Plastic From Potatoes

This is a hands-on laboratory exercise that lets kids make their own plastic using potato starch and other natural household chemicals (vinegar, vegetable glycerine, and water).  Kids love to play chemist and help their colorful mixture transform from a soupy liquid to a stunning flubber-like substance and finally a brittle plastic sheet after drying.


After completing this activity, students will be able to
  1. Compare and contrast landfill lifetimes of various materials (paper, plastic, styrofoam, organics) and justify these based on material composition.
  2. Define "biodegradable", explain what makes a material biodegradable, and discuss why this property might be desirable.
  3. Provide a definition of "polymer" and explain how many polymers come together to form a "plastic".
  4. Perform hands-on laboratory work, such as the ability to measure exact quantities with graduated cylinders, operate hot plates safely, and follow detailed, step-by-step instructions.

Procedure Outline

  1. Introduction Conversation (5 min)
  2. Laboratory Orientation (5 min)
  3. Laboratory Exercise: Make a Plastic! ( 30 min )
  4. Polymers Game (10 min)
  5. Wrap-up (3 min)

Introductory Conversation

Before experimenting, we need to motivate why making new kinds of plastics that are biodegradable is a worthwhile endeavor. So, we have a short conversation with learners that explains what plastics are, what happens when they get thrown away, why this might be bad for the environment, and what we can do about it.

Laboratory Orientation

Laboratory Exercise: Make a bioplastic from potato starch!

•    Make the bio-plastic (15-20 minutes)
o    Blend potatoes
o    Measure water, starch, etc.
o    Put plastic in some container? (leave without dried plastic—takes 1 day)
o    Print steps for parents to try at home
o    Other activities/challenges: bury plastic with some manufactured plastic; see how long it takes to decompose

Polymers Game

Motivate materials science/polymer component (polymer chain activity)
o    Get 5th graders thinking about molecules, linking, etc. (draw upon idea of solids, liquids, gasesmolecules, etc.)
o    Talk about crosslinking

•    Explanatory activity – how crosslinking changes the strength of a material
o    Do you know what is inside of materials?
    Molecules
o    In polymers, there are lots of molecules bonded together in a chain. We’re going to show this now with you. Do we have volunteers to be molecules in a polymer chain?
    Get series of people to link hands, modeling a chain of molecules in a polymer.
o    Now, try to move around.
    Get the “polymer chains” to try to move around each other.
o    How easy is it for you to move around?
    Should be pretty easy for them to move when there is no crosslinking.
o    Now, we’re going to see what happens when we add a cross-linking material. Do we have any volunteers to be cross-linkers?
    Get the cross-linkers to grab different portions of the “polymer chains” to hold them together.
o     Now try to move around. How easy is it?
    It should be harder for the polymer chains to move around with more cross-linking material.
o    Now that we’ve thought about what is happening to the really small polymer chains in the material, what do you think is going to happen to the silly putty you make when there isn’t a cross-linker? What about when there is a cross-linker?
    It will be harder to work with when there is cross-linking, but more viscous without.
o    When we’re making silly putty, the polymer that we have to start with is going to be Elmer’s glue, and the cross-linker is borax. When you mix the materials more and more, you make more bonds between the cross-linker and the polymer chains, which should make the silly putty stiffer. You can play around with that now, by making your own silly putty.
•    Making silly putty
o    Put materials on tables; give kids recommended amounts to mix.
o    Hopefully, they will see that adding more cross-linking material (borax) to the silly putty makes it stiffer, and that mixing the material more adds more cross-linking bonds that also make the putty stiffer.
•    After the activity
o    What did you notice when you added more borax to the silly putty?
    Hopefully it got stiffer.
o    What happened when you mixed the silly putty more?
    Hopefully it got stiffer.
o    Do you remember why this is? What did we do before to show what was happening to the polymer chains in the material?