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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.

Plasticizer in Polymer Chains

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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