Why can't you drink coffee from a Styrofoam cup?
Because there is no such thing. Styrofoam is the registered trademark of Dow Chemical Corp., covering their range of extruded, foamed polystyrene materials. Dow sells the material into two main applications: insulation for buildings, in which genuine Styrofoam is always blue, and the hobby and crafts market, where it might be blue, green or white.
If you drink coffee from a cup made of expanded polystyrene, then, according to Dow, it is not Styrofoam (which is always extruded) but some other brand, and the cup will have been moulded.
Here is what Dow says on the subject (http://www.dow.com/craft/about/cup.htm):
STYROFOAM* is a registered trademark for a line of extruded polystyrene foam products made exclusively by The Dow Chemical Company. STYROFOAM Brand Foam are often Blue* in color and used as insulation, except in the Floral and Craft markets, where STYROFOAM Brand Foam is white or green.
STYROFOAM Brand Foam is not used in the manufacture of disposable foam products, such as food packaging, cups, plates, coolers or egg trays. These disposable products are made of either molded expanded polystyrene beads or thin extruded polystyrene sheet, neither of which is manufactured by Dow in the United States.
In the same way that Hoover became a synonym for vacuum cleaner, Biro became a synonym for ballpoint pen and Neoprene became a synonym for synthetic rubber, Styrofoam is in the process of entering the language as a synonym for expanded or foamed polystyrene. Dow wants to keep its well-known trade name for its own use and is fighting back, albeit without much success. The word Styrofoam has become too popular.
Since most people now think of Styofoam as being another word for expanded, or foamed polystyrene, I guess we ought to say something about that.
Expanded polystyrene
Polystyrene is a hard thermoplastic polymer, most often used in its foamed form, or in a blend or a copolymer with other materials. This writeup concerns the foamed product.
Styrene, the monomer, is a fairly common chemical building block made originally from crude oil and used in many different types of thermoplastic. Chemically speaking, it is phenylethene - a benzene ring with one hydrogen replaced by an ethenyl radical. (Thanks HexFailure). Polystyrene is a long chain of styrene (phenylethene) monomers linked up to form a large molecule. The backbone of the polymer is formed by radical polymerization of the ethene. to form -(CH2-CHR)- (where the R signifies a phenyl-group). (Thanks Professor Pi)
Foamed polystyrene is made in a fairly standard process. It starts out as beads of solid polystyrene, mixed with a blowing agent. These are warmed in steam and as they warm up, the steam softens the thermoplastic and the blowing agent expands dramatically in volume to create the foam. During this phase, the beads increase in size by a factor of between 20 and 60.
The next phase is critical in that the blowing agent is removed from the bubbles and replaced by air. In many factories, the blowing agent is recovered to be re-used in the subsequent manufacturing operations. During this phase the newly expanded beads stabilise and the walls of the foam cells stabilise and strengthen.
Historically the bowing agent was often a chlorofluorocarbon, but since the Kyoto Protocol, most manufacturers have replaced CFCs with HCFCs, which offer around 1/16th of the ozone depletion potential.
Finally, the beads are brought together in a mould or extrusion die, again at an elevated temperature, so that the individual beads fuse together into the desired shape. Extrusion processes are much cheaper, but can be used only to create shapes with a constant cross-section (blocks, cylinders, pipes and suchlike). The moulding process can make any shape you like: a cup, or the packaging for a computer monitor, but is a little more expensive.
The end result is a very light product with excellent thermal insulation properties.
sources / further reading
- http://www.epsrecycling.org/
- http://www.dow.com/craft/about/cup.htm
- http://www.styrofoam.com/