Shrinky Dink Chemistry
Students learn how thermoplastics are made. They will learn that the household plastic #6 is an example of polystyrene, plastic that has been heated, stretched, and cooled in a thin layer. They will experiment by heating different #6 plastics, and create shrinky dinks.
2. Students will identify #6 plastics, and then experiment by heating the plastic, to verify that thermoplastics go back to their original state.
Skills – observation of shrinky dinks shrinking
Key concepts –
-Polymer chains are very long, and can be manipulated to create a lot of different properties (shrinky dinks – heated and stretched out polymer chains, #6 plastic, polystyrene)
-When reheated, thermoplastics go back to their original state (shrinks). This is the same concept as shrink-wrapping.
Context for Use
Resource Type: Activities:Classroom Activity
Special Interest: Quantitative
Grade Level: Middle (6-8), Intermediate (3-5)
Description and Teaching Materials
* Colored pencils/permanent markers
* Hole punch
* Cookie sheet
* #6 plastic container (look at the recycling numbers of the bottoms of containers around your house. You want the clear plastic typically used as containers at grocery store salad bars. Alternatively, buy some sheets of #6 plastic at your local craft store – better yet, try them both and compare results!).
What You Do:
1. Preheat the oven to 350 degrees Fahrenheit.
2. Cut the plastic containers into roughly flat sheets and lightly sand one side with the sandpaper.
3. Cut the plastic sheets into various shapes. Use the hole punch to make a hole to thread a string through the shrinky dink after it has been cooked.
4. Use the colored pencils to color the sanded side of the plastic sheets. Be creative!
5. Place the finished pieces onto the cookie sheet. Place the cookie sheet in the oven and watch for the plastic to shrink. Don't get distracted: it takes a couple minutes, but once the plastic begins to shrink, it happens quickly! The shrinky dink has "shrunk" once the plastic is mostly flat on the cookie sheet. The whole process should only take about three minutes, give or take a little.
6. Use the potholder to remove the cookie sheet from the oven. Allow the shrinky dinks a few minutes to cool before handling. Thread string through the hole if desired.
The lesson will be introduced with a short explanation of how thermoplastics are made. Narrative directly taken from Lori Steward, Middle School Science – Plastics are made of long chain-like molecules called polymers. Because polymer chains are so long, they can be manipulated to create a wide-range of properties, in this case for #6 plastic, polystyrene. Polystyrene is a thermoplastic, meaning the long polymer chains are heated and stretched, then cooled to form the plastic sheet. The polystyrene remains in this "stretched out" state unless something causes it to change. The cool thing about thermoplastics is that upon reheating the plastic, it reverts to its original state, in other words, it shrinks. This is the same process used to "shrink wrap" items like food containers or other products that have protective plastic wraps.
This lesson can be closed with a quick dialogue between students on their observations during the activity. The teacher can pose questions, and let the students discuss at their pods or they can do a walking narrative (walk around the room until the teacher says "stop", the students then need to partner up with someone near them). Questions: What did you observe? What type of household #6 plastics did you use? Did different objects melt differently? Did it matter the size, shape, or thickness of the original object?
Teaching Notes and Tips
- Set up multiple stations with at least 3 toaster ovens. This will increase efficiency and allow students to create multiple shrinky dinks.
- Plastic – you can obtain plastic containers (#6) from your grocery store in the bakery department (cookie containers, etc.)
- Get parent/community volunteers to help manage the ovens.
- If while melting the plastic, the shrinky dink folds over on top of it self, keep heating the plastic until it unfolds. Sometimes you have a "bad one"
How this activity is different?
I've only done this activity as a filler or art activity. I've never opened it with the chemistry make-up and reasoning. Also, an interesting extension and twist to this short lesson would be to have students experiment with other types of plastics. What happens when you add heat?
The key component of this activity is to understand that when you melt a #6 plastic, you are not creating a chemical change, merely a physical one. The plastic is simply going back to its original state.