Introduction: (Initial Observation)
Natural and synthetic robbers with many different compositions are used in many machineries and equipment. The elasticity of rubber makes it a perfect choice for products such as washers, tubes, tires, balls, joints, pads, boots, hoses, and bands.
Most polymers have little resistance to high temperatures. Polymers used in household plastic products tend to melt, deform, decompose or burn in high temperatures.
Many rubber parts used in water valves, automobiles and other machineries are exposed to heat from hot water, hot oil or holt metal parts. The question is “How do rubber products react in high temperatures?”; How does temperature affect the elasticity of rubber? In this project we will investigate the effect of heat on rubber.
Gather information about the properties of rubber (history of rubber, where it comes from, how it’s made, elasticity, and cross links) and how heat affects the elasticity.
Following are samples of information that you may find:
Approximately 50 % of the industrial chemists in the United States work in some area of polymer chemistry, a fact that illustrates just how important polymers are to our economy and standard of living. These polymers are essential to the production of goods ranging from toys to roofing materials. So what exactly are polymers? Polymers are substances composed of extremely large molecules termed macromolecules.. The macromolecules consist of many smaller molecular units, monomers joined together through covalent bonds. The molar mass of the polymer is quoted as an average molar mass.
As Ralph Wolfe’s poetic prose confirms, rubber is as indispensable to modern society as steel and wood and mortar. We use products made of rubber at work, at home, at play, even when we travel. Automobiles, trains and aircraft rely on it for safety and comfort. Industry uses it to produce hoses, belts, gaskets, tires, molding, and thousands of other products. Rubber in the modern world is omnipotent.
It comes to us from two sources: nature and man. Natural rubber is siphoned from cultivated trees on plantations in Asia and Africa. Synthetic rubber is man-made and is produced around the world in manufacturing plants that synthesize it from petroleum and other minerals.
Whether it’s natural or synthetic, rubber in its native form is virtually useless. But after chemicals are added, it takes on properties that, as Ralph Wolf noted, make it “totally unlike” any material the world has ever known. Depending on the chemicals used, products made of rubber can be as soft as a sponge, as resilient as a rubber band, or as hard as a bowling ball. As a result, we use thousands of rubber products with varying degrees of hardness in our daily lives.
Natural rubber has been available for centuries, synthetic rubber for less than a hundred years. Although man began experimenting with synthetic in 1906, not until after World War II did he improve the quality to the point that it rivaled that of natural rubber. Wartime necessity became the impetus for the emergence of synthetic on a large-scale basis when governments began building plants to offset natural rubber shortages.
Rubbers are all 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 rubber, 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.
Following are some synthetic rubber materials:
• NATURAL RUBBER • NEOPRENE
• NITRILE (Buna-N) • SILICONE
• VITON • HYPALON
You may use Internet search to learn more about the chemical structure of each synthetic rubber.
Elasticity is the property of returning to an initial form or state following deformation. Elasticity of material is expressed by their elastic modulus. For example the elastic modulus of rubber is less than 0.1, the elastic modulus of nylon is about 3 and the elastic modulus of aluminum is about 69. As you see, material that have a higher elasticity, have a smaller elastic modulus.
An important materials property is termed the tensile elastic modulus, or Young’s Modulus. This is usually given the symbol E. Loosely, the modulus is defined as the force you need to provide to elongate your material.
Measuring The Elastic Modulus
The elastic modulus is measured by pulling a sample of a material in a tensile testing machine, an instrument which measures force.
Let’s define stress, denoted by the Y, as the force (F) normalized by the cross-sectional area (A) of the material:
Y = F / A
The standard unit of stress is N/m2 (Newton per Square meter). So F should be in Newton and A should be in Square Meter.
Now attach an extensometer to the sample. The extensometer measures the change in length of the sample as it is being pulled.
Let’s define strain, denoted by the letter X, as the change in length of the fiber normalized by the initial length. (It simply means change in length per unit of length. It can also mean the percentage of length increase.) P.A.
X = (L1 -L0) / L0
Now, plot stress versus strain. The slope of this line will give you the elastic modulus E of the material.
Y = E X or E = Y / X
This technique applies for small forces which do not irreversibly stretch the material. The material is in the elastic regime.
Source… (Changes have been done to make it more understandable for students.)
Elasticity = Elasticity is the condition or property of being elastic; flexibility.
In physics elasticity is the property of returning to an initial form or state following deformation.
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 elasticity of rubber.
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 elasticity of rubber.
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.
This is a sample hypothesis:
The elasticity of rubber decrease as the temperature increase.
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.”
Select only one of the two experiments for your project.
Experiment 1: Comparing the elasticity of rubber at different temperatures.
Introduction: In order to see the effect of different temperatures on the elasticity of rubber, we must first have a definition for elasticity and plasticity. Elasticity is the property of returning to an initial form or state following deformation. Plasticity is the ability of undergoing continuous deformation without rupture or relaxation. For example rubber bands and balloons are elastic while a freshly chewed gum is plastic. For the purpose of this experiment we will measure the ability of returning to an initial form in rubber bands. If a rubber band retracts to its initial state after being stretched, we call it 100% elastic and 0% plastic. If a rubber band maintain its state after being stretched, we call it 100% plastic.
In other words the ratio of retraction distance to the stretching distance is a measure of elasticity. The ratio of elongation distance to the stretching distance is a measure of plasticity. In this way the sum of elasticity and plasticity is always 1.
- Construct a wooden frame about 70 cm tall
- Secure one end of a rubber band to the top of the frame and let it hang freely
- Place a ruler vertically behind the rubber band so you can observe and record the position of the lower end of the rubber band.
- Use a thermometer to measure and record the temperature in the area of rubber band.
- Get the lower end of the rubber band and pull it down to 3 times its original length. Record the distance that you stretch the rubber band. This is called stretching distance.
- Slowly let the rubber band retract. Observe and record the new position of the end of the rubber band. Record the distance that the rubber band retracts.
- Divide the retraction distance by the stretching distance. Call it elasticity rate.
- Divide the elongation distance by the stretching distance. Call it plasticity rate. (Note that if the rubber band does nor retract 100%, then it is permanently lengthen. The amount that is added to the length of the rubber band is the elongation distance)
- Repeat the above procedures with the same type of rubber band at different temperatures. Each time turn on your heating device and wait until your thermometer shows the right temperature; then perform the stretching and retraction test described above.
- Record your results in a table like this:
|Temperature||Stretching Distance||Retraction Distance||Elasticity Rate*|
* Elasticity rate is the ratio of retraction distance to the stretching distance.
If you do not have access to a thermometer, you can record the heat exposure time instead. Your heat source can be a hair dryer or an electric heater. As you know more heat will accumulate and the rubber band will get hotter if the heating device is on for a longer time. For example you can repeat this experiment with different heat exposure periods from like 0, 1, 2, 3, 4 and 5 minutes.
Experiment 2: Elastic modulus of rubber band at different temperatures
Elastic modulus is a physical property that shows the elasticity of a substance. In this experiment you measure the elastic modulus of a rubber band at different temperatures. Elastic modulus is the ratio of stress to strain.
- Construct a wooden frame about 70 cm tall
- Get a rubber band and hang it to the frame
- Tie a string at the bottom of the rubber band so you can use it to hang something.
- Measure and record the length of the rubber band (L0) before adding any weight.
- Hang a known weight (F) to the rubber band. Select the weight so that the rubber band will be stretched about 10%. Record the new length of the rubber band (L1)
- Measure and record the cross section area (A) of the rubber band
- Use a thermometer to measure and record the temperature next to the rubber band
- Calculate the stress Y = F / A. In this equation F is the mass or weight hanged to the rubber band in Newtons. A is the area of the cross section of the rubber band in square meter.
- Calculate the strain X = (L1 -L0) / L0
- Divide the stress by strain to calculate the elastic modulus. E = Y / X
- Repeat the above steps at 5 different temperatures. You may create different temperatures using an electric heater or hair dryer. A thermometer placed near the rubber band will show the temperature.
Your results table may look like this:
Materials and Equipment:
List of material can be extracted from the experiment section. Following is a sample list of material:
- Wooden frame
- Rubber bands
- Electric heater
- Small weights
- Long ruler (measuring stick)
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.
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.
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.
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.
I built a wood apparatus that had a base and stood 75 cm. high and attached a ruler. Using binder clips, string, and a gravel weight cup holding a total of 90 grams, I attached the various measured rubber bands (three widths: skinny, medium, and wide which were all the same length). A 1500 watts blow dryer was my heat source. Rubber band measurements were taken: at the beginning (before heat), after 10 seconds of heating, after 20 seconds for cooling, and after they were taken down from the testing apparatus.
The skinny rubber bands (1/10 cm.) contracted an average of 0.0333 cm. after heating, and then stretched an average of 0.25 cm. past its starting point after cooling. The medium (2/5 cm.) and wide rubber bands (½ cm.), after 10 seconds of heat both stretched out an average of 0.0333 & 0.01666 respectively. After cooling the medium rubber bands stretched farther to 0.0666 while the wide rubber bands did not change from their heated length.
Heating the rubber bands caused them to shrink a little (contract) but when they cooled, they ended up stretching out because the cross links had been stretched beyond their elastic limit. There was a relationship to the width of the rubber bands as to how much they stretched out. They skinny rubber bands stretched out the most while the widest rubber bands stretched the least.