Jump to main content

Chemical Reactions: What is Plastic Made From?


Grade Range
Group Size
2-3 students
Active Time
65-75 minutes
Total Time
2 days (drying time for casein plastic)
Area of Science
Key Concepts
Chemical reaction, polymerization, plastic, properties of matter
Svenja Lohner, PhD, Science Buddies
Video narration by Jennifer E Paz
Free for a limited time thanks to individual donors


Chemical reactions can result in interesting products! In this lesson, students learn how plastics are made by conducting a polymerization reaction in a simple milk-to-plastic transforming experiment. During their experiments, students will be able to compare the physical properties of their reactants (milk and vinegar) and their resulting organic casein polymer.

Learning Objectives


For teacher preparations:

Per group:

Per student:

Prep Work

  • Print out a worksheet for each student.
  • Heat all the milk you need for your class (1 cup per student group) in a pan on a stovetop or burner until the milk is steaming. Alternatively, you can microwave the milk in a microwaveable container by warming it at 50% power (two minutes at a time) and watching it to make sure it does not overflow. The milk will be steaming when it is sufficiently hot.
  • Store the steaming hot milk in a thermos until it is needed. It should stay warm enough for at least two hours.
  • Prepare a materials station for students. Place the measuring cup, the thermos with the hot milk, and a bottle of distilled vinegar at the station so that students can measure out these materials during class. Optional: if you decide to use decorative materials such as small cookie cutters, food coloring, and/or markers, place these at the materials station as well.
  • For the explore part of the lesson, provide the students with a work surface that can get damp.

Prep Work ()

Engage (10-15 minutes)

Explore (40 minutes + 1-2 days of drying time)

Reflect (15-20 minutes)



Free science fair projects.