Baby diapers. Boring…right? Well, they contain a little secret.
Each diaper has a super-absorbent chemical powder. This powder can hold between 2 to 4 cups of water. If you’ve ever changed a diaper, you may have noticed small crystals on the baby’s skin. These are a nontoxic, super-absorbent polymer found in the diaper’s lining.
- Disposable diapers (various brands). (Amazon link: Disposable Diapers)
- Clear plastic cup (at least 8 ounces). (Amazon link: Clear Plastic Cups)
- Colored, not-see-through plastic cups (at least 8 ounces). (Amazon link: Red Plastic Cups)
- Ziplock bag (Amazon link: Ziploc Gallon Bags)
- Table salt (Amazon link: Table Salt)
- Scissors (Amazon link: Scissors)
- Set a new unused diaper on some newspaper. Using the scissors, cut through the inside lining and remove the cottony material. Place this material inside a clean ziplock bag.
- Take the polymer powder that may have spilled onto the newspaper and pour it into the ziplock bag. Blow some air into the bag to make it puff up. Then, seal the bag.
- Shake the ziplock bag for a couple minutes. This will remove the polymer powder from the cotton-like stuffing. Notice how the powder falls to the bottom.
- Carefully remove the stuffing from the bag, leaving the dry polymer you just extracted from the diaper.
- Pour the powder into a clear plastic cup and fill the cup with approximately 4 ounces (120 mL) of water. Mix it with your finger until the liquid starts to thicken.
- You will see that a gel begins to form. Turn the cup upside down and notice how the mixture has solidified. Now you know how a diaper works!
- Smoosh the pieces of gel with your finger. Add a teaspoon of salt and stir. Watch as the gel turns back into a gooey liquid. When finished, pour all the saltwater goo down the drain.
- Slowly pour about ¼ cup of warm water into the center of a new diaper. Hold the diaper over a sink or large pan and keep adding water, a little at a time, until the diaper can’t hold any more. Keep track of how much water the diaper can absorb.
- Try a “magic” trick. In step 6, you held the cup upside down. In many cases, the polymer will stay inside the cup. You may need to add more powder and less water for this to work. To prepare your trick, pour the powder into a non-see-through plastic cup. Then, gather some friends and pour some water into the cup. As you stir, say some magical incantation to make the water disappear. Hold the cup upside down. Your friends will be amazed at how the water disappeared!
The powder inside the diaper is called sodium polyacrylate. This chemical is a polymer, or a long chain of repeating molecules. Super-absorbent polymers expand when they come in contact with water. This is because water is drawn into and held by the molecules inside the polymer. Like sponges, polymers soak up more than twice their weight in water. The diaper’s cottony fibers help spread out the polymer powder and the liquid.
Super-absorbent polymers are used in other applications, like gardening and landscaping. In these cases, polymers are a means to conserve water for plants. They can store water in the soil and then release it to the plant roots as needed.