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Paint Properties Experiments
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This experiment is courtesy of 
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Quantitative Determination
of the Composition of Water-based Paints
and the Correlation of Paint Properties
to Paint Composition
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Developers:
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Sally Breen
Springfield Township High School
Erdenheim, PA
Tienne Moriniere Myers
Hancock Demonstration School
Philadelphia, PA
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Meredith Morgan
Architectural Coatings Research
Rohm and Haas Company
Spring House, PA
John Hook
Architectural Coatings Research
Rohm and Haas Company
Spring House, PA
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Grade
Levels:
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High School
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Background:
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This lab, appropriate for high school chemistry students,
was developed as a continuation of the 1991 Project Labs for
elementary and middle school students entitled "Experiments
with Paints," developed by Tienne Myers, Meredith Morgan,
and John Hook. Appendix A, entitled "What is Paint," will
give the teacher and students a working knowledge of
water-based paints, so they will be able to understand the
objectives of the experiment and interpret the results.
Furthermore, as a result of having done this experiment,
students will gain an understanding of the function of
various paint types and the relationships between cost,
function, and composition.
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Objective:
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Through experimentation students will learn the
composition of water-based paints and mathematically
determine the composition by volume of the organic, mineral,
and water fractions of four different types of paints. In
addition, the students will test scrubability and stain
removal properties of these paints and then formulate an
hypothesis concerning these tested properties, paint cost
and the compositions they determine.
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Specific
Objectives:
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- determination of density of the four paints
- determination of the water fraction from dried paint
samples
- determination of the polymer content using combustion
analysis of dried paint samples
- calculations of volume fraction concentrations of the
water, polymer, and the mineral components
- test of scrubability and stain removal for each paint
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Equipment:
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Safety Goggles
Lab Apron and Gloves
Balance (capable of massing to 0.01 g)
Drying Oven (optional)
Four Different Types of Latex House Paint
(Suggested paints: an (inexpensive) ceiling paint, a (medium
grade) interior flat, a (top grade) exterior flat, and a
(medium grade) interior semigloss. The grades suggested will
produce the most dramatic results. The experiment will
produce interpretable results with any grades of the above
four types. All of the paints should be white or off-white.)
Each lab group will need:
- ringstand, ring, pipestem triangle
- Bunsen burner
- tongs and wire gauze (on which to cool hot
crucibles)
- 4 crucibles with covers (10 mL or larger
capacity)
- 10mL graduated cylinder
- 4 test tubes (approximately 18 x 150 size)
- 4 paper cups (8 oz)
- 4 disposable plastic dropper pipettes
- approximately 100mL of each paint
- a 2-inch wide paint brush
- 4 cereal box panels (front and back of 2 boxes)
- 2 x 6 inch strips of gauze or fabric
- 4 or 5 staining agents for stain removal test
(suggested staining agents: mustard, spaghetti sauce,
dark lipstick, crayon, marker, etc.)
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Suggested
Timetable:
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Approximately 4 laboratory single class periods or two
double periods are needed to complete the experimental
portions of this lab.
Lab period 1: -introduction of procedure and density
determination of the four paints.
Lab period 2: -massing of the crucibles and paint samples
for overnight drying painting of cereal box panels
Lab period 3: -combustion of the 4 samples, cooling, and
massing
Lab period 4: -scrub and stain tests and clean up
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Procedure:
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A. Density Determination of Wet Paints:
- Mark each of four test tubes A, B, C, and D and then
mass, recording your results in Data Table I.
- Calibrate each test tube using the graduate and 20.0
mL of water. Mark the 20mL level, then empty and dry the
test tubes.
- Obtain approximately 100 ml (3 oz) of each of the
four paints in the four paper cups. Record which paint is
A, which is B, etc.
- Using the plastic dropper pipettes, fill the tubes to
the 20mL mark, being careful not to get any paint on the
side of the test tube. Mass ( to the nearest 0.01 g) and
record mass of test tube plus paint. Record volume.
(Snipping off part of the ends of the pipettes will allow
the paint to enter them more easily.)
- Pour paint from test tubes into a disposal cup
provided by the teacher. Rinse and clean the test
tubes.
B. Massing and Drying of Paint Samples:
- Clean and dry 4 crucibles and covers. Mark them
(crucibles and lids) A, B, C, and D.
- Mass each crucible with its lid to the nearest 0.01 g
and record in Data Table II.
- Using the dropper pipette with the crucible still on
the balance, add approximately 2.5 g of each paint sample
to the corresponding crucible. Record the mass of
crucible + lid + paint in Data Table II
- Gently swirl the crucible so that the paint partially
covers the interior surface of the crucible for better
drying.
- Place the crucibles, uncovered, in a drying oven
(40�-70�C) for at least 24 hours. If a drying
oven is not available to you, the paints may be dried at
room temperature for three or more days.
- Mass the crucible + lid + dried paint for each sample
and record in Data Table II. Store in a safe place until
you are instructed to do the combustion portion of this
lab.
C. Painting Panels for Scrub and Stain Tests:
- Cut the front and back panels from two cereal or
cracker boxes. Draw a one-inch border around the edges
with a pencil. This border is for handling the freshly
painted surface.
- Label each of the 4 panels A, B, C, or D to
correspond to each of the paints being tested.
- Using the technique illustrated in Figure 1, paint
each panel and then put them some place to dry until you
are ready to do the scrub and stain tests. Note which
coats of paint are particularly thick or thin; thickness
affects the observed hiding and scrubability.
Figure 1. Painting Instructions

- Observe the hiding ability of the 4 paints while wet
and after they have dried. Record your observations
(poor, good, excellent) in Data Table IV. Also observe
the gloss and texture of the paints after they have
dried.
- Wipe the excess paint from the brush using a paper
towel; then clean the paint brush under running water.
- Dispose of the cups of paint in the trash after they
have been allowed to dry completely.
D. Combustion (Burning) of Paint Samples:
In this part of the lab you will be using a Bunsen burner
to heat your crucibles containing the paint samples to very
high temperatures. The polymer portion of the paint will
ignite and burn off with a flame that is several inches high
and of several minutes duration, so extreme caution and
attentiveness are required. Long hair must be tied back
and no baggy or loose sleeves should be near the flame. As
with burning any substance, do it only with adequate
ventilation and avoid breathing the fumes. (Refer to teacher
notes for further discussion.)
- Record the mass of the dried paint + crucible + cover
from Table II into Table III.
- Using an opened paper clip, poke a small hole through
the skin that may have formed over the dried paint in the
crucible. This will allow for the escape of gases when
the paint is burned.
- Place the crucible, with the cover on completely, on
the pipestem triangle which is on the ring/ringstand, as
in Figure 2a below.
Figure 2. Crucible Cover Position for
Combustion

2a. Sketch of crucible, with cover on completely, on
pipestem triangle. This is the position during the early
stage of combustion when the polymer is flaming.
2b. Sketch of crucible, with cover resting on triangle
and crucible. This is the position after the flames have
died down, while the crucible is being heated to red hot
in order to oxidize the black carbon.
Adjust the height of the ring so the hottest part of the
burner flame will be on the bottom of the crucible.
- Light the burner and place under the crucible. Do not
hold the burner.
- Step back and observe a flame around the crucible
cover as the polymers in the paint ignite and combust.
The flame will extinguish itself after approximately two
minutes.
- Once the flames have extinguished themselves, rest
the crucible cover on the crucible and triangle, as
pictured above in Figure 2b. Continue heating the
crucible and cover strongly for a total of 6 or 7 minutes
or until all or most of the carbon (black) has been
burned off the crucible and the bottom of the crucible is
red hot.
- Turn off the burner and allow the crucible to cool
for several minutes. Using the tongs, as demonstrated by
your teacher, remove the crucible and cover to the wire
gauze to cool completely (about 5 minutes). Do not
attempt to touch the crucible prior to this! Be sure to
remember which sample is which since your markings will
have burned off also! Repeat these first 7 steps with the
other 3 samples.
- When the samples are cool, mass them with the covers,
and record in Table III. The contents of the crucible at
this point are the total mineral components (also
referred to as ash) of the paint samples.
- Using a stirring rod or spatula, scrape the dried
contents out of the crucibles into a waste container
designated by your teacher. Wash and dry the crucibles
and covers.
E. Scrubability and Stain Tests
- Cut each of your cereal box panels into four
equal-size parts. Be sure all pieces are labeled. Each
lab partner will have two panels of each paint sample,
one for scrub testing and one for stain testing.
- If a microscope is available, you might want to
examine the dried panels under the microscope and observe
the textural differences in the paints. Can you relate
the dried paint texture under the microscope to the
glossiness or shininess of the paint? Record your
observations in Table IV.
- On two of the panels, place horizontal applications
of the staining materials as illustrated in Figure 3. Set
aside to dry and continue with the scrub test.
Figure 3. Layout for stain testing.

- Each lab partner should perform the scrub test on
each of the four paints. A difference in scrubbing
pressure will produce a variation in results.
a. wet one of the squares of cloth or gauze and wrap
it around your finger.
b. with the painted panel flat, rub up and down until
the paint first wears off the panel. Count a stroke up
and down as one stroke.
c. record the average number of strokes for you and
your lab partner required to first remove the paint from
each of the 4 different panels.
d. put class data on the board and compute the average
for each type of paint. Record the class average in your
Data Table IV.
- Using the same technique as described for the scrub
test, rub up and down the panel across all of the stains,
but stop after 5 strokes ( or 10 passes across the
panel.). Record your observations in Table V.
- Wet a corner from a panel of each of your four
paints. By doing this, you will fill any air voids in the
paints with water, and thus decrease the hiding. Which
paints have a significant amount of air voids in their
films? Record your observations in Table V.
Data Table I. Densities of Wet Paints

Data Table II. Mass Fraction Water

Data Table III. Combustion of Samples

Data Table IVa. Scrub Test and Observations of Hiding

Table IVb. Gloss/Texture of Dry Paints and Microscope
Examination

Data Table V. Stain Test

Fractional concentrations are used widely in industry. A
fractional concentration is
the amount of a single ingredient
total amount of all ingredients.
Fractional concentrations can be determined using either
the masses of the ingredients or the volumes of the
ingredients. When the "amount of ingredient" is expressed as
a mass, it is called a mass (or weight) fraction. When the
amounts are expressed in terms of volume, it is called a
volume fraction. The sum of all the fractional
concentrations of all the ingredients in a material is 1.00.
Because we are interested in volumetric concentrations in
paint, (see explanation in Appendix A) we will use the mass
fractions of water, polymer and mineral, along with the
densities of the wet paints, polymer, and water, to
calculate the volume fractions in the wet paint and then in
the dry paint.
In order to simplify your calculations you may want to
refer to the Letter-Coded Table and use letters to represent
the different values in your equations. It is also a a good
idea to set up your equations using the appropriate units
for each quantity and to use the factor label or dimensional
analysis method of solving or checking your calculations.
Letter Code Table
Density of wet paint (g wet paint/mL wet paint)
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A
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Mass fraction of water in wet paint (g water/g
wet paint)
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B
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Mass fraction of polymer in wet paint (g
polymer/g wet paint)
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C
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Mass fraction of minerals in wet paint (g ash/g
wet paint)
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D
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Density of water (1.00 g/mL)
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E
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Density of polymer (1.13g/mL)
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F
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Volume fraction of polymer in wet paint
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G
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Volume fraction of water in wet paint
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H
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Volume fraction of minerals in wet paint
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J
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Volume fraction of polymer in dry paint (BVC)
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K
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Volume fraction mineral in dry paint (PVC)
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To calculate volume fraction of polymer in wet paint (G):

To calculate volume fraction of mineral in wet paint (J):

Summary Table of Volume Fractions for Wet Paints

Now you are able to calculate the concentrations of these
ingredients in the dry paint.

To calculate the volume fraction of mineral (PVC) in dry
paint (L):

Summary Table for Concentrations in Dry Paint

Graph:
Plot BVC (K) for each paint (abscissa) versus # of
strokes in the scrub test (ordinate).
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Conclusion
Questions:
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- Make a table of your experimental results to
correspond to Exercise 1 in Appendix A. Compare your
results with your predictions.
- Compare your graph to the example graph in Appendix
A. What conclusion can you draw concerning binder
(polymer) concentration and scrub resistance?
- What trends did you observe for BVC content, scrub
resistance and stain removal?
- If wet hiding is a function of TiO2, and TiO2 is the most expensive ingredient
in paint, what correlation can you make concerning cost
of paint and wet hiding? Does this correlation correspond
to the costs of your four paints? Obtain cost per gallon
information from your teacher. What other factors might
affect the costs of your paints?
- Why would you choose a semigloss paint and not a
ceiling paint for your kitchen walls?
- You were able to calculate the Binder Volume Fraction
in wet paint directly from the mass data. What
information would you need to calculate the corresponding
Mineral Volume Fraction from the ash mass? (Remember the
mineral fraction is composed of both TiO2 and extenders.)
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Extended
Activities:
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- Have someone bring in some "mystery" scrap latex
paint from home. Can you figure out what kind it is from
its composition or properties? (Because mercury was used
as a preservative in some paints as late as 1991, we do
NOT recommend combusting in the laboratory old scrap
paint from home unless it is done in a hood.)
- Is exterior paint worth the extra money? Brush your
four paints on some scrap pieces of wood and put them
outside. Check on them over a period of a few months.
Which paints have good exterior durability?
- Latex paint is a suspension of binder and mineral
particles in water. The stability of that suspension is
pH dependent. What are the pHs of your paints? What
happens if you add acid (lemon juice, vinegar, or dilute
HCl), or base (dilute NaOH, dilute ammonia) to your
paints?
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Optional
Calculations:
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If you knew the density of the extender in your paint
(and there is only one of them!) you could actually
calculate the volume fraction of your dry paint which is
TiO2 (letter code W). You
would need the following equations and values.
You can calculate the density of the total mineral
material (Z) as:

The volume fraction of the total mineral material which is
TiO2 (R), is then calculated as:

where T is the density of TiO2 (4.00 g/mL) and U is the density of
the extender in your paint. Values for U vary between 2.3
and 4.0 g/mL, and a representative value is 2.7 g/mL.
The volume fraction of the dry paint which is
TiO2 (code letter W), is
then calculated as:

Can you derive the equation for R? (Hints: You need 2
equations with 2 unknowns. The density of the mineral
material is equal to the sum of the volume-weighted
densities of TiO2 and
extender. The sum of the volume fractions of TiO2 and extender is unity.)
You might try doing the calculations for your paints. Do
you obtain reasonable values for R (positive) and for W
(positive, ranging between 0.03 and 0.30)? If not, why might
this calculation not be meaningful? If your values for W are
reasonable, do they match your predictions from your wet
hiding observations?
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Appendix A:
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What Is Paint?
Paints are used for two main purposes: to decorate and to
protect. Decorative properties include gloss, color, and the
ability to hide what is underneath the paint. Protective
properties include resistance to stains, scrubbing, and
damage caused by the weather. All these paint properties
depend on the paint's formulation. In this series of
laboratory experiments you will determine the formulas of
some paints, and then correlate the paints' properties with
their formulas. You will explore some ways that paints can
be tested, how the properties of gloss, hiding, scrub
resistance and stain resistance vary from one type of paint
to another, and why you would choose different paints for
different uses.
Latex paints are suspensions of mineral and polymer
particles in water. The particles are very small (0.1 to 15
microns) and can only be seen with a powerful microscope.
The polymer particles are called "binder" because they are
the glue which binds the mineral particles together. The
mineral particles make the paint film hard and may impart
color. The colored particles are called pigment particles.
Titanium dioxide (TiO2)
makes the paints in this experiment white. Other mineral
particles, called mineral extenders, are colorless. There
are a variety of other minor ingredients, collectively known
as additives, which also go into the paint and play
important roles in its performance. But well over 90% of the
volume of latex paint consists of the big four: water,
binder, pigment and extender. Many of the paint properties
depend on the relative amounts of these four ingredients.
For example, as we increase the amount of binder we tend to
bind things together better so we have better resistance
properties, and usually more gloss. TiO2 makes the paints whiter, and,
volume for volume, is the most expensive ingredient in
paint. As we increase the amount of extender we tend to make
it less glossy (flatter). When there's a lot of extender in
the paint, the dried film contains air voids, which also
make the paint whiter. Extenders are less expensive than
binder, and much less expensive than TiO2, so paints with a lot of extender
in them are usually much less expensive. By knowing only the
ratio of binder (polymer) to total mineral ingredients, you
can make good predictions about the scrub resistance, stain
resistance, hiding ability, and gloss of a paint. Of course,
the choices that are made as to which mineral ingredients
and what kind of polymer is used also affect these
properties.
We recommend that you look at four different types of
paint for this experiment: a semigloss paint, an exterior
flat paint, an interior flat paint, and a ceiling flat
paint. These four different types were chosen because they
typically have very different ratios of the four main
ingredients. You will measure the density of your paints,
the amount of water in your paint (by evaporation), the
amount of polymer in your paint (by combustion), and the
amount of mineral material in your paint (by what's left).
From these measurements, you will be able to calculate the
amount of polymer and mineral material in the dried paint,
and thus predict its scrub, stain, hiding and gloss
properties. The following "Sand and Glue" analogy will help
you make your predictions.
The Sand and Glue Analogy
The different types of paints can be likened to sand
(mineral) and glue (polymer) mixtures with different ratios
of sand and glue. The semigloss paint is analogous to a
mixture which has a lot of glue in it and not much sand. The
flat paints are analogous to mixtures which have a lot of
sand but not much glue. In fact, in typical interior flat
paints and ceiling paints, there is not enough glue to coat
all the sand particles, so when the paint dries, air voids
are left in the paint film. The following cartoon may help
explain this concept.
Figure 4. Sketch of ceiling paint drying.

A lot of properties of paint are affected by the ratio of
"glue" to "sand," and by the air voids. For the purpose of
most of this discussion, we'll consider TiO2 as white sand, and the mineral
extenders as colorless sand.
Gloss:
With a lot of glue and not much sand, the dried mixture
has a very smooth surface. This smooth surface is shiny.
When a dried paint is shiny, it is called a glossy paint. A
semigloss paint reflects a little less light than a gloss
paint, but more than a flat paint. With a lot of sand and
not much glue, a flat paint has a very rough surface after
it dries. You may be able to see the roughness with a good
microscope! Light which hits the rough surface is reflected
in all different directions, so it appears "flat" to the
eye. This concept is illustrated in the following sketch.
Figure 5. The Effect of Surface Roughness on Gloss

Scrub Resistance:
Paints which have a lot of sand and not much glue are not
held together very strongly. If you scrub them, they fall
apart. An extreme example is Tom Sawyer's whitewash. It's
like a mixture of chalk dust and water. When the water
dries, the fence might be white, but the first time you rub
it, the whitewash comes right off. Since few people need to
scrub their ceiling, ceiling paints contain very little
binder. On the other hand, semigloss paints are often used
to paint kitchens, where you might want to wash some
splatters off the wall.
Stain Resistance:
The more porous a film is, the more difficult it is to
wash off a stain. The stain seeps into the air void and is
very difficult to wash out. Thus, in the interior flat and
ceiling paints where there's not enough glue to coat all the
sand particles and the films have air voids in them, stain
resistance is generally very poor. On the other hand, dried
films of exterior flat paints and of semigloss paints, which
don't have significant amounts of air in them, generally
have good stain resistance.
Hiding:
Hiding is a measure of a paint's ability to cover the
colors in the wall behind it. This is perhaps the most
difficult concept, since there are actually two ways to get
hiding in a paint. TiO2 is
a white mineral that makes a paint white. This is what gives
semigloss and exterior flat paints their hiding. However,
air in the film can also make a paint white. Thus, even
ceiling paints, which don't have much TiO2 in them, can have good hiding. It
works similarly to the way that beer foam is white. Even
though the beer is translucent, the foam looks white because
of the air bubbles.
In the lesson you'll compare the wet hiding and dry
hiding of the four recommended paints. Because the semigloss
paint depends on TiO2 for
its hiding (remember: not much sand, most of it white sand,
plenty of glue to go around, so no air voids), its hiding
doesn't change much as the paint dries. However, because the
ceiling paint depends mainly on air voids for its hiding, it
will start out fairly transparent and become whiter as the
paint dries.
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Exercise 1:
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You can now make some predictions about the properties of
your paints. Fill in the blanks in the table, rating the
predicted properties as very low, low, medium, high, or very
high.

Volume Concentrations
In the paint industry, the levels of binder, pigment, and
extender are quantified in terms of volume concentrations.
The level of binder in a paint can be described by its
"Binder Volume Concentration," or BVC. BVC is defined as the
volume fraction of the paint ingredients in the dried film
which is binder and can be calculated as

Many properties of paint track with Binder Volume
Concentration. The following plot shows scrub resistance as
a function of Binder Volume Concentration for four typical
paints. As you increase the level of binder, scrub
resistance goes up because mineral particles are held in
place strongly by the binder.
Figure 6. Plot of Scrub Resistance vs. Binder Volume
Concentration

If you try to plot scrub resistance versus mass fraction
binder, you would probably not get a good correlation
between scrub resistance and binder content. This is because
TiO2 is so much denser
than extenders. Semigloss paints, which have a lot of
TiO2 in them, have about
the same mass fraction binder as an inexpensive interior
flat paint but have a much higher volume fraction binder and
usually have much better scrub resistance. It doesn't take
any more binder to bind a dense mineral particle than a
light one, so it is the volume fraction that matters. You
might get a good correlation between scrub resistance and
mole fraction of binder in a paint, but it's very difficult
to know how many moles of binder and mineral particles you
have when they're all different sizes and shapes! For these
reasons, while you will measure the mass fraction water,
polymer, and mineral material in your paint, you will use
the densities of polymer, water, and your paint to convert
your mass fractions to volume fractions in order to
interpret your data.
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Appendix B:
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Glossary
Additives are ingredients in a paint formulation
which are used in relatively small amounts. They are the
"salt and pepper" of the formulation. There are many of
these materials used in paint including: thickeners, which
keep the paint from being too runny; solvents, which protect
it from freezing; dispersing aids, which keep the small
particles separated; mildew inhibitors; and preservatives.
Additives are essential for good paint performance, and like
spices in cooking, they're often expensive.
Binder is the glue that holds the pigments and
extenders together and holds the paint onto the surface it
was applied to. In latex paints, the binder consists of very
small (0.1 to 1.0 micron) particles of plastic or polymer
which are suspended in water. White glue is made up of very
similar polymer particles to those used in latex paints. In
solvent paints, like alkyd and oil paints, the binder is
quite different. There it is dissolved in the solvent, so
there are no particles of binder. But in solvent paints too,
the binder is the glue which holds things together.
Binder Volume Concentration (BVC) is the volume of
binder solids divided by the volume of total paint solids
(binder, extender, and pigment) in the paint film. It is the
measure of how much "glue" is in the formulation.

In this experiment you calculate BVC as a fraction. In
industry, it is usually calculated as a percentage.
Ceiling Paint is designed to be very flat and have
excellent hiding. Since ceilings do not normally get dirty,
ceiling paints do not need to have good resistance
properties, and the flatness and hiding can be designed into
the paint inexpensively by using a lot of extender.
Colorants are the small amounts of dye that are
added to white paint to give it its color, often right at
the paint store. In this experiment we recommend that you
work with the white paints themselves, in that it makes it
easier to interpret your hiding results.
Decorative properties are those properties which
affect the appearance of the paint. In these experiments
we'll be looking at the decorative properties of gloss,
color, and hiding.
Dry Hiding is the hiding of the paint after it
dries (see Hiding).
Extender (see Mineral extender).
Extender Pigment is a term sometimes used in the
paint industry. In this laboratory we are using the terms
"extender" or "mineral extender" for clarity.
Exterior Paint is used outside. It needs to have
good resistance to sun, rain, mildew, and dirt. Exterior
paints often use binders which have special resistance to
light, heat, and moisture. Because of these special
properties and their high binder content, exterior paints
are often more expensive than interior paints.
Flat Paint is paint which is not glossy. The lack
of gloss helps mask imperfections in a surface. A dent in a
glossy surface is very easy to see by the change in the
reflections. Since the light reflecting from a flat paint is
diffuse (i.e., it bounces off the surface in all
directions), it is harder to see where the dent is. This is
one reason why we often use flat paints on large wall areas
and semigloss or gloss paints on small areas such as trim.
The discussion and diagram of gloss in the "Sand and Glue
Analogy" shows how the microscopic roughness induced by the
extenders in the flat paint film reduce the gloss and give a
diffuse reflectance.
Formulation is a term that means the recipe of the
paint. Most paint formulations include ten to twenty
ingredients. In the latex paints we're discussing here
water, binder, pigment, and extender make up the bulk of the
paint. The remaining ingredients are called additives.
Gloss is a measure of how shiny a paint is. A
gloss paint is very smooth, and light reflects off it as it
would off a piece of clear glass.
Hiding is the ability of a paint to obscure colors
beneath it. If a paint does not have good hiding, the
painters may need to apply several coats of paint before
they have the uniform color they want. In white paints,
hiding comes from the white pigment titanium dioxide. In
paints with high levels of extenders and low levels of
binder, air pockets may develop which also provide some of
their hiding. Since air is not present in the wet paint,
paints which rely on air have poor wet hiding. They develop
good dry hiding once the air pockets form.
Interior Paint is paint used inside a building.
These paints do not usually require the weather resistance
of exterior paints, but they often need to have good stain
resistance and washability.
Latex is a term derived from the latex which comes
from rubber trees. The sap of the rubber tree is a white,
milky substance which has tiny particles of rubber suspended
in it. When synthetic rubber was discovered, the term
"latex" was kept. We now use "latex" to describe many
suspensions of small rubbery or plastic particles. Latexes
used in our paints are most often based on vinyl or acrylic
polymers.
Micron. A micron is 0.000001 meters, or
10&endash;6 meters.
Mineral Extenders are hard, colorless minerals
used as fillers in the paint. Mineral extenders are low in
cost, make the paint flat, and can provide hardness to the
paint. Extenders range in particle size from 0.1 to 15
microns.
Pigment Volume Concentration (PVC) is a term
frequently used in the paint industry which is closely
related to the BVC concept. PVC is the volume of pigment
(both primary and extender pigment) solids divided by the
volume of total paint solids (binder, extender, and pigment)
in the paint film. The PVC is simply 1 minus the BVC. In
industry PVC is usually expressed as a percentage.
A Polymer is a large molecule made up of a large
number of smaller molecules (monomers) joined together.
Plastics, protein, nylon, starch, and cellulose are all
polymers.
Primary Pigment is the pigment which gives the
paint its main hiding and color. In the paints in this
experiment, the primary pigment is titanium dioxide,
TiO2. Like the extenders,
pigments are hard mineral particles.
Resistance Properties are measures of how the
paint performs under stress. They include scrubability,
stain resistance, exterior durability, and flexibility.
Scrub Resistance measures how tough a paint is and
how much washing it can withstand. Much of the variation in
prices of interior flat paints relates to their scrub
resistance. Higher binder volume content normally increases
scrub resistance. In addition, the specific choices the
paint maker makes for extenders, pigments and binder all
significantly influence the scrub resistance.
Semigloss Paints are less glossy than high gloss
paints but still appear shiny. They have either low levels
of extenders or no extenders in their formulations.
Stain Resistance measures how easily a stain can
be removed from a paint. If the stain penetrates into the
paint it can be very hard to remove. In porous paints, such
as ceiling paints, stains can get into the air voids and be
hard to remove.
Suspension is a word describing a liquid which
contains small particles of solid materials. The term
"suspension" contrasts with the term "solution." In a
solution one material dissolves in another and becomes part
of the liquid. Once dissolved, the material cannot be
removed by filtration or other mechanical means. In a
suspension, the small particles remain as solids and do not
dissolve. They are so small that they look like part of the
liquid to the unaided eye. But the suspended particles may
be seen with a microscope and they may be separated from the
liquid with a fine filter.
TiO2, or Titanium
dioxide, is a crystalline mineral which makes paints and
other materials white. TiO2 can also be found in cream filled
doughnuts, white plastic, paper, and toothpaste. The
TiO2 particles in paint
are about 0.2 micron in diameter - so small that they are
barely visible with the most powerful optical microscopes.
Weathering Resistance is the ability of the paint
to withstand exposure outside. Important factors in
weathering resistance are resistance to ultraviolet and
visible light, to moisture, to temperature extremes, air
pollution, and to changes in the painted surface.
Wet Hiding is the hiding of the paint before it
dries. An interesting way to simulate the wet hiding of a
dry paint is to rewet it with water. By doing this, any air
voids are filled with water, thereby decreasing the hiding
in a paint which has a significant amount of the air voids.
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Appendix C:
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Teacher Notes and Sample Data
This lab is best viewed as a Unit on Paint and not as an
isolated experiment using paint. The Appendices A and B are
an important preliminary assignment which should be provided
in advance of attempting the experiment. These appendices
are also excellent reference material for understanding and
explaining the experimental results.
The experiment itself has been organized to allow for
completion over a four forty-five- minute class period
timetable with adequate time to complete each part. The
experimental techniques needed by students are for the most
part ones with which they are probably familiar (i.e.
massing, using a crucible and cover and Bunsen burner).
The calculations of Binder Volume Concentration (BVC) and
Pigment Volume Concentration (PVC), although somewhat
involved, have been set forth in such a way as to enable
most students to "walk through" them with some guidance. The
BVC values enable students to compare and correlate the
properties they test to the paint composition they have
experimentally determined. A set of sample data tables
follows, along with the calculated values for volume
fractions for the wet and dry paint.
The amount of paint needed to do this experiment will
vary according to the total number of students, 3-5 ounces
(100&endash;150 mL) of each paint per lab group should be
ample. It might be possible to get a local paint store to
donate the paints and inexpensive brushes, or use paints
(white or off-white) donated by students. However, if you
are using paints made prior to 1991, the burning of the
paints should be done in a hood, since up until this time
some paints contained mercury as a preservative. Be sure to
use water based paints only. Obtain cost per gallon for each
paint also so that the cost can be correlated to the
properties tested.
If equipment limitations do not allow you to do the
drying and combustion portion of this lab with all of the
students, you may want to have one class perform the
experiment and share the data with your other classes, so
that all of the students will be able to do the
scrub/stain/extended activities portion as well as the
calculations and questions. The sample data included here
could be used, but you would probably want to obtain your
own set of data for your paints.
The cautions pertaining to this lab involve:
a) the handling of very hot equipment
b) the use of a Bunsen burner
c) the 2-3" flame produced during the burning off of the
polymer (the flame lasts for about 2 minutes only)
d) burning should be done with adequate ventilation, and
as with any burning substance, students should avoid
breathing the fumes as much as possible. If hood space and
time allow, we recommend that the combustion portion of the
lab (Part D) be done in a hood.
e) if paints are brought from home rather than newly
purchased, the paints should be burned in a hood, since up
until 1991 some paints contained mercury as a preservative.
f) only water borne latex paints should be used
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Sample Data
Tables:
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Data Table I. Densities of Wet Paints

Data Table II. Mass Fraction Water

Data Table III. Combustion of Samples

Data Table IVa. Scrub Test and Observations of
Hiding

Table IVb. Gloss/Texture of Dry Paints and Microscope
Examination
description of appearance under

Data Table V. Stain Test

Summary Table of Volume Fractions for Wet Paints

Summary Table for Concentrations in Dry Paint

Exercise 1 from Appendix A.
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This experiment is courtesy of 
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