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The Stress of being a Recycled Bag

Grades: 6-12
Author: Joseph DeAngelis
Source: This material is based upon work supported by the National Science Foundation under Grant No. EEC-1161732.


Abstract

Students will test the tensile strength of a shopping bag and discover that the polyethylene film has a higher tensile strength when pulled parallel with the extrusion lines then when pulled perpendicular to the extrusion lines. The students then apply what they learn to design an experiment to compare the strength a shopping bag made from recycled polyethylene to one that contains no recycled material. This lesson can be done with common inexpensive materials which may be collected from the home. Teacher Notes attached


Objectives

What should students know as a result of this lesson?

  • The students should recall that gray and tan shopping bags are made from recycled material.
  • The students should know the definitions of the terms tensile strength and strain as they apply to material properties.
  • The students will recognize the structural formula of polyethylene.
  • The students should know why plastic shopping bags are an environmental concern.
  • The students should know why the recycling of plastic shopping bags, as well as other plastics, is important.
  • The students should recognize the relationship between the structure and properties of polyethylene film.
  • The students will know that the tensile stress and strain of a material depends upon the area of the sample being tested.

What should the students be able to do as a result of this lesson?

  • The students will construct samples of polyethylene film from shopping bags.
  • The students will measure the volume of water needed to break samples of polyethylene film from shopping bags.
  • The students will collect and display group data for class discussion.
  • The students will analyze class data to draw conclusions about the relationship between the orientations of the extrusion lines and the tensile strength of their samples.
  • The students will design an experiment to compare the tensile strength vs. strain of a shopping bag made with recycled material and a shopping bag made with no recycled material.
  • The students will construct graphs showing the tensile strength vs. the strain of tested material.
  • The students draw conclusions about the relative quality of shopping bags made with recycled material vs. those made without recycled material.

Materials

(For each group of students)

  • 1 Plastic shopping bag made with recycled HDPE (gray or tan)
  • 1 Plastic shopping bag made without recycled HDPE (white or blue)
  • Five gallon bucket
  • Ring stand
  • 100 ml graduated cylinder
  • Scissors
  • Metric ruler
  • Miscellaneous 1 liter container for water
  • Large Plastic Juice Jug with handle
  • 1 C clamp and one utility clamp, or 2 C clamps
  • Permanent marker

Procedures

Engagement/Assessment

Introduce polymers

Take pre-assessment

Exploration/Assessment

Test the tensile strength of a plastic bag and share results

Explanation/Assessment

Class discussion about the results of the tensile strength activity

Teacher explanation based on results

Elaboration/Assessment

Show "The Magnificent Plastic Bag" youtube video and discuss the importance of recycling.

Students now test a bag made with recycled HDPE and a bag not made with recycled HDPE.

Students are assessed through a presentation of their findings and a post-assessment.


Prerequisites

The students should know the basic types of chemical bonds - ionic and covalent.

The students should know that physical properties depend upon structure


Best Teaching Practices

  • Inquiry based
  • Hands-On/ Minds-On
  • Learning Cycle
  • Authentic Problem Based Learning
  • Questioning

Alignment with Standards

NGSS Standards:

  • MS-PS1-1 Develop models to describe the atomic compostion of simple molecules and extended structures.
  • MS-PS1-3 Gather and make sense of information to describe that synthetic materials come from natural resources and impact society.
  • HS-PS2-6 Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials.

Common Core Standards:

  • RST.6-8.1 Cite specific textual evidence to support analysis of science and technical texts.
  • RST.6-8.3 Follow preciesly a multistep procedure when carrying our experiments, taking measurements, or performing technical tasks.
  • WHST.6-8.2 Write informative/explanatory texts, including the narration of historical events, scientific procedures/experiments, or technical processes.
  • RST.9-10.3 Follow pecisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks, attending to special cases or exceptions defined in the text.
  • WHST.9-10.2 Write informative/expanatory texts, including narration of historical events, scientific procedures/experiments, or technical processes.

National Standards:

  • Chemistry: Intermolecular Chemical Bonding

Ohio Standards:

  • Identify questions and concepts that guide scientific investigations;
  • Formulate and revise explanations and models using logic and evidence (critical thinking);
  • Design and conduct scientific investigations;
  • Communicate and support a scientific argument

Content Knowledge

The testing of the properties of materials is an ongoing part of modern technology.

The development of improved methods of collecting and recycling materials.

The development of biodegradable materials.


Safety

Follow General laboratory safety - there are no hazardous materials used in this lab.

Caution should be taken when using sharp scissors.

Water spilled from the tensile test may create a slippery floor and walking hazard.


Applications

Materials structure determines function.

Recycling materials and ecological responsibility of consumers.


Assessment

The pre-assessment and post-assessment

Group presentation of "Stress of a Recycled Bag" activity


Other Considerations

Lesson Sequence: (based on 50 minute periods)


Printable PDF Worksheets

Pre-assessment

Post-assessment

Determining the Tensile Strength of Polyethylene Film

The Stress of a Recycled Bag with Presentation Rubric

Teacher Notes