Polystyrene - A great packaging material...almost too great?

Seth Gilchrist
23 January 2012

Here's a riddle for you: What material can be found in the grocery store, the music store, under roads and in the hospital? Give up? The answer is polystyrene! Yes, polystyrene is everywhere: in its foam form it is used as a base material for road construction, and to package everything from computers to food; in its compact form it is used for things like CD jewel cases, computer cabinets, and appliances.

Did you know? Polystyrene was discovered by accident in 1839 by Eduard Simon.

Obviously polystyrene is a very versatile material, but what is it that makes it good for so many different uses? This question can be answered by looking at its chemistry. Polystyrene is a plastic which, as its name suggests, is made up of many ("poly") styrenes.

Styrene is a small building block that can be connected together into long chains. When you make lots of chains and mix them together they get tangled up and make a strong, interconnected mesh which is polystyrene. A good analogy is strands of Christmas lights. Each individual light and the short bit of wire that connects it to the next light is like a styrene molecule. On their own they don't do much, but if you connect them together into long strands, put them in a box, and mix them up you get a tangled mess that cannot be pulled apart - just like polystyrene!

Did you know? Polystyrene is commonly found in two forms: hard, extruded plastic and soft, expanded foam.

This structure gives polystyrene lots of interesting properties such as low weight and high strength, but one other property in particular is both useful and bothersome at the same time... This is that polystyrene is very stable. Another way to say this is that it hates to react chemically and is happy just the way it is. You can leave polystyrene outside, you can heat it up, and you can put harsh chemicals with it and it will stay just like the day you made it and not contaminate its surroundings. This is a good thing for making durable products like cell phones and packaging for food and medical supplies because it won't change taste or make people sick.

So how is this bad? Well, when we are finished with our polystyrene food container, syringe, or computer case, what do we do with it? If we put it in the trash it simply gets placed in a landfill where it will happily sit for hundreds or thousands of years. We have to break it down, reuse or recycle it, all of which cost money and take effort. The best of these options is to reuse everything that we can. Some places will recycle polystyrene but it is expensive and actually fairly rare. The most common ways to dispose of polystyrene are to burn it or bury it. When done correctly burning is effective with the only byproducts being carbon dioxide, water and a small amount of soot. In fact, one tonne of polystyrene cups can be reduced to only 7 grams of soot! Carbon dioxide is also non-toxic and stable, but since it leads to climate change, it is an undesirable pollutant.

Did you know? Polystyrene's recycling identifier is the number "6".

So what do we know about polystyrene? It's made of long chains of styrene molecules that are all tangled together to make a cheap, stable, non-toxic and durable plastic. It has many different uses and can be a great help to us in many ways, but is must be treated with respect and reused or recycled to keep it from damaging or polluting our environment.

Learn More!

Recycling #6 Plastic

Plastics In Wiki: Polystyrene

Polymer Science Learning Center: Polystyrene

Article first published May 25, 2009

Seth Gilchrist

I am a PhD candidate at the University of British Columbia in Biomedical Engineering. I obtained my bachelors degree at the University of Wyoming in 2003 and my Masters at the University of British Columbia in 2006. My current research focuses on bone fracture mechanics in hip fractures sustained by osteoporotic individuals. I perform measurements on proximal femurs that are loaded as they would be in a fall inside a high resolution CT machine and also perform video analysis of femurs loaded in a drop tower under physiological loading rates and conditions.

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