Glue from Milk
Grade Level: 5th - 8th; Type: Organic Chemistry
The goal of these experiments is to create glue by combinging curdled milk and baking soda.
- Why do curds form in milk?
- What is a protein? How does it differ from a sugar or a fat?
- What is casein? How can you extract it from milk? How is it used?
Milk can be transformed into curds and whey by adding (1) rennet or (2) a mild acid such as acetic acid. Since vinegar is acetic acid, it is used in this experiment instead of more expensive reagent grade materials. After curds form and are separated from the whey, the acid is neutralized with the sodium bicarbonate.
The clumps of curds are comprised of casein, a protein found in milk. Casein proteins make up 3% of whole milk. Glues made from casein include products such as Elmer’s and other woodworking glues. The relationship between the Borden Company, it’s mascot Elsie-the-Cow and glue becomes more apparent when you consider that Borden purchased the Casein Company in 1929, and introduced its first glue, called Casco glue in 1932. Casein can also be poured into molded into forms to making a variety of plastic items such as combs, bead, button and umbrella handles.
- Non-fat milk or skim milk
- Glass or enamel saucepan
- Access to a stove
- White vinegar
- Sodium bicarbonate (baking soda)
- Babyfood jar or similar contain for the glue
- Put a pint of milk into a saucepan. Add six tablespoons of white vinegar and stir.
- Heat the saucepan on a stove using low to medium heat. Stir continuously and watch closely. After a while, you will observe clumps forming in the milk.
- Remove the saucepan from the heat as soon as you observe clumps forming in the milk. These clumps indicate that the milk is curdling.
- Continue stirring until the curdling stops.
- Pour off the liquid portion (this is called whey) of the milk, leaving the curds behind in the pot. Remove as much of the liquid as possible.
- Add ¼ cup water and 1 tablespoon of sodium bicarbonate (baking soda). Stir well. Don’t be alarmed if small bubbles appear because this means that the bicarbonate is neutralizing the vinegar. The resulting product will be glue.
- Transfer the glue to a baby food jar.
- Glue two pieces of paper using a small amounts of mixture you made in step 6 and let me them. Once the glue is completely dry (roughly 5 minutes), you should find that the papers are permanently stuck together.
Terms/Concepts:Curds and whey; Curdling milk; Neutralization of acid with bicarbonate; Rennet; Casein
- Joey Green’s Mad Scientist Experiments: Plastic Milk http://www.wackyuses.com/experiments/plasticmilk.htm
- The Plastics Historical Society: Casein http://www.plastiquarian.com/index.php?id=60&osCsid=15ea42c03992923bd58716f5c471178b
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