Diapers: What Keeps Babies and Astronauts from Springing a Leak?

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Key Concepts
Materials Science, polymers, volume, absorption
Four cups filled with different amounts of diaper filling and different color liquids.

Introduction

When we think about diapers we usually think about babies, because most of us wore them when we were babies and now maybe our siblings or friend’s siblings wear them. But did you know that astronauts also have to wear diapers sometimes? Astronaut diapers are called Maximum Absorbency Garments (MAGs), and astronauts wear them when they have to stay in their suits for long periods of time, such as during spacewalks, or as their ships are re-entering the atmosphere. 

For babies and for astronauts, the most important thing for a diaper is to prevent leaks. But did you ever wonder how a diaper works? What’s inside the diaper that allows it to absorb all that ‘stuff’, without making a mess? 

In this activity we’re going to explore the substance in diapers that allows them to stay leak-free, in a cradle and in outer space! 

This activity is not appropriate for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.

Background

When we think about diapers we usually think about babies, because most of us wore them when we were babies and now maybe our siblings or friend’s siblings wear them. But did you know that astronauts also have to wear diapers sometimes? Astronaut diapers are called Maximum Absorbency Garments (MAGs), and astronauts wear them when they have to stay in their suits for long periods of time, such as during spacewalks, or as their ships are re-entering the atmosphere. 

For babies and for astronauts, the most important thing for a diaper is to prevent leaks. But did you ever wonder how a diaper works? What’s inside the diaper that allows it to absorb all that ‘stuff’, without making a mess? 

In this activity we’re going to explore the substance in diapers that allows them to stay leak-free, in a cradle and in outer space! 

Materials

  • Adult Helper
  • 8 clear plastic cups (glass will also work, as long as the glass is clear)
  • 2 - 3 diapers (number needed will vary slightly depending on size and brand of diaper)
  • Food coloring 
  • Permanent marker
  • Scissors
  • 1 clean, gallon size Zipper-lock bag
  • Measuring spoon 
  • Measuring cup
  • A spoon or something to use to stir
  • A teaspoon of table salt (optional- but fun!)
  • Newspaper (optional, to cover work surface)

Preparation

  1. If desired, spread a few sheets of newspaper over your workspace. The chemical you’ll be working with is perfectly safe, but this will help with clean-up.
  2. Use the permanent marker to label 4 of the cups (if you’re using glass cups, write the labels on a piece of tape and stick the tape to the cup). Label the cups as follows:
    Cup 1 – Label ‘1/8 tsp’
    Cup 2 – Label ‘1/4 tsp’
    Cup 3 – Label  ‘1/2 tsp’
    Cup 4 – Label ‘1 tsp’
  3. Place 2-3 drops of food coloring in the 4 unlabeled cups. Use the measuring cup to pour 1/3 cup of water into each cup. Use a spoon or stirrer to mix the coloring and water.
  4. Open a diaper on your workspace. Have an adult help you use the scissors to cut through the inside lining of the diaper, and remove the cottony stuffing material inside. Place the stuffing in your zipper-lock bag. 
  5. Check the diaper for any leftover powder- either scoop this up with your hands (or use your spoon), or you can carefully pick up the diaper and shake the remaining powder into the zipper-lock bag. 
  6. Set the diaper aside. With all the stuffing inside the bag, carefully seal it and shake the bag for 1-2 minutes. You should see more powder collecting at the bottom of the bag as you shake it loose from the stuffing. 
  7. Carefully remove the stuffing from the bag (it’s ok if there is a little left inside the bag). 
  8. If necessary, repeat this process with 1-2 more diapers, until you have collected at least 2 teaspoons of the powder in your zipper-lock bag. 

Procedure

  1. Use your measuring spoon to transfer the appropriate amount of powder from the bag to the corresponding cup. Start by putting 1/8 of a teaspoon of powder into the cup labeled ‘1/8 tsp’, then ¼ teaspoon of the powder into the cup labeled ‘1/4 tsp’, etc. Continue until you’ve put the correct amount of powder into each labeled cup. Notice the look and texture of the powder. How much space does it take up in the cup?
  2. With help from an adult, carefully pour 1/3 cup of the colored water you measured into the cup labeled ‘1/8 tsp’. Use your spoon to stir the water and powder. Stir the liquid for approximately 1 minute. What do you notice about the water as it mixes with the powder? Is the consistency changing as you stir? Can you still see the powder? 
  3. Repeat this process, pouring 1/3 of the colored water you measured into the cup labeled ‘1/4 tsp’. Use your spoon to stir the water and powder for approximately 1 minute. What do you notice about the water as it mixes with the powder? Is the mixture’s appearance changing as you stir? What about the consistency of the mixture? Is it different from the mixture in the ‘1/8 tsp’ cup? 
  4. Repeat this process, pouring 1/3 of the colored water you measured into the cup labeled ‘1/2 tsp’. Use your spoon to stir the water and powder for approximately 1 minute. What do you notice about the water as it mixes with the powder? Is the mixture’s appearance changing as you stir? What about the consistency of the mixture? Is it different from the mixture in the ‘1/4 tsp’ cup? 
  5. Repeat this process for a fourth time, pouring 1/3 of the colored water you measured into the cup labeled ‘1 tsp’. Use your spoon to stir the water and powder for approximately 1 minute. What do you notice about the water as it mixes with the powder? Is the mixture’s appearance changing as you stir? What about the consistency of the mixture? Is it different from the mixture in the ‘1/2 tsp’ cup? 
  6. Line all 4 of the labeled cups up next to each other. You can observe the volume of the mixture by noticing the height of the liquid in the cup labeled ‘1/8 tsp’. Compare this to the height of the mixtures in the other cups. Which cup has the largest volume? Which has the lowest? What other differences do you notice about the mixtures in the different cups? Do they look different? Do they feel different?

Extra: Using your measuring spoon, add 1 teaspoon of salt to the mixture in the cup labeled ‘1 tsp’. Stir the mixture for about 1 minute. What do you notice happening to the mixture as you stir? Is it changing? What is different about it after adding the salt?

Extra: Try increasing the amount of powder up to 1 tablespoon, always adding 1/3 cup of water. Notice how the consistency changes as you increase the amount of powder. 

Extra: If you have an extra diaper, try soaking it in water for a minute, then sit it somewhere to dry. Observe whether the diaper changes shape or texture after being soaked in the water. 

Observations and Results

As the amount of powder increased in each cup, you may have noticed that the volume of the mixture increased. In addition, you should have noticed that texture of the powder changed. When there was enough powder to absorb all of the water, the powder went from tiny crystals to larger, gel spheres, almost the consistency of round pieces of rice. This is the expected result. Sodium polyacrylate is a polymer, which means it’s a large chain of molecules made up of many smaller units, which are known as monomers. Superabsorbant polymers expand when they come into contact with liquids like water, because water is drawn into and held by the molecules of the polymer. Therefore the sodium polyacrylate acts like an extremely powerful sponge! 

If you tried adding salt to the mixture, you noticed that the texture and volume of the gel mixture changed back to a liquid. This is because salt breaks up the attraction between the water and the polymer chains. The added salt breaks up into negative and positive ions, which are also attracted to the water molecules. Each salt ion attracts several water molecules to it, and pulls those water molecules away from the polymer. Eventually enough water is pulled away so that the mixture goes from being a gel back to being a liquid. 

More to Explore

Credits

Megan Arnett, PhD, Science Buddies

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Key Concepts
Materials Science, polymers, volume, absorption
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