Super absorbent polymers were first developed for use in the oil industry. They were put into almost-dry oil wells and water was pumped in. A gel was formed that would get into all the cracks and crevices, and force the remaining oil to the top of the well where it could be pumped out.

Today, there are many uses for superabsorbent polymers. One good example is the sodium polyacrylate used in disposable diapers. In this experiment, you will see how disposable diapers keep babies dry.

Materials:

• 100 gm sodium polyacrylate (water sorb)
• 50 paper cups, 5 oz.
• 50 craft sticks
• 5 taster spoons (2 taster spoons equals 1 gm)
• 4 graduated cylinders 10 ml
• 12 – 12” x 10” plastic zip-lock bags
• 500 gm salt

Local Materials:

• 1 gal. distilled water
• Several pairs of sharp scissors
• Disposable diapers

Procedure:
Part I:

1. Place about 1 gram of sodium polyacrylate into each of the two small cups.
2. Add 100 ml of distilled water to one cup and add 100 ml of tap water to the other cup.
3. Stir the contents of each cup with craft sticks.

1. Cut the edges off of a disposable diaper. Remove the thick cotton padding.
2. Cut the remainder of the diaper into strips and place them into the sealable bag.
3. Shake the bag for several minutes. A white powder will come out of the diaper.
4. Put the powder into a cup and add 100 ml of distilled water. If a thick gel forms, measure some more water and pour it into the cup. See how many milliliters of distilled water the powder will absorb.

Teaching Tips

1. Sodium Polyacrylate is considered nontoxic, but it can be dangerous if ingested. If it gets into the eyes or nose, it will cause drying and irritation. Flush with plenty of water if this happens. Wash hands after use.
2. Sodium Polyacrylate can absorb about 800 times its weight in distilled water, about 300 times its weight in tap water, and about 60 times its weight in urine. The more ions in the solution, the less solution is absorbed. The water equalizes the concentration of ions inside and outside the gel, so if there are more ions in the solution not as much water is needed to dilute the polymer. This flow of solvent from low concentration to high concentration is called osmosis.
3. If you stir quite a lot of salt (NaCl) into the gel, it will turn back to a liquid. The water comes out of the gel to dilute the salt. When the gel is completely broken down, it may be poured down the drain with plenty of water.
4. Dispose of the gel in the trash.
5. A similar polymer, Polyacrylamide, is used in plants to retain moisture.