This Week's Experiment - #312 A Clean Windshield
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.
From Robert Krampf's Science Education Company
PO Box 60982
Jacksonville, FL 32236-0982
904-388-6381
krampf@aol.com
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