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From Glue to Glob


PURPOSE

Observe the change in properties when polymer chains (formed from linking monomer units together) are joined with other polymer chains through a cross-linking reaction.
 

PERFORMING THE EXPERIMENT

  1. Pour 1 tablespoon Elmer's Glue-All® into a plastic cup.
  2. Add 1 teaspoon water and mix well with the stirring stick. 
  3. Add 2 teaspoons Borax solution, and stir with the stirring stick until a solid sticky material forms.  If the glob is too sticky to handle, stir in more Borax solution until it has a good kneading consistency.
  4. Pull the "glob" off the stirring stick and knead it in your hands until it dries and is no longer sticky. 
  5. Form a ball with the glob, and see if it will bounce. 
  6. Stretch the glob slowly.  Does it stretch?  Now, stretch it quickly.  What happens? 
  7. Place your glob in a plastic bag, and seal it with a twistee. 
  8. Place your plastic cup and stirring stick in the trash container.  Wash your hands thoroughly under running water. 

You may take the glob home.  Check later to see what form it has taken.  You may want to draw a picture on a piece of paper, or write your name backwards, with a water-soluble marker.  Press your glob against the paper and quickly remove it.  What happens? 
 

QUESTIONS TO THING ABOUT

1. Why would you add more Borax solution (a liquid) to the Elmer's Glue-All® mixture in order to make the mixture dryer? 
 

DISPOSAL

Your glob will last for several days in the plastic bag.  If the glob starts to mold, or when you are finished with it, dispose of the glob in the plastic bag with solid trash.  Do not eat the glob or allow it to remain on clothing, upholstery, carpet, or wood since it will stain these materials.
 

EXPLANATION

Polymers are the basis of plastics, styrofoam, polyesters, and adhesives among many other items in our everyday world.  Polymers, which means many units, are formed from monomers, which means single unit.  The straight-chain polymer we use is called polyvinyl acetate and is contained in Elmer's Glue-All® which flows with little difficulty.  Borax is added to the glue to cross-link the chains.  The "glob" is able to stretch a little, but the cross-linking prohibits much movement. 
 

EQUIPMENT NEEDED

Elmer's Glue-All® (other glues do not work as well); water; saturated solution of 20-Mule Team Borax (1 Tablespoon dissolved in 1 cup of water); 5-oz clear plastic cups marked at the 1 Tablespoon level; wooden popsicle sticks; plastic spoons; water-soluble markers; small sheets of paper; plastic bags and twistees.
  

REFERENCES

Modified from CHEM FAXTM, Flinn Scientific Company, Inc., along with ideas from Robert Becker, Al Hazari, David Katz, and Andy Sae.
 
 
Kids Involved Doing Science is at http://www.kids.union.edu.   Modified 02/25/03 by C. & P. Scaife