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Smart Materials - Shape Memory Polymers - Shrink-Wrap.

What are Smart Materials?

Smart materials have properties that change in response to
their environment.
Smart materials include hydrogels,
packaging, shape memory alloys and shape memory polymers.
An example of a shape memory polymer is called shrink-wrap.

What is Shrink-Wrap?

A number of thermosoftening polymers including
PVC and poly(ethene) can be used to make shrink-wrap.
Shrink-wrap is made at a temperature high enough
for the polymer to be soft and floppy like a thick liquid.
The molecules in the thick liquid are in a randomly coiled
like a tangled ball of string. The polymer is
rapidly stretched as it cools down to form a thin clear film.
The molecules become stretched out in the film and get
trapped in this stretched shape as it cools from liquid to solid.

When the film is heated the molecules suddenly return
to their coiled shape and the film
shrinks to wrap itself tightly around the object.

Shrink-wrap showing Stretched and Coiled Molecules

Shrink-wrap is used as packaging on a large number of items
including food, DVDs, electrical goods and software.

Shrink-wrap is a good insulator
and is also used to cover electrical wiring.

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