Purpose: Students will evaluate experimental methods for recycling plastics, gather data about the types of plastics they use, analyze information about plastics recycling in their community and write a letter to local officials advocating for the use of a specific plastic recycling method.

Procedural overview: After reading the online Science News article “Chemists are reimagining recycling to keep plastics out of landfills,” students will discuss with the class experimental plastics recycling methods and options and guidelines for recycling plastics in their community. A version of the article, “Recycling reimagined,” appears in the January 30, 2021issue of Science News.

Then, students will collect data on the types of plastics used in their homes or school and add their findings to a class dataset. Finally, students will identify a way to improve plastics recycling in their community and write a letter to encourage local officials to use new recycling technologies.

Approximate class time: 2 class periods

Supplies:
Paper
Pencils
Reimagining Plastics Recycling student worksheet
Teacher background sheet
Computer with access to the internet
Interactive meeting and screen-sharing application for virtual learning (optional)
Audio or video capture and editing hardware and software (optional)

Want to make it a virtual lesson? This activity can be performed virtually by using interactive meeting software. Student groups should use screen-sharing and file-sharing applications.

Directions for teachers:

The setup

Ask students to read the online Science News article “Chemists are reimagining recycling to keep plastics out of landfills” and answer the discussion questions for homework. A version of the article, “Recycling reimagined,” appears in the January 30, 2021issue of Science News. During the discussion, provide students with the table titled “Classifying plastics” that is included in the teacher background sheet. The table will be useful for the class discussion and for the second homework assignment.

Class discussion

Use the teacher background sheet and the following prompts to review the various types of plastics and discuss commonly used plastic recycling methods and the experimental recycling methods described in the online Science News article. During the discussion, encourage students to take notes that they can use when developing a recycling proposal later in the activity.

1. What types of plastics are commonly recycled?

No. 1 (polyethylene or PET) and No. 2 (HDPE polyethylenes) plastics are commonly recycled, and most other plastics are rarely, if ever, recycled.

2. What percentage of the world’s plastics are routinely recycled? What happens to plastics that aren’t recycled?

According to the article, of the 6.3 billion tons of plastic discarded around the world, only about 9 percent has been recycled. Another 12 percent has been burned, and almost 80 percent has piled up on land or in waterways.

3. What issues limit the usability of recycled plastics? Identify at least three issues facing plastic recycling mentioned in the article.

Melting plastic down to recycle breaks some of the chemical bonds in the plastic, which changes its consistency. So, plastic from bottles has to be mixed with brand-new plastic to make a sturdy final product.

Additives like dyes or flame retardants cannot be removed from recycled plastics, which limits the usability of recycled plastics for new products and purposes. Recycling a mix of multicolored plastics creates dark plastic that can be used for making nonfood safe products like park benches and waste bins, in which properties like color don’t matter much.

One of the biggest challenges in plastic recycling is that every type of plastic has to be processed separately because the different types of plastic have varied characteristics and do not mix. This is a challenge because the efficient collection of mixed plastic items must involve separating plastics for processing and because many plastics are made of layers of different plastics that must be separated before the separate layers could be recycled.

Recycling plastics into new, usable materials requires significant energy and effort. The process is almost as expensive as making new plastics from raw materials and faces difficulties in scaling up for widespread use.

4. Identify and briefly describe five potential solutions for recycling plastics mentioned in the Science News article. Identify the types of plastics for which each solution has been successfully tested.

Use liquid solvents to dissolve specific types of plastics to break multilayer plastics down into their constituent plastics to recover those plastics separately. This process has been used on No. 1 plastics and No. 6 (polystyrene or PS).

Use additives called compatibilizers to help different melted-down plastics blend so that unsorted plastics can be treated as a single batch. This process has been tested on No. 1 and No. 2 and No. 5 (polypropylene or PP) plastics.

Use chemical recycling to break sorted or separated plastics down into their fundamental molecules (called monomers) and to separate the monomers from dyes or other additives or contaminants. Then, the purified monomers can be recombined to generate new plastics. This process has been tested on No. 1 plastics and on No. 6 plastics.

Break down sturdy plastics by using platinum or other metals, under lower temperatures and longer time frames, to transform plastics into biodegradable substances called alkylaromatic compounds. This process has been tested on No. 1, No. 2, No. 3 and number No. 5 plastics.

Develop and use next-generation polymers that break their bonds under relatively mild temperature and pressure conditions by dunking the material in an acid solution. The monomers formed from these next-generation polymers can be reused to make new plastic over and over. A new type of plastic called PDK (polydiketoenamine) has been developed, but this solution does not apply to existing plastic types.

Group research

In groups, students will use internet resources, phone books or other printed materials to identify plastic collection facilities and processing plants located in their town, county, state or region.

Students should seek information about what materials are accepted, guidelines for the cleaning and separation of the materials and information about how the materials are handled after collection. To streamline the information students will be processing, direct them to look up the facilities that serve the area in which the school is located rather than facilities that serve their individual homes. Students can then more easily compare the information they gather and the resources they used to find the information.

Depending on the information available on the internet, you may want to contact local recycling facilities in the days before the class begins the activity. You may need to ask clarifying questions of the recycling facility operators or government officials in charge of local recycling programs. Provide students with information they may have difficulty finding.

Each group should answer the following questions.

1. What plastics are collected for recycling in your local area?

Student answers will vary. In general, most collection facilities accept No. 1 and No. 2 plastics, and some accept No. 4 and No. 5 plastics. Fewer and fewer facilities are accepting No. 3 and No. 6 plastics, and practically no facilities accept No. 7 plastics.

2. What happens to plastic items that cannot be recycled by your local recycling facilities?

Student answers will vary.

3. Is processing and recycling of plastic materials performed at your local facility, or are the plastic materials collected and shipped to a new location for processing? If the latter, where are the materials shipped?

Student answers will vary. In general, most facilities wrap recyclables into bales and ship them to another location for processing. A significant amount of baled plastic waste is shipped out of the United States to foreign countries, especially to poor and developing countries that do not have adequate facilities or processes for dealing with that plastic waste. However, there are U.S. facilities that recycle various plastics.

4. Create a flow chart or process diagram that illustrates the path of at least three different types (numbers) of plastic items after they enter the recycling bin at your local facility.

Student answers will vary.

5. Which of the proposed recycling solutions described in the Science News article, if any, are being implemented in any recycling facilities near you?

Student answers will vary.

Collect plastic use data

For homework in preparation for the second class period, have students conduct a quick inventory of the plastics used in their homes. Remember to refer them to the table “Classifying plastics” when doing the homework. Students should not spend a long time on this assignment, perhaps 15 minutes. Advise students to use caution when handling plastic containers and avoid contact between chemical substances and their eyes, skin or clothes. Students should wash their hands after handling plastic containers or their contents.

Be aware of sensitivity issues related to the conduct of home inventories and the disclosure of this information to the class. For students or groups for whom gathering these data at home may be difficult, provide representative inventories based on your own home or school.

1. Most plastic containers are stamped with the triangle symbol and number identifying the type of plastic of which they are made. Using the chart labeled “False advertising” from the Science News article and the reference sheet titled “Classifying plastics” provided by your teacher, tally how many disposable plastic items in your house fit into each category. Begin with containers in the kitchen and bathroom, and include at least 10–15 items in your inventory. Then, write a sentence or two that describes which type(s) of plastic are most common in your home.

Plastics inventory

Type of plasticNumber of itemsPercentage of total plastic inventoried
No. 1  PET  
No. 2  HDPE  
No. 3  PVC  
No. 4  LDPE  
No. 5  PP  
No. 6  PS or EPS  
No. 7  Other  

Student answers will vary. Students will probably find a range of plastics in their homes or classroom.

Analyze the data

Collect students’ home inventories and compile the data for the class as a whole into the table below. For your convenience, a version of the table is included in the teacher background sheet that can be printed and distributed. Students should refer to the class table and their personal table when answering the following questions.

Class inventory

Type of plasticNumber of itemsPercentage of total plastic inventoried
No. 1  PET  
No. 2  HDPE  
No. 3  PVC  
No. 4  LDPE  
No. 5  PP  
No. 6  PS or EPS  
No. 7  Other  

1. Are most of the plastics you encounter in your daily life of the types (or numbers) that are regularly recycled? Explain your answer.

Student answers will vary. Sample answer: No, only about 30 percent of the plastics we inventoried were No. 1 or No. 2 plastics. Therefore, most of the plastics we use daily are of plastic types that do not get regularly recycled.

2. Which one of the proposed solutions described in the Science News article would lead to the largest increase in the amount of plastic waste that your class could recycle?

Student answers will vary. Students should identify the type(s) of plastic that their household and class use the most and identify whether any of the proposed recycling solutions have been successfully tested for the plastic(s). For example, a group that uses a significant percentage of No. 6 (polystyrene or PS) plastics may propose that chemical recycling would provide the biggest increase in the number of plastics reclaimed from their waste plastics.

Advocate for change

Students should use the following questions to craft and submit a formal letter asking local officials to implement a proposed recycling technology that students identified in the previous section. Student answers will vary. Example answers are provided.

1. Which new plastic recycling technology are you advocating?

Because of the high amounts of No. 1, No. 2, No. 3 and No. 5 plastics used in our sample, recycling centers in our area should focus on the technique of breaking down plastics into alkylaromatic compounds under low-temperature conditions. The breakdown products can then be used to make new substances like shampoos or detergents.

2. How does that technology work to recycle plastic waste?

The process involves placing sorted and cleaned plastic waste inside a reaction chamber set to a specific temperature with a catalyst powder containing platinum nanoparticles. The platinum particles break the carbon-hydrogen bonds in the polymer. The breaking of the bonds generates hydrogen. The free hydrogen then can be used to break the carbon-carbon bonds in the molecule. The orderly breaking of chemical bonds at controlled low temperatures forms short fragments of carbon chains that arrange themselves into the six-sided ring structures of alkylaromatic compounds after about 24 hours. These materials can then be used as biodegradable ingredients in other products, such as shampoos and detergents.

3. How could this technology reduce the plastic waste produced by your community and increase plastics recycling? Make sure to provide evidence.

We have gathered data about the types of plastics most likely to be used and discarded in our community. These data suggest that polyethylene and polypropylene (No. 1, No. 2, No. 3 and No. 5) plastics make up a significant portion of the plastic waste in our community. Because these materials have been successfully decomposed by using this method, we think it deserves the attention of our local environmental protection agency and the people in charge of local waste management.

4. What actions would your local officials need to take to implement these new recycling techniques? Consider what changes will have to be made to the recycling or waste-management infrastructure and whether the collection process needs to change. Other issues to consider are the cost of implementation and how the public will be educated about the changes.

The outlined process is still experimental and would need further study. If the process is determined to be safe and effective, the recycling facility management team will need to determine how to scale up the operation to handle the amount of plastic waste produced by the community and figure out how to collect, transport and store the plastics before and after recycling. The first step is to research the process and to perform an environmental impact study and a feasibility study for implementing these procedures on a community-wide scale.

5. Use your answers to write a formal letter addressed to your local officials asking them to implement your proposed recycling method. Submit the letter to your teacher.

Possible extension: For students interested in pursuing an independent research project, have them brainstorm disposable plastic items and products that they use but that are not recyclable. Students should choose one item and calculate the amount of that material they consume in a day, a month and a year. Students should research, calculate or estimate how much of that material is used and discarded globally each year and where the discarded materials end up. Finally, have students research or propose alternative materials that the item could be made from and create a simple public service announcement describing what they learned and advocating for an alternative material or behavior.

Additional resources

Science News articles:

M. Temming. “Tiny magnetic coils could help break down microplastic pollution.” Science News. Published online July 31, 2019.

L. Hamers. 4 ways to tackle ocean trash besides Ocean Cleanup’s broken system. Science News. Published online January 4, 2019.

L. Hamers. “This plastic can be recycled over and over and over again.” Science News. Published online, April 26, 2018.

S. Schwartz. “This microbe makes a meal of plastic.” Science News. Published online April 5, 2016.

B. Mole. “Recyclable superplastics made with old chemistry.” Science News. Published online May 15, 2014.

Scientific articles:

T.W. Walker et al. Recycling of multilayer plastic packaging materials by solvent-targeted recovery and precipitation. Science Advances, Published online November 20, 2020. doi: 10.1126/sciadv.aba7599.

V. Tournier et al. An engineered PET depolymerase to break down and recycle plastic bottles. Nature, Vol. 580, April 9, 2020, p. 216. doi:10.1038/s41586-020-2149-4.

P.R. Christensen. Closed-loop recycling of plastics enabled by dynamic covalent diketoenamine bonds. Nature Chemistry. Vol. 11, May 2019, p. 442. doi: 10.1038/s41557-019-0249-2.

R. Geyer, J.R. Jambeck and K.L. Law. Production, use, and fate of all plastics ever made. Science Advances, Published online July 19, 2017. doi:10.1126/sciadv.1700782.

Other resources:

A.H. Tullo. “Plastic has a problem; is chemical recycling the solution?Chemical & Engineering News. Vol. 97, October 7, 2019.

Plastics: What is Advanced Recycling?” American Chemistry Council.

How Plastics Are Made.”American Chemistry Council.

Recover & Repurpose: Keeping Plastics Out of the Environment.” American Chemistry Council.

Plastic Recycling Plants in United States. ENF Recycling.


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