Summary

In this lesson students will use lab activities and discussion to explore polymers and their use in 3D printing, with an emphasis on the benefits of 3D printing in automotive manufacturing.

Grade Level

Middle school

NGSS Alignment

This lesson will help prepare your students to meet the performance expectations in the following standards:

• MS-PS1-1: Develop models to describe the atomic composition of simple molecules and extended structures.
• MS-PS1-2: Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
• MS-PS1-3: Gather and make sense of information to describe that synthetic materials come from natural resources and impact society.
• MS-PS1-5: Develop and use a model to describe how the total number of atoms does not change in a chemical reaction and thus mass is conserved.

Objectives

By the end of this lesson, students should be able to

• Accurately define monomer and polymer
• Describe qualitative properties of polymers
• Identify the patterns of elements present in monomers and polymers
• Create a model of a polymer
• Compare and contrast different types of polymers
• Explain the process of extrusion in 3D printing
• Identify benefits of 3D printing in the automotive industry

Chemistry Topics

This lesson supports students’ understanding of

• Molecules
• Polymers
• Monomer
• Molecular Structure
• Chemical reactions
• Observations

Time

Teacher Preparation: 30-45 minutes

Lesson (Part One):

• Engage: 10 minutes
• Explore: 15 minutes
• Explain: 15 minutes
• Elaborate: 20 minutes
• Evaluate: 10 minutes (outside of class)

Lesson (Part Two):

• Engage: 10 minutes
• Explore: 10 minutes
• Explain: 15 minutes
• Elaborate: 15 minutes
• Evaluate: 15 minutes (outside of class)

Materials

• Variety of automotive objects made of polymers i.e. carpet sample, tire valve stem caps, engine belts, dashboard knobs/buttons, seat foam, handles, light covers, etc. (for observation and comparison)
• For Nylon 6-10 Demonstration – See Safety section for proper handling of chemicals
  • 5mL of 4% Sebacoyl Chloride
  • 5mL 1,6-Hexanediamine
  • 25 mL beaker
  • Forceps
  • Stirring rod
  • Fume hood
  • 2 pipettes
  • Acetone
  • Distilled water
  • Chemical resistant gloves
  • Safety goggles
  • Lab apron
• Paper clips or other linkable items (to demonstrate polymer structure)
• For Making Polymers lab
  • Microwave
  • Small plastic baggies (for mixing and microwaving ingredients)
  • Corn starch
  • Water
  • Corn oil
  • Small spoon
• Glue bottle or tooth paste (to demonstrate extrusion)
• 3D printer with PLA filament (to facilitate understanding of 3D printing)

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals. Exercise caution when using a heat source (microwave).
• An operational fire extinguisher should be in the classroom.
• Students should wear proper safety gear during chemistry demonstrations. Safety goggles and lab apron are required.
• Parts of this activity (Nylon 6-10 Demonstration) are to be done in a fume hood, as toxic gas is released.

Teacher Notes

Part One: What is a Polymer?

• Engage: The students will compare and contrast different types of plastics from a vehicle. They will begin by documenting qualitative characteristics, such as flexibility, transparency, and thickness of the plastic item they have been given. After three minutes, they will switch objects with another group and compare and contrast the two items, based on the items’ qualitative characteristics. After another three minutes, the teacher will lead a discussion on the similarities and differences of all of the items. This can be charted on the board or written by the students. The teacher should ask probing questions about the observations until the students note that all of the items are made of plastics/polymers. The teacher should then ask the students to explain how polymers/plastics are made. The teacher will ask the students to complete a quick Think-Pair-Share about the answer and will then call on volunteers to share their responses with the class.
  
  It may be helpful to briefly review the definition and provide examples of qualitative observations. This activity may also be completed on a Google doc or other shared document, so students may observe all of the written characteristics at the same time, eliminating the need to switch items with other groups. The Think-Pair-Share technique requires students to first think about their answer. Having the student write down their thoughts is one way to increase student participation for the Pair segment, in which they turn to a neighbor and discuss their thoughts before Sharing out to the whole class.

• Explore: The teacher will perform the Nylon 6-10 demonstration, while the students carefully write down observations for the chemicals before, during, and after the reaction. This demonstration requires significant safety precautions, background information can be found here.
  
  This demonstration must be completed in a fume hood as toxic vapors are produced. Chemicals should be disposed of properly and safety equipment (chemical resistant gloves, goggles, lab apron) should be worn by teacher and students during the demonstration.

1. Place 5 mL of 1,6-Hexanediamine in a 25 mL beaker.
2. Tilt the beaker and carefully pour 5 mL of sebacoyl chloride down the side of the beaker to form a layer on top of the 1,6-Hexanediamine.
3. Use a pair of forceps to reach down to the interface between the two chemicals to grab the thin polymer film.
4. Pull up the film and wind it around the stirring rod.
5. Continue winding until the beaker is empty.
6. If the beaker still contains chemicals, it should be placed in the fume hood to evaporate.
7. The nylon should be washed with acetone and distilled water before handling.

As this demonstration requires significant safety precautions and great attention to lab materials, an alternative to conducting this demonstration would be to have the students view the video of the chemical reaction. A benefit of this is that the video can be paused for discussion and reviewed as necessary to explore concepts.

This lab demonstration is a condensation reaction that occurs when the molecules of two different monomers join to create a polymer.

• Explain: The teacher will ask the students to use their written observations to describe what happened during the Nylon 6-10 demonstration. The teacher will ask the students to describe what might have happened to the molecules of the two chemicals. This will lead into a discussion of how monomers join to create polymers.
  
  This portion of the lesson will include explanations of terminology such as monomer and polymer. Students can asked to look at the word parts in polymer and to break it down into poly meaning many and mer meaning part. The concept of bonding may be added to the discussion, but is not a part of NGSS for students at the middle school level. This video or a similar video could be used in a flipped classroom to familiarize students with the key concepts regarding polymers (for part one of the lesson) and PLA (for part two of the lesson).
  
  The teacher will begin by describing monomers and provide visual examples of monomers either written out or in model form. The teacher will then explain that polymerization is the process by which monomers attach to one another to create polymers. This can be reinforced by the use of an analogy, for example, linking paper clips together to create a chain. The teacher will give each student a chemical symbol and have them work together to form a stated monomer. Each monomer group will add their symbols to a bulletin board in order to create a polymer. The teacher will also explain that some polymers are synthetic while others are natural.

Letter cut outs can be given to students to create the monomer/polymer bulletin board shown in the photo (polyethylene). It is important to note that the picture provided is a segment of polyethylene as polyethylene is terminated by reaction peroxide.

As an alternative, each student could also be given a paperclip that represents a monomer and the students could link their paperclips together to create a polymer.

For an additional hands on model of the polymerization process of nylon, Legos or other types of linking structures could be used to model the reactive and unreactive parts of polymers. A ten unit Lego block, with tape blocking all of the linking units on the bottom and all but one of the linking units on either side of the top, could be used to represent a hexamethylene diamine monomer and a six unit block, with tape blocking all of the units on the bottom and all but one of the units on either side of the top, could be used to represent a sebacoyl chloride monomer.

Information about additional ways to create different models of polymers with Legos can be found online.

• Elaborate: After establishing an understanding of the chemical structure of polymers, the teacher will have the students conduct the Making Polymers lab. In this section of the lesson, students will have an opportunity to complete a synthesis reaction by making corn plastic. Prior to the activity, the teacher should acquire the necessary materials. Students should wear safety goggles and aprons while working on the lab. Throughout the activity the students will be asked to write quantitative and qualitative observations about their lab. It may be helpful for students to have access to a balance in order to accurately record quantitative observations. The teacher should heat the mixture in the microwave. Make sure the bag is open during the heating process. Heat the mixture for 25 seconds. It takes a bit of time for the mixture to cool down, so the students should be provided with an alternate activity while they wait.
  
  The student lab sheet includes a link to a video that the students may view while waiting. This works best when students have access to at least one computer per group and can complete the lab information online. Clean up for this lab is simple as everything can be thrown away. The corn plastic created by the students may grow mold, so it may be best to keep in the lab.
  
  
• Evaluate: As homework, the teacher will ask the students to define polymerization in their own words and to develop their own analogy as a demonstration of the polymerization process. Reviewing the structure of polymers and the paper clip analogy with the students prior to assigning the homework will result in higher quality products.

Download the "Teacher Guide" for Part Two: Polymers and 3D Printing lesson.

Further reading

• Corn Starch
• How to Make Nylon video
• LEGO Molecular-Scale Models
• Nylon 6-10 demonstration – ASM Materials Education Foundation – Materials Camp
• The Basics: Polymer Definition and Properties
• Types of 3D printing
• What are the Chemicals in Cornstarch?
• What is PLA