How does temperature affect the strength and adherence of glue?

Introduction: (Initial Observation)

Natural and synthetic glues with many different compositions are used in many products. The ease of use and the strength of glue makes it a perfect and inexpensive choice for fastening different materials. With growing use of glue in different products it becomes necessary to study the safety, reliability and the strength of different glue in different temperatures. After all glues are polymers (like plastics) and polymers are often sensitive to the heat.

Heat can melt, soften, decompose and deform many polymers. How does heat affect glue? Is it possible that glued parts will come apart if they get warm or hot? How strong are glues at different temperatures?

Please select one specific glue for your study and refer to that by name in your hypothesis and results.

Information Gathering:

The dictionary defines an adhesive as “a substance capable of holding materials together by surface attachment.”

Glues are 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, rubber, and glue, 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 on glue.

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 the strength of glue.

Constant is the type of glue 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 strength of wood glue decrease as the temperature increases, and rubber will be softer and more flexible in higher temperatures.

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.”

Experiment 1:

Effect of temperature on the strength of glue

Introduction: In order to see the effect of different temperatures on the strength of glue, we will measure the strength of glued samples in different temperatures. To measure the strength, you simply apply a force at the glues point in order to brake apart the glued pieces. The amount of that force is a representation of the strength of the glue. Source of heat can be a hair dryer or an electrical heater. Temperature may be measured by a thermometer placed next to the glued joint.

Please note that the temperatures suggested for test in this experiment may change. You may choose to test higher or lower temperatures.

Safety Requirements:

Since you are applying force to brake apart the glued pieces, you must protect your eyes using goggles to avoid injury by flying wood pieces. Adult supervision is also required. This experiment involve using high temperatures.

Procedure:

1. Use the glue to connect 25 pairs of wood dowels. This will give you 25 double length wood dowels. Let the glue dry for 24 hors.
2. Separate the wood dowels into 5 groups of 5. Each group is for testing the strength in one specific temperature. Mark the wood dowels of each group with one specific color.

3. Use a thermometer to measure the room temperature. Record the temperature. Place the wood dowels one at a time between two stands. Hang the spring scale at the joint and start to pull it down while watching at the amount of applied force. Record the final force that brakes the pieces apart. Repeat this step for all 5 glued wood pairs of group 1. Calculate the average strength for group 1.

4. Place the wood dowels of the second group one at a time between two stands. Turn on your heat source. Use a thermometer to measure the temperature in the area of the joint. Wait until the temperature is exactly 50º Celsius. Record the temperature. Hang the spring scale at the joint and start to pull it down while watching at the amount of applied force. Record the final force that brakes the pieces apart. Repeat this step for all 5 glued wood pairs of group 2. Calculate the average strength for group 2.

5. Place the wood dowels of the third group one at a time between two stands. Turn on your heat source. Use a thermometer to measure the temperature in the area of the joint. Wait until the temperature is exactly 75º Celsius. Record the temperature. Hang the spring scale at the joint and start to pull it down while watching at the amount of applied force. Record the final force that brakes the pieces apart. Repeat this step for all 5 glued wood pairs of group 3. Calculate the average strength for group 3.

6. Place the wood dowels of the fourth group one at a time between two stands. Turn on your heat source. Use a thermometer to measure the temperature in the area of the joint. Wait until the temperature is exactly 100º Celsius. Record the temperature. Hang the spring scale at the joint and start to pull it down while watching at the amount of applied force. Record the final force that brakes the pieces apart. Repeat this step for all 5 glued wood pairs of group 4. Calculate the average strength for group 4.

7. Place the wood dowels of the fifth group one at a time between two stands. Turn on your heat source. Use a thermometer to measure the temperature in the area of the joint. Wait until the temperature is exactly 125º Celsius. Record the temperature. Hang the spring scale at the joint and start to pull it down while watching at the amount of applied force. Record the final force that brakes the pieces apart. Repeat this step for all 5 glued wood pairs of group 5. Calculate the average strength for group 5.

Your experiment results table may look like this:

Need a control?

Someone may question your results and claim that changes in the strength had nothing to do with the temperature. The fact is that you will not do all the tests in one moment, so time is also a variable that may affect your results. It may seem unreasonable; however, the scientific method requires having a control experiment at the same time you do your other experiments. Control experiments need another group of wood dowels that you glue to each other in pairs. Every time you test one specific temperature, you do one more test at room temperature and you call it control.

For example in your main experiment you may test brake force of glued wood dowels at room temperature, 50ºC, 75ºC,100ºC, and 125ºC. At the same time that you do one of these tests, you must test another pair of glued wood dowels at room temperature.

Braking five pairs of glued wood dowels at five different temperatures are called main experiments.

Braking five pairs of glued wood dowels at room temperature are called control experiments.

Each control experiment must be performed at the same time with one main experiment.

Make a graph:

Make a bar graph with 5 vertical bars. Each bar is for one of the temperatures that you test. The height of each bar shows the strength of the glue at that specific temperature. To make your graph more understandable, write the temperature below each bar. Also write the strength above each bar. The strength can be specified as Newtons, Grams or Kilograms.

Experiment 2:

Effect of temperature on the strength of glue

Introduction: You may not have a thermometer to record the temperature. You may also not have a spring scale to apply a force. This experiment is a variation of the previous experiment; however, instead of measuring temperature you will record the heat exposure time. Obviously the temperature starts to increase as soon as the heat exposure starts. The longer a joint is exposed to the heat, the warmer it gets. (After a certain temperature it does not get any warmer; however, we will not get to such temperatures)

procedure:

1. Use the glue to connect 25 pairs of wood dowels. This will give you 25 double length wood dowels. Let the glue dry for 24 hors.
2. Separate the wood dowels into 5 groups of 5. Each group is for testing the strength in one specific temperature. Mark the wood dowels of each group with one specific color.
3. Place the wood dowels of the first group one at a time between two stands. Hang an empty bucket on the joint and gradually start to add water to that using a measuring cup until the joint pairs brake apart. Using the amount of water estimate the weight of the bucket with water in each test. Then calculate the average weight that broke the glued pieces.
4. Place the wood dowels of the second group one at a time between two stands. Hang an empty bucket on the joint. Use a hair dryer to heat up the joint for one minute and then start to add water to the bucket using a measuring cup until the joint pairs brake apart. Using the amount of water estimate the weight of the bucket with water in each test. Then calculate the average weight that broke the glued pieces.
5. Repeat the previous step for the third, the fourth and the fifth group of glued pairs; however, increase the heating time to 2, 3 and 4 minutes.

Your results table may look like this:

Make a graph:

Make a bar graph with 5 vertical bars. Each bar is for one of the heat exposure periods. The height of each bar shows the strength of the glue (or average weight of water bucket that broke the glued joint). To make your graph more understandable, write the heating minutes below each bar. Also write the strength above each bar. The strength can be specified as pounds, grams or kilograms.

Materials and Equipment:

List of material can be extracted from the experiment section. This is a sample list of material:

1. Pack of 6″ long wood dowels with diameter of 3/8″ or 1 cm (from a local craft store)
2. 5000-gram spring Scale (from MiniScience.com)
3. Thermometer (from MiniScience.com)
4. Plastic bucket (found at home)
5. Nylon string to hang the bucket (from a local hardware store)
6. Measuring cup (found at home)
7. Hair Dryer (found at home)
8. Electric heater (found at home)

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.

Calculations:

In both experiments you will need to calculate the average strength of glued pieces of each group. In the experiment number 2, you will also need to calculate the weight of bucket with water based on the amount of water. Note that each liter of water is 1 kilogram.

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.

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:

Websites:

1. Wikipedia Encyclopedia
2. Glue
3. Adhesives, An introduction
4. Gums
5. Adhesives, resins (slow download)