Materials Included In Kit

Additional Materials Required

Prelab Preparation

Cut the shrink plastic sheets in half to obtain approximately two 8" x 5" sheets. One sheet should be given to each student group to complete the procedure as written. Note: The size of the original shrink plastic sheets supplied in this kit may be slightly larger.

Safety Precautions

Shrink material is HOT when removed from the oven. Allow to cool before touching. Wear an oven mitt or insulated gloves when removing the baking pan from the oven. Protect a metal pan or cookie sheet with a piece of aluminum foil to prevent shrink plastic from sticking to the metal. Do not put shrink plastic material on a hot plate or in a microwave oven. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Dispose of the shrink plastic material in the solid waste disposal.

Teacher Tips

• Enough materials are provided in this kit for 15 groups of students working in pairs.
• Store shrink plastic sheets in a cool, dry place until use.
• Extra shrink plastic sheets have been supplied in this kit for teacher demonstrations, practice, etc.
• Do not use a microwave oven! For best results, use an electric oven or a toaster oven. A gas oven may not provide even heat and may cause uneven results.
• If an oven is not available, you can shrink shrink plastic with a heat gun. Simply hold the shrink plastic with tongs or an insulated glove above a heat-proof surface such as a baking sheet. Heat the material with a heat gun. Keep the heat gun moving. Occasionally turn the shrink plastic over to heat the opposite side. Heating one spot for too long will melt the shrink plastic. As it shrinks, the plastic will curl. When done, lay the shrink plastic on a heat-proof surface to cool. (Note: This procedure takes a lot of practice to perfect.) The final shrink plastic will not be as flat as they would have been if shrunk in an oven.
• Compile the classroom results for density and the percent change in dimension values to obtain classroom averages.
• Other plastics can also be shrunk. Obtain two clean, dry, plastic soda bottles (16-oz, 1-L or 2-L). Remove the cap and plastic base. Keep one bottle as a control. Place the other bottle on a baking sheet and bake it in a preheated 325 °F oven. Heat the plastic for three to five minutes. Remove carefully and allow the bottle to cool. Compare the bottle to the control.
• Additional shrink plastic sheets are available from Flinn Scientific (Flinn Catalog No. AP5451).
• Additional metal calipers are available from Flinn Scientific (Flinn Catalog No. AB1006).

Further Extensions

• Place a shrunken shrink plastic on the tray in the oven. Heat at 325 °F for three to five minutes and remove. Wearing insulated gloves, pick up the hot shrink plastic and stretch it. Does it stretch easily? If the restretched shrink plastic is placed in the oven, does it shrink back to its previous size?

Sample Data

Answers to Questions

1. Calculate the loss in dimension and the percent loss in dimension (shrink rate) for the length, width and area of each shrink plastic sample using Equations 4 and 5.
   {12688_Answers_Equation_4}
   {12688_Answers_Equation_5}
   {12688_Answers_Table_2}
2. Did the shrink plastic samples shrink uniformly in all directions (length, width and height)?

   Overall, the length and width shrinkage ratios were fairly similar. The length shrinkage ratio was slightly smaller than the width. The area shrinkage ratios (81%–84%) were higher than the length and width values.

3. How did the thickness (height) and volume of the shrink plastic samples compare before and after they were shrunk?

   The height or thickness of the shrink plastic samples increased dramatically after they were shrunk. The calculated volume values were nearly identical before and after the shrinking process.

4. How did the calculated densities of the three shrink plastic samples compare before and after they were shrunk? Calculate the average density of the three shrink plastic samples after shrinking.

   The calculated densities of the three shrink plastic samples remained the same before and after they were shrunk. The average density of the samples was 1.03 g/cm³.

5. How does the calculated average density of the samples compare to the density of water?

   The calculated density average density of the samples was slightly greater than that of water. Given this average density, each individual shrink plastic sample may or may not sink in water.

6. How do the results of this activity relate to the law of conservation of mass?

   The masses of the two shrink plastic samples were exactly the same before and after they were shrunk. The other sample’s mass was only 0.1 g heavier after shrinking. In general, the given results support the law of conservation of mass—during any chemical reaction or physical change mass is neither created or destroyed, it is conserved.

Introduction

Measurement is a basic and essential component in many science laboratory investigations. In this activity, measurements of an incredible shrinking material known as shrink plastic will be taken before and after the material is shrunk and the results compared.

Concepts

• Polymers
• Density
• Measurement
• Law of conservation of mass

Background

Shrink plastic is made of a special bi-axial oriented type of polystyrene; a common plastic or polymer. Bi-axial means that the material shrinks evenly in both directions when heated. The bi-oriented material is made by extruding, or stretching, polystyrene film under stress. Upon heating to 275 °F, the film exhibits what is called a “memory effect,” softening and shrinking to its original pre-stressed size. The polystyrene most commonly used in food packaging is mono-axial oriented polystyrene, which means that it will shrink more in one direction than the other when heated. This will have the effect of distorting a picture as it shrinks.

Precise measurement of the properties of an object or substance is an essential skill in many laboratory investigations. In the science classroom, students use basic instruments to measure properties of objects. The first goal of this activity is to measure the dimensions of shrink plastic pieces before and after they are shrunk and then determine their area and volume. The area and volume of any regular solid can be calculated using Equations 1 and 2, respectively. The length, width, and height of the shrink plastic in this activity must be estimated using reliable measuring instruments.

Once the shrink plastics’ volume has been calculated, and the mass has been obtained, the density of the shrink plastic can also be calculated using Equation 3. In this activity, the law of conservation of mass will also be studied. The law of conservation of mass states that in any chemical reaction or physical change mass is neither created or destroyed, it is conserved. For example if an ice cube weighing 20 g is melted, 20 g of liquid water should remain. This law will be further explored using the data gathered from this experiment.

Experiment Overview

The purpose of this activity is to take careful measurements of shrink plastic before and after it has been shrunk. The area, volume, mass and density of the shrink plastic will then be compared and contrasted.

Materials

Safety Precautions

Shrink material is HOT when removed from the oven. Allow to cool before touching. Wear an oven mitt or insulated gloves when removing the baking pan from the oven. Protect a metal pan or cookie sheet with a piece of aluminum foil to prevent shrink plastic from sticking to the metal. Do not put shrink plastic material on a hot plate or in a microwave oven.

Procedure

1. Preheat an oven (or toaster oven) to 275 °F.
2. Obtain an 8" x 5" sheet of frosted shrink plastic material.
3. Using a ruler and a pencil, outline three rectangular and/or square pieces on your sheet.
4. Cut out these three rectangular or square pieces using scissors.
5. Make each shrink plastic piece unique by drawing a picture, design or writing a message on each piece using colored pencils.
6. Distinguish each piece using the features drawn in step 5. Give each shrink plastic piece a unique name and record these names on the Shrink Plastic Measurement Worksheet.
7. Using a metric ruler and/or calipers, measure the original length and width of each piece to the nearest 0.1 cm. The height (thickness) of the shrink plastic sheet has been predetermined to be 0.025 cm. Record these values on the worksheet.
8. Using a balance, weigh each of the shrink plastic pieces. Record the mass to the nearest 0.1 g on the worksheet.
9. Calculate the area of each piece using Equation 1 from the Background section. Record these values on the worksheet.
10. Calculate the volume of each piece using Equation 2 from the Background section. Record these values on the worksheet.
11. Calculate the density of each shrink plastic piece using Equation 3 from the Background section. Record these values on the worksheet.
12. Place your three shrink plastic pieces on a baking sheet and place them in the oven. If the oven has a window and a light, watch as the plastic material shrinks. Observe the behavior of the shrink plastic as it shrinks.
13. Heat for five to six minutes. Carefully watch the baking process. Once the pieces are in the oven, within one to two minutes, the shrink plastic material will usually begin to curl. It will shrink in size and then begin to flatten. When the material flattens, immediately remove the baking sheet from the oven using an oven mitt or insulated gloves. Note: Do not overbake! Over-baking will dull the colors on the shrink plastic and cause the edges to become irregular.
14. Allow the material to cool before removing it from the baking sheet.
15. Using a metric ruler, measure the final length and width of each shrunken shrink plastic piece to the nearest 0.1 cm. Using calipers, measure the height (thickness) of each shrunken shrink plastic piece to the nearest 0.01 cm. Record all measurements on the worksheet.
16. Calculate the final area of each shrunken shrink plastic pieces using Equation 1 from the Background section. Record these values on the worksheet.
17. Calculate the final volume of each shrunken shrink plastic piece using Equation 2 from the Background section. Record these values on the worksheet.
18. Using a balance, weigh each of the shrunken shrink plastic piece. Record the mass to the nearest 0.1 g on the worksheet.
19. Calculate the density of each shrunken shrink plastic piece using Equation 3 from the Background section. Record the calculated density value on the worksheet.
20. Answer the Post-Lab Questions on the Worksheet.
21. Please consult the instructor for proper disposal of the shrink plastic.

Student Worksheet PDF

12688_Student1.pdf