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Plastics Made Simple
name Alexandria M.
status student
age 7
Question - How do you make plastic? (In words my 7 year old can understand)
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Alexandria,
Most plastics are made by joining little molecules (monomers) together to
make bigger molecules (polymers). The properties of the reactants (the
starting materials) are very different from those of the product molecules.
1. You could use a modified version of the above to explain how an epoxy
resin sets up. Purchase some two-component epoxy from the automotive
department of a Wal-Mart (or the like) and make mixtures -- both according
to and in contradiction to the package directions. Properly done, the
result will be a very hard plastic quite unlike the original two
components. Those mixtures wherein you didn't follow the directions will
not set up hard because one or the other of the necessary components was in
short supply. Do take care to not allow the child to contact either
component of the original components or the failed mixtures. It is safe to
touch the hardened result of the correct mixture.
2. Of course, you could simply burn a little sugar in an old tin can. The
black, bitter-tasting residue is a sort of polymer of decomposed and
partially decomposed sucrose molecules. You could demonstrate that the
original sugar (the little molecules) will dissolve in water, whereas the
polymeric goop resulting from the heating will not dissolve because its
molecules are too large.
Because of the vast differences in the chemistry operative in the two
experiments outlined above, neither component of the epoxy, or the
resulting resin, will dissolve in water.
Regards,
ProfHoff
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Plastics are a type of polymer ("poly -- mer" literally means "many --
units") from the Greek words. Every molecule has a certain weight (mass)
depending upon the number and weight of the atoms that make up the
molecule -- usually less than 1000 for most molecules. Because a polymer is
made up of many, many units, it has a very high molecular weight -- many
thousands. Often the units (the "--mers") are often strung together in long
strands. You can think of them as long thin strings of spaghetti. These
strands become entangled, just like spaghetti does, and it is the tangling
that gives plastics their toughness. Just like it is difficult to separate
single strands of spaghetti, it is difficult to untangle polymer molecules.
Because there are many different chemical units that can form these polymers
they have a wide range of properties. Chemists who study polymers design the
polymer to have a desired set of physical and chemical properties.
I hope this gives a start without getting too complicated -- the spaghetti
analogy is a good one to use. It gives a pretty accurate qualitative picture
of polymers, but that requires a whole other platform for discussion.
Vince Calder
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NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators.
Argonne National Laboratory, Division of Educational Programs, Harold Myron, Ph.D., Division Director.