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# Polymer Crystals vs. Ice (page 2)

based on 33 ratings
Author: Mike Calhoun

In this project, find out if hydrogel polymer crystals can keep items coolerfor a longer period than the same amount of crushed ice.

A special kind of polymer called a hydrogel superabsorbent crystal is able to absorb water, and swell to many times its original size. Does this absorbency mean that the crystals will stay cold for longer than ice? Let's find out!

### Materials

• Hydrogel superabsorbent crystals
• 4-mil re-sealable sandwich size freezer bags
• Two small medicine thermometers
• Watch or clock

### Research Questions

• What is a hydrogel polymer crystal?
• How did the hydrogel change when placed in the freezer?
• Which item stayed cold longer the crystals or the ice?
• Would it be practical to use hydrogel crystals in place of crushed ice to keep items cold for long time periods?

### Procedure

1. Fill a clear large plastic cup or glass with water.
2. Place five to ten crystals in the water. The crystals will begin to grow immediately.
3. Allow the crystals to grow to the point where they cannot be seen clearly inside the container.
4. Fill a sealable freezer plastic bag with the jelly-like hydrogel crystals.
5. Close the bag and place in the freezer.
6. Remove the bag of crystals after about 12 hours.
7. In a separate plastic bag add about the same amount of crushed ice as you added in the crystal bag.
8. Place both items in separate small bowls. Insert a thermometer inside each bag.
9. Compare the length of time that the crystals stay cold to that of the crushed ice. Record the data in a table like the one below.

 Hydrogel crystals Crushed ice Time Measurement Began Beginning Temperature Time Measurement Ended Final Temperature

1. Using the data in the table plot a bar graph showing the time the ice and crystals stayed cold along the y-axis and the name of each substance along the x-axis. Place the final recoded temperature at the top of each bar.

### Results

Research shows that these polymer crystals will keep cold 2 times longer than ordinary water ice.

### Why?

Hydrogel polymer crystals are used for hot/cold wraps in sealed containers by hospitals and in sports medicine. These containers are microwavable and freezable. The cold retaining capacity of hydrogel materials offers the potential for developing novel, biodegradable packaging applications, particularly for foods, to meet the ever-increasing demands for natural and environmentally compatible materials.