In this activity, students will answer questions while watching the video, How Science is Fixing Recycling’s Grossest Problem, from the Ingenious series produced by the American Chemical Society. Each episode investigates a different topic related to how leading-edge chemistry is taking on the world’s most urgent issues to advance everyone’s quality of life and secure our shared future. This episode investigates the stinky problems associated with polypropylene recycling. Current polypropylene recycling techniques are more down-cycling than re-cycling, but a new technique, called dissolution recycling, is changing all that.
By the end of this activity, students should be able to:
- Identify the polymer that is in plastic #5 as polypropylene.
- Differentiate between downcycling and recycling.
- Explain the challenges associated with recycling polypropylene.
- Give a basic explanation of both pyrolysis and dissolution, as well as comment on the pros and cons of each process.
This activity supports students’ understanding of:
- Molecular Structure
- Organic Chemistry
- Chemical Properties
Teacher Preparation: minimal
Lesson: 10-20 minutes
- Ingenious Video: How Science is Fixing Recycling’s Grossest Problem
- Student Handout
- Computer and projector with volume, or student device to access video
- No specific safety precautions need to be observed for this activity.
- The Ingenious video series spotlights stories from the frontlines of chemistry research and development, where passionate innovators are stepping up to confront problems like pollution, overfishing, sustainability, and personal safety.
- In this video, How Science is Fixing Recycling’s Grossest Problem, students will learn about the stinky problems associated with polypropylene recycling. Food and other residues are almost impossible to remove entirely from polypropylene (the number “5” plastic of grocery store fame). Those residues—anything from yogurt to garlic, from fish oil to baby food—not only stick to polypropylene, but they also degrade there and start to smell even worse! Current polypropylene recycling techniques are more down-cycling than re-cycling. Unless you break down its molecules through a highly energy-intensive refining process, the material can only get a second life as a black trash can or an underground pipe—wherever its smell doesn’t matter. But a new technique, called dissolution recycling, is changing all that. Dissolution recycling uses a special hydrocarbon polymer-solvent under finely controlled conditions of temperature and pressure to eliminate ALL of the contaminants embedded in the plastic.
- The running time of this video is about 6 minutes and 40 seconds. As it is a short video and it moves quickly, you may want to show it twice, or instruct students to pause the video as needed on their own devices to ensure that they can record answers to all of the questions.
- The student questions are presented in sequential order in the video.
- An answer key has also been provided for teacher reference.
- The final questions are reflection-based and might be helpful in prompting a class discussion after students have a few minutes to answer them independently.
- The AACT classroom resource library offers many related teaching ideas. Below are several focused on the chemistry of plastic:
For the Student
While watching the video, answer the following questions:
- How many main types of plastic are there?
- This video focuses on “plastic #5”. What polymer makes up plastic #5?
- Give a couple of examples of products made up of “plastic #5”:
- What is the “gross” problem associated with polypropylene?
- True or False? Hydrocarbons are attracted to other hydrocarbons.
- True or False? If polypropylene is downcycled it will not smell.
- What are the three general steps of the pyrolysis process?
- Identify one negative outcome associated with pyrolysis:
- True or False? Dissolution recycling still requires that the polypropylene molecules are first broken down.
- What is an important part of the molecular structure of alkanes that allows it to be such an helpful component of the dissolution process?
- After the dissolution process, what color are the recycled polypropylene pellets?
- True or False? The dissolution process takes less energy to recycle plastic than making new plastic pellets from scratch.
After you watch the video, reflect on the following questions:
- Does this video make you think about recycling differently than before? Explain.
- What additional questions would you have for a scientist in this field? What more do you want to know?