5. Polystyrene – It is a synthetic aromatic hydrocarbon polymer made from the monomer known as styrene. Chemical formula (C8H8)n
Polystyrene plastic contains only carbon and hydrogen. Burning it produces only carbon dioxide CO2 and water H2O. Example: Styrofoam.
Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and brittle. It is an inexpensive resin per unit weight. It is a poor barrier to oxygen and water vapor and has a relatively low melting point.
Polystyrene is one of the most widely used plastics, the scale of its production being several million tons per year. Polystyrene can be naturally transparent, but can be colored with colorants. Uses include protective packaging (such as packing peanuts and in the jewel cases used for storage of optical discs such as CDs and occasionally DVDs), containers, lids, bottles, trays, tumblers, disposable cutlery, in the making of models, and as an alternative material for phonograph records.
As a thermoplastic polymer, polystyrene is in a solid (glassy) state at room temperature but flows if heated above about 100 °C, its glass transition temperature. It becomes rigid again when cooled. This temperature behavior is exploited for extrusion (as in styrofoam) and also for molding and vacuum forming, since it can be cast into molds with fine detail.
Under ASTM standards, polystyrene is regarded as not biodegradable. It is accumulating as a form of litter in the outside environment, particularly along shores and waterways, especially in its foam form, and in the Pacific Ocean.
6. Polyurethane often abbreviated PUR and PU – It refers to a class of polymers composed of organic units joined by carbamate (urethane) links.
A carbamate is a category of organic compounds that is formally derived from carbamic acid (NH2COOH).
Burning polyurethane (which contains nitrogen) produces nitrogen oxides, aside from carbon dioxide and water. Most nitrogen oxides have short half lives in the atmosphere, except for nitrous oxide (N2O).
In contrast to other common polymers such as polyethylene and polystyrene, polyurethane is produced from a wide range of starting materials (monomers) and is therefore a class of polymers, rather than a distinct compound.
This chemical variety allows for polyurethanes with very different physical properties, leading to an equally wide range of different applications. These include: rigid and flexible foams, varnishes and coatings, adhesives, electrical potting compounds, and fibers such as spandex and PUL. Of these, foams are the largest single application, accounting for 67% of all polyurethane produced in 2016.
Polyurethane polymers are traditionally and most commonly formed by reacting a di- or triisocyanate with a polyol. Since polyurethanes contain two types of monomers, which polymerize one after the other, they are classed as alternating copolymers. Both the isocyanates and polyols used to make polyurethanes contain, on average, two or more functional groups per molecule.
Global production in 2019 was some 25 million metric tons, accounting for about 6% of all polymers produced in that year. This is a sufficiently high volume for it to be regarded as a commodity plastic.
7. Polycarbonates (PC) – These are a group of thermoplastic polymers containing carbonate groups in their chemical structures. Chemical formula C15H16O2.
Polycarbonates plastics contain only carbon and hydrogen and oxygen. Burning it produces only carbon dioxide CO2 and water H2O.
Polycarbonates used in engineering are strong, tough materials, and some grades are optically transparent. They are easily worked, molded, and thermoformed. Because of these properties, polycarbonates find many applications. Polycarbonates do not have a unique resin identification code (RIC) and are identified as “Other”, 7 on the RIC list. Products made from polycarbonate can contain the precursor monomer bisphenol A (BPA).
Bisphenol A (BPA) is a chemical compound and one of the simplest and best known bisphenols. (To be continued)/PN
