Plastics are man-made materials that can be shaped into almost any form. They are one of the most useful materials ever created. Our homes, schools, and businesses are filled with plastic products. Imagine cars without synthetic bumpers, dashboards, steering wheels and switches; medicine without plastic hypodermic syringes and artificial hip joints. And what about telecommunications, dependent on plastic telephones, circuit boards and cable insulation. Our entertainment and leisure relies on the unique combination of characteristics offered by plastics in sports equipment and clothing, CDs, video and audio tape, television and cinema.
Most plastics are lightweight, flexible, durable and often colorful. They are resistant to chemicals, have hygienic surfaces, and provide insulation from electricity or heat. There are many types of plastics, each exhibiting some of these properties and characteristics. They also have their own individual strength and weaknesses. For example, the characteristic strength of nylon is well suited to producing clothing, fishing line or machine bearings, whereas if you tried to use the plastic Bakelite for the same function you would find it quite useless.
To understand how plastics are made, it is helpful to know something about the chemistry of polymers. The polymers in plastics are made up of small molecules called monomers. Most of these molecules are composed of carbon, hydrogen, nitrogen, and oxygen atoms. Some include chlorine, fluorine, silicon, or sulfur atoms. A polymer chain consists of hundreds, thousands, or even millions of monomer links. In some polymers, these links are made up of the same kind of monomer, repeated over and over again. Others are composed of two or more kinds of monomers, which may be linked randomly or in alternating sequences. In some polymers, blocks of one kind of monomer are joined to blocks of another kind.
Generally, plastics can be classified as either thermoplastics or thermosetting plastics.