Developers:
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Stockton T. DuPont
C. E. Pickett Middle School
Philadelphia, PA
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Noel G. Harvey
Plastic Research Department
Rohm and Haas Company
Bristol, PA
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Topic Area:
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"Glyptal Resin Plastic (Thermoset Polymer)"
Phthalic anhydride and glycerol are heated in a beaker.
The clear plastic that is formed is poured into an aluminum
cupcake tin. A penny (or some other object ) is placed in
the cupcake tin and permanently embedded in the plastic.
This experiment may be extended over several classroom
periods.
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Grade
Level:
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7 and 8
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Discipline:
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Atomic Structure (molecular motion)
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Goals:
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- To enhance the basic understandings for making
"observations".
- To gain a better understanding for collecting
data.
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Objectives:
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- Upon completion of this activity the students will
demonstrate a knowledge of laboratory skills by:
a. being able to identify a thermoset polymer and use
laboratory equipment.
b. using metric terms applicable to the apparatus being
used.
c. applying recognized safety rules to all laboratory
work.
d. being able to use observation skills previously
taught.
e. being able to chart and tabulate the data learned from
the observation process.
- Emphasis is on making accurate observations and
measurements to qualify the various and varied
observations.
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Definitions:
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Thermoset. A high polymer that solidifies or
"sets" irreversibly when heated. This property is usually
associated with a crosslinking reaction of the molecular
constituents induced by heat or radiation, as with proteins,
and in the baking of doughs. In many cases, it is necessary
to add "curing" agents such as organic peroxides or (in the
case of rubber) sulfur . For example, linear polyethylene
can be crosslinked to a thermosetting material either by
radiation or by chemical reaction. Phenolics, alkyds, amino
resins, polyesters, epoxides and silicones are usually
considered to be thermosetting but the term also applies to
materials where additive-induced crosslinking is possible,
e.g., natural rubber.
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Background:
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The reaction between glycerol and phthalic acid is
basically an esterification. Water is produced during
esterification and is removed by boiling the mixture. This
plastic, glyptal resin, is a thermoset polymer; phthalic
anhydride acts as a cross linker to hold strands of glycerol
molecules together in a polymer.
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Materials:
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The teacher will procure the following items - a beaker,
heat (hot plate, alcohol lamp, Bunsen burner) glycerol,
phthalic anhydride, sodium acetate, goggles (safety
glasses), and disposable gloves.
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Procedure I:
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Do this demonstration in a hood (proper ventilation);
wear safety goggles and disposable gloves.
- Place 20 grams of phthalic anhydride, 1.0 gram of
sodium acetate, and 8.0 ml of glycerol into a small
beaker.
- Heat the beaker slowly (while stirring) to dissolve
all remaining solids. Continue heating until the mixture
boils for five minutes.
- Prepare an aluminum cupcake tin by cleaning and
drying.
- Pour approximately half of the hot liquid into the
aluminum cupcake tin.
- Carefully place a penny (or some other coin) into the
liquid in the aluminum cupcake tin. Then add the
remaining liquid on top of the penny.
- Let the plastic cool about 10 minutes at room
temperature. Then place it on top of a container of
crushed ice (or in a refrigerator) for further
cooling.
- Using scissors, strip away the aluminum to free the
plastic with its embedded penny.
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Noticeable
Observations:
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- The phthalic anhydride, in the mixture, when boiling
will gather at the rim and sides of the beaker. This
solid phthalic anhydride will be in a pure state.
- The solid materials (phthalic anhydride and sodium
acetate) become liquefied when heated with glycerol.
- At room temperature, the mixture will not solidify if
all of the water molecules are not evaporated.
- When you place a container of the polymer in a
freezer (for approximately 2 hours), the mixture will
crack and become very brittle - easily cracked into many
pieces or fragments.
- During the esterification reaction, you will see
bubbles produced by the formation of water.
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Procedure II:
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Follow the procedure in I but vary the heating time - 2,
4, 6, 8 minutes. Observe and record differences in the
polymer.
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Vocabulary:
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Plastic
Embedded
Glyptal
Thermoplastic
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Polymer
Molecule
Glycerol
Gram
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Aluminum
Mixture
Phthalic Acid
Milliliter
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Thermoset
Resin
Ester
Sodium Acetate
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References:
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- Hawley's Condensed Chemical Dictionary, 11th Edition,
1987, Van Nostrand Reinhold, New York, page 1146.
- This experiment was adapted from an experiment
entitled" The Embedded Penny: Making Glyptal Resin
Plastic" from the following book: Chemical
Demonstrations, Vol I, by Lee R.Summerlin and James
L. Ealy, Jr. (American Chemical Society, Washington, D.C.
1988.
- The Everyday Science Sourcebook; Lawrence
F.Lowery, Dale Seymor Publications, Palo Alto, CA
1985.
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Questions
for Students:
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- When the reaction appears to boil, what substance is
actually boiling off?
- What is the function of the sodium acetate?
- How does the structure of the phthalic anhydride
molecule change in the esterification process?
- How does the structure of glycerol change?
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Extended
Activities:
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The following experiment may be used to further enhance
the student's understanding of making accurate observation
and charting data observed.
A. Change the cooling time frame.
B. Change the method (crushed ice, refrigerator, freezer,
room temperature only, etc.) of cooling.
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Teacher Hints:
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- Perform activities yourself before assigning them to
students to determine where students may have
trouble.
- Arrange the laboratory in such a way so that
equipment and supplies are easily accessible to students.
Avoid confusion where solutions and reagents are
dispensed.
- Have available only equipment and supplies needed to
complete the assigned activity. This practice helps
eliminate the problem of students doing unauthorized
experiments.
- Review the procedures with students and emphasize
cautions found within the procedure. Give the students
copies of the Material Safety Data Sheets on Phthalic
anhydride, glycerol, and sodium acetate (readily
obtainable from the supplier) and discuss safety.
- Be sure all students know proper procedures to follow
if an accident should occur.
The Glyptal Resin is a cross-linked thermoset, like
connected spaghetti.
Magnify
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