Baby Diaper Polymer

Description

Modern baby diapers contain polyacrylic acid, a super-absorbent polymer. When some of this polymer was added to a beaker with water and stirred, it absorbed many times its weight in water.

Explanation

Polyacrylic acid is a polymer made from the monomer acrylic acid. These long chains contain thousands of monomer units, and the polymer also has some cross-linking between the chains. Many polymers, such as polyethylene and polystyrene (used in trash bags, plastic bottles, and Styrofoam, for example) are hydrophobic, meaning they repel water. Polyacrylic acid, however, is very hydrophilic - it attracts water. That's because of the carboxylic acid groups (COOH) in the polymer, which can hydrogen-bond to water molecules.

Diapers contain a small amount (4-5 grams) of polyacrylic acid in a powder form, which is mixed into the fluff in the middle layer of the diaper. The inside layer of the diaper allows water to pass through it into the absorbent middle layer, and the outer layer is waterproof, so both baby and mommy stay dry. Polyacrylic acid can absorb about 30 times its weight in water, or about 30 mL (1 oz) of water per gram, so a typical diaper can absorb 120-150 mL of water (about a half cup). That's about how much a baby... um... pees.

How can I do it at home?

An adult must be present. 

  1. Lay out a garbage bag on the table.
  2. Take a baby diaper (a clean one) and carefully tear it open to get the cottony material out from inside.
  3. Pull the cottony material apart, tiny specs of white powder will fall out - this is what you want to collect.
  4. Throw the cotton away, and spoon the white powder (poly acrylic acid) into a cup.
  5. Add some food coloring if you wish
  6. Add water to the cup.
  7. Stir.

What would happen if...

  • you try adding more or less water?
  • you try adding more or less poly acrylic acid?
  • you try adding hot water or cold water?
  • you don't stir after you add the water?

still have questions?  email us!

explanation furnished by UCCS's Dr. David Anderson

 

 
 
   


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