Casein
Milk Plastic/GlueIn this exploration students use milk to extract the protein casein, add borax to polymerize the molecules and then either remove water and bake to form a plastic, or add water and leve a runny consistency to make glue.
Materials Needed
• 50 ml of warm milk per group
• 5 ml vinegar
1) Pour about 50 ml of warm milk into a cup.
2) Add 5 ml of vinegar. Stir. Note the reaction of the curds forming from the whey.
3) Strain the solids out of the milk so that the white curdled (or clabbered) part of the milk is in one container and the liquid (whey) is in another.
4) The students can carefully separate the liquid whey from the clabbered milk by straining it through a filter. Cheesecloth or a paper filter made from paper towels can be used. Fold the paper towel to make a filter as shown below:
Making Glue
Now we have milk in two parts, the watery whey, and the solid proteins (and fat if you have used anything but non fat milk). In this next segment, students will add a polymerizing agent to the milk to form a chain of proteins.
Materials Needed
• Clabbered milk
• Mixing cups
• Spoon or stirring rod
• Borax
• 1/4 teaspoon measure
1) Separate the clabbered milk into two cups. This way two different polymerizing experiments can be attempted.
2) To one cup add 1/4 teaspoon of powdered borax. To the other suggest to students that they choose either a larger amount of borax or that they add a measured amount of whey back into the mixture. Stir the mixtures with separate spoons. Make sure each cup is clearly labeled.
3) Have them record their processes in the Engineering Notebook.
4) Watch the mixture carefully as you stir. Describe the activity of the mixture in the Notebook.
5) When the consistency is to your satisfaction, try out the glue by pasting samples together. This glue will require drying time, so it may be convenient to set aside the samples over a period of time to test the mixture.
6) If the consistency is very dry and clay-like, the students can remove the mixture and mold it into a desired shape. This kind of polymer becomes a basic plastic--the kind used to manufacture buttons for much of the 19th century.
Making Plastic
If the process above is repeated and less water is added back to the mixture, the milk polymer can be shaped as desired and baked. The result is a plastic. Before modern plastic, most clothing was adorned with milk buttons!