Ask A Scientist Chemistry Archive

Question:  How is plastic made?  Plastic bottles, plastic bags?
 elliot r barenbaum

Answer:
Well, I looked this up in the "McGraw-Hill Concise Encyclopedia of
Science and Technology." (second ed., 1981). Plastics are relatively
stiff materials made of polymers (long molecules made of smaller molecular
units joined together) and other ingredients such as fillers, pigments
(for color), plasticizers, flow improvers, and stabilizers.
The polymers are made by finding small molecules which will chemically
bond together at at least two places in each small molecule (these
are called "active sites"). There are two basic mechanisms for forming
chains out of the smaller molecules, but I won't get into that (unless
you ask me to).
Anyway, let's say you have some plastic and you now want to shape it
into a bottle or something.  There are a number of processes, and you
use whichever process leads to the kind of shape, thickness, and utility
you need for your job.  One way to go is "thermomolding," in which you
form plastic sheets into parts by the application of heat and pressure.
On the other hand, to make a bottle you might use a process called
"blow-molding," in which you form a tube from your plastic material
and use hot gas to force the tube to expand into a mold, forming a hollow
object with a definite size and shape. There are many other possible
processes.
-dr topper