Polystyrene: The Pros, the Cons, the Chemistry

Here's a riddle for you: What material can be found in the grocery store, under the road and in the hospital? Give up? The answer is polystyrene! Polystyrene is everywhere. In its expanded foam state, polystyrene can be found in coolers, materials used in road construction, and to package everything from computers to food. The most common and recognizable form of polystyrene is called Styrofoam. In its compact form, it is used as a material to make things like bottles, disposable cutlery, toys, car parts, and many more objects that we use every day.

Misconception Alert

Many people refer to the expanded foam state of polystyrene as Styrofoam. However, Styrofoam is a brand name. 

So, what is it that makes polystyrene so useful for so many different things? To answer this question, let’s look at its chemistry. 

What is the chemical structure of polystyrene?

Polystyrene is a plastic. As its name suggests, it is made up of many ("poly") styrenes. Styrene is a small organic compound with the chemical formula C₆H₅CH=CH₂. Styrene is also known as vinylbenzene. That’s because it has a vinyl (-CH=CH₂) functional group attached to a benzene ring (C₆H₆).

Did you know?

Styrene is named for storax balsam, which is an oily resin produced by sweetgum trees (Liquidambar styraciflua). 

Styrene is a clear, colourless liquid. When it is heated, the individual molecules (monomers) join together to form long chains. Long chains of repeating monomers are called polymers. 

When lots of styrene chains get mixed together, they get tangled up and make a strong, interconnected mesh. This is polystyrene. When you were a kid, did you ever play the game Barrel of Monkeys? It makes a good analogy for polymer chains. Each individual monkey, with its two hooked arms, are like styrene molecules. On their own, they don't do much. But if you hook their arms together, they will form a chain -- similar to a polymer chain. Then, if you toss them back in their barrel, they'll get tangled up and be more difficult to pull apart -- just like polystyrene! 

What are the properties of polystyrene?

Polystyrene exists in two main forms: as a solid or as a foam. As a foam, its two forms are expanded polystyrene (EPS) and extruded polystyrene (XPS). Expanded polystyrene is commonly used in packaging. Extruded polystyrene (XPS) is commonly used in architectural models.

Did you know?

Styrofoam was discovered by accident in 1954 by Dow Chemical Co. chemist Ray McIntire while he was trying to find a flexible electrical insulator.

This chemical structure of polystyrene gives it valuable properties, such as low weight and high strength. It is easy to make things with because it is a thermoplastic. Thermoplastics will fully become a liquid when they reach their melting point. When the thermoplastic is cooled, it becomes a solid again. This is a valuable property, as the process can be repeated several times. 

Did you know?

The melting point of polystyrene is between 210°C and 249°C.

Polystyrene is known for another property that is both useful and bothersome. Like many other plastics, polystyrene is very stable. In other words, it hates to react chemically. You could say that it’s happy just the way it is. 

You can leave polystyrene outside. You can expose it to harsh chemicals. It will stay just like the day you made it. As we’ll see, this can be both a good thing, and a bad thing.

How do you dispose of polystyrene?

Chemical stability is a good thing when making products that you want to last for a long time, like cell phones, food packaging, and medical supplies.

But what about those products we don’t need to last a long time? When we are finished with our polystyrene food containers, syringes, or cutlery, what do we do with them? If we put them in the trash, they become solid waste in a landfill. And remember, polystyrene doesn’t like chemical reactions. That means these items will happily sit in that landfill for hundreds or thousands of years. 

Recycling polystyrene is possible. First, it is shipped to a recycling facility, where it is sorted and cleaned. Next, the polystyrene is shredded into tiny pieces.Then, it is exposed to heat, which causes it to melt into a paste. The paste is compressed and dried into pellets or blocks before it is shipped to another facility. There, it is made into new products.  

Did you know?

The recycling number of polystyrene is 6.

Unfortunately, this process is expensive and difficult. Because of this, recycling polystyrene is uncommon. In particular, the foam form of polystyrene is seldom recycled. It is inexpensive to make. Also, it is so lightweight that shipping companies don’t find it cost-effective to ship to a recycling centre. Plus, when polystyrene is used to store food or drinks, it is often too contaminated to reuse. That’s because the organic particles stick into the foam.

The most common ways of disposing of polystyrenes are to bury or burn it. When done correctly, burning is an effective method of disposal. The only waste byproducts are carbon dioxide, water, and a small amount of soot. These are the same waste products that result from gasoline combusting in a car’s engine. 

Carbon dioxide is also non-toxic and stable. But it also leads to climate change, so it is not something we want to add to our atmosphere. 

There has been much debate about how long polystyrene will last in the environment, and scientists estimate that it could last anywhere from 500 years to possibly even forever. Because of all this, it’s important to reuse all of the polystyrene products that we can. It’s also important to reduce the amount of polystyrene we use to begin with!

Did you know?  

The world produces more than 12.7 billion kg of polystyrene each year. Americans alone throw away around 25 billion polystyrene cups every year.  That works out to 82 cups per person!

Summing up...

So what do we know about polystyrene? It's made of long chains of styrene molecules. Those styrene molecules are all tangled together to make a cheap, stable, non-toxic, durable plastic. Polystyrene has many different uses. It can be a great help to us in many ways. But we must reduce our use of it, reuse it or even recycle it. That way, we’ll help prevent it from damaging or polluting our environment.