Sunday, November 20, 2011

Winter's coming- stay insulated!

Trying to think of a new blog post topic, I decided to ask friends what they wanted to understand the chemistry behind. One friend, Skylar, responded without hesitation to say the spray foam insulation.

Two chemicals come out of a spray gun and upon combining react to form polyurethane in an energy producing reaction. Poly(which means many)urethane(one type of organic compound) is many organic compounds (not urethane, but actually an organic compound called carbamate) linked together.

Upon hitting a surface the new mixture rapidly grows to fill the space it is in, growing to 100 times its original volume. This growth is what makes it so amazing to watch, as it expands from a line of liquid to a wall of solid foam.

Polyurethane comes in many shapes and sizes, determined largely by other chemicals added to the mix. To make spray foam so light and so large, the makers add a chemical that keeps space between the polyurethane molecules. This chemical is called a blowing agent. In many cases water is the blowing agent. With the energy from the combination of the sprayed liquids, water vapor is dispersed throughout the mixture as the foam forms around it. The water then turns into a liquid, leaving voids where it had previously been a gas.

The foam, because it has all these pockets inside, serves as a great thermal insulator and holds heat. In a house, the foam keeps heat from escaping the house, keeping energy bills low in the winter.

The foam is also a great insulator because of the rapid expansion it undergoes. When it expands so quickly, it fills every crevice, leaving few places for heat to escape through exposed walls.

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