Today in “Huh, I had no idea” – ice hockey pucks are technically one single molecule. That molecule is called polyisoprene. Here’s a little history on how rubber was invented, and also how pucks (and car tires!) are each one single molecule:
Then there comes onto the scene a tinkerer named Charles Goodyear. In the winter of 1839 Goodyear was in Massachusetts trying to figure out how to make natural rubber more useful so that he could finally make a living at his until-now fruitless tinkering. He had mixed rubber latex and sulfur together when he had a little accident. He spilled the mixture on a hot stove top. When the mixture was through frying, Goodyear couldn’t believe what had happened.
Wouldn’t you know sulfur was just the extra ingredient he needed to make rubber work in cold weather. After mixing hot gooey rubber latex and sulfur and letting the mixture cool, he took the rubbery solid that resulted and tacked it to the outside of his door. The cold Massachusetts winter didn’t make it brittle. What’s more, it didn’t become gooey when heated anymore, either. Goodyear was onto something here. This process for making rubber more useable became known as vulcanization.
What Goodyear had done was this: he crosslinked the rubber. Let me explain. The sulfur molecules each contain eight sulfur atoms, arranged in a ring. When these sulfur molecules are heated with polyisoprene molecules, something nifty happens. The sulfur rings open, and fall apart. Fragments of the sulfur rings will join with the polyisoprene, joining the chains together.
Here’s the intriguing part. Once the rubber has been crosslinked, all the molecules have joined into one big molecules. Polyisoprene molecules are big as molecules go already, having molecular weights sometimes over one million. But now they have all joined into one molecule, one so big that a person can see it, feel it, and pick it up. A piece of crosslinked rubber contains one molecule. Amazing, isn’t it?
This crosslinking makes the rubber stronger. It also allows the rubber to keep its shape better when it is stretched over and over again. It keeps the rubber from getting gooey in hot climates because, think about it, a single molecule can’t flow like a substance made up of many molecule. Think of the way you can pour a bucket full of gravel, but you can’t really pour a boulder, and you’ll get the idea.
So this sounds pretty useful right? It sure does to hockey players, and arguably to anyone who owns and drives a car. However, there are some downsides:
Now there are some drawbacks to this crosslinking which makes natural rubber so useful. First of all, because it doesn’t get gooey and flow when it gets hot, one has to mold it into whatever shape one wants before crosslinking. But that isn’t a really big problem, just something for an engineer to keep in mind when making things out of natural rubber. But it’s related to a bigger problem. Because rubber doesn’t flow when hot after it has been crosslinked, it is very difficult to recycle. This is a big problem. Just think of how many tires are used up each year by all the cars in the world. That’s a lot of waste to dispose. Several experimental processes are being investigated for recycling crosslinked rubber.
I’ve kind of been on a hockey kick lately, so it was cool to actually find something sciencey to be able to post about it here.