How is paint affected by temperature changes?

Introduction: (Initial Observation)

You may have noticed blisters on painted surfaces that are very close to an electric or gas heater. Blisters are not the only affect of heat on paint! Some paints will become extra dry and crack or peal off when exposed to the heat. Paint applied to certain products and certain areas need to have a higher resistance to heat. Chemists often need to test the resistance of different paints to high temperatures in order to determine the usability of certain paints for certain applications.

Paint is not just a decorative layer, but often it is a protective layer and any defect on a protective layer caused by temperature change or other environmental factors will raise concern.

In this project you will study the effect of heat on one type of paint of your choice. Design experiments to test how the physical properties of the paint are affected by heat. Physical properties such as color, texture, adherence and odor may be tested. Finally report your results in a the form of a table or graph.

Why this project is important?

Imagine you go out and buy a new stove. It is painted white and it looks beautiful. You turn it on for the first time to cook something and you notice disturbing fumes and smoke from a burning paint, and soon the stove paint changes to brown, blisters, peels off and your beautiful stove does not look beautiful any more. Obviously you will not be a happy customer.

Such occurrences were common a few decades ago when the paint industry was not advanced and small shop manufacturers would try different methods. Desk lamps, stoves, heaters and many other equipment could show paint problems. Many people got used to that and would think that any new kerosene heater must have such fumes. They would simply leave the doors and windows open in the first few days so the fumes can exit the room.

Testing the effect of heat at small scale can allow manufacturers to try different formulas and find out what paints are usable in hot environment and how they can be improved.

Should I do all 3 experiments?

The most difficulty with this project is when students use high quality paints and low temperatures, so they will not observe any noticeable change in the appearance or the quality of paint. For best results you must try all 3 experiments and maximize the test temperature or temperature changes.

Information Gathering:

Find out about paints and their physical and chemical properties. Read books, magazines or ask professionals who might know in order to learn about the effect of heat on paint or ingredients of paint. Keep track of where you got your information from. Following are samples of information you may find:

Paints are materials based on polymers. Molecules of certain chemicals have a tendency to bind with each other and create a larger molecule. Such small molecules are called monomers, and when they bind with each other and form a larger molecule, they are then called polymers.

By studying the properties of paint, you are actually studying about polymers. Although there are so many different polymers, we can divide them in two major groups, which are thermoplastics and thermosets. A polymer is thermoplastic if it becomes softer and more flexible by heat. It is thermoset if it becomes more rigid and harder by heat.

Studying the effect of temperature change, heat, light, moisture, and other factors on polymers is often a routine task performed in the quality control laboratories of manufacturers.

When the paint is dry, temperature change will cause the layer pf paint to expand and contract. Such expansion and contraction can cause the paint to get separated from it’s supporting surface or may cause stress and strain in the paint layer, resulting in cracks.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The aim of this study is to examine the effect of temperature change on paint.

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

The independent variable (also known as manipulated variable) is the temperature.

The dependent variable (also known as responding variable) is one of the physical properties of paint. Color, texture and adherence are among the factors that may be measured as dependent variables.

Constant is the type of paint that you choose to study.

Hypothesis:

Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

My hypothesis is that the interior water based latex paint may not be used for hot metal surfaces; such paints will lose color, adherence, and may form blisters when exposed to heat.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Hint 1: White paints and bright color paints are less resistant to heat and it is easier to observe the effect of heat on them.

Hint 2: You may use an oven as the source of heat for your experiments.

Hint 3: It is easier and quicker to test the effect of heat rather than the effect of temperature change on paint.

Experiment 1:

In order to see the effect of different temperatures on wet paint, we will place fresh painted samples in different temperatures and make observations.

Procedure:

Get a heat source such as an electric heater or a heat lamp. Place your heat source somewhere safe, away from any flammable material and turn it on. It is very hot close to the heat source, but as you get away from it the temperature will decline.

Use a thermometer to identify the temperature in different regions. You may divide the area in front of your heater to 10 different heat zones, and mark the area with the average temperature of that zone. If you want to cover this area and make a heat canal, use only non-flammable materials to do so. Fiberglass insulation boards covered by aluminum may be used for this purpose.

Get some paint, a brush, and 10 identical pieces of wood or metal. Paint the top surface of all the pieces with the same amount of paint. Place painted pieces in 10 different heat zones. Inspect the samples every hour in the first 6 to 10 hours and every 12 hours after that for 2 days. Record your observations in a table like this.

Smooth surfaces are the best for this experiment.

Table 1: Rate of different affects on wet paint samples.

The numbers in the above table are in the form of percentages. For example 15% in the color change row of column 110-120 indicates that the sample had 15% color change in temperature range of 110° C to 120° C. You may visually estimate them.

If you are testing pure single color paints, you may make a color chart that can help you to determine the color change. For example you may make a color chart that starts from white, 10% red, 20% red,… up to 100% red if you are experimenting on a red paint.

For cracks you can divide your sample to small squares (1″ x 1″) and count how many of the squares are cracked and how many are free from cracks. You can do the same for blisters.
Note that these are methods that you create in order to have a fair comparison.

You may perform your tests in other temperature ranges.

Experiment 2:
In order to see the effect of different temperatures on dry paint, we will place painted samples in different temperatures and make observations.

Procedure:

Get a heat source such as an electric heater or a heat lamp. Place your heat source somewhere safe, away from any flammable material and turn it on. It is very hot close to the heat source, but as you get away from it the temperature will decline.

Use a thermometer to identify the temperature in different regions. You may divide the area in front of your heater to 10 different heat zones, and mark the area with the average temperature of that zone. If you want to cover this area and make a heat canal, use only non-flammable material to do so. Fiberglass insulation boards covered by aluminum may be used for this purpose.

Get some paint, a brush, and 10 identical pieces of wood. Paint top surface of all the wooden pieces with the same amount of paint. Let all the samples dry at room temperature for at least 2 days or any length of time suggested by the manufacturer. When all painted samples are fully dry, place them in 10 different heat zones. Inspect the samples every hour in the first 6 to 10 hours and every 12 hours after that for 2 days. Record your observations in a table like this.

Table 2: Rate of different affects on dry paint samples.

You may perform your tests in other temperature ranges.

As you noticed in all of the above experiments, we studied the effect of temperature. In other words we changed the temperature to see what physical changes may happen to our sample.

In some cases, a painted surface needs to be tested in order to find out how resistant the paint is against natural phenomena such as daily change of temperature that may cause stress and strain in a paint layer. A bridge for example is absorbing the heat from sun every day and loses that temperature and gets cold at night. Such constant change may have a different affect on paint than occasional high temperature. In a laboratory we can accelerate such affects by reducing the hot and cold periods.

Experiment 3:

In order to see the effect of temperature change on paint, we will place some dry painted samples exposed to changing temperature. In nature, temperature change has a pattern or a cycle that takes 24 hours. For our experiment we will reduce this cycle to 0ne hour. In this way 24 hours of experiment will have the same results as 24 days natural change in temperature.

Procedure:

As a heat source use a lamp and place it close to the painted samples in a way that samples get at least 80º C hot. Use an oven thermometer to verify this temperature.

Keep some of your samples away from your experiment area. That will be your control. Place the other samples under the lamp.

Plug the lamp to a timer programmed to turn off and on every 30 minutes. (You can buy such a timer from a hardware store for about $5 to $10).

When the light is on the paint will get hot. Light will almost work like a direct sunlight. When the light is off, paint will get chance to cool off.

After about 5 to seven days visually inspect the paints. Look for any obvious defect. Compare them with your control. And do the peel test! For peel test place a piece of clear adhesive tape on the paint. Rub it a few seconds to make it stick firmly. Then pill it off suddenly. Look at the tape and see if it removed any paint. Do the peel test with your control as well. Compare the results of two peel test.

For this experiment, you will usually need many samples. Keeping 5 painted samples as control and using 20 samples for heat test seems sufficient. In this case starting the second day, you can can perform peel tests and see what is the effect of heat change after 2, 3 or 4 days.

Note: Popsicle sticks that we used for this experiment have a very rough surface, so the paint has a strong bond with wood fiber. This condition will give extra strength to the paint. If small pieces of flexible or hard plastic or metal are used for this experiment, it will be easier to see the effects of temperature change.

Materials and Equipment:

List of materials can be extracted from the experiment section. Final list of materials may vary based on the changes you may make in your experiments. Following is a sample list of equipment:

1. 1. Toaster oven as the heat source
   2. Aluminum plates (to be painted)
   3. Paint samples (White or other bright colors)
   4. Brushes
   5. Oven thermometer

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

The paint used to make the stop sign in the right is all cracked and pilled off. Part of such changes are caused by temperature changes. The substrate (under laying layer) expands and contracts by changes of temperature. The amount of such expansions and contractions depend on the expansion coefficient of each material.

Often dry paints do not expand and contract at the same rate as their substrate. This will cause the paint to crack and pill off gradually.

Many modern paints are made from advanced polymers with extreme resistance to temperature changes and other environmental factors. Inexpensive paints and home made paints will be more susceptible to defects caused by temperature changes and high temperatures.

Calculations:

No calculation is required for this project.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

In your conclusion you may include what you have learned from your studies and experiments. A conclusion may include information such as this:

Oil based and latex paints are both organic thermoplastic polymers that soften by heat. Excess heat can cause decomposition, discoloration and pilling. As a result of such problems neither latex paints nor oil based paints can be used to paint things like frying pan, kettles, pots, electric stoves, toasters, and gas stoves.

So what types of paints are used for such products? Are those paints or glazes? what is the difference? Use these questions for further or future studies.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

References:

Visit your local library and review books about paints, polymers, organic chemistry, and plastics.

Websites:

• • http://www.buicks.net/shop/body/paint_basics.html
  • http://www.ecn.purdue.edu/CMTI/Technology_Transfer/NORINDP2
  • http://www.paintquality.com.au/press/newspaper/BOAPT01.html
  • http://en.wikipedia.org/wiki/Paint
  • Search for thermal stabilizers that are added to polymers
  • Search for heat stabilizers that are added to polymers

Books:

Paint and Coating Testing Manual, Gardner-Sward Handbook, 14th Edition