Making Glue
Making Glue
Now the milk is in two parts: the watery whey and the solid curds, the proteins from the milk (and fat if you have used anything but non fat milk). In this next exploration, we add a polymerizing agent to the proteins to form a chain of proteins.
Materials Required
• Clabbered milk (the curds from separated milk)
• Mixing cups
• Spoon
• Borax (Can be found in the laundry section of the market)
• 1/4 teaspoon measure
Procedure: Making Glue
1. Separate the curds into two cups. This way two different glue experiments can be done.
2. To one cup add 1/4 teaspoon of powdered borax. Leave the other cup for later.
3. Stir. Watch the mixture carefully. Describe the activity of the mixture.
4. When the mixture is a smooth consistency, you have made white glue! If you want glue that is thinner, add a little whey or water.
5. Test your glue by trying it on different things--paper, cardboard, plastic, wood. How can you test the strength of your glue?
Discussion
Carver knew that milk was composed of water, fat, protein, sugar and other trace ingredients. Milk is a colloid. A colloid is liquid where solid materials are help up into the water for an extended amount of time by loose chemical bonds. A colloid can also be a mixture of other kinds of materials. Fog and smoke are colloids. Fog is water suspended in air. Smoke is particles suspended in air. Milk is an example of a colloid because fat and protein are suspended in a liquid. Colloids remain able to suspend their particles for a long time and will remain unchanged unless there are external influences.
A good representation of the difference between solutions, colloids and suspensions can be found at
The authors at that site demonstrate how larger molecules (blue and green spheres) of a colloid are held up by water molecules (red and black molecules). In milk, the large molecules of proteins are held in place but are not in solution.
When an acid is present, the colloid is weakened and the protein can no longer remain upheld by the water. The proteins and fats fall out. The acid continues to tear apart proteins into small particles. This is called denaturing (or altering) the protein.
Milk can be separated into the two basic components, whey and curds, by adding acid. Stomach acid from a cow, called rennet, it used for many food processes. Other acids like vinegar also work.
Extensions
How can the different glue formulas be tested? Some chemical engineers are interested in this kind of research because they can bring products to the market and advertise that they have "Gorilla Glue" see http://www.gorillatough.com/
1) Repeat the processes above to separate the protein from milk. Set aside portions of the protein (casein) for additional trials of specific amounts of borax, say 1/8, 1/4, 3/8 teaspoon. Or, consider another variable, skim milk, soy milk, 1% milk etc. Have students set the formulas for at least three different trials.
2) Have students design a testing apparatus. Cut test materials (paper, etc.) so that the surface area of contact is the same throughout the trials. Test the glue by pulling the test materials apart. Have students experiment with different ways of pulling the test papers apart. How will one know the force necessary to pull the paper apart? How will the test remain consistent so that the strength of the glue can be verified?
