Silly putty

Crosslinking a Polymer

Objective
The objective of this experiment is to crosslink a polymer and observe the changes in the physical properties of the polymer as a result of the crosslinking.  Changes in physical properties are also sensitive to amount of crosslinking.  This experiment could be expanded to investigate various levels of crosslinking.

Materials
2-4 oz Elmer's Glue-All
1 tablespoon 20 Mule Team Borax
Water
Food coloring (optional) Choose whatever color you want for your silly putty.
¼ cup for measuring
1 cup for measuring
Wooden stick or plastic spoon for stirring
Styrofoam cups, beakers, or small bowls for holding reagents and mixing
Paper towels
1 zip lock quart size bag

Safety Guidelines
-  Wear safety goggles.
- Since borax solid (20 Mule Team Borax) and solution is a cleaning product it could burn your eyes.
-


Procedure
1. Dissolve 1 tablespoon of borax in 1 cup of water.  Stir it, but it may not completely dissolve.
2. In a separate beaker, bowl, or Styrofoam cup add ¼ cup of water.  Squeeze in 2 to 4 oz of Elmer's glue.  Stir with a clean plastic spoon or wooden stick.
3. Optional:  Add one or two drops of food coloring to the glue solution, if you wish to have colored silly putty.  Stir the food coloring and glue solution.
4. Pour the glue/water/food coloring solution into a quart size zip lock plastic bag.
5. Add ¼ cup of the borax/water solution to the bag.
6. Close the zip lock bag tightly.  Hold it at the top to make sure it is closed securely and begin kneading the mixture in the bag by squeezing and pressing vigorously the outside of the bag with your other hand.
7. Observe that the consistency of the mixture in the bag changes as you knead it.
8. When the consistency is that of silly putty, remove it from the bag and form it into a ball.  Pat off excess water with a paper towel.  [If you see liquid glue squirting out of the silly putty, then it has not fully reacted with the borax water.  If your material is very gooey or slime-like, you probably did not add enough of the borax crosslinker.]


Questions

9. If you have a ruler to measure, drop the ball from a height of 30 centimeters.  To what height does it rebound?

Questions
1. How do the glue/water solution change when the borax solution is added.
2. What would you predict would happen if you added more borax crosslinker.
3. One measure of elasticity is how far it will rebound when dropped.  If you measured the distance, how far did your ball rebound?