Barnard Chemical Society

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Barnard Chemical Society
Making a Polymer Bouncy Ball
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Materials

• Borax
• Corn Starch
• White Glue
• Warm Water
• Food Coloring (optional)

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Procedure

• Label one cup 'Borax Solution' and the other cup
  'Ball Mixture'.
• Pour 6 spoons warm water and 1/2 spoon borax
  powder into the cup labeled 'Borax Solution'.
  Stir the mixture to dissolve the borax. Add a
  drop of food coloring and stir.
• Pour 2 spoons of glue into the cup labeled 'Ball
  Mixture'.
• Add 2 spoons of corn starch and excess (about 3
  spoons) of the borax solution you just made.

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• Do not stir. Allow the ingredients to interact on
  their own for 10-15 seconds, and then stir them
  together to fully mix.
• Once the mixture becomes impossible to stir, take
  it out of the cup and start molding the ball with
  your hands.
• The ball will start out sticky and messy, but
  will solidify as you knead it.
• Once the ball is less sticky, go ahead and bounce
  it on the tabletop!

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How Does it Work?

• Polymers are long chains of molecules.
• They can be joined in several ways. Each type of
  linking gives the polymer different properties.
• The polymer contained in Elmers White Glue is
  polyvinyl acetate (PVA).

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How Does it Work?

• Adding borax to PVA causes the molecules to join
  together into one giant molecule. This is called
  cross-linking.

Non-cross-linked polymer
Cross-linked polymer
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How Does it Work?

• Cross-linking makes the mixture less runny as the
  chains can no longer slide past each other
  easily.
• As more borax is added, more molecules join
  together and the mixture starts to look more like
  a solid.
• Cross-linking is also what makes the ball elastic
  and allows it to bounce.

References http//www.msm.cam.ac.uk/seek/slime.ht
m http//en.wikipedia.org/wiki/Polyvinyl
_acetate
http//www.pslc.ws/macrog/exp/rubber/sepisode/ent.
htm
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Bouncing Polymer Balls