Polymers - Properties.
The properties of
a polymer (or any other material) include
strength,
stiffness,
hardness,
density and melting
point.
The properties of a polymer can be changed in a number of ways.
1. Chain length. 2. Plasticizers.
3. Crystallinity. 4. Cross linking.
Chain Length.
A polymer molecule is a long
chain of
(mainly
carbon)
atoms.
The effect on the properties
of increasing the length
of the polymer chain
is similar to the effect of increasing
crystallinity.
The material becomes stronger,
stiffer
and the melting
point gets higher.
Plasticizers.
A plasticizer is a chemical
which is added to a polymer to increase
its flexibility.
The plasticizer gets between the polymer
chains and keeps them further apart
which reduces the forces
of attraction between them and makes the
material
more flexible. The polymer will probably have a reduced
strength and stiffness
because of the plasticizer but it will be more
useful where flexibility
is required.
Some polymers are
available with or without
a plasticizer.
An example is poly(chloroethene) (PVC).
Without a plasticizer
it is often called uPVC where the u
means unplasticized.
uPVC
is rigid and is used to make drain
pipes and window frames.
With a plasticizer
PVC is flexible and is
used to make
all of the other examples on the list of uses
of PVC.
There is a danger that some
plasticizers can get out
of PVC
(called leaching out) and cause harm
to the environment.
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