Mix It Up, Sort It Out

The day before the lab activity, show students plastics you’ve collected and then challenge them to add to your collection (assign for homework and have students bring in items the following day). The following day, ask students if the collection has any value. There are at least three kinds of answers that might be discussed: economic value, saving energy and saving the planet.

Ask students to describe what they know about recycling, and if they can identify products which are made from recycled plastics in the school. The easiest examples might be fencing or landscape materials.

Do you ever wonder where all the plastics you put in the recycling bin go? Thanks to new technology, the plastic you recycle today might become the running shoes on your feet tomorrow! Recycling technology has come a long way. Once such innovator is Dr. Vilas Pol, a materials scientist, who works at Argonne National Laboratory in Illinois. He has invented a “green”, environmentally friendly way to convert used plastic bags, plates, and recycled bottles into new materials through a process called “upcycling.” During this process, plastic is heated to a temperature of 7000C and converted into a fine black powder that can be used in products like batteries, toners and printer inks, lubricants, and tires. In 2010, 9.2 billion pounds of plastics were recycled. But making new products from plastics require that they are properly sorted. Plastics are generally classified into one of seven categories. When plastics are collected for recycling, they are generally mixed and may also be collected with denser glass and metals. In this activity, you will consider why recycling plastic is valuable. Next, you will investigate the properties of plastic and how one of those properties can be used to sort the different types as an important step in recycling.

Insert row of images from page 7 of PDF bottom of first paragraph.

Plastic bags, plates, and bottles can be made into items such as fencing, running shoes, wristbands, and even bridges!

Materials:

• Device with internet access
• Student Data Sheet (printable PDF or you can easily copy and paste the tables into an electronic document)
• Champions of Recycling, Mike Biddle Article Grace, this article is no longer on Jason.
• Goggles
• Graduated cylinders (2.50 ml) for each group
• Beakers (5), 200 ml or larger, for each group
• Isopropyl alcohol (350 ml per group)
• Water (400 ml per group)
• Sugar (sucrose, 75 g per group)
• Stirring rod or plastic spoon (per group)
• Balance (accessible to each group)
• Samples of unidentified plastics: HDPE, LDPE, Styrofoam, PETE, PP and polycarbonate per group ( “hole punch” size if possible or something comparable- each team will need at least 5 bits of each kind of plastic – 1bit/solution)
• Calculators

Safety Notes:

• When using technology, engage in safe, legal, and ethical behavior; this applies to devices (hardware), application or programs (software), and interactions with others.
• You must wear eye protection (goggles) while doing this activity.

Part 1: Prepare the Solutions

Follow lab instructions provided, and have students discuss 5-7 different properties that might be used to identify the different types of plastics (examples students may give might include: color, shape, texture, transparency, size, smell, melting point, boiling point, density). Challenge students to consider why some characteristics cannot be used to identify materials – like size, weight, color, volume (may not be representative of that kind of plastic, and may only represent that particular sample).

1. Review with class that there are 7 different types of plastics. They are often recycled together and mixed with other materials like glass, aluminum, and paper. Have students identify the properties of plastic that might be used to help sorting process. Consider all the different kinds of plastics there are. Using the samples provided by your teacher, make observations and list at least 5-7 different properties that might be used to identify the different types of plastics. Can any of these properties be used to help sort them?
2. Put on your eye protection.
3. Find the mass of five empty beakers and record.
4. Create solutions of 70 percent isopropyl alcohol, water and sugar as directed in the table.
5. Find the mass of each solution (what do you need to do with the mass of the beaker?)
6. Write the formula for calculating density. Calculate the density of each solution, and show the math. Discuss density and review. Students should have some previous experience with density. This should not be the first time students calculate the density of an object. If it is, consider frontloading this activity with an introduction to density and having students do some basic calculations. Review the concept of “floating” and “sinking” as this relates to density. Objects that are more dense than the solution in which they are placed will sink; objects that are less dense will float. You may need to do a demonstration (oil and water is a good example where oil is less dense than water and thus floats when placed in water).

Table I. Densities of Solutions

Formula for Density: __________________________________

Part 2: Determine Density

Have students work in teams of 3-4. Review safety procedures. Rotate around the room as students prepare solutions. Students should be wearing goggles and wearing gloves (vinyl preferred in case of latex allergies).

1. Obtain samples of plastics from your instructor. Distribute samples of plastic to the students. Students should submerge the samples initially or stir them into the solution so they do not float from surface tension.
2. Wearing eye protection, carefully place a bit of the first plastic into each of the five solutions (choose the one you wish to start off with). Make sure they aren’t placed flat, floating on the surface, by stirring them into the solution a bit. Make observations.
3. Repeat step # 2 for each of your samples.
4. Categorize the plastics by whether they float or sink in the solutions. Have students make observations and categorize the plastics by whether they float or sink in the solutions.
5. Try to determine the category for each of the plastics you tested. Describe how you determined this.

Table II. Observation of Plastic Samples When Placed in Solution

* Densities of plastic may be equal to the density of the solution, or may slightly vary due to sources of error when mixing solutions or depending on what kind of plastic is being used. If the densities of the plastic and solution are the same, the plastic should neither float nor sink, but remain suspended (neutrally buoyant).

Table III. Classification of Samples

These will sink in all solutions, and thus, students should understand that they all have densities greater than 1.14 g/ mL. Unless students know something more about the items, it is acceptable to place items in these categories as “possible”. Some students may recognize polyvinyl chloride as PVC, in which case they can go ahead and classify it as such. The Resin Identification Code Classification Chart will allow students to further classify the items into their correct categories. A water bottle is PETE; PVC is V (polyvinyl chloride); and cd bits are Other (Polycarbonate).

For all items above, the category may not be obvious – the plastic bag, for example, might also be placed in HDPE if it sinks in solution 2. This could happen if the particular plastic bag being sampled has a density on the higher range – 0.94 g/mL. Important concept is that the plastics have different densities and can be sorted in this manner. More fine-tuned methods to determine density might be necessary to get down to the exact category in some cases.

Reflect and Apply:

Facilitate a class discussion to allow teams to share their findings and come to a consensus on the items. Consider projecting Table III on a screen, and adding results based on class consensus as discussed.

• Compare your findings with your classmates and come to a class consensus based on the evidence. Why might some of your findings differ? Discuss potential sources of error.
• There may be samples that sink in all of the solutions. What further investigations could you conduct to determine which categories of plastic these represent? (One idea may be to make new, more dense solutions. This could be done by mixing in different amounts of karo syrup – dark karo syrup has a density of about 1.37g/mL).
• With your group, construct an explanation that describes how the methods you’ve used in this lab might be used in the process of recycling plastics. Optional: one way to have students describe this is by using a concept flow chart (see sample below). Students may require further instruction regarding this.

Extension:

How does a plastic bottle become a shoe starting from the curbside pick-up? Write a narrative from the perspective of a plastic bottle depicting its journey from new to used, to recycled, to renewed. Have students construct an explanation of how a plastic bottle might become a shoe starting from curbside pick-up. Have students write a narrative from the perspective of a plastic bottle depicting its journey from new to used, to recycled, to new again!

Make a list of other products made from recycled plastics by conducting research. Next, find some of these products in your home, or at local businesses like a building supply store, and take some pictures. Prepare a communication for your community that shows the advantage of re-using plastics, using your photos as illustrations. Have students make a list of other products made from recycled plastics by conducting research. Have them find some of these products in their homes, or at local businesses like a building supply store, and take some pictures. Students can then prepare a communication for their community that shows the advantage of re-using plastics, using their photos as illustrations.

Read about Mike Biddle, Plastics Engineer. Why is the work that Mike Biddle and Dr. Vilas Pol do important? Could you see yourself in this field someday? Journal Question: Have students read the article about Mike Biddle, a plastics engineer. Why is the work that Mike Biddle and Dr. Vilas Pol do important? Could they see themselves in this field someday?

Additional Resources to Explore:

• Grace: this link cannot be found on Jason Article: Mike Biddle, a profile of a Plastics Engineer http://www.jason.org/node/2163