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Polymer Science for the Elementary
School Classroom*
Catherine A. Chess
Laura Kosbar
Sharon L. Nunes
IBM Research
Thomas J. Watson Research Center
Yorktown Heights, New York 10598
* adapted from the IBM Research "Family Science" Program. Sponsored by the IBM Research
Local Education Outreach program, Jim Wynne - Program Manager.
-2Updated: 01-18-2010
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Polymers
There are many solid materials that occur naturally in the world around us. Rocks, sand, salt, and
diamonds are all examples of such solids. In contrast, polymers are materials that generally DO
NOT occur naturally. There are a few natural polymers such as cotton and some biological
polymers such as proteins and DNA (found in your body) but most polymers are man-made materials. The more common terminology for man-made polymers is plastics. These materials are
specifically engineered to have many different and useful properties. All of the plastics used in
your house are polymers, as are many of the clothes you wear.
The word polymer comes from Greek, and means MANY (poly) PARTS (mer). Polymers are
very long "chains" (they look like cooked spaghetti!) which are composed of many small molecules. The small molecules can be attached together in many different ways to make polymers
with very different physical properties. We can engineer polymers that prevent food from sticking to frying pans; polymers can be made to be 'oxygen permeable' for soft contact lenses; or
polymers can be very strong (like fishing line). Some polymers are soft, like foam pillows and
some are hard like PVC pipes.
Polymers and plastics are found in every aspect of our life. Nylon and polyester are two important polymers used to make clothes. Think of sports helmets, garbage bags, soda bottles, water
bottles, food containers, plasticware, foamed insulation, toothbrushes, transparent tape, epoxy
glue, acrylic paint, refrigerator housing, tires, electronic parts, radio casings, beepers, cosmetic
containers, toys, swim suits and beach toys, racquet balls, lunch trays, sunglasses, camera film,
tents, and many, many more items. There is hardly a part of our life today that is not touched by
these man-made materials.
Polymers are often classified according to how they behave when heated. THERMOPLASTIC
polymers can be melted and hardened over and over again (like "Perler Beads" and "Fantastic
Plastic"). Drinking cups, polyethylene milk jugs, and plastic sandwich bags are examples of
thermoplastic polymers. THERMOSETTING polymers undergo a chemical reaction when
heated and cannot be melted after they are set (molded). Examples of a thermoset polymer are
electrical outlets, kitchen-utensil handles, Formica counter tops, and Creepy Crawlers.
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Demonstration: Spaghetti as a model for polymers
Here are two bowls of spaghetti. The small bowl has a few strands of spaghetti that are tangled
up together. If you pull on one end of the tangle, the strands easily pull apart. However, in the
large bowl of spaghetti there are many more strands of spaghetti and they are much more entangled. If you try to pull the bunch apart it is much more difficult since the strands are tangled up
and sometimes tied in knots. The big bowl of spaghetti is like a polymer with superior chemical
and physical strength (like a car tire). The small bowl of spaghetti is more like a weak polymer
such as paraffin wax where the molecular chains break easily. Notice that cold spaghetti chains
are not very flexible and it is difficult for the chains to move without breaking.Warm spaghetti
chains are more flexible, and move around each other more easily.
-4One way to change the way these polymer chains slip and slide over each other is to put an additive into the original formulation. If we take our bowl of (cold) spaghetti "chains" and add some
oil or spaghetti sauce, the chains will become more flexible and move around easily . Many
polymers are made with additives in them to make the chains more flexible. PVC pipes are very
rigid, but PVC raincoats are very flexible and pliable. The additives used to make the PVC raincoat help the polymer chains remain flexible. Other additives are used to add stiffness, or color.
Separation and Identification of Polymers
Plastics used in our homes can be recycled and reused so as to minimize waste. Have you ever
wondered what the numbers on the bottoms of the plastic containers mean?
Codes for Recycled Plastics: All the items with the same numbers are made of the same polymers:
Type 1 is polyester (PETE)
Type 2 is high-density polyethylene (HDPE)
Type 3 is vinyl (V)
Type 4 is low-density polyethylene (LDPE)
Type 5 is polypropylene (PP)
Type 6 is polystyrene (PS)
Type 7 is "Other".
What does this mean? Is it recyclable? (Answer: Type 7 plastics are laminated materials, meaning that they are composed of layers of different plastics. Since these plastics cannot be separated, these items are not as easy to recycle).
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An Experiment to Try at Home: Sorting Activity - Collect several pieces of plastic in
a box over the period of a couple weeks. Try to sort the same materials (ie all number 1 together)
without looking at the code printed on the surface. Try some of the following:
milk containers
soda bottles
detergent bottles
water bottles
containers and covers from dairy foods
meat trays
microwave trays
Sort out the materials and try to find all the pieces that are made of the same polymer. This is
not as easy as it sounds!! Look for the recycling numbers on the bottoms to match the similar
materials. Did you know that women's stockings and the brushes on toothbrushes can both be
made of nylon, and that soda bottles and shirts can both be made of polyester? Even though two
materials look and feel very different, they can still be made of the same polymer. Lots of times,
the color or thickness of the container can fool you into thinking two plastics are different when
they are not. To understand how different polymers can have the same chemical formula and yet
have very different physical properties, lets compare this to a common example such as baking.
List 1: Basic materials: milk, sugar, flour, eggs, butter
-5List 2: Additives: nuts, chocolate chips, M+M's, raisins, flavorings, food coloring
From the items in List 1 you can make all kinds of things: cakes, breads, waffles or cookies, depending on the ratio of the starting ingredients. If you add List 2 items, you can change the properties of the baked good; its texture and flavor depend very much on which additives you use.
Yet they are all still composed of the same main ingredients. Thus, we can engineer the properties of a cookie (texture, taste) in much the same way we engineer polymer materials to have different properties.
Look through your home to see what plastics are in each room of your house. If you did not have
this plastic item, what would you use in its place? (e.g. for toothbrushes, for stockings, for containers, for transparent tape...what would you substitute that is not plastic?) Can you identify any
of the plastics you find? Keep count of the types of plastic containers that you and your family
discard each week for 2-3 weeks. Are you conscientious about recycling your plastic containers?
What do you think happens to containers that cannot be recycled?
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Experiment: Identification of Polymers (Density)
Materials:
* Small samples of the following polymers: PETE, HDPE, V, LDPE, PP, PS (see above section)
* Liquids to test polymers (vegetable oil, alcohol, water, glycerin)
* Small bottles or cups to hold liquids (or styrofoam egg cartons)
* Craft sticks
Procedure: Place four clean containers on a flat surface. Pour vegetable oil, water and glycerin
into containers for testing plastics (one liquid per container; do not mix). Mix three parts of 70%
isopropyl rubbing alcohol with two parts water, and pour this into last container. Test plastics by
dropping into one of the liquids. If it does not sink immediately, push it below the surface with a
craft stick and see if it sinks or floats. Test all of the plastic samples in the liquids provided and
compare your results with the chart below. If you use the same plastic sample in more than one
liquid, the glycerin and oil should be tested after the water and alcohol/water. Try to wipe the
plastic sample before immersing into another liquid. Ideally only one sample should be tested in
one liquid to prevent contamination and incorrect results. (Recommend 4 identical samples be
prepared and one tested in each liquid to prevent contamination.)
PLASTIC
PETE
HDPE
V
LDPE
PP
PS
Density Table - Do the plastic samples float?
VEG.OIL
ALC/H20
H20
GLYCERIN
NO
NO
NO
NO
NO
NO
YES
YES
NO
NO
NO
NO
NO
YES
YES
YES
YES
YES
YES
YES
NO
NO
NO
YES
Discussion: Did you notice that the vinyl (V) and polyester (PETE) samples respond the same?
How can you tell them apart? Try bending a piece of each plastic. Are they different? (The vinyl
-6should whiten when bent). When polymers are recycled, they must be separated by type. An easy
way to do this is to shred the plastics, place them in a large water bath and recover the "light"
plastics (they float on water) separately from the "heavy" plastics (they sink in water). Several
liquid baths can be used to continue separating the plastics, similar to what you did in the experiment above.For reference information, approximate densities of some common plastics
(g/cc) are included here. Using this information and the previous table (floating plastics), can you
estimate the densities of the liquids used?
PP = 0.90, LDPE = 0.915, HDPE = 0.95, PS = 1.04 V = 1.3, and PET = 1.35.
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Demonstration: Happy/ Unhappy Balls
The Happy and Unhappy balls are both small black spheres of polymers. If you drop them both
at the same time from the same height you will find that one bounces and one just lands with a
thud! This is an example of two very similar looking materials that have extremely different
physical properties. Both balls are made from a rubber-like material. The molecular structure of
the two materials is obviously very different!!
BE CAREFUL NOT TO BOUNCE THE HAPPY BALL INTO A FRAGILE OBJECT!! USE
IT OUTSIDE. WEAR PROTECTIVE GLASSES INSIDE!
Happy Ball: Polybutadiene with additives- Used for basketballs, racquetballs, and other objects
which must bounce. Unhappy Ball: (Co-polymer of poly styrene-butadiene or poly vinylbutadiene.) Good for automobile tires to absorb bumps; used as lining of ballistic containers;
used by bomb squads to absorb energy
References: D.A. Katz, 'Investigations in Chemistry', 1990 (David Katz is a Professor at the
Community College of Philadelphia, 1700 Spring Garden Street, Philadelphia, PA 19130. He
has written extensively about the chemistry of toys.)
Edmund Scientific Co, 101 E. Gloucester Pike, Barrington, NJ 08007
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Experiment: Bubble Gum Fun
Did you know that bubble gum was made of rubber, plastic and wax??? Of course, sugar and
flavorings are also added to make the gum taste good, and coloring is added to make the gum
more appelaing. The rubber makes the gum stretch and expand. Plastic helps make the gum easier to chew, while the wax helps maintain the shape of the gum in the package. In fact, gum with
a high rubber content produces better bubbles. The rubber polymer chains in the gum are in a
tangled mess (like the spaghetti demonstration we mentioned earlier). When you blow on the
gum, the polymer strands stretch out into long chains allowing the gum to expand. The chains
relax again into a tangle when the bubble pops. Lets investigate what happens when we chew on
a piece of bubble gum!
Materials:
* A piece of bubble gum
* A scale capable of measuring 10 grams
* Weights for the scale (or paper clips)
-7* Some sugar (restaurant packets are good)
Procedure: Unwrap the piece of bubble gum. Do not throw out the wrapper. Place the wrapper
on the scale and then put the gum on top of the wrapper Determine the combined weight of the
gum and its wrapper..Take the gum off the scale and chew it for 3-4 minutes.Put it back on the
scale (in the wrapper) and determine its new weight. Why do you think the gum weighs less?
What happens to the gum as you chew on it? If you chewed the gum for 30 minutes, how would
it taste after this amount of time? Remove the gum/wrapper from the scale. Place some sugar on
the scale to equal the amount that was lost by chewing the gum. Are you surprised??
References: Article by Josh Plaut, 'Popse', in Science World, Sept. 4, 1992
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Demonstration: Needle and Balloon trick
Have you ever seen a magician stick a needle through a balloon? You can do the same trick at
home, and can explain to your friends that it is not a trick at all, but science! A balloon is made
up of long tangled polymer chains (remember our spaghetti model?). As a balloon is blown up,
the polymer chains stretch, but they stretch mostly on the sides, and very little at the tied end,
and the nipple end opposite the tie. If you use a lubricated needle or bamboo skewer and poke it
through the nipple end of the balloon, the balloon should not pop. The polymer chains are not
stretched very much and they will be able to move out of the way of the needle. If the needle is
poked through the side of the balloon however, it should pop; this is because the polymer chains
are stretched very tightly on the sides, and as the needle breaks these chains, air rushes out of the
balloon and enlarges the tear. (A small air leak may be felt after the needle is pulled out of the
nipple end of the balloon. Pop the balloon quickly or it may become too deflated to pop even
from the side.)
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Experiment: GLUEP (Homemade Slime)
Materials:
* Saturated Borax solution (see below)
* Neon color Elmers' Glue (not all brands work as well) or white Elmer's Glue and food coloring
* Water
* Measuring utensils (for 10 ml and 15 ml)
* Disposable cup and stirrer for mixing
* Baggie recommended for storage
Procedure: (PARENTAL SUPERVISION REQUIRED) Prepare saturated Borax solution by
mixing 1/4 cup of 20-MuleTeam Borax with 1 qt WARM water. Stir/shake well (not all solid
will dissolve).Measure 15ml of Elmers glue and pour into disposable container. Add 10ml of water and stir well. Add 15 ml of Borax solution, stirring continuously. "Knead" the mixture if necessary (after placing in Baggie). Pour excess liquid into waste container or toilet (LIQUID
ONLY).
-8DO NOT DISPOSE OF GLUEP IN TOILET!! (USE WASTE BASKET ONLY). THIS
MATERIAL MAY STAIN WOOD FURNITURE/FLOORS; KEEP IN BAGGIE WHEN
NOT IN USE!
Discussion: When the Borax solution is added to the Elmer's glue, it crosslinks the long polymer
chains (chemically reacts with the glue and ties the polymer chains of the glue in "knots"). A
way to demonstrate this effect to children is by comparing it to a ladder. The sides of a ladder
can move (flow) up and down before the rungs (steps) of the ladder are added to it. The rungs, or
steps, prevent the sides of the ladder from moving up and down. Young children may enjoy making a human ladder (without rungs, then with rungs) to demonstrate this effect.
References: GLUEP and polymer density experiments were adapted from "POLYMERS-all
around you!". Sponsored by the American Chemical Society; authored by Linda Woodward,
University of Southwestern Louisiana, Lafayette, Louisiana.
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Experiment: Disposable Diapers
Materials:
* Disposable Diapers (unused!)
* Water
* Salt
* Sugar
* Measuring utensils (graduated cylinder or measuring cup)
* Magnifying glass
Procedure: List all the functions of a disposable diaper, using the chart below. Look closely at
the diaper, and list all the materials you find (inside and out). Match each material you listed
with one of the functions. Do both lists match? Are there functions which are not met according
to your materials list? After you have finished your chart, pour about 50ml (or 1/4 cup) water
onto inside, soft part of the diaper. Gently pull apart the diaper and observe. Where did the water
go? What happens if you shake some salt onto the gelled material? Sugar?
Observe the effect of salt concentration by preparing various salt solutions and adding the same
amount (different concentrations of salt) of these solutions to the diaper. Put 1 cup of water in 3
different containers. Add 1/8 tsp of salt to one container, 1/2 tsp salt in another, and 1 tsp in the
third. Add 1/4 cup of the salt water to the diaper and observe the amount of gelling.
(**Alternately, the diaper can be cut into strips, placed into a baggie and the gel can be shaken
out, then used with these solutions.)
Sections of the dipaer can be sorted into recyclable materials and non-recyclable materials. This
can be used as part of a lesson on recycling and trash. Can you think of other uses for this gel?
Discussion: Disposable diapers contain a material called sodium polyacrylate. This polymer is
extremely absorbant, and will absorb about 800 times its weight in distilled water. If ordinary tap
water is used, it will absorb only about 300 times its weigh as the salts and minerals in tap water
decrease the absorbancy of the powder. A 1% salt water solution decreases the absorbancy of the
sodium polyacrylate even more - to about 50 times its weight. Sodium polyacrylate can be found
-9in nurseries (potting soil) and some pet stores (cat litter). Ionic (salt) solutions affect the gelling,
but non-ionic solutions(sugar) do not.
CAUTION: THIS MATERIAL WILL DRY OUT MUCOUS MEMBRANES AND CAN BE
AN EYE IRRITANT. PLEASE ONLY ALLOW CHILDREN TO DO THIS EXPERIMENT
WHEN PROPERLY SUPERVISED.
References: National Science and Technology Week 1991 brochure; D.A. Katz "Instant Glop",
Investigations in Chemistry, 1988.
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Experiment: Naturally occurring polymers – DNA from strawberries
We have talked about man-made polymers, but did you realize that nature makes polymers too?
In fact, humans (and all other animals and plants) have lots of naturally occurring polymers in
them. Have you heard of things like protein, carbohydrates, cellulose, RNA, and DNA? They
are all naturally occurring polymers, and they are essential to life. DNA is the one of the longest
polymers we know of – each strand of can have up to 250 million monomers. If you could
stretch out all of the DNA strands in the genes in a single human cell and place them end-to-end,
they would be between 2-3 meters (6-10 ft) long.
Materials:
• 1 strawberry
• 1 quart-size zip-loc freezer bag
• 10 ml (about 1 tablespoon) of the DNA extraction buffer (recipe below)
• test tube or small jar
• funnel
• cheese cloth or coffee filter
• glass rod or plastic loop made from a tie wrap
• 5 ml (about 1.5 teaspoons) ice cold 95% isopropyl alcohol (rubbing alcohol)
Recipe for DNA extraction buffer:
• 1 Tbsp of shampoo (without conditioner) or dishwashing liquid
• 1/2 teaspoon of salt
• 2/3 cup water
Procedure: Remove the green top from the strawberry and place it in the zip-loc bag. Press the
air out of the bag and seal it. Mash the strawberry for two minutes to break open the cell walls.
Add 10 ml of DNA extraction buffer to the bag. Press the air out and seal the bag. Mash the
bagged strawberry with the buffer for one minute. This will help dissolve the membranes of the
cell nuclei and release the DNA. Filter the liquid into the test tube by passing it through the
cheese cloth or coffee filter in the funnel. This will separate out the undissolved parts of the
strawberry. Do not fill the test tube more than ¼ full.
Add the ice cold isopropyl alcohol to the test tube by letting it slowly run down the side of the
tube so that the alcohol will form a layer on top of the water/strawberry solution. Dip the glass
- 10 rod or plastic loop into the test tube until it reaches the point where the alcohol and water solutions meet. Twirl the rod to let the DNA strands collect on it. They may look like fine white
threads. While these may look like individual strands of DNA, a single strand would be too
small for us to see. They are actually bundles of DNA molecules (and they may include some
protein – another polymer - too).
So – how are we getting the DNA out of the strawberries? Well, when we mash the strawberry
we are break the walls of individual cells of the strawberries. The contents of those cells leak out
and form the red liquid in the bag. But, the DNA is not loose in the fluid of the cells - it is in the
nucleus of each cell. The nuclei are very small, and hard to break open by just mashing with our
hands. The shampoo or dishsoap helps us break open the nucleus of the cells and let the DNA
out. The cell walls are made out of lipids, which are somewhat similar to soap or detergent in
their structure (you will learn about emulsifying agents in Kitchen Chemistry).
from Biotechnology in the Classroom 2005 – see reference below
Once the walls of the nuclei have been destroyed, the salt helps the DNA stay dissolved in the
water, and allows the DNA strands to be close to each other. The DNA will not dissolve in the
alcohol, however. Where the water/strawberry solution and the alcohol meet, the DNA will
“precipitate” out - turn into a solid we can see and collect.
We can also collect the DNA from other types of cells. You can try this at home with other plant
materials, or even try to collect your own DNA by swabbing the inside of your cheek (although it
can be hard to get enough cells this way). If you try to get the DNA out of other plants (peas,
corn, or leaves), you need to make sure that the cells are mashed or ground up as much as possible before you add the DNA extraction buffer – sometimes a blender, small food processor, or
coffee grinder can be used to help grind up harder plant matter before you add the buffer.
References: Biotechnology in the Classroom 2005, University of California Davis, Adapted from
Diane Sweeney Labs Biology: Exploring Life
http://ppge.ucdavis.edu/Equipment/Protocols/strawberry_dna_extraction_05.pdf
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Diaper Functions/Materials
1) List of Diaper Functions
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2) List of Diaper Materials
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Density Table - Do the plastic samples float?
PLASTIC
VEG.OIL
Alcohol/H20
H20
GLYCERIN
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(list color)
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GUM WORKSHEET
original weight of gum and wrapper
_________________
weight of gum and wrapper after ____minutes
__________________
weight of gum and wrapper after ____minutes
__________________
weight of gum and wrapper after ____minutes
__________________
weight of gum and wrapper after ____minutes
__________________
weight of gum and wrapper after ____minutes
__________________
1) amount of weight lost (last measurement - original measurement)____________
2) percent of weight lost (answer from #1 divided by original weight, then times 100)______%
Variations
* compare sugar gum to sugarless gum; compare various kinds of sugar gum; graph results;
older groups can do averages and standard deviations; create a graph of weight-loss as a
function of time