The History of Polystyrene
How the Widely Used Expanded Packaging Material was Developed
Jun 17, 2009
Polystyrene was accidentally discovered by a German apothecary, called Eduard Simon, in 1839, as recorded on the website of the Plastics Historical Society. When his newly discovered chemical “Styrol” which was an oily substance he had isolated from a natural resin, hardened after a few days, he assumed it had oxidised. In 1845, English chemist John Blyth and German chemist August Willhelm von Hoffmann proved that the same reaction took place in the absence of oxygen, showing that it was not oxidation.
Stabilising the Monomer
Then, in 1866, Marcelin Berthelot demonstrated that the hard material was actually a polymer. The problem was that the monomer was too unstable and tended to turn into the polymer before it should, preventing useful application of polystyrene, as it came to be known in the mid-twentieth century. A step forward was taken in 1922 when Dufraisse and Moureu found that the monomer could be stabilised by adding small amounts of aromatic amines and phenols. This led to the use of the reaction to study the mechanism of polymerisation through the 1920s.
Commercial Manufacture
Eventually, work by Herman Staudinger and Carl Wolff enabled the I.G Farben company in Germany to begin the commercial manufacture of polystyrene in 1931. They developed a reactor vessel which extruded polystyrene through a heated tube and cutter, producing the polymer in a pellet form which is much easier to use.
Wide Usage of Polystyrene
The polymer is hard and colourless and can be cast into moulds with very fine detail. In this form it is used for economical, rigid plastic items, such as plastic model assembly kits, plastic cutlery, and CD cases. Butadiene/styrene co-polymers can be used to produce synthetic rubber, and this was used extensively during the Second World War.
Its main use now, of course, is in its expanded form. This form is produced by heating a mixture of polystyrene and a gaseous blowing agent like pentane or carbon dioxide, using steam, to make a foam, which is then cooled to make the material most commonly associated with the name polystyrene.
The bubbles of trapped air in the material give it very low thermal conductivity, which make it useful as an insulation material in building applications. It is used for many types of packaging where fragile material needs protection from impact damage.
Environmental Impact
Unfortunately the widespread use of expanded polystyrene is not all good news. The polymer does not bio-degrade, and its light weight means that it floats on water and is blown by the wind, causing a serious problem of litter in the countryside and being washed up on beaches. It is possible to recycle waste expanded polystyrene, by using it in the manufacture of more polystyrene, although facilities for this activity are not readily available to most consumers.
 |
