Summary:

You will make a simple polymer using glue and borax and investigate the properties of this polymer. You will then break this polymer down by adding vinegar, and then make a new polymer by adding baking soda.

Elmer’s glue is made up of mostly polyvinyl acetate, which, being a polymer itself, is more resistant to flow than other liquids, but not quite as resistant as gluep. When you add the borax, borate ions cross-link or join two polyvinyl acetate chains together, increasing the rigidity of the polymer and resulting in an even more viscous substance. This gluep is an example of a Non-Newtonian fluid, in that its viscosity changes with the rate of the applied strain. One result of this is that the fluid acts like a solid under application of a great force, like jabbing with your finger or squeezing it in your hand. More gentle treatment results in the material acting more like a liquid.

Vinegar is acetic acid, so it breaks the links holding the polymer together just like scientists do when recycling plastics commercially. The baking soda used here is a “blowing agent” because it produces carbon dioxide gas in a reaction with the vinegar, and makes the polymer expand. Blowing agents are added to make foams, sponges, and other fluffy polymers.

Learning Goals / Objectives:

Learning Objectives
Purpose
To see that a chemical reaction has occurred if mixing two substances makes a new substance with different properties. To investigate the crosslinking reaction between Elmer’s glue and borax. To investigate how adding talc and lotion changes the properties of the resulting polymer.

Learning Goals
1. When two or more substances come together to produce a new and different product, a chemical reaction has occurred.
2. Chemical reactions result in the production of new substances with different properties.
3. One visible sign of a chemical reaction is the production of a solid.
4. Crosslinking of polymer chains increases the rigidity of a polymer.

Background

We all know that recycling is an important thing we should do to help conserve our natural and man made resources, but most people probably don’t realize what really happens on a chemical level when plastics are recycled. Plastics are polymers, or materials formed from the chemical combination of smaller molecules known as monomers. This process involves forming new chemical bonds between these monomers in order to create HUGE molecules. When polymers are recycled, the bonds holding the polymer together are broken when the plastic is dissolved in a solvent or reacted with another chemical, like an acid or a base. When the polymer dissolves or reacts, it becomes a solution of monomers to which other ingredients or reactants can be added to allow the monomers to be reconstructed into a new polymer. Also, when plastics are recycled, they are often not turned back into the same type of polymer they were created from. After the polymer is broken down, it is often put back together using a different reaction so the new polymer that is created has different properties than the polymer that it was created from. For example, peanut butter jars made from PETE can be recycled into new bottles and containers, as well as carpet, backpacks, clothing, and more!

Setup:

Have the glue solution made in advance, as well as the borax solution. Have them in clearly labeled containers.

Anticipatory Set:

Preparation
1. To make the glue solution, mix equal parts water and glue, shaking well to mix.
2. To make the Borax solution, mix 2 tablespoons of borax in two cups water. Not all the solid will dissolve.

You should have already discussed chemical properties and chemical changes. It would also help if you’d had the class do other activities that illustrate chemical reactions before this. Talk about polymers and the importance of recycling immediately before the activity.

Instructions / Activities:

1. In each of TWO disposable plastic cups, pour 4 tsp of the glue solution. Write down observations of this solution (color, thickness, etc). Color this solution in just one of the cups with a few drops of food color. Slowly add, with stirring, 1 tsp of the borax solution to both cups. Also note some observations about the borax solution. Your gluep will likely stick to the spoon, just try to keep stirring to get all the starting materials mixed as well as you can.

2. Take the colored gluep off the spoon and play with it. How does it feel? How is this product different from the original starting materials?

3. When you pull it apart, does it stretch or break easily? Pull it slowly but also pull it apart quickly. Do you observe different behavior here?

4. Fashion the gluep into a ball and drop it on the table. When you drop it, does it bounce?

5. When you place the gluep on a flat surface, does it keep its shape or spread out? If it spreads, does it do so rapidly or slowly?

6. Now to the uncolored gluep, add ~1 tsp of vinegar and mix well until the polymer is totally dissolved (may take up to 5 minutes or more – be patient!). Describe this substance. How is it different from the original gluep?

7. Now, add 1-2 tsp of baking soda to the dissolved polymer, and stir for 2-5 minutes until the polymer resembles cottage cheese. Remove the polymer from the cup and squeeze out excess liquid. Describe this substance. How is it different from the original gluep?

8. Fashion this new polymer into a ball and drop it on the table. When you drop it, does it bounce?

9. When you place this new polymer on a flat surface, does it keep its shape or spread out? If it spreads, does it do so rapidly or slowly?

Assessment:

Questions to Investigate
1. How do you determine if a chemical reaction has occurred?
2. How do the properties of the reactants (glue solution, borax solution) in this activity compare to those of the gluep?
3. How is the polymer made with borax and glue (gluep) different from what forms after you add the vinegar and baking soda?

Wrap-up / Closure:

Discuss the activity with the students, particularly the properties of the two different polymers. Further discuss recycling with your students. For more information on recycling, go to http://en.wikipedia.org/wiki/Plastic_recycling.

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