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The Great Goo Challenge
 Are some homemade glues stronger than others? Grab your apron and an adult helper then set up a test lab in your kitchen.
What You Need
• Liquid measuring cup (with handle)
• Approx. 230 mL milk (just less than 1 cup)
• 45 mL white vinegar (3 tbsp)
• Microwave
• 3 spoons or stir sticks
• Paper towel
• 10 mL baking soda (2 tsp)
• Coffee filter (or cheese cloth or fine-mesh strainer)
• 3 plastic or glass containers
• 1 package unflavored gelatin
• White flour
• 3 Q-Tips
• Small pieces of paper, cardboard, waxed paper, aluminum foil, plastic, wood (e.g., Popsicle sticks), cloth
Part A
Casein Glue
1. Mix the milk and vinegar in the measuring cup.
2. Have an adult help you with this step: Microwave the mixture for 10 seconds on high. Stir. Repeat two more times. (The milk should be curdled.)
3. Allow the mixture to cool. It will separate into curds (white solids) and whey (liquid).
Separate the curds and whey using the coffee filter or strainer. Press out as much liquid as possible. Leave the curds on the paper towel to dry.
4. Place the curds in a container and add 30 mL (6 tsp) water and 10 mL (2 tsp) baking soda. Mix.
Gelatin Glue
1. Put the gelatin in a container.
2. Add warm water drop by drop until you have a thick paste. Stir well.
Flour Glue
1. Add a few spoonfuls of flour to a container.
2. Add water until you have a thick paste. Stir well.
Part B
1. Using a different Q-Tip for each glue, stick two pieces of paper together. Let the glues dry. Which glue works best?
2. Repeat step 1 using different materials. For example, try gluing foil to wood or cloth to plastic. Compare how well the glues stick to the different materials.
How it Works
The proteins in milk and gelatin and the starch in wheat flour are chemicals that are sticky. They make good glues and were used in the past to make adhesives. For glues and adhesives to work they need to stick well to both materials you are trying to join. So, if you are trying to stick plastic to wood, the glue has to stick to both.
Glues stick by getting into the microscopic spaces, dents, cracks, and holes on materials. Some materials have more of these spaces than others. For instance, glue usually sticks better to paper than it does to plastic or glass.
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