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Name: Holly Rippee
Status: student
Age: 14
Location: N/A
Country: N/A
Date: Around 1999


Question:
When you place a foam cup in acetone, the cup melts. My question is why? I know that the acetone is taking the air out of the cup, but how?


Replies:
The foam cup is made out of polystyrene foam, which is a foam of poly styrene. This means that there is a chemical styrene which is made into a plastic. Its like jello. Styrene is the jello mix you pour into the bowl. When you put the jello into the refrigerator, the jello turns thick. This is like the styrene turning into polystyrene. Now somebody comes along and takes this thick hard stuff, polystyrene and pushs it into the shape of a cup. (You can make the jello take the shape of a mold too, maybe some fancy cup, or funny shapes to eat).

So now you have this polystyrene cup. But if you come along now and pour on acetone, it breaks down the connections between the strands of polystyrene. The cup dissolves.

OK, its not exactly the same thing but if you made a cup out of jello and then poured in hot water, the jello would dissolve in the hot water. The cup would fall apart. Its too small for you to see, but little blobs of water are getting in between the globs of jello, dissolving it, and ruining the cup.

S. Ross


Actually, the acetone is dissolving the plastic in the cup, and the blow gas inthe foam is just escaping into the air. It's exactly the same type of process as when you put popcorn into water.

Richard Barrans Jr., Ph.D.
Chemical Separations Group
Argonne National Laboratory



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