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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
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
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 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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