
| Plasticisers |
Make the PVC more flexible and easier to mould
for specific applications |
| Impact modifiers |
Help plastic mouldings absorb shock without damage |
| Fillers |
Inexpensive, inert materials that simply add
bulk to the plastic |
A PVC product may therefore consist of up to 60% additives.
The use of plasticisers leads to
two basic types of PVC:
- Rigid PVC (used for window frames) - PVC-U or uPVC ("unplasticised")
- Flexible PVC (used for flexible medical tubing)
PVC is such a versatile plastic because of its compatibility with many
different additives, though the use of some additives has been a source
of environmental concern
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