Styrene is a chemical derived from petroleum. We most commonly encounter it as a type of plastic. It’s an inexpensive and versatile type of plastic, so it’s been very popular for many decades.
Styrene’s cost effectiveness and relative strength make it a common material in construction and also in the manufacture of consumer goods. With the right prep work and materials, it is easy to glue and paint and repair as well.
Commercial uses of styrene
One of the most common uses of styrene today is for signs. Styrene is easy to produce in thin sheets, it’s reasonably durable, and it’s easy to print on. It’s not as durable as metal, but it’s cheaper and lighter. The small signs sold in hardware stores and that you commonly see in windows are usually made of styrene.
Styrene works well for low strength structural work. It machines well, so it’s very useful for prototyping.
The other place we frequently encounter styrene is foam. Rigid building insulation is usually made of a form of styrene. It works well in that application because it’s easy to work with, highly moisture resistant, and it’s a good insulator of heat. You have probably encountered styrene foam, also called polystyrene foam or styrofoam, as food packaging, such as meat trays, or coffee cups. At one time almost all fast food products came in polystyrene packages, but cost and environmental concerns lessened that use. It kept food hot longer than paper because of its insulating properties, but isn’t biodegradable and is harder to recycle than paper. The higher price of oil also contributed to its decline as food packaging.
History of styrene plastic
Although it didn’t come into widespread use until after World War II, styrene is an old discovery. Eduard Simon discovered polystyrene in 1893, though he didn’t recognize it for what it was. He thought he had discovered a monomer. Herman Staudinger, working decades later, recognized it as a polymer plastic. He published his discoveries in 1922 and won the Nobel Prize in 1953.
Polystyrene’s chemical formula is C8H8. If you remember your high school chemistry, that makes it a long chain hydrocarbon. The hydrogen bonds to the carbon in an alternating pattern. The two atoms have opposite charges, so the attraction is relatively weak. This weak force is one reason why polystyrene is so flexible. Sometimes weakness is strength.
BASF introduced polystyrene for commercial use in 1939. World War II slowed its adoption, partly because the war limited what consumer goods could be produced and sold. After the war ended, the new plastic came into widespread use very quickly, displacing older types of plastic like Bakelite. It was cheaper, easier to work with, easier to repair, and generally more practical than earlier plastics.
It is used in many consumer products, but especially toys. Most of what we call hard plastic toys are polystyrene. Plastic model kits are also usually polystyrene, especially commercially produced kits. Newer plastics that are more durable, softer, and/or less brittle have offset polystyrene in some consumer applications, but nothing has fully displaced it.
Painting and gluing
Not all types of glue work well with plastics, but polystyrene has more options for painting and gluing than many of its alternatives. The right types of glue to use with it depends on its form. For foam, PVA glues such as Elmers work fairly well, since it can absorb into its pores. Glues with solvents in them don’t work so well with foam, because their structure breaks down too quickly. In its more solid forms, the opposite is true. PVA glues are mediocre at best on solid styrene, because it can’t soak into it very well. Glues with solvents in them work very well, because they can weld two pieces together and essentially turn them into one solid piece.
Super glues also work pretty well on polystyrene, depending on how the joint will be stressed. Super glues have extremely good tensile (up-and-down) strength but poor shear strength. If the joint will get uneven pressure or may get twisted, super glue isn’t a good choice. Super glues can work fine for plastic models since plastic model parts often have small pegs and holes for assembly. Those pegs and holes often provide adequate shear strength to compensate for super glue’s weaknesses.
This is why older plastic toys are generally easier to repair than newer ones are. Newer plastics don’t break as easily, but once they do, there are fewer glues you can use on them.
Water-based paints like acrylic and latex work adequately on foam. They work less well on solid styrene because they can’t soak in. Using an oil-based primer helps. Once the primer is dry, acrylic or latex will bond to it pretty readily.
Modern oil based paints are generally formulated to bond with plastic, and work well on styrene. Regardless of the type of paint you use, it’s a good idea to clean them with a good degreaser beforehand, as oils on the surface will interfere with the paint.