IDENTIFICATION OF RECYCLABLE PLASTICS
THROUGH CHEMICAL, PHYSICAL, AND FTIR PROPERTIES
PA State Standards Addressed:
1.2.11.A
Read and understand the central content of informational texts and documents in all academic
areas.
Use teacher and student established criteria for making decisions and drawing conclusions.
2.4.11.E
Demonstrate mathematical solutions to problems.
3.1.12.C
Assess and apply patterns in science and technology.
Compare and contrast structure and function relationships as they relate to patterns.
3.4.10.A
Explain concepts about the structure and properties of matter.
3.7.10.A
Identify and safely use a variety of tools, basic machines, materials and techniques to solve
problems and answer questions.
3.7.12.A
Apply advanced tools, materials and techniques to answer complex questions.
Introduction:
Plastics are made to last forever (or almost!). Rather than continue to pollute the planet with this
“permanent” waste, most communities have an active program to RECYCLE plastic material
and to reprocess it into useful forms (packaging film, soda bottles, insulation, etc). There are
actually only a dozen or so BASIC polymer types, but there are hundreds of DERIVATIVES of
these basic forms of plastic. Using IR Scans and a Reflectance attachment, you can easily
characterize the TYPE of plastic in a sample and then compare it to a "Library" of Known
plastics in order to identify it.
Recycle
Number
1
2
3
4
5
6
7
Type of
Plastic
PETE
HDPE
V or PVC
LDPE
PP
PS
OTHER
Common Uses of Recycled Plastic
Soft drink bottles
Milk bottles, detergent bottles, orange juice bottles
Shampoo bottles, salad dressing bottles, vinyl, PVC pipes
Newspaper bags
Catsup bottles, yogurt cups
Foam cups, prescription bottles, plastic knives, forks, & spoons
Plastic fences, other plastics
The MD-IR region from 4000-600cm-1 that generates the most specific data on organic
molecules that is used to do both Qualitative ID and Quantitative Concentration analyses of
many types of Sample materials.
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Guiding Questions:
1. Explain how it is possible to determine the recycle number of an unnumbered plastic.
2. How can infrared spectroscopy be used to identify certain bonds in recycled plastics?
Vocabulary:
Density – mass (g) divided by volume (mL)
Archimedes' principle - Any body wholly or partially immersed in a fluid experiences an
upthrust equal to, but opposite in sense to, the weight of the fluid displaced. ("Fluid" means
liquid or gas.)
Materials:
4 Beakers
Methanol
dI water
Acetone
NaI
Hot plate
Plastic samples
Forceps
2 Test tubes
Stirring Rod
4 Disposable pipets
Weigh boat
Scale
Volumetric Pipet
FTIR
Printer
Safety:
 Do not eat or drink anything in lab.
 Wear safety goggles at all times.
 If you get any chemicals on your hands, wash immediately with soap and water.
 Be careful Hot plates can melt wires and cause burns.
Procedure:
Part A: Measuring the density of the plastic
1. You should have 4 beakers one labeled methanol, a second labeled water, a third labeled
acetone, and a fourth labeled NaI. Put the water on the hot plate and turn the temperature
knob to 8.
2. Cut a sample of plastic about the size of a mini-M&M from one of the labeled pieces at your
station and record the letter identifying your unknown plastic in your data table.
3. Using the forceps, immerse the sample of plastic in methanol beaker. This removes any
bubbles that might affect the density test. Then transfer the sample to the test tube labeled
water. Try sinking your sample with a stirring rod. Record whether the sample floated or
sank in your data table.
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4. If the plastic floats:

Add methanol – a few drops at a time using the disposable pipets – to the test tube and
carefully swirl or stir the solution. Then stir it again (it must be thoroughtly mixed).
During the stirring process, be careful not to create tiny air bubbles, which can attach to
the piece of plastic. If this happens, the plastic will float regardless of the solution’s
density. Using the stirring rod, carefully remove the bubbles from the plastic piece.

Continue adding drops of methanol, stirring frequently, until the plastic is suspended in
the solution.
If the plastic sinks:

Add the NaI – a few drops at a time using the disposable pipets – to the test tube and
carefully swirl or stir the solution. Then stir it again (it must be thoroughtly mixed).
During the stirring process, be careful not to create tiny air bubbles which can attach to
the piece of plastic. If this happens, the plastic will float regardless of the solution’s
density. Using the stirring rod, carefully remove the bubbles from the plastic piece.

Continue adding drops of methanol, stirring frequently, until the plastic is suspended in
the solution.
5. At this point, the density of the plastic should equal that of the solution. Place a weigh boat
on the scale and zero. Remove 1.00 mL of the solution using the volumetric pipet and place
it in the weigh boat. Record the mass of the solution.
6. Repeat steps 1-5 with your second piece of plastic. When you have done both pieces of
plastic, continue.
Part B: Other physical and chemical properties
1. If the plastic sample floated in water in Part A, skip steps 2-4 of this part, go to step 5 of this
part.
2. Using forceps, place a sample of your plastic in acetone for 20 seconds. Remove the sample
and press firmly between your fingers or the forceps. Try to scrape off some plastic with
your fingernail or your forceps. Discard in the container provided. (Acetone is a major
ingredient in nail polish remover. If you are sensitive to it, you may want to avoid testing
with your hands.) Record your observations.
3. If you have a reaction, STOP. Skip the following steps and proceed to Part C if you have
done your second piece of plastic. If you have not done your second, go back to step l of this
section.
4. Using forceps, hold a sample in boiling water for 30 seconds. See if the plastic curls in the
hot water. Record your observations. STOP. Skip the following steps and proceed to Part B
if you have done your second piece of plastic. If you have not done your second, go back to
step l of this section.
5. If your sample floats in water, place another sample about the same size in a test tube
labeled isopropyl alcohol. Record your observations.
6. If your sample sinks, STOP. Skip the following steps and proceed to Part C if you have
done your second piece of plastic. If you have not done your second, go back to step l of this
section.
7. Force the sample to the bottom of the test tube. Wait 5 minutes. Record your
observations. If you have done your second piece of plastic, proceed to Part C; otherwise,
return to step 1 for the second piece of plastic.
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Part C: Identification using FT-IR Spectrometer
1. Make sure that there is no sample left in the FT-IR.
2. Click on Collect; BACKGROUND on the right side of the screen. A keyboard will come
up, type in Background and click on the Green Arrow.
3. A graph will come up. Go to View, Clear all Spectra, click Yes to save.
4. Place your sample on the Swaptop, screw down the sample compression tip.
5. Click on Collect; SAMPLE on the right side of the screen. A keyboard will come up, type
in SampleName.Period.Initials (ie: Recycle2.pd1.jse) and click on the Green Arrow.
6. The spectrum will be displayed. To print choose File; Print; Landscape; Ok.
7. Remove your sample from the FT-IR and Repeat steps 4-6.
Data Table:
Sample 1
Sample 2
Sample Identification Letter
Sample Appearance
Water Test (circle one)
SINKS
or FLOATS
SINKS
or FLOATS
SINKS
or FLOATS
SINKS
or FLOATS
Density (g/mL)
Isopropyl Alcohol Test (circle one)
Submersion Test
Acetone Test (circle one)
SOFTENS or DOESN'T SOFTEN
SOFTENS or DOESN'T SOFTEN
Heat Test (circle one)
SOFTENS or DOESN'T SOFTEN
SOFTENS or DOESN'T SOFTEN
Questions:
1. When you have completed all parts of the lab, ask your teacher for the density table. Which
plastic samples did you have?
2. Check this against the flow chart for chemical and physical properties. Do they agree with
your conclusions from the density experiment?
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3. Which plastic did you test on the IR? Did it agree with your previous data?
4. Identify which tests are chemical and which tests are physical?
5. From what you observed, tell the approximate density of the isopropyl alcohol solution and
explain.
6. Your boat is sinking about two miles off shore and you cannot swim. You notice six large
solid plastic blocks labeled 1, 2, 3, 4, 5, 6. Which three would you grab and why?
7. You wish to make a plastic handle for a cooking pan out of recycled plastic. Which would
be good choices? Which would be poor choices? Why?
8. Why is it important to dislodge any adhering bubbles in the density tests?
9. What would happen to the water density test if LDPE and PP were mixed? If PET and
HDPE were mixed? Why?
10. You decide to jazz up your bathroom cabinet by transferring your fingernail polish remover
into a more stylish container. The next day you find a messy blob. What type of plastic was
the container made of? What type(s) would have been better choices?
11. What do you use in the FT-IR to characterize the plastic? What do these represent?
Credits: This experiment was written by Teresa Setliff of Bassett High School and Gail Cook of
Radford High School. Portions of the activity were adapted from the "Hands On Plastics" Kit
(www.HandsOnPlastics.com)
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IDENTIFICATION OF RECYCLED PLASTICS
Teacher Notes
Time needed to complete lab: This lab will take on average two single periods or one double
(block) period.
Target grade level: This lab is primarily for Chem I or Chem II, but it may be adapted for
applied or practical chemistry.
Objectives:
The objective is for the student to be able to identify different recycled plastics using physical
and chemical properties and infrared spectroscopy. Students will be able to identify certain
bonds in the plastics through the use of infrared spectroscopy.
Major concepts:
This lab teaches about physical and chemical properties, density, and chemical bonds.
Preparations:
Find different plastics with Recyclable numbers 1-7 and some that are not labeled.
Typical results or sample data:
Sample 1
Sample 2
Sample Identification Letter
Sample Appearance
Water Test (circle one)
SINKS
or FLOATS
SINKS
or FLOATS
SINKS
or FLOATS
SINKS
or FLOATS
Density (g/mL)
Isopropyl Alcohol Test (circle one)
Submersion Test
Acetone Test (circle one)
SOFTENS or DOESN'T SOFTEN
SOFTENS or DOESN'T SOFTEN
Heat Test (circle one)
SOFTENS or DOESN'T SOFTEN
SOFTENS or DOESN'T SOFTEN
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Answers to questions:
1. When you have completed all parts of the lab, ask your teacher for the density table. Which
plastic samples did you have?
Plastic
1 = PETE
2 = HDPE
3 = PVC
4 = LDPE
5 = PP
6 = PS
7 = Other
Density (g/mL)
polyethylene terephtalate
high density polyethylene
polyvinyl chloride
low density polyethylene
Polypropylene
Polystyrene
(often a mixture)
1.39
0.95 - 0.97
Varies
0.92 - 0.94
0.90 - 0.91
1.05 - 1.07
Varies
2. Check this against the flow chart for chemical and physical properties. Do they agree with
your conclusions from the density experiment?
3. Which plastic did you test on the IR? Did it agree with your previous data?
Answers will vary
4. Identify which tests are chemical and which tests are physical?
Chemical – Acetone test, Heating test
Physical – IPA test, Density, Appearances, Submersion test, Water test
5. From what you observed, tell the approximate density of the isopropyl alcohol solution and
explain.
IPA’s density = 0.7854 @ 20ºC
6. Your boat is sinking about two miles off shore and you cannot swim. You notice six large
solid plastic blocks labeled 1, 2, 3, 4, 5, 6. Which three would you grab and why?
I would grab 2, 4, and 5 because their density would be less then the density of
water.
7. You wish to make a plastic handle for a cooking pan out of recycled plastic. Which would
be good choices? Which would be poor choices? Why?
I would use the densest plastic to make the handle. The less dense the plastic the
more likely it will be to curl.
8. Why is it important to dislodge any adhering bubbles in the density tests?
Bubbles cause all plastics to float no matter what the density is of the plastic and
the liquid it is in.
9. What would happen to the water density test if LDPE and PP were mixed? If PET and
HDPE were mixed? Why?
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If LDPE and PP were mixed the density would not change greatly, but would be
around 0.92.
If PET and HDPE were mixed the density would change greatly, because there is
a large difference in the density of the two plastics.
10. You decide to jazz up your bathroom cabinet by transferring your fingernail polish remover
into a more stylish container. The next day you find a messy blob. What type of plastic was
the container made of? What type(s) would have been better choices?
11. What do you use in the FT-IR to characterize the plastic? What do these represent?
In the FT-IR the chemical bonds form peaks at certain wavenumbers between
4000-600cm-1, these peaks are used to identify different plastics by identifying
what the plastics are made of.
Extension:
As an extension to this lab, you can take plastics that the companies choose not to mark with the
recyclable number and determine what the recyclable number.
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