The polystyrene is the styrene polymer. It is an aromatic thermoplastic polymer with a linear structure. At room temperature is a glassy solid; to above its glass transition temperature, about 100 °C, acquires plasticity and is able to flow; it begins to decompose at a temperature of 270 °C.
The expanded polystyrene looks like a very light white foam, often molded into pellets or chips, and used for packaging and insulation. Chemically inert to many corrosive agents, it is soluble in chlorinated organic solvents, in trichlorethylene, acetone and in some aromatic solvents such as benzene and toluene.
Polystyrene was discovered for the first time in 1839 by Eduard Simon, an apothecary in Berlin. He distilled an oily substance from the resin of Liquidambar orientalis, obtaining a monomer that he named styrol, inspired by the German
resin Styrax. A few days later, he noticed that the monomer had turned into a jelly and gave it the name of Styroloxyd (styrene oxide), thinking it was a product of oxidation. In 1845, chemists John Blyth and August Wilhelm von Hofmann showed that the same transformation of styrene could occur in the absence of oxygen, called their substance metastyrene
and was later shown that the substance was identical to Styroloxyd. In 1866, Marcellin Berthelot correctly identified the process as a polymerization reaction.
The non-expanded polystyrene has a density of about 1050 kg / m3, while it ranges from 15 kg / m3 to 100 kg / m3 in the expanded form. It is transparent, hard and rigid. It also has discrete mechanical properties and is resistant to many chemicals watery. It is also an excellent insulator for electrical capacitors, and is virtually not hygroscopic.
It can be easily colored, both with either opaque or glossy hues. The addition of the color can be made at the time of molding, by adding the pigment directly into the mold, or before molding, by incorporating the pigment in the mass of the first polymer to reduce it to chips for molding.
The polystyrene is used in many industries for its mechanical and electrical properties. For example, is used as material for the creation of models in place of the wax in casting foundry processes (lost foam). The advantage, respect to the wax that must be dissolved and go out from the mold, is that the polystyrene, in contact with the molten metal, sublimates leaving the empty cavity. It is also widely used for insulation systems, thanks to its excellent thermal insulation capacity when it is in expanded form. The food industry produces many types of polystyrene glasses, dishes, trays and pans, cutlery.
It is increasingly widespread the use of disposables made of polystyrene to serve drinks and snacks to refreshments, as takeaway container for delis. The extruded polystyrene is also available in crystallized form that is transparent and rigid while the simple extrusion leads to the realization of a product not transparent and less rigid. A further technological evolution is represented by the bi-oriented polystyrene (OPS) which has a pleasant and high transparency in addition to having considerable rigidity.
The oriented polystyrene is used for the realization of airtight trays for foods (typical use in the bench fresh food for the exposure of the pre-packaged product or for removal).
Various containers used for the maintenance of the temperature are made of polystyrene foam (containers for hot drinks to taste, packaging for the transport of fresh and
frozen fish etc.). The polystyrene can’t be used as a container for the reheating of the food or in the microwave oven or conventional oven.
Only the polystyrene foam is able to withstand negative temperatures and is therefore suitable for freezing food.