Nov. 16, 2005

Diaper Polymers

Make a cup of water disappear and learn about chemistry, polymers, molecular bonding, and crystals.

Description:

Super-absorbent polymer crystals are removed from diaper fibers.

You Will Need:

1. super-absorbent disposable diapers
2. distilled water
3. table salt
4. large paper bag
5. spoon
6. 2 paper cups
7. magnifying glass (optional)

Instructions:

Remove the fiber filling from a disposable diaper. Look at it through a magnifying glass. You'll notice tiny flakes or crystals attached to the filaments. In some brands, these filaments are obvious without a microscope.

Shred the fiber filling into very small pieces. Place the filling in a large paper bag. Close the top of the bag and shake it strongly for 5 minutes. The crystals will dislodge and collect in the bottom of the bag. Remove the fibers from the bag and dispose of them.

Place a spoonful of the crystals in the bottom of a paper cup. Pour 200 milliliters of distilled water into the cup. Distilled water is a better choice for this activity because it does not contain any ions that would compete with the sodium in the polymer. Tap water works, but not as effectively; the water is absorbed by the crystals. The gelatinous mass can be held in your hand.

Sprinkle table salt on the mass and stir. It will re-liquefy.

Content:

A molecule is two or more atoms bonded together by an exchange or sharing of electrons. At the beginning of this century, chemists began to learn how to create special molecules made of long chains of atoms or groups of atoms. These long molecules were called polymers. Most common polymers are made of long chains of carbon atoms. It is relatively easy for chemists to manipulate the bonding of carbon atoms.

The super-absorbent molecule found in many brands of disposable diapers is called sodium polyacrylate. It is a long polymer that has sodium ions attached to it. Water molecules are attracted to sodium ions. Each sodium polyacrylate molecule is able to attract and hold thousands of water molecules.

Common table salt is sodium chloride; one sodium atom and one chlorine atom bonded to form a molecule. Sodium chloride easily ionizes, or breaks into its constituent atoms, in water. Pouring salt on the polymer gel provides the trapped water molecules an abundance of sodium ions. The water molecules leave the polymer and return to the solution.

Sodium polyacrylate and several other similar molecules were designed by chemists to perform a specific task: attract and hold water molecules. These molecules are also used for soil additives and seed coatings.

Teacher's Notes

Activity excerpted by permission of the Chemical Educational Foundation (www.chemed.org) from You Be The Chemist. For additional information about these activities and lesson plans, see www.chemed.org/Kit.html.

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