Glass transition of the parking permit

Right. Time to come up for air after a hectic month. I can breathe again, at least until the end of tomorrow, when the next pile of assignments land on my desk for marking.

I bought a new car last week. Well, new for me. The previous 22-year-old piece of machinery had finally succumbed to the effects of old age and high mileage. One coolant leak too many and it was off to the scrapyard for recycling. With the new car came the need for transferring my University of Waikato 'Licence to Hunt' out of one vehicle and into the other.

No, this is not a licence to hunt big game, rabbits, students or other campus life. Come to think of it, I don't ever recall seeing any big game on campus, but there are certainly plenty of rabbits and students around. It's a licence to hunt an on-campus staff parking space, a privelege for which I pay a few dollars a week . Yes, since the beginning of the year we've had to pay to park on campus, although it has to be said there has never been any difficultly in finding somewhere to park.

The licence is a credit-card sized piece of plastic, that sits in a holder, rather like what is used for the registration tag on a car. But pulling the licence out of its plastic holder was actually a bit of a tricky task. Having been sitting on a car windscreen over summer, it was no longer flat. I got it out of one holder, with a bit of tugging,but in its bent condition it certainly wouldn't fit in a new holder and stick on the windscreen of the new car.  What do I do with it?

Having mentioned this to a colleague, the answer was very straightforward. Iron it. Basically repeat the process that caused it to distort in the first place, namely undergoing the 'glass transition'. Thermoplastics, when cold, are hard and brittle. They are in a 'glass' state; they have long chain molecules that are twisted together and can't easily move. But heat it sufficiently, and it reaches a transition point (the 'glass transition') where the long molecules are able to twist and move much more easily. As a result the whole material becomes rubbery and distortable. I don't know exactly what material the permit is made from (I'm sure someone here could tell me), but it's one that clearly has its glass transition at a temperature lower than that exhibited inside a car on a hot day.

So, with a low-heat iron, I ironed my parking permit (Yes, I did put a piece of scrap material on top so it didn't get too hot too quickly). And quite suddenly the whole thing went rubbery. I could have folded  it in half, or scrunched it up. I ironed it nice and flat, then just waited for it to cool. Pretty suddenly, in went from soft and flexible to hard and brittle again. Result: a parking permit that was back to its original condition.

If you want to try this at home I suggest doing some research first and picking the right material. Ironing a credit-card might not be a clever idea.

There are some good YouTube videos of this with various materials, for example this one.




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