Polystyrene is a polymer made from the monomer styrene, a liquid hydrocarbon that is commercially manufactured from petroleum by the chemical industry.
The chemical makeup of polystyrene is a long chain hydrocarbon with every other carbon connected to a Phenyl group.
Expanded polystyrene (Styrofoam) is produced from a mixture of about 90-95% polystyrene and 5-10% gaseous blowing agent, most commonly pentane or carbon dioxide.The solid plastic is expanded into a foam through the use of heat, usually steam.
Pure solid polystyrene is a colorless, hard plastic with limited flexibility. It can be cast into molds with fine detail. Polystyrene can be transparent or can be made to take on various colors. It is economical and is used for producing plastic model assembly kits, license plate frames, plastic cutlery, CD "jewel" cases, and many other objects where a fairly rigid, economical plastic of any of various colours is desired.
When Styrofoam is added to acetone (a common organic solvent) it very rapidly dissolves, making it look like it is disappearing. The melted plastic can be recovered from the acetone to make hard solid Styrofoam plastic (polystyrene). In other words, you don't actually make plastic you just transform an existing form of plastic. The acetone sort of serves as a molecular "lubricant" between the polymer chains, allowing them to slide around each other. The Styrofoam becomes soft, releasing the air bubbles trapped in the foam, and the polystyrene ends up as a soft blob in the acetone. When the blob is removed and the acetone is allowed to evaporate, it solidifies into a piece of hard plastic.
Their are two type of solvents, polar solvents and non polar solvents. Bio-plastics will dissolve in polar solvents like water, while polystyrene will dissolve in non-polar solvents like acetone.
Let's consider two solvents that are pretty different in their polarities in order to explore this topic. Water, which we said is a polar solvent, dissolves almost anything that is polar, such as salt and many other ionic compounds. Water can't dissolve everything, though. Try removing fingernail polish with water and you'll see what I mean. Acetone, a solvent with some non-polar properties, is commonly used to do that job. Acetone is an effective solvent for all sorts of non-polar substances.
The resin identification code symbol for polystyrene, developed by the Society of the Plastics Industry so that items can be labeled for easy recycling, is 6. However, the majority of polystyrene products are currently not recycled because of a lack of suitable recycling facilities.
Hence, even tough this is a petroleum based plastic, you probably are helping the environment since you reuse a plastic that would usually go to waste and that would take thousands of years to decompose.