Polymers In Plastics example essay topic

PLASTICS 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, plastic can be classified as either thermoplastics or thermosetting plastics. The difference between the two types is due to their chemical structure, i.e. the way the large chains of molecules are constructed. When heated, the long chains of polymers in thermoplastics are able to move apart and if put under pressure they can slide past each other. This is why thermoplastics can be shaped. Thermosetting plastics cannot be shaped because they have chemical linkages between their long chains of monomers.

These linkages are called crosslinks because they join individual strands of chains in the plastic's structure and are unable to change after polymerization has occurred. Making plastic products involves seven main processes to shape plastics into products. They are (1) moulding, (2) casting, (3) extrusion, (4) calendering, (5) laminating, (6) foaming, and (7) thermoforming. Moulding is a shaping technique in which force is applied to the plastic material during and after it enters the mould.

Casting, unlike moulding, does not depend on any external pressure to shape the plastics. Extrusion is used to produce pipes, rods, fibres, wire coatings, and other products that have the same shape along their entire length. Calendering produces a continuous plastic sheet or film by pressing molten plastics between pairs of polished, heated rollers. Laminating uses plastics to bind together stacks of fibreglass, wood, paper, cloth, or metal-foil sheets. Foaming refers to the steps of melting, shaping, and solidifying. Thermoforming is an inexpensive process used to mould items from sheets of plastics.

The industry of plastics is continually developing or modifying materials to further extend the incredible range of plastics already meeting our needs and enhancing the world's technological progress. However, as useful as they are, plastics do have drawbacks. The biggest problem is that most plastics take a very long time to decompose (break down into simple compounds). Deciding how to dispose of plastic wastes has become a major environmental concern, for consumers of plastic product as well as those who produce it.