HISTORY OF PLASTICS

Humankind has been using natural plastics for thousands of years. For example, the early Egyptians soaked burial wrappings in natural resins to help preserve their dead. People have been using animal horns and turtle shells (which contain natural resins) for centuries to make items such as spoons, combs, and buttons.

During the mid-19th century, shellac (resinous substance secreted by the lac insect) was gathered in southern Asia and transported to the United States to be molded into buttons, small cases, knobs, phonograph records, and hand-mirror frames. During that time period, gutta-percha (rubberlike sap taken from certain trees in Malaya) was used as the first insulating coating for electrical wires.

In order to find more efficient ways to produce plastics and rubbers, scientists began trying to produce these materials in the laboratory. In 1839 American inventor Charles Goodyear vulcanized rubber by accidentally dropping a piece of sulfur-treated rubber onto a hot stove. Goodyear discovered that heating sulfur and rubber together improved the properties of natural rubber so that it would no longer become brittle when cold and soft when hot. In 1862 British chemist Alexander Parkes synthesized a plastic known as pyroxylin, which was used as a coating film on photographic plates. The following year, American inventor John W. Hyatt began working on a substitute for ivory billiard balls. Hyatt added camphor to nitrated cellulose and formed a modified natural plastic called celluloid, which became the basis of the early plastics industry. Celluloid was used to make products such as umbrella handles, dental plates, toys, photographic film, and billiard balls.

These early plastics based on natural products shared numerous drawbacks. For example, many of the necessary natural materials were in short supply, and all proved difficult to mold. Finished products were inconsistent from batch to batch, and most products darkened and cracked with age. Furthermore, celluloid proved to be a very flammable material.

Due to these shortcomings, scientists attempted to find more reliable plastic source materials. In 1909 American chemist Leo Hendrik Baekeland made a breakthrough when he created the first commercially successful thermosetting synthetic resin, which was called Bakelite (known today as phenolic resin). Use of Bakelite quickly grew. It has been used to make products such as telephones and pot handles.

The chemistry of joining small molecules into macromolecules became the foundation of an emerging plastics industry. Between 1920 and 1932, the I.G. Farben Company of Germany synthesized polystyrene and polyvinyl chloride, as well as a synthetic rubber called Buna-S. In 1934 Du Pont made a breakthrough when it introduced nylon—a material finer, stronger, and more elastic than silk. By 1936 acrylics were being produced by German, British, and U.S. companies. That same year, the British company Imperial Chemical Industries developed polyethylene. In 1937 polyurethane was invented by the German company Friedrich Bayer & Co. (see Bayer AG), but this plastic was not available to consumers until it was commercialized by U.S. companies in the 1950s. In 1939 the German company I.G. Farbenindustrie filed a patent for polyepoxide (epoxy), which was not sold commercially until a U.S. firm made epoxy resins available to the consumer market almost four years later.

After World War II (1939-1945), the pace of new polymer discoveries accelerated. In 1941 a small English company developed polyethylene terephthalate (PET). Although Du Pont and Imperial Chemical Industries produced PET fibers (marketed under the names Dacron and Terylene, respectively) during the postwar era, the use of PET as a material for making bottles, films, and coatings did not become widespread until the 1970s. In the postwar era, research by Bayer and by General Electric resulted in production of plastics such as polycarbonates, which are used to make small appliances, aircraft parts, and safety helmets. In 1965 Union Carbide Corporation introduced a linear, heat-resistant thermoplastic known as polysulfone, which is used to make face shields for astronauts and hospital equipment that can be sterilized in an autoclave (a device that uses high pressure steam for sterilization).

Today, scientists can tailor the properties of plastics to numerous design specifications. Modern plastics are used to make products such as artificial joints, contact lenses, space suits, and other specialized materials. As plastics have become more versatile, use of plastics has grown as well. By the year 2005, annual global demand for plastics is projected to exceed 200 million metric tons (441 billion lb).

Date: 2015-01-02; view: 856