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Smart Materials - Shape Memory Polymers - Shrink-Wrap.
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.
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 shape 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 stuck 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 is used as
packaging on a large number of
items
including food, CDs, electrical goods
and software.
Shrink-wrap is a good insulator and is also used to cover electrical wiring.
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