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A Science Odyssey Title Technology In-Depth Investigation Title


Super Polymers!

Overview: Determine the absorbency of sodium polyacrylate
Learning Goal: Understand some properties of a polymer
Video Link: Faith in Technology's Benefits

Introduction

W.H. Carothers' 1935 invention of nylon launched the era of synthetic materials. Today, synthetic polymers are found just about everywhere -- surfboards, medical supplies, cookware, space suits, and more. Students can investigate sodium polyacrylate, a commonly used synthetic polymer found in disposable diapers.

Demontration subtitle

To spark student inquiry, compare the absorbency of a disposable diaper to cotton dish towels. Fold two dish towels together to match the area and thickness of a diaper. Have students guess how much water each will absorb. Slowly and uniformly pour 100 ml of distilled water on both the diaper and the towels. Let students touch and describe them, and continue adding water until each stops absorbing. If possible, weigh the two materials before and after the soaking. What accounts for the difference?

Carefully dissect a diaper. Holding the diaper inside a large garbage bag, peel back its outer lining. Pull the filling out of the diaper into the bag. Discard the outer lining. Shred the filling into small bits. Hold the bag shut and shake vigorously. Repeat three times, then discard the filling. Shake the granules into a corner of the bag. Cut off the corner and empty the granules into a paper cup.

Invite a student to slowly add 100 ml distilled water to the granules, and stir. What happens? Make sure all students can see the gel that forms.

Procedure subtitle

Determine Polymer Absorbency

Materials for each group:

  • 10 g sodium polyacrylate*
  • distilled water
  • graduated cylinder
  • 10 beakers

Caution: Sodium polyacrylate is nontoxic, but should be handled with care. It can be harmful if ingested. Avoid getting it into eyes or nasal passages, as it will cause drying and irritation. Discard dry and gelled polymer in the trash, not in the sink. Store dry polymer in a sealed container to keep it from absorbing water vapor in the air.

* Sodium polyacrylate can be purchased from most
school science suppliers for about $5 per 25 grams.
Explain that the granules are a superabsorbent polymer called sodium polyacrylate. Have students find out how much distilled water 1 g sodium polyacrylate absorbs. Divide the group into teams and let each one develop its own procedure, or suggest the following:

  1. Place 1 g sodium polyacrylate in a beaker. Add 100 ml distilled water; stir, and let stand for a few minutes. Create a chart to record observations (see below).
  2. In a second beaker mix 1 g sodium polyacrylate with 200 ml distilled water. Repeat the procedure, increasing the amount of water by 100 ml each time until the polymer no longer absorbs all the water.

  3. Students will need to develop a way to judge when saturation occurs. Then, using the volume of the maximum amount of distilled water the polymer absorbed, have students determine the absorbency by calculating the ratio of mass of absorbed water to mass of dry polymer.

  4. Have students compare their results and discuss the procedure. What other uses of this polymer can they envision?
Polymer equations

Sample chart
For results for this activity, click here.
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