Plastic Materials

Plastic Materials

A plastic substance is one that can be molded to any desired shape. In this sense, common clay is a plastic. For most purposes, a plastic is widely useful only if, after being molded, it can be hardened so as to retain its shape. Clay is hardened by baking.

But the term "plastics" has been more narrowly defined in modern industry, as will be explained later. It now refers to certain artificial substances. But the great utility of plastics was shown long ago, when natural rubber first began to be used in industry. Rubber is a "natural plastic." It can be molded while soft, then hardened, and it can be given a variety of properties as to hardness, toughness, and so on, by mixture with different kinds and amounts of chemicals. It is, for example, "vulcanized" or made hard by the addition of sulfur. Hard rubber has long been used for electrical insulation, instrument panels, casings; we all know how vital rubber is in the manufacture of automobile tires; the very name "rubber" came from the use of soft rubber to rub out pencil marks.

Curiously enough, although this natural plastic, the sap of a tropical tree, has long been used, it was only recently that scientists began to make artificial plastics.