Recycle

2-3
40-
to 50-minute sessi
ons
B-65
ACTIVITY OVERVIEW
In this activity students determine the chemical and physical properties of four plas-
tics. They then test a “mystery” sample to find out what it is. Based on the plastics’
chemical and physical properties, students relate possible uses for each plastic to its
properties.
KEY CONCEPTS AND PROCESS SKILLS
(with correlation to NSE 5–8 Content Standards)
1. Plastics can be identified based on their physical properties, including flexibility,
hardness, and density. (PhysSci: 1)
2. The properties of a material determine how it can be used. (PhysSci: 1)
3. Making decisions about complex issues often involves trade-offs. (Perspectives: 4)
4. Scientists think critically and logically to make the relationship between evidence
and explanation. (Inquiry: 1)
KEY VOCABULARY
chemical property
physical property
plastic
relative density
18Properties of Plastics
LA BO RAT
O
RY

MATERIALS AND ADVANCE PREPARATION
For the teacher
32 vials with caps
8 packets of table salt
ethanol
* water
10-mL graduated cylinder
2 strips each of:
blue polypropylene (PP)
green polyvinyl chloride (PVC)
red high-density polyethylene (HDPE)
yellow polystyrene (PS)
8 strips each of four unknown plastics (clear, black, orange, white)
1 bottle of acetone
* 1 glass container (beaker, petri dish, or jar)
* 1 heat lamp, hairdryer, or other heat source
* 1 metal ring stand and clamp (or similar setup)
* 2 wood strips or glass slides
* 1 pair of heavy-duty scissors (optional)
* 1 overhead projector
* paper towels
1 Transparency 18.1, ”Four Common Plastics”
1 Transparency 18.2, “Some Common Plastics and Synthetic Fibers
1 Transparency 18.3, “2005 U.S. Plastics Production”
1 Transparency 18.4, “Plastic Recycling Codes”
Scoring Guide: ANALYZING DATA (AD) and/or
Scoring Guide: EVIDENCE AND TRADE-OFFS (ET)
For each group of four students
* 1 petri dish or other container to hold set of plastic strips and plastic
squares
1 strip and square each of:
blue polypropylene (PP)
green polyvinyl chloride (PVC)
red high-density polyethylene (HDPE)
yellow polystyrene (PS)
unknown plastic (orange, clear, black, or white)
1 30-mL graduated cup
1 vial of alcohol
1 vial of water
1 vial of alcohol-water mixture
1 vial of saltwater
Activity 18 • Properties of Plastics
B-66

Properties of Plastics • Activity 18
B-67
1 15-mL bottle of hydrochloric acid
1 paper clip
1 pair of plastic forceps
* 1 additional plastic strip from plastic containers brought from home
(optional)
For each student
1 Student Sheet 18.1, “Properties of Different Plastics” (optional)
* 1 pair of safety goggles
1 copy of Scoring Guide: ANALYZING DATA (AD) (optional) and/or
1 copy of Scoring Guide: EVIDENCE AND TRADE-OFFS (ET) (optional)
*Not supplied in kit
Masters for Scoring Guides are in Teacher Resources III: Assessment.
For each group, prepare a set of four labeled vials, each containing one of the follow-
ing solutions: alcohol, water, alcohol-water, and saltwater.
Alcohol: fill with 8mL of denatured alcohol (ethanol)
Alcohol–water: fill with 4mL of alcohol and 4 mL of water
Water: fill with 8mL of water
Saltwater: fill with 8mL of water and one packet of salt.
Place the blue, green, red, and yellow plastic strips and squares for each group in a
small container for easy distribution. You will distribute the orange, clear, black, and
white plastic pieces when the students begin Part B of the Procedure. Be prepared to
provide fresh strips for each group.
Set up the equipment for the effects-of-heat test and effects-of-acetone test before class.
You may want to start these demonstrations as described in Teaching Suggestion 2 that
there will be observable differences in the plastic pieces to show the class in Teaching
Suggestion 3.
To demonstrate the effects-of-heat test you will need to set up a ring stand with a heat
source attached to it. Use a heat-lamp apparatus or a hair dryer as the heat source.
Clamp the four plastic strips to the ring stand, and with two strips of wood or two glass
slides sandwich the ends of the strips flat in the ring stand. A diagram of the setup is
shown below.
2461 LabAids SEPUP IAPS TG
Figure: PhysTG B 18.01

B-68
Students can test additional plastics by bringing in clean, empty plastic containers
from home. You can then use scissors to cut plastic strips for testing. Because of the
shape and sturdiness of many plastic containers, cutting strips can be time-consum-
ing and possibly hazardous were students to do the cutting. If you are planning to
have students test additional strips, be sure to prepare them in advance. Containers
for shampoos, medicines, milk, soft drinks, juices, or other foods are best. Be sure to
eliminate the recycling code on the containers from the samples. The recycling code
shows a number that identifies the type of plastic, as shown on Transparency 18.4,
“Plastic Recycling Codes.”
SAFETY
Students should wear safety glasses during this investigation. It is recommended that
students wear protective plastic gloves when working with caustics, such as
hydrochloric acid. Note, however, that the concentration that is used in this activity is
low enough that wearing gloves is not imperative. Check your school’s and district’s
safety requirements to determine if you must provide them in this activity.
Acetone is an extremely flammable liquid. Keep acetone and its bottle away from
heat, sparks, and open flames. Acetone will degrade most plastic containers except
polypropylene and polyethylene. Use acetone with adequate ventilation. Avoid
inhalation, ingestion, or repeated skin contact.
TEACHING SUMMARY
Getting Started
1. Discuss the useful properties of plastic.
Doing the Activity
2. Students investigate the properties of four plastics.
3. Students test the chemical and physical properties of an unknown plastic .
Follow-Up
4. (AD ASSESSMENT) The class discusses how the properties of plastics affect their use
and applies evidence to identify the unknown plastic sample.

B-69
BACKGROUND INFORMATION
Plastics
The first completely synthetic plastics to be commercially produced were those made
from phenol and formaldehyde. Leo Baekeland developed the chemical process in
1907 which created “Bakelite,” the first synthetic plastic. Phenolic plastics eventually
led to the development of urea and thiourea, which were used to make such products
as foam rubber cushions and melamine laminate furniture. As petroleum became a
major source of polymers the development of plastics through the 20th century accel-
erated and organic chemists invented sophisticated techniques that allowed them to
tailor a plastic for a specific purpose.
Today, most synthetic plastics are produced from oil or natural gas. Crude oil is com-
posed of hydrocarbons that vary in length and configuration and, as a result, have
different properties. To separate these hydrocarbons, chemists heat crude oil to
400˚C. Because the various hydrocarbons have different boiling points, they con-
dense at different temperatures. For example, naptha, a liquid, is made up mostly of
molecules containing 8–12 carbon atoms, and it condenses at 150˚C. Gases, includ-
ing ethane, methane, and propane, generally have 1–4 carbon atoms and condense
at 110˚C. The smaller hydrocarbons, particularly ethane (which is converted into eth-
ylene), are used for the manufacture of a whole variety of polymers, which will be
treated in more depth in later activities. About 84% of a typical barrel of crude oil is
converted to fuels that are burned for heating or to gasoline and jet fuel. Less than 3%
of the oil goes into the synthesis of plastics.
Even though the manufacture of most plastics begins with just carbon and hydrogen,
other elements can be involved. Oxygen, chlorine, fluorine, nitrogen, silicon, phos-
phorous, and sulfur are added to hydrocarbon chains to create certain plastics. Poly-
ethylene (PET) contains only hydrogen and carbon, while tetrafluoroethylene, better
known as Teflon, contains fluorine in place of the hydrogen atoms.
There are two categories of plastics:
1. Thermoplastics are those that can be continually and repeatedly formed and
reshaped with the application of heat and pressure. About 85% of all plastics pro-
duced are thermoplastics. Most recyclable plastics, such as polyethylene, polypropy-
lene, polystyrene, and polyvinyl chloride are thermoplastics.
2. Thermosets are those that cannot be reshaped once they are formed. This is usually
because those plastics have been cross-linked, and the cross-linked bonds cannot be
broken. About 15% of all plastics produced are thermosets. Examples include poly-
ester, polyurethane, and epoxy resins such as silicone.
REFERENCES
American Plastics Council. PIPS Year-end Statistics for 2005. Production, Sales, and
Captive Use. Plastic Industry Producers’ Statistics Group. Retrieved January 2007 from
www.americanplasticscouncil.org/s_apc/docs/1700/1678.pdf.

B-70
TEACHING SUGGESTIONS
GETTING STARTED
1. Discuss the useful properties of plastic.
Ask each student to name a product made of plas-
tic. Next ask, What makes plastic a useful material?
Develop a list of students’ responses. Some possible
answers are that plastics are lightweight, strong,
long lasting (durable), flexible, and available in all
sorts of shapes and colors. Point out that often one
plastic item has properties that are not shared by
another plastic item. For example, the clear plastic
wrapping on items such as CDs is easy to tear, while
plastic detergent bottles are fairly sturdy. This sug-
gests that there are different types of plastic, each
with its own physical properties.
Emphasize that physical properties of a substance
are characteristics that can be observed without
seeing how it reacts chemically with other sub-
stances. Make a list of some physical properties that
might distinguish plastics from other materials.
Prompt students to think back to the materials they
considered for drink containers in Activity 12, “Eval-
uating Materials,” and Activity 13, “ Life Cycle of a
Material.” Ask, If you were going to manufacture a
product such as a drink container, why might you
make it out of plastic? To this students may respond
that containers made of plastic are strong, durable,
flexible, and lightweight. They might also add that
it comes in many colors. Then ask, What are some
physical properties of plastics? Possible responses
include that they are hard, solid, flexible, and light
in weight. Point out that they are in fact relatively
low in density (mass per volume) compared to glass
and most metals. If students suggest color, point out
that it is not a physical property of the material
itself. Reiterate that most things made of plastic can
be dyed any color. Because of this, color is not an
inherent physical property for characterizing plas-
tics. In this activity, students will identify the prop-
erties of four different types of plastics.
DOING THE ACTIVITY
2. Students investigate the properties of four
plastics
Tell students they will investigate some of the chem-
ical and physical properties of four plastics. They
will use these characteristics to distinguish one type
of plastic from another and then use their data to
identify an unknown, or “mystery,” plastic. Explain
to students that their investigations involve a vari-
ety of chemicals and equipment. Review classroom
safety guidelines.
Go over how to pronounce each of the four types of
plastics. Display Transparency 18.1, “Four Common
Plastics.” Explain that the four pieces they will test
fall into one of these four types. There are many
more types, but these are the four major types they
will investigate. Point out the color coding that has
been done so students visually can tell one piece
from the next.
Review the physical and chemical properties listed
in Table 1, “Testing Properties of Plastics,” in the
Student Book. Explain to students that since plastics
can be molded and dyed, the shape and color of a
plastic is not characteristic of the type of plastic.
Review the information in the table that describes
how to test the properties of the plastic samples.
This activity provides the opportunity for students
to construct their own data table. You may decide as
a class or in groups of four the best data table for-
mat, which will reinforce students’ ability to design
a data table. Depending on the developmental
appropriateness, however, you may choose for stu-
dents to use optional Student Sheet 18.1, “Properties
of Different Plastics,” to record the results of their
tests.
As necessary, review the tests that students will con-
duct. One additional test, for which the materials
have been supplied, but that is not described in the
student book, is the affect of hydrochloric acid. To
conduct this test, show students how to drop 2 drops
of the acid on each of the strips of plastic. After
observing if the acid and the plastic react, students
should dip the plastic in water to rinse it, and dry it
with a paper towel.

B-71
While students are completing their tests, demon-
strate for the class the effects of acetone and heat on
the four known plastics as described in the Materi-
als and Advance Preparation section. Students
should notice that polystyrene bends the most in
response to heat, followed by polyvinyl chloride.
Polypropylene and high-density polyethylene are
unaffected. Polystyrene is soluble in acetone and
may swell and become very loose and stretchy. The
polyvinyl chloride will react to acetone in the same
way but to a lesser degree. Sample results for all
tests are shown in the table below.
Testing the Effect of Heat on Different Plastics
Clamp the four plastic strips to the ring stand as
shown below. Use two strips of wood (or two glass
slides) to sandwich the ends of the strips. Use a heat
lamp or hair dryer to test the effect of heat on the
plastics. Turn the heat source on the samples for at
least 10 minutes, making sure that the heat falls
evenly on all four strips. You may begin the test
while students are completing their own investiga-
tions, or you may have them observe the entire test
as you conduct it.
If you use a heat lamp (or 150–200 watt light bulb)
with a reflector as your heat source, the reflector
must have a ceramic base. Be careful when han-
dling these items; they can become very hot. An
illustration of the setup is shown in Advanced
Preparation above.
Testing the Effect of Acetone on Different Plastics
Pour a small amount of acetone into a glass con-
tainer, using enough to cover half the length of a
plastic strip. (Because acetone quickly evaporates
and diffuses through a room, you should wait to
pour the acetone until right before you conduct the
acetone test, and cover the container while con-
ducting the test.) Place one strip of each of the four
plastics in the acetone for at least five minutes. After
five minutes, remove the strips from the acetone
and place them on a paper towel in a well venti-
lated area away from any flames or sources of com-
bustion. Students can then examine the strips.
Sample Results, Student Sheet 18.1, “Properties of Different Plastics”
Polypropylene
(PP)
Polyvinyl chloride
(PVC)
High-density
polyethylene (HDPE)
Polystyrene
(PS)
Plastic is color-coded Blue Green Red Yellow
Flexibility Fairly flexible Very flexible Fairly flexible Not very flexible
Crease color Slightly white Still green Still red White
Hardness Gets scratched Gets scratched Gets scratched Gets scratched
Density relative to alcohol Sinks Sinks Sinks Sinks
Density relative to alcohol-
water mixture
Floats Sinks Sinks Sinks
Density relative to water Floats Sinks Floats Sinks
Density relative to saltwater Floats Sinks Floats Floats
Effect of acetone None Softens None Softens greatly
Effect of heat None Bends None Bends greatly
Reaction with HCl None None None None

B-72
3. Students test the chemical and physical
properties of an unknown plastic.
Tell students that they will now receive samples of a
mystery plastic. This plastic has been dyed a color
different than the four original samples. Not all
groups will be receiving samples of the same color.
Ask the student groups to decide which of the tests
used in this investigation they will conduct to iden-
tify the plastic, as described in Procedure Step 4.
Then they should design a data table to record their
results.
After students have constructed their data tables,
give each group a sample of one of the unknown
plastics, and allow them to conduct their tests. They
should check their results with the information they
recorded for each strip in their data table, “Proper-
ties of Plastics,” to determine the type of the mystery
plastic. If they do not have adequate information,
encourage groups to conduct additional tests until
they are able to identify the mystery plastic.
The color key that follows will help you check the
results of students’ tests. The results for each plastic
are shown in the table “Properties of Different Plas-
tics” in Teaching Step 2.
Students are not given this color key.
Key to Plastic Types
FOLLOW-UP
4. (AD ASSESSMENT) The class discusses how the
properties of plastics affect their use and
applies evidence to identify the unknown
plastic sample.
Ask students to identify the similarities and differ-
ences among the plastics they tested. Some of the
similarities, which may not be obvious to students,
are shown in their results in their tables, “Properties
of Different Plastics.” The plastics tested are fairly
low in density, somewhat flexible, scratch easily,
and are easily molded and dyed. In Analysis Ques-
tions 1 and 2 students are asked to identify specific
properties and to back their answers with their test
results.
Summarize the activity by highlighting the fact that
plastics are materials that can be shaped. The word
plastic itself comes from the Greek word plastikos
that refers to the ability to be molded or shaped.
Suggest the following as a working definition for
plastics: Plastics are a group of materials manufac-
tured primarily from petroleum and natural gas.
Many plastics are used to create products because
they can easily be formed, dyed, and molded into
any shape.
Begin by asking students, Which of the four types of
plastic you tested do you think is used most today
and why? Students may postulate that polystyrene
is used extensively because of its relative inflexibil-
ity, which could make it more sturdy and good for
forming food containers. They might also say that
low-density polyethylene would be used a lot to
hold certain chemical substances since it does not
weaken in acetone. To give students an idea of the
myriad types and names of common plastics and
those that are produced in the greatest numbers,
project Transparency 18.2, “Some Common Plastics
and Synthetic Fibers,” and Transparency 18.3,
“2005 U.S. Plastics Production.” You may choose to
ask the class to summarize the information shown
on Transparency 18.3 as an exercise in interpreting
data contained in a table.
Point out that it is not usually easy to tell one plastic
from another by simply looking. One way plastic
Plastic Type
Color of identified
plastic strip
Color of
“unknown”
plastic strip
Polypropylene
(PP)
blue clear
Polyvinyl
chloride (PVC)
green orange
High-density
polyethylene
(HDPE)
red black
Polystyrene
(PS)
yellow
white

B-73
manufacturers indicate the type of plastic is
imprinting its recycling code somewhere on the
product. Project transparency 18.4, “Plastic Recy-
cling Codes,” to show students the codes for types of
plastic containers. By finding this number on the
container, they will be able to easily identify the
type of plastic it is made of.
For Analysis Question 3, students’ responses will
depend on which plastic sample that they are given
to identify. They should support their identification
with their test results and then compare the physi-
cal properties of the unknown with the four known
plastic types investigated in Part A. Check their
responses for consistency between the properties of
the plastic and its identification. Use the ANALYZING
DATA (AD) Scoring Guide to provide feedback on
students answers. A sample Level 3 response is pro-
vided below.
Analysis Question 4 serves as a review of the con-
cept of relative density first developed in Issues and
Physical Science, Unit A, Activity 7, “Properties of
Solids.” You might find it useful to put one of each of
the plastic squares in each of the liquids to provide a
visual as students answer this question. Then lining
up the liquids as they are shown in the diagram will
help students determine which liquid is the most
dense and which it is the least dense.
EXTENSION
To further explore and identify kinds of plastics you
can have students test samples they bring from
home. Some students may be frustrated to find that
some of the samples do not exactly fit the properties
found with the pure sample strips from the kit. Tell
them that plastic products often contain additives,
such as fillers, plasticizers (which make them more
flexible), stabilizers, and lubricants that may alter
the properties. If students cannot make an exact
match from their data, they should select the plas-
tic that their sample resembles most closely.
SUGGESTED ANSWERS TO QUESTIONS
1 Using evidence from your table, “Properties of Plas-
tics,” identify the plastics which were scratched. How
will this property affect their use?
All of the plastics were scratched.
2. Below is a scale showing the relative density of the
four liquids you used to determine the density of the
plastics.
a. Which plastic sample was the most dense?
Explain your evidence.
Polyvinylchloride (PVC) is the densest
because it sinks in saltwater, the densest solu-
tion. The others float in saltwater.
b. Which plastic sample is the least dense? Explain
your evidence.
Polypropylene is the least dense because it
floats in the alcohol/water mixture, and all
of the other samples sink.
c. In your science notebook, make a copy of the
scale shown above. On it draw a labeled arrow
that shows where each plastic fits on this scale of
relative density.
3. (AD ASSESSMENT) What type of plastic is your
mystery sample? Explain the evidence you used to
come to this conclusion.
Level 3 Response
The white unknown sample is polystyrene. It is
not very flexible, the crease color is white, and it
sinks in water and water-alcohol mixture, but
floats in saltwater. Further testing showed that
the unknown plastic piece is softened greatly by
acetone and bends greatly when heat is applied.
It was also observed that it gets scratched, but
all of the plastics shown in the table do, so this
test doesn’t help determine which type of plastic
it is.
2561 LabAids SEPUP IAPS SB
Figure: PhysTG B 18.02
LegacySansMedium 10/11.5
0.80
Alcohol
1.10
Saltwater
1.00
Water
0.90
Alcohol/water
Relative density
PP HDPE PS PVC

B-74
4. You are a materials scientist asked to rec-
ommend a type of plastic for manufacturing three
products. Using the information in your table,
“Properties of Plastics,” choose the best plastic for
each of the following products. Be sure to include evi-
dence from the activity in your answer.
a. nail polish (high in acetone)container
Polypropylene or high-density polyethylene
because they are not affected in acetone
since it needs to not soften when containing
acetone.
b. dishwasher-safe food container
Polypropylene or high-density polyethylene
because they are not affected by heat, and a
dishwasher-safe container needs to be able to
withstand high temperatures.
c. sports drink container
High-density polyethylene because it does
not crease, and is not affected by heat. So if
the drink bottle sits in the sun it will not be
affected.

Issues and Physical Science • Transparency 18.1
©2007TheRegentsoftheUniversityofCalifornia
B-75
Four Common Plastics
Type of Plastic Common Uses
Polypropylene (PP)
Ketchup bottles,
yogurt containers
Polyvinyl chloride (PVC)
Shampoo and salad
dressing bottles
High-density polyethylene
(HDPE)
Milk containers,
orange juice bottles,
and bleach bottles
Polystyrene (PS)
Prescription bottles,
plastic utensils, cups
Color Key
Polypropylene (PP) Blue
Polyvinyl chloride (PVC) Green
High-density polyethylene (HDPE) Red
Polystyrene (PS) Yellow

B-77
Some Common Plastics and Synthetic Fibers
Material name Common or trade names Some uses
Acrylic Acrylan, Orlon Sweaters, carpets
Cellulose acetate Tenite, Chromspun, Celera
Toys, plastic forks, double
knit fabrics, curtains
Nylon Cantrece, Antron Clothing, carpets
Polyacrylic acid Acrylic paint Cards, homes, art work
Polyacrylonitrile Orlon, Acrilan Clothing fabrics
Polybutadiene Rubber Automotive tires
Polycarbonate Lexan, Merlon Football helmets
Polyethylene Alathon
Shopping bags,
electrical insulation
Polyethylene
terephthalate (polyester)
Mylar, Dacron, Avisco,
Jetspun, Zantrel
Soft drink bottles,
photographic film, audio
tapes, clothing, fabric
Polymethacrylate Lucite, Plexiglass
Aircraft windshields
and windows
Polypropylene Herculon, Vectra Luggage, fabrics
Polystyrene Styrofoam Foam cup
Polytetrafluoroethylene Teflon
Stain-proof coating on
upholstery, non-stick
coating on cookware
Polyurethane Foam rubber Sofa cushions
Polyvinyl acetate Vinylite Chewing gum, adhesives
Polyviny chloride Naugahyde, Koroseal
Raincoats, drain pipes,
records
Silicone RTV 615, Silastic
Water-repellant coatings,
lubricants
Spandex Lycra, Spandelle
Elastic waistbands, tights,
ski pants
Viscose rayon Cellophane Transparent tape

B-79
2005 U.S. Plastics Production
Type of Plastic Abbreviation Common Uses
Percentage of
U.S. Plastics
Production
in 2005
Polypropylene PP
Drinking straws,
bottle caps
and lids
21%
Polyvinyl
chloride
PVC
Food wraps,
water pipes
17%
High-density
polyethylene
HDPE
Milk jugs,
detergent bottles
19%
Liner low-density
polyethylene
LLDPE 14%
Low-density
polyethylene
LDPE
Grocery bags,
trash bags
9%
Thermoplastic
polyesters
(primarily
polyethylene
terephthalate)
PET, PETE
Soft drink
bottles, water
bottles
9%
Polystyrene PS
Fast food
containers,
foam cups
7%
Other plastics — Packaging 3%
Nylon — Clothing 1%

B-81
Plastic Recycling Codes
Plastic
Code
Abbreviation Type of Plastic
Common
Uses
PET, PETE
Polyethylene,
terephthalate
Soft drink bottles,
water bottles
HDPE
High-density
polyethylene
Milk jugs,
detergent bottles,
water bottles
PVC Polyvinyl chloride
Food wraps,
water pipes,
shampoo bottles
LDPE
Low-density
polyethylene
Grocery bags,
trash bags
PP Polypropylene
Drinking straws,
bottle caps
and lids
PS Polystyrene
CD jackets,
fast-food
containers
— Other plastics
Packaging,
some food bottles

Name Date
Issues and Physical Science • Student Sheet 18.1
B-83
Properties of Different Plastics
Polypropylene
(PP)
High-density
Polyvinyl
Chloride
(PVC)
Polyethylene
(HDPE)
Polystyrene
(PS)
Unknown
plastic
Plastic is
color-coded
Blue Green Red Yellow
Flexibility
Crease
color
Hardness
Density
relative
to water
Density
relative to
saltwater
Density
relative to
water-alcohol
mixture
Density
relative to
alcohol
Reactivity with
hydrochloric
acid
Effect of
acetone
Effect of
heat

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