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Published online by Cambridge University Press: 05 May 2013
Introduction
The man-made and the natural environment surrounds man with a wide array of plastics and polymers both natural and man-made. A polymer is a molecule which contains repeated units of a particular chemical base segment, and there are many types found across organic chemistry. A plastic is a term that covers a wide range of mostly synthetic but also some natural organic products that can be moulded or extruded. Thus while all plastics are organic polymers, not all polymers are plastics and in general may need to be modified with other additives to form useful materials. In everyday parlance plastic and polymer are terms often used interchangeably but in fact there are many other types of molecules, both biological and inorganic, that are also polymeric.
The word polymer has ancient Greek roots, compounded from poly (meaning many) and meros (meaning parts or units), whilst plastic has a root that indicates a solid that is malleable being easily shaped or moulded. Natural plastics may originate in biological systems such as tar and shellac, tortoise shell and horns, as well as tree saps that produce amber and latex. These plastics may be processed with heat and pressure into a host of different products. If natural polymers are chemically modified then other plastics result and during the 1800s these processes produced such materials as vulcanised rubber and celluloid. In 1909 a semi-synthetic polymer was produced called Bakelite, soon followed by fibres such as rayon (1911). The ability to work and particularly to cast or mould them to component shapes made plastics increasingly dominant for manufacturing. However, restrictions on supply of natural materials during the Second World War led to the modern predominance of synthetic plastics. This time period saw development of nylon, acrylic, neoprene, polyethylene and many more to replace the natural products that could no longer be imported. Post-war the plastics business has developed into one of the fastest growing industries in the world.
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