Adhesive Investigation - Moo Glue

What makes glue, paste or tape stick to things? Adhesives are used to stick things together. Wood, paper and many other materials have tiny cracks and holes in them.

When we glue things together, sometimes the glue seeps into the tiny openings and hardens, making the materials stick together. Other times, the molecules on the surface of an object mix with the glue molecules, making the objects stick together.

Did you know you can make glue from milk? Try this investigation and the results will “stick” with you for a long time.

Notes: 

1) This is a neat investigation. It is not an "experiment." 

Experiments are a special type of investigation that requires manipulating variables in a controlled way. Investigations like this do not do so and are not experiments. Not all investigations are experiments.

2) This can get rather odoriferous.  You may NOT want to use this as an adhesive on any projects that you plan to keep. :-)

What You Need:

• A tall, clear glass
• Non-fat or skim milk
• White vinegar
• Coffee filters or paper towels
• 2 pieces of paper

What You Do:

1) In a glass, put seven tablespoons of non-fat or skim milk. Make sure to use low-fat milk because 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.
 

3) In a about a minute, the mixture will separate and settle toward the bottom of the glass. Then drain the liquid off, using a coffee filter or paper towel.
 

4) Now, pat the solids with a paper towel to absorb any excess liquid. You can use the resulting slimy substance as glue!
 

5) Last, coat two pieces of paper with the milk slime, stick them together, and let it dry. How well does your homemade glue work compared to tape or other glues?

WHY DOES THIS WORK?   The science behind milk glue.

Milk is a colloid.  A colloid is a mixture of substances that do not settle out over time (like a mixture of sand and water would for example). 

Unlike a suspension (sand and water or orange juice and pulp) that mixes together when stirred or shaken then settles into separate parts when left at rest, a colloid does not settle because the particles that make it up are extremely tiny.

Looking at a glass of milk, one would not be able to see the particles that make it up, namely the curds (solid casein protein particles) and whey (liquid particles) because they are so small. 

So -- remember that the liquids are called whey and the solids are called curds. The curds are full of the protein called casein.

Interestingly, milk appears white even though the particles that make it up are mostly clear, because light is scattered by the tiny particles as it passes through the colloid. 

The milk was “curdled” when the acidic vinegar was added and lowered the pH of the milk, causing the casein particles to come out of the solution as solid chunks of curds floating in the liquid whey.  Gross - definitely don’t drink!

Glue can be made from lots of things like:
plant saps
animal bones and hides
cassava root
bread
fruit and other vegetables

Casein (that protein that is found in milk) was used by ancient Egyptians as a glue for boat building and to weatherproof airplanes during WWII. Casein is what makes the milk adhesive (or, "moo glue") work.

Exact Link Sources:
Ick Stick  author: Alicia Danyali
Curds and Whey author: Lori Stewart
General source: education.com