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    Paint Properties Experiments
    Density, Scrubability, Stain Removal and Contents
    For Science Labs, Lesson Plans, Class Activities & Science Fair Projects
    For High School Students & Teachers







    Paint Properties Experiments
    This experiment is courtesy of 

    Quantitative Determination

    of the Composition of Water-based Paints
    and the Correlation of Paint Properties
    to Paint Composition



    Developers:

    Sally Breen
    Springfield Township High School
    Erdenheim, PA


    Tienne Moriniere Myers
    Hancock Demonstration School
    Philadelphia, PA

    Meredith Morgan
    Architectural Coatings Research
    Rohm and Haas Company
    Spring House, PA

    John Hook
    Architectural Coatings Research
    Rohm and Haas Company
    Spring House, PA


    Grade
    Levels:

    High School


    Background:

    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.


    Objective:

    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.


    Specific
    Objectives:

    • 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


    Equipment:

    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.)


    Suggested
    Timetable:

    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


    Procedure:

    A. Density Determination of Wet Paints:

    1. Mark each of four test tubes A, B, C, and D and then mass, recording your results in Data Table I.

       

    2. Calibrate each test tube using the graduate and 20.0 mL of water. Mark the 20mL level, then empty and dry the test tubes.

       

    3. 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.

       

    4. 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.)

       

    5. 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:

    1. Clean and dry 4 crucibles and covers. Mark them (crucibles and lids) A, B, C, and D.

       

    2. Mass each crucible with its lid to the nearest 0.01 g and record in Data Table II.

       

    3. 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

       

    4. Gently swirl the crucible so that the paint partially covers the interior surface of the crucible for better drying.

       

    5. 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.

       

    6. 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:

    1. 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.

       

    2. Label each of the 4 panels A, B, C, or D to correspond to each of the paints being tested.

       

    3. 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



    4. 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.

       

    5. Wipe the excess paint from the brush using a paper towel; then clean the paint brush under running water.

       

    6. 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.)

       
    1. Record the mass of the dried paint + crucible + cover from Table II into Table III.

       

    2. 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.

       

    3. 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.

       

    4. Light the burner and place under the crucible. Do not hold the burner.

       

    5. 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.

       

    6. 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.

       

    7. 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.

       

    8. 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.

       

    9. 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

       
    1. 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.

       

    2. 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.

       

    3. 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.



    4. 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.

       

    5. 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.

       

    6. 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)

    A

    Mass fraction of water in wet paint (g water/g wet paint)

    B

    Mass fraction of polymer in wet paint (g polymer/g wet paint)

    C

    Mass fraction of minerals in wet paint (g ash/g wet paint)

    D

    Density of water (1.00 g/mL)

    E

    Density of polymer (1.13g/mL)

    F

    Volume fraction of polymer in wet paint

    G

    Volume fraction of water in wet paint

    H

    Volume fraction of minerals in wet paint

    J

    Volume fraction of polymer in dry paint (BVC)

    K

    Volume fraction mineral in dry paint (PVC)

    L


    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).


    Conclusion
    Questions:

    1. Make a table of your experimental results to correspond to Exercise 1 in Appendix A. Compare your results with your predictions.

       

    2. Compare your graph to the example graph in Appendix A. What conclusion can you draw concerning binder (polymer) concentration and scrub resistance?

       

    3. What trends did you observe for BVC content, scrub resistance and stain removal?

       

    4. 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?

       

    5. Why would you choose a semigloss paint and not a ceiling paint for your kitchen walls?

       

    6. 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.)


    Extended
    Activities:

    1. 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.)

       

    2. 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?

       

    3. 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?


    Optional
    Calculations:

    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?


    Appendix A:

    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.


    Exercise 1:

    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.


    Appendix B:

    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.


    Appendix C:

    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


    Sample Data
    Tables:

    Data Table I. Densities of Wet Paints

    Data Table 1

    Data Table II. Mass Fraction Water

    Data Table 2

    Data Table III. Combustion of Samples

    Data Table 3

    Data Table IVa. Scrub Test and Observations of Hiding

    Data Table 4a

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

    description of appearance under

    Data Table 4b

    Data Table V. Stain Test

    Data Table 5

    Summary Table of Volume Fractions for Wet Paints

    Summary Table of Volume Fractions

    Summary Table for Concentrations in Dry Paint

    Summary Table for Concentrations

    Exercise 1 from Appendix A.

    Exercise 1


    This experiment is courtesy of 



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