Pfizer Education Initiative
ala KaZOO ala KASAM
+ Water =
Super Absorbent Polymers
Polymer is a Greek word that means “many parts” (poly = many, meros
= parts). The simplest definition of a polymer is something made of
many units. Think of a polymer as a chain. This can be demonstrated
using a long chain of paperclips.
Super absorbent polymers encompass a number of polymers all having the basic ability to
absorb massive quantities of water. They soak up water using the process of osmosis
(water molecules pass through a barrier from one side to the other). When water comes in
contact with the polymer, it moves from outside the polymer to the inside and causes it to
swell. The polymer chains have an elastic quality, but they can stretch only so far and
hold just so much water.
Four commonly used super absorbent polymers include sodium polyacrylate, polyacrylamide
crystals, polyacrylamide plant spikes, and Gro-Creatures. While each polymer may have a
somewhat different mechanism used to achieve the super-absorbing phenomenon and the rates
of absorption can differ, they all effectively absorb water. All are essentially hydrophilic (water
loving) non-toxic cross-linked polymers that can absorb several hundred times their weight in
water, but cannot dissolve because of their three-dimensional polymeric network structure.
They are fascinating materials and very versatile because of their unique solubility and
transport properties. The liquid-like properties result from the fact that the polymer is
composed almost entirely of water. However, the polymer also exhibits solid-like properties due
to the network formed by the cross-linking reaction. Composed of potassium, carbon, and
nitrogen, these polymers are currently being used in many areas such as pharmaceuticals, food
packaging, paper production, the horticultural industry, and oil drilling. Everyday examples
include gelatin, disposable diapers, contact lenses, and even gravy.
Sodium Polyacrylate
The Super Slurper
Sodium polyacrylate is nicknamed the "super slurper" because of its ability to absorb as much
as 400-800 times its mass in water. These polymers were originally developed by The
Department of Agriculture from hydrolyzed starch and polyacrylonitrile, but today a much
more absorbent, totally synthetic polymer has been developed. The powder we find in today’s
disposable diapers is made from sodium salts cross-linked with polyacrylic acid to form sodium
polyacrylate. Polymerization produces a linear molecule that has a very high molecular weight
usually greater than one million molecular units.
Lesson Plan
Insta-
now
Materials
Insta-snow
Distilled or Deionized water
Graduated cylinder
Teaspoon or available Insta-snow scoop
Cups or bowls
Insta-Snow is perfectly safe to
touch and squeeze. As with any
chemical, do not put Insta-Snow in
your mouth or eyes. Flush with
generous amount of water if it does
get into the eyes or mouth.
Procedure
1. Let each student take one scoopful (3 grams) of insta-snow and place it in a
clear cup or plastic bowl. Another way to measure is to use balance and
weigh boat.
2. Using a graduated cylinder, have them measure out 50-60 ml of distilled
water and add to the Insta-snow.
3. Watch how they react to the results.
Explanation
Insta-snow is an amazing super absorbent polymer, sodium polyacrylate, which turns
ordinary water into a white fluffy substance that looks like real snow! This faux snow is
so realistic that it is used on movie sets and indoor snowboarding parks.
Scientists accidentally created a variation of the diaper polymer that was far more fluffy
when it absorbed water. Insta-snow soaks up water using the process of osmosis (water
passing through a barrier from one side to the other). When water comes in contact with
the polymer, it moves from the outside of the polyer to the inside and causes it to swell.
The polymer chains have an elastic quality, but they can stretch only so far and hold just
so much water. Add a little water and your Insta-Snow expands to 100 times its original
size. Let the students feel the insta-snow and acknowledge how cool it feels. This is the
water evaporating off the polymer that gives it a cooling effect. If you allow the instasnow to dry and all the water has completely evaporated, the original amount of instasnow should be recovered. This proves that the reaction is a physical rather than a
chemical reaction.
To get a reaction from the students, tell them that Insta-Snow is similar to the superabsorbent polymers found in diapers (next activity). When water is added to a diaper, the
polymer quickly turns into a gel-like solid. Insta-snow, on the other hand, becomes very
fluffy when water is added. Both polymers look and feel the same before water is added;
however, Insta-snow has much higher degree of “cross-linking” between the long chains
of molecules. This tightly cross-linked network rapidly unfolds when it comes in contact
with water which accounts for its greater ability to swell up into a fluffy material.
Insta-Snow Mixing Ratios
Powder
Water
1 blue scoop
2 oz
1 teaspoon
2 oz
1 tablespoon
6 oz
Metric
3 grams
60 ml
50 grams
1200 ml
190 grams
3800 ml (1 gallon)
Other Activities
 Experiment with different mixing ratios of powder to water to find the perfect
fluffy snow mixtures
 Compare qualities of Insta-snow with polymer found in disposable diapers
 Put some Insta-snow in the freezer (should freeze in about 8 hours)
Super Absorbent Polymers in Diapers
Materials:









diaper (large, disposable and super-absorbent)
zip-closing plastic bag (1 qt or 1 gallon size)
scissors
tap water
distilled water
salt water (0.9% NaCl solution)
small cups
clear plastic cups
measuring spoons or pipettes/droppers
CAUTION:
The powder found in the
diaper (sodium polyacrylate)
will irritate the nasal
membranes if inhaled. Avoid
eye contact; if it gets into eyes,
they will become dry and
irritated.
Procedure
1. Let student work in pairs or in groups of three. Have each student use a pair of
scissors to cut the diaper in half (in the middle). Make sure that both ends remain
upright. Place the open middle part of the diaper downward into the plastic bag.
2. Pull open and separate the cotton, paper, and plastic layers of the diaper and
shake the sodium polyacrylate to the bottom of the bag. Look at the bottom of the
bag as you tilt it to one side. You should notice white granules collecting in the
corner of the bag.
3. Now, remove the first half of the diaper and do the same with the second half.
Try not to shake or pull the cotton out of the diaper. If large pies of material or
cotton get mixed in with the sodim polyacrylate, close the bag, move the cotton,
plastic, or other large pieces of material toward the top of the bag. Keep the
material up there as you shake the bag again. This will allow the granules to fall
down to the bottom without getting picked up by the cotton again.
4. After you have about teaspoon of granules in the corner of the bag, slowly
open the bag and remove the large pieces of material. Throw them away.
6. Add 1/2 teaspoon of granules to each of the three clear cups labeled, “distilled
water”, “tap water”, and “salt water”. Mats with circles can be used to place the
three cups used for the 3 different solutions. The salt water is a 0.9% solution,
approximate concentrate of salt in urine.
7. Add 1 tablespoon or a specific volume (i.e. 10-mL via a syringe) of each type
of water to the appropriate cup. Watch the granules to see if they will absorb the
water. Keep adding the same measured amount at a time until it appears that the
granules are no longer absorbing the water. Record how many tablespoons or
total volume of each of the liquid you added.
8. To the distilled or deionized water cup, add 1 tablespoon of table salt and stir.
What happens? Why?
The electrolyte concentration in water being absorbed greatly affects the amount of water
which can be absorbed per gram of polymer. For Example:
 The super absorbent will absorb about 800 times its own weight in distilled water.
 The same polymer will absorb only about 300 times its own weight in tap water.
 This polymer will absorb only about 60 times its weight of 0.9% sodium chloride
solution. (Similar to the NaCl concentration of urine.) Explain.
Sodium polyacrylate is termed a hydrophilic or "water-loving" polymer because of its great
affinity for water. So how does this polymer work? In the dry powdered state the chains of the
polymer are coiled and lined with carboxyl groups or ( -COOH ). When it is put into water, it
just breaks apart into positive and negative ions as sodium chloride.
H2O
[ CH2
CH2]n
C
O- +
Na
[ CH2
O
+ Na+
CH2]n
C
O
O-
Normal uncharged polymer molecules, when they're in solution tend to be tangled up in
what big shot scientists call a random coil,
When hydrated with water, the carboxyl groups dissociate into negatively charged carboxylate
ions ( COO-1 ). These ions repel one another along the polymer chain thereby widening the
polymer coils allowing water to move into contact with more carboxyl groups. As the polymer
continues to uncoil the ultimate swelling forms a gel-like consistency. The polymer does not
form a solution because it still has cross-linking due to hydrogen bonding where hydrogen atoms
in water are being attracted to the oxygen atom in the carboxylate ions between chains.
To reliquify the gelled polymer for disposal purposes, common table salt is added. When salt is
added, each ion of sodium ( Na ) and each ion of chlorine ( Cl- ) is quickly surrounded by six
molecules of water which is drawn out from the polymer-water complex. The presence of
sodium chloride in the solution greatly decreases the ability of polyacrylate to absorb and retain
water. In the case of a negatively charged polyelectrolyte, the positively charged Na+ ions
will get in between the negative charges on the polymer, and cancel them out in effect.
When this happens, the polymer chain collapses back into random coil again
Other ionic compounds such as baking soda or vinegar can also be used. Once the gel has been
liquefied, it can be safely poured down the drain.
The practical application for this super absorber was realized in the early 1980's when the
Japanese marketed the first successful disposable diaper. Later, other applications such as fuel
filters and feminine hygiene products followed.
Other activities
The Pouring Test Determine the amount of water a disposable diaper can hold by slowly
pouring about 1/4 cup (approximately 50 ml) of warm tap water into the center of the
diaper. Holding the diaper over a dishpan or sink, and continue to add increments of
water. Tip the diaper back and forth after adding water each time. Record the amount of
water the diaper holds before it becomes saturated and steadily leaks. Try testing different
brands of diapers.
Polyacrylamide Crystals
Polyacrylamide "Spikes"
A similar polymer, polyacrylamide, (Soil Moist and Soil Moist Spikes ) is sold in nurseries as a
soil conditioner to hold water in the soil. Super absorbent crystals are cross-linked
polyacrylamide copolymer.
Lesson Plan
Materials
 Super Absorbent Crystals
 Potting Soil
 Bean, grass, radish or other fast-starting seeds
 Cups
 Plastic Spoons
Super absorbent crystals
are non-hazardous but
with every chemical use
caution. Flush affected
area with water. Flush
eyes with water for 15
minutes and see a
physician. Do not ingest.
Procedure
Have the hydrated crystals ready for the students.
1. Using plastic spoons have the students fill one cup with just dirt and another cup
with half gel crystals mixed with half dirt.
2. Using their finger, have them push 2-3 seeds as recommended on the package of
seeds and cover the seeds.
3. Place cups in a sunny place and have the students record their observations. How
many days did it take for each of the cups to germinate? Students can measure the
height of the plants as they grow and create a chart of days versus inches or
millimeters (centimeters) of growth for both cups over a period of time.
Polyacrylamide is crosslinked with a bisacrylamide and this copolymer is not affected by salts in
water or soil. A major difference between the sodium polyacrylate polymer and the
polyacrylamide polymer is that polyacrylate has a sodium ( Na+ ) while the polyacrylamide has
an amide ( NH2 ). The sodium ion works more efficiently and will absorb approximately 800
times its weight in distilled water while the amide ion is considerably less efficient in its water
absorbing ability and will only absorb around 40-200 times its weight in water. This lack of
ionic strength in the polyacrylamide polymer greatly reduces its water absorbing
characteristics.
Demonstration
1. A very common demo is for a teacher to grow some of the "ghost crystals" in water.
2. Carefully insert a needle with thread through the hydrated crystal and lower the crystal into
the water.
3. Ask the students what they see. They should only be able to see the thread hanging in the
water. Gently rise the crystal out of the water and watch their reactions!
An interesting physics application created by polyacrylamide is its ability to
effectively mimic the optical qualities of water. Because the crystals of the
polyacrylamide when hydrated are made up almost entirely of water, they
essentially "look" like water and light will pass from the surrounding water into
the crystal without being refracted at all. These crystals are sometimes referred
to as "ghost crystals" because when hydrated the crystal is almost invisible in a
glass of water. A fully-grown hydrated crystal contains so much water that
optically it behaves like water. Light does not bend or become distorted as it
passes from water into the crystal. However, when the crystal is lifted into air,
it becomes visible because the speed of light in the crystal is different from the
speed of light in air.
Other Uses
Polyacrylamide "spikes" are used commercially in the horticulture industry to absorb and
release water or fertilizer to individual plants and thus are a favorite of gardeners who do not
have a green thumb. Much like the crystal, the spike has a limited ability to absorb vast
quantities of water. Its value is that it can be hydrated and dehydrated a seemingly unlimited
amount of times over the course of from 2-3 years according to the manufacturer. This quality
also makes it a favorite of teachers on a budget to investigate diffusion and for students to
practice measurement skills with the hydrated and dehydrated spikes. A growing biological
application is the controlled release of pharmaceutical agents or even fertilizer from the matrix.
Cold crystals: Place a zipper lock bag of jelly-like crystals in the freezer and examine it after 12
hours. Compare how long the crystals stay cold as oppose to a same size bag of ice. The polymer
crystals should hold the cold 2.5 times longer than ordinary ice.
Gro-Creatures
Gro-Creatures are toys shaped like dinosaurs, alligators, lizards, and other assorted animals
that increase in size when placed in water. These interesting creatures are made up of two
polymers: One is poly (vinyl acetate) which keeps the original proportions and the color of the
"creature" and the other is polyacrylamide which is the super absorbent material. These
critters can be dried out and rehydrated over and over again since the super absorbing material
is polyacrylamide. They have a number of classroom activities connected with science such as
observations, data collection, graphing, making hypotheses, following a time sequence, drawing
conclusions, and measurement using linear, mass, and volume.
Included in the kit are an alligator that was hydrated in tap water and another in distilled or
deionized water. These can be rehydrated for demonstration. As a classroom activity, leave one
fresh alligator and/or lizard to be used for measurement in the classroom.
1. Measure and record the length of your alligator and/or lizard in inches and in
centimeters.
2. Place the alligator and/or lizard in large plastic containers filled with distilled, deionized
or filtered water (i.e. Brita filtered water). Hard water has minerals that will interfere
with the growth of the alligator and/or lizard.
3. Measure and your alligator and/or lizard every day and record the measurement. If you
have both, you can compare growth daily.
4. Make a graph of your measurement.
5. If comparing both, see how long each takes to finish growing. After growing, take your
alligator and/or lizard out of the water and allow it/them to shrink.
6. Measure your alligator and/or lizard as it shrinks. How many days does it take your
alligator and/or lizard to get back to its normal size? Which occurred faster (growth or
shrinkage)?
7. Place your alligator and/or lizard back into the water. Does it grow to the same size as it
did before? Did it grow faster or slower. Can you figure out why?
Some words of caution relating to the use of these creatures include:
1. Don’t allow the critters to remain in the water once they have reached their maximum size.
2. Placing the critters in boiling water will cause the creature to disintegrate.
A Hydrocarbon Stabilization Polymer Lesson
Although Enviro-Bond 403 is not classified as a super-absorbent polymer
since it does not absorb 25 times its weight on a weight to weight ratio, it
has been added to the kit to demonstrate a hydrophobic, oil absorbing
polymer.
Oil is a major source of ground water contamination and waste management
problems. The vast majority of this oil enters the ocean from ship oil spills
during petroleum transport or from land manufacturing operations. Oil can
also seep into the ocean naturally from cracks in the sea floor. Oil well and oil
tanker accidents can have lasting effects.
Oil stabilizing polymer called Enviro-Bond 403 is especially formulated to
bond quickly and safely to many types of hydrocarbon liquids including
crude oil, diesel fuel and gasoline. The bonding is do complete that it literally
encapsulates the liquid hydrocarbons in just minutes.
Hydrocarbon
Time
Temperature
Ratio by Weight
(minutes)
(ºF)
(Polymer:Hydrocarbon)
Crude Oil
5
70
1:1
Diesel Fuel
5
70
1:6
Gasoline
5
70
1:15
Hydrocarbon (crude oil, diesel fuel, gasoline, etc.) consists of three basic
components: Paraffinics, naptinics, and aromatics. The polymer is specifically
formulated to bond to these components. The mechanism is three dimensional
with cross-link bonding, and the polymer structures are referred to as
dieblock, triblock, branched, radial and linear. When the polymer comes into
contact with the liquid hydrocarbon, the free hydrocarbons bond to the
polymer forming a solid mass. The hydrophobic properties of the polymer
cause it to float on the water, there is no need for mixing since the density of
the polymer is great enough to allow it to sink through the hydrocarbon and
maximize the bonding potential.
Suggested Demonstration
Materials
600-ml beaker
Wax paper
Marvel Mystery Oil
ENVIRO-BOND 403 polymer
Gloves, spoon, scoop
This demonstration is greatly enhanced if you do not show your students
the polymer until they are given the opportunity o come up with their own
oil spill cleaning solution.
Fill a 600-ml beaker with 500-ml of tap water. Add approximately 50 ml of
Marvel Mystery Oil or enough to form a thin layer on the surface of the water.
Discuss oil spills and how it affects the environment like birds, fish, and
recreational areas. When oil gets onto the feathers of a bird, it makes it harder
for the birds to stay warm because it makes the bird less water proof. Oil on
the fir of sea mammals, such as otters or seals, also reduces their ability to
stay warm. If they ingest the oil, it will weaken the animal. Ask them what they
would use to clean up the oil spill.
Discuss some of the traditional ways to clean up oil spills:
1. Placing a ring of floating devices around the spill to prevent it from
spreading and then siphoning the oil off by using pumps or skimming
devices.
2. Sheets or particles of floating oil absorbing material such as saw dust
and spun fabrics can be used to recover spilled oil. These however may
cause serious land fill problems.
3. Burning the oil cleans up the spill but in turn causes air pollution.
4. Detergents help break up or disperse the oil spills but can cause harm
to marine life.
5. High pressure hoses with 140ºF water heated on barges are used to
blast oil from the surface of rocks. This unfortunately kills shoreline
bacteria useful to the environment.
6. The use of microorganisms to “eat” the oil
Add just enough of the polymer to completely cover the oil. The polymer will
form a sponge-like matrix that floats on the surface of the water. When all the
oil is absorbed and bonded, remove using your gloved hand, spoon or scoop
and place it on a piece of wax paper. As the polymer dries, it becomes firm
and rubbery. The free molecules find bonding sites and become three
dimensionally entangled with the polymer structure.
This material can be shaped into a ball and bounced. On a large-scale crude
oil clean-up, the solidified oil can be recovered and turned into a solid fuel
source.
This polymer will not work on other types of oil such as motor oil or vegetable
oil since these oils do not have the necessary hydrocarbon components as
mentioned above.
Tying in the hydrocarbon stabilization polymer and super-absorbent
polymers:
Demonstrate the absorbing properties of sodium polyacrylate in conjunction
with the oil polymer bonding characteristics. Sodium polyacrylate, a super
absorbent water polymer that has no affinity for liquid hydrocarbons.
Similarly, the oil polymer has no affinity for water.
Fill the 600-ml beaker with 300 ml of water and 50 ml of Marvel Mystery Oil.
Add 2 teaspoons of sodium polyacrylate and watch the polymer absorb the
water, leaving the oil untouched. After the polyacrylate absorbs the water,
add just enough oil absorbing polymer to bond to the Marvel Mystery oil.
During the demonstration, stress the difference between the super-absorbent
polymer and the hydrocarbon stabilization polymer.
Major oil spills…
 June 1979, an oil well blew out off the east coast of Mexico and spilled
about 130 million gallons of oil
 March 1978, a tanker ran aground off the coast of France, spilling 68
million gallons of oil
 March 1989 a tanker ran aground off Alaska and leaked more than 10
million gallons of oil
References:
Buchholz and Peppas, Super absorbent Polymers, ACS Symposium Series, 1994.
Buchholz and Graham, Modern Super absorbent Polymer Technology, John Wiley &
Sons, 1998.
Absorbent Polymers: AMCOL International, 1996
Flory, Principles of Polymer Chemisty, Cornell U. Press, 1953.
American Chemical Society, November 18, 2003 Diapers – The inside story.
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