Plastics

Thomas Edmunds

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