What type of plastic wrap prevents evaporation the best?
Here is how you can test it. Some plastics undergo an unusual transition, from a hard, glassy state to a soft, rubbery state, with increased temperature. For this project, you should do background research on the effects of temperature on different types of plastics. Make sure that you understand the difference between thermosetting and thermoplastic polymers. You should also look for information on the glass transition temperature (Tg) for different plastics. Pure polyvinyl acetate has a Tg of 28°C (about 82°F). You can make a sample of this polymer by pouring some Elmer's Glue-All into a plastic bowl or plate and allowing it to evaporate for several days. Cut strips of the resulting material for your experiments. Try dipping the strip into warm water and immediately wrap it around a pen or pencil to make a spiral. Dip it in ice water. Describe the properties of the polymer at the two temperatures. What happens if the spiral is reheated? Additives in the glue may shift the Tg away from that of pure polyvinyl acetate. Use water heated to different temperatures to determine the Tg for your polymer. Other plastics, such as polystyrene (recycling code #6), have higher Tgs. With an adults help, you can investigate these materials using boiling water. (To raise the temperature of boiling water slightly higher, add a few tablespoons of salt. Search on "colligative properties" to find out how this works.) (Goodstein, 2004, 105-109)