Science | Science Experiment of the Week 11 | 312 - A Clean Windshield

Phthalates, Plastics, PVC, Flexible, Rigid, Chemicals - Normally, a ray of sunshine on a rainy day's travel is a good thing, but today I was driving west, which let me see something that is usually not visible.

This Week's Experiment - #312 A Clean Windshield

These experiments are from Robert Krampf - The Happy Scientist

This week's experiment is something that I thought about quite a bit today. In fact, it occupied my mind every time the sun broke through the clouds. Now normally, a ray of sunshine on a rainy day's travel is a good thing, but today I was driving west, which let me see something that is usually not visible. To find out what it was, you will need:

a car
a sunny day
cleaning supplies

Pick a nice, sunny day. Park your car so that the windshield is facing the sun. Get in the car and look at the windshield. Look very close and you will probably see an oily film on the inside of the glass. Not sure if it is on the inside? Rub a clean cloth across it and you will see the oily smudge it leaves behind. What is that stuff? Has someone been smoking in your car? Is it the result of air pollution? Is it residue from the box of french fries that were left on the front seat? (Or am I the only one that does that?)

That film is a mixture of chemicals, mostly a group of chemicals called Phthalates (pronounced Thall-eights). These chemicals are called plasticizers, and they are used to soften plastics. Many of the plastic items around you are made of polyvinyl chloride, also known as PVC. This is normally a very stiff plastic, but by adding phthalates, it can be made soft and flexible. Then it is made into dashboards, seat covers, and all sorts of other things. When the plastic gets hot, some of the phthalates evaporate. At night, when things cool off, they condense on the cool glass, leaving the film that you see. They are also a part of the "new car" smell that many people like.

As more and more of the phthalates leave the plastic, it becomes less flexible. Eventually, the plastic gets rigid enough so that it will crack when it is bent. Then it is time to get new seat covers or a new dashboard.

You can experiment to see how quickly the phthalates are collecting on the glass. First, clean the entire inside of the windshield. Besides being a good experiment, this will also make the driver of your car VERY happy. Then each day, rub a new section of the windshield with a clean, dry cloth. Be sure to pick spots that are not in the driver's view, so you don't leave smudges that could be distracting. See how many days it takes to get enough residue to leave a visible smudge. You will find that several factors will influence this. The newer your car is; the faster the film will form. New plastics contain a lot of phthalates; so there is plenty to evaporate. Hot weather will also cause it to form faster. The hotter it gets, the more phthalates are driven out of the plastic. Not driving the car will also speed things up. Why would that make the film form faster? Remember that the phthalates are driven out of the plastic by the heat of the sun and then they condense on the glass when it cools at night. If people are getting in and out of the car, running the air conditioning, driving with the windows down, etc., then most of the vapors will be removed before they have time to condense.

As always, have a great week.

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