Polymers are very large molecules, formed by repeated patterns of chemical units strung together. Although “polymer” might bring to mind rubber or slime, did you know that there are polymers all around us, including inside our bodies? The protein DNA, which is the “blueprint” for cellular reproduction, is a naturally-occurring polymer. The protein casein, in cow’s milk, is a polymer as well. Other natural polymers are cellulose and starch. Bone, horn, cotton, silk, rubber, paper, and leather all come from naturally-occurring polymers!
There are manmade polymers, as well. Fabrics such as rayon and polyester, polystyrene (used in styrofoam coffee cups), and PVC (used in pipes) are common examples of these artificially-occurring polymers.
You can use the following recipes to learn more about non-edible, naturally-occurring polymers. (Adult supervision recommended.)
1. Did you know you can make glue using the polymers in milk protein? In a glass, put seven tablespoons of non-fat or skim milk—whole milk contains more fat, which can change the experiment results.
2. Add a tablespoon of white vinegar to the milk; you should see solids begin to form that are suspended in the liquid. The solids will have a grainy appearance. Allow them to settle toward the bottom of the glass, then drain the liquid off, using a coffee filter or paper towel.
3. Now, pat the solids with a paper towel to absorb any excess liquid. You can use the resulting slimy substance as glue—coat two pieces of paper with it, stick them together, and let it dry. How well does your homemade glue work compared to other glues?
When you added the vinegar to the milk, it caused the milk’s protein, the polymer casein, to separate from the liquid part of the milk and clump together to form solids. Casein is used in adhesives, paints, and even plastics.
1. You can make a slimy substance using milk, vinegar, and baking soda. Form solids like you did in the glue project, using seven tablespoons of milk and one tablespoon of white vinegar. After the solids have formed within the liquid, use a coffee filter or paper towel to drain off the remaining milk.
2. Gently squeeze the filter or paper towel to wring as much liquid out as possible, and then use a paper towel to soak up any remaining liquid from the clump of solids. Next, mix baking soda with the solids; start with 1/4 teaspoon and then add more if necessary to pull the solids together. Make sure you mix the substance well! The end result should have the consistency and appearance of custard or thick vanilla pudding. Now you have a slime made from the polymers in milk protein!
For a different kind of slime, mix white glue (like Elmer’s) with cornstarch and water. (White glue contains polyvinyl alcohol, a polymer.) Use four parts glue to one part cornstarch mixed with one part water: combine the water and cornstarch, and then add the glue gradually, stirring well. You’ll need to let the mixture stand for several minutes before it turns to a solid putty-like slime.