Plastics are a type of polymer characterized by the fact that they can be molded with heat. Thermoset polymers are extremely rigid and once molded and hardened cannot be remelted. Thermoplastic materials are softer, more flexible and may be remelted. They are also recyclable.
The first plastics were often based on cellulose. One of the first plastics was developed to take the place of a material in short supply. In 1836, the Phelan and Collender company, makers of ivory billiard balls, sponsored a contest with a $10,000 prize for the inventor of synthetic ivory. John Wesley Hyatt and his brother set out to win the prize. Building on the research of Parkes and Schonbein they formed celluloid out of colloidian in 1875. Although they did not win the prize, the Hyatt brothers founded a company and successfully marketed celluloid. Alexander Parkes (1813-1890) patented his cellulose nitrate material called Parkesine in 1855. The patent was the culmination of years of investigation into rubber and cellulose nitrate solutions. Unfortunately, there was no market for it and Parkes sold the patent to the Hyatts.
Christian Friedrich Schönbein, a German chemist, announced his discovery of guncotton, an explosive, in 1846. He produced the guncotton by treating cotton with fuming nitric and sulfuric acids, a process simultaneously discovered by Bettger and Nikolas August Otto. Another product developed by Schönbein was derived from a solution of guncotton in ether. It was called collodion and was used in medicine and photography.
The first man-made fiber, rayon, was developed by Comte Louis de Chardonnet, a French chemist who devised artificial silk from cellulose nitrate. He began searching for an alternative to silk because an epidemic threatened to wipe out the silkworms in France. In 1884, Chardonnet applied for a patent for extruding cellulose nitrate through very fine glass capillaries. He developed the technique by making a close study of silkworms.
Edward John Bevan, Charles Frederick Cross and Beadle created viscous rayon when they dissolved cellulose in carbon disulfide and aqueous sodium xanthate. The mixture was passed through small holes (or spinerettes) into a dilute acid solution to regenerate the cellulose. The fibers were then spun and woven into fabrics. Jacques E. Brandenberger later developed a process for making films from the mixture, creating a new market-- cellophane packaging.
In 1907, Leo Baekeland, a Belgian chemist, created a substitute for shellac. He had learned that Adolf von Baeyer, when mixing phenol and formaldehyde, had produced an insoluble mass. Baekeland thought that if he could find a solvent to dissolve the material he could use it as shellac. He failed to find the solvent but did end up with a castable, moldable material. He called it Bakelite. It is still used today for automotive applications. Bakelite was the first totally synthetic plastic in that it was not created to replace a natural product.
Around 1907, Frederic Stanley Kipping, a British chemist, prepared the first silicone in an attempt to produce double-bonded silicon compounds from simple carbon compounds. Nearly forty years after Ripping's research, Rochow discovered the method for obtaining silicones rapidly. Further research by Patnode of General Electric and Hyde of Dow Corning showed that treating silicones with acid produced an intermediate which could be polymerized using acid or basic catalysts. Silicon oils, resins, and elastomers were produced in great quantity during World War II.
Hermann Staudinger (1881-1965), a German chemist, began his study of macromolecules with rubber, a natural elastomer. He was one of the first to express the belief that covalent bonds were the integral bonds in large molecules. Staudinger and his research group began a systematic investigation into the formation of polymers. They succeeded in proving that polymers are chain molecules with normal valance bonds, terminated by characteristic groups. These terminating groups may be used to determine the length of the chain. Staudinger's research into condensation reactions proved that the polymerization requires the activation of a monomer, which in turn attracts other monomers. Staudinger laid much of the foundation for modern polymer science and he was awarded the Nobel Prize in chemistry in 1953.
Wallace Carothers, an American chemist conducting research at DuPont, confirmed Staudinger's view of polymers and distinguished between addition and condensation reactions. Carothers went on to develop nylon in 1938. His research group also developed cold drawing--a technique that straightened the polymer chains and greatly increased the strength. Dickson and John Rex Whinfield, British chemists, picked up the research where Carothers left off and went on to develop Polyesters in 1941. Polyesters also benefit from cold drawing.
Research conducted by Karl Ziegler and Giulio Natta resulted in the production of high density polyethylene and polypropylene. They also discovered the organometallic and stereospecific catalysts that revolutionized the plastics industry by making room temperature and low pressure polymerization possible.
Plastics are often formed into powders or pellets before they are processed. A few may be in liquid or sheet form. Injection molding, blow molding, casting, foaming, thermoforming, laminating, extrusion and cold drawing are just a few of the ways plastics are processed. The choice of processing technique depends on the composition and state of the plastic and the type of end product being manufactured.
While plastics have greatly simplified some production processes and led to inexpensive substitutes for natural products, they have also created other problems. Plastics do not biodegrade quickly--some apparently do not degrade at all. This quality helps them last, but makes them difficult to dispose of once they have outlived their usefulness. To some extent, recycling has helped reduce this problem. Additionally, scientists have developed new polymers and additives that help the plastics breakdown more readily when they are discarded.
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