Activity 5.1.2 Gluing It All Together

The first commercial glue, created around 1750, was made from fish. Other early adhesives used natural rubber, animal bones, blood, starch, and milk protein or casein. Today animal glues have mostly been replaced with cheaper synthetic glues made from manmade chemicals synthesized from petroleum and natural gas.

When milk and vinegar are mixed together, the vinegar makes the protein in the milk, called casein, stick together to form small white lumps called curds. The leftover liquid is called whey; you will make the glue from the curds. When you add glue between two pieces of paper, the glue seeps into tiny cracks in the papers. When the glue hardens, it forms a bond to hold the paper together. In real life, engineers design special glues when they need to hold things like envelopes, sneakers, and even airplanes together.

In this activity you will use the internet to research glue, and then use the information to evaluate bonds made with your homemade glue.
  • Engineering notebook
  • Computer with Internet access
  • Pencil
  • Measuring cups and measuring spoons
  • Paper, felt, cardboard, popsicle sticks, craft foam, magazine(slick) paper, variety of paper plates, wax coated paper cups
  • Toothpicks
  • Scissors
  • Pennies
  • Ruler
  • Safety goggles
  • Hole punch
  • Masking tape
  • Ingredients for each batch of glue:
  • ¼ cup hot tap water
  • 2 tablespoons powdered milk
  • 1 tablespoon vinegar
  • 3 large paper cups
  • 5 paper towels
  • 1 rubber band
  • Plastic spoon
  • ¼ teaspoon baking soda
  • 1 teaspoon hot water
  • ¼ cup flour
  • Salt
Use any of the websites listed below to find the answers to the following questions:
1. What are considered to be among the earliest adhesives?
2. What animals, or parts of animals were used to make glues?
3. What is the “technical” name for “super glue” type adhesives?
4. What are the two requirements for glue to “work” (form a bond between two materials.)
5. Explain the difference between adhesion and cohesion.

6. It is thought that bonding of adhesives occurs at the molecular level. What is the technical name of the force which holds glue to its bonding materials?
7. What type of molecule is important for this “force” to be effective in bonding?

8. Why do “super glue” adhesives bond to skin?
9. List three types of “adhesives” that do not resemble traditional liquid or semi-solid adhesives.
10. Explain one of the theories on how Post-It® notes work?
11. How do geckos climb on everything?
Making the Glues:
  1. Your teacher will divide the class into engineering teams of 2 - 3 students. Each team will make and test two different glues on several different substrates, then compare the results.
Casein Glue
  1. Mix the hot water and powdered milk. Stir until dissolved.
  2. Put the vinegar into the cup holding the milk. Stir for about 30 seconds. The milk will begin to separate into solid curds and watery whey. Continue stirring until the milk is well-separated.
  3. Make a strainer to separate the curds from the whey. Put a folded paper towel or coffee filter over one of the large paper cups. Push down in the center to form a bowl shape. Put a rubber band around the top of the cup to hold the paper towel.
  4. Pour the curds and whey into the strainer.
  5. Wait about 5 minutes for all of the whey to drip through. Use a spoon to carefully scoop out the curds and put them on a clean paper towel.
  6. Put another paper towel on top of the curds and gently press down. Soak up the remaining liquid until the curds feel firm, not squishy.
  7. Put the curds in a clean paper cup. Add about 1 teaspoon of water to the curds and stir.
  8. Add the baking soda and stir. Some foaming may occur from the carbon dioxide gas being released when the baking soda and vinegar mix.
9. Mix thoroughly until the glue becomes smooth and more liquid. If the mixture is too thick, add a bit more water. If the glue is too lumpy, add more baking soda.

Flour and Water Paste
  1. In a small bowl or cup, mix flour with enough water to make a smooth, creamy mixture.
  2. Add a pinch of salt; and stir.
Testing the Glue:
  1. Cut 1 in. x 8 in. strips of substrate material (if foldable) or two 1 in. x 4 in. strips if the material cannot be folded. Measure two inches from one of the edges, and make a mark where you will place the glue. Dip the end of a toothpick into your glue so you use the same amount of glue on each paper strip. Place a very small dot of glue on the 2” mark. Fold the substrate in half if possible, or put a second piece of the same substrate on top, and press on the location of the adhesive. Clamp the bonds, or place weights on them. Make a duplicate bond using the same material and glue.
  2. Repeat the procedure for each type of material provided to you by your instructor.
  3. Let strips dry until next class.
  4. Make a test cup by poking holes on opposite sides of a small paper cup and taping a string to the holes for a handle.
  5. Reinforce one end of the test material with masking tape, and then punch a hole in it approximately 1” from the end. Attach the string with cup to the strip with the hold using a paper clip. Hold the top strip with your fingers.
  6. Drop pennies one at a time into the cup until the strip pulls apart. This is testing the adhesive in a “peel” configuration. Count the pennies and record the results in your GTT notebook. Describe the failure (ex: the material tore apart, or the glue let loose.)
  7. Repeat for each test substrate and adhesive.
Number of Pennies held with Casein Glue and description of bond failure
Number of Pennies held with Flour Glue and description of bond failure.


1. Which adhesive gave better bonds overall?
2. Explain which adhesive you would use if you had to build a toothpick bridge?
3. In the glue making process describe the role of a chemist and the role of a chemical engineer.
4. Explain how you used the design process to design, prototype, and test your glue.

Design Process Step
What We Did at This Step:
Define the Problem



Develop Ideas

Choose Best Idea

Model or Prototype

Test and Evaluate

Improve Design

Communicate Results

  1. Optional: Read The Glue Test from this website: **** Why is it important to test the materials you are using to solve an engineering problem?