Introduction: (Initial Observation)
The sun emits rays in a large spectrum of wavelengths. These rays include UV light which has been determined to be harmful in the form of:
- sunburn and skin cancer
- eye cataracts
- suppression of the immune system
- premature aging
Because of these adverse health effects, it is important to limit exposure to UV radiation and use proper protection when outdoors.
We use sun-glasses and sun-tan lotion to shield ourselves from harmful effects of UV radiation from the sun. Does sunlight have harmful effects on other material around us?
We have seen discoloration of clothes and magazine covers caused by sunlight. Are other materials also affected in a similar way.
In this project we test 3 organic substance – rubber, ink and paper to see how they are affected by the sunlight.
Harmful effects of sunlight on different products has led to invention of many new products that can stop or reduce such effects. You are already familiar with sunglasses and sun lotions. In addition there are a large number of industrial products called UV stabilizers and UV filters. UV stabilizer is a substance added to a sample to prevent photo-deterioration by ultraviolet (UV) light. UV stabilizers are a main ingredient of many of today’s products. Almost all paints, most fabrics and most plastics contain such additives. Manufacturing UV stabilizers is one of the profitable businesses that can be performed in small scale. Many manufacturers have a quality control lab and among the equipment in this lab is a UV test box. UV test box has a few UV lamps and in total, it produces a UV radiation that is about 100 times the UV radiation of sunlight. You may place a sample in this box for only 24 hours and see how does sunlight affect that object in one year. This is a quick way of testing the effect of sunlight.
Information Gathering:
Find out about sunlight. Read books, magazines or ask professionals who might know in order to learn about the effects of sunlight. Keep track of where you got your information from.
The science that studies the effects of light on material is called photochemistry. The most common effect of light on material is called photodegradation.
Decomposition of material by light is called photolysis.
Hazards of Ultraviolet Light
UV or ultraviolet lamps are used in biological safety cabinets, light boxes, and crosslinkers in many University laboratories and in some patient care rooms. One of the problems in working with UV radiation is that the symptoms of overexposure are not immediately felt so that persons exposed do not realize the hazard until after the damage is done.
UV radiation is that radiation just outside the visible range, or under 400 nanometers (nm). There are three ranges of UV (see table below).
| Region | Also known as | Range in nm | Hazard Potential |
|---|---|---|---|
| UV-A | near UV | 320-400 | low |
| UV-B | mid UV | 290-320 | mid to high |
| UV-C | far UV | 190-290 | high |
(Early “black lights” emitted in the range of 360-390 nm.)
Health Effects
The biological effects of the 3 regions vary greatly as implied by the “hazard potential” column in the table. The health effects of exposure to UV light are familiar to anyone who has had a sunburn. However, the UV light levels around some UV equipment greatly exceeds the levels found in nature. Acute (short-term) effects include redness or ulceration of the skin. At high levels of exposure, these burns can be serious. For chronic exposures, there is also a cumulative risk of harm. This risk depends upon the amount of exposure during your lifetime. The long-term risk for large cumulative exposure includes premature aging of the skin and even skin cancer.
| Damages from UV exposure are not immediately felt . . . user may not realize hazard until after damage is done. |
|---|
The eyes are also susceptible to UV damage. Like the skin, the covering of the eye or the cornea, is epithelial tissue, too. The danger to the eye is enhanced by the fact that light can enter from all angles around the eye and not only in the direction you are looking. The lens can also be damaged, but since the cornea acts as a filter, the chances are reduced. This should not lessen the concern over lens damage however, because cataracts are the direct result of lens damage.
Burns to the eyes are usually more painful and serious than a burn to the skin. Make sure your eye protection is appropriate for this work. There are specially-made safety glasses for the different UV ranges. NORMAL EYEGLASSES OR CONTACTS OFFER YOU VERY LIMITED PROTECTION!!
You must not forget to protect the rest of your face, too. Severe skin burns can happen in a very short time, especially under your chin (where most people forget to cover). Full-face shields are really the only appropriate protection when working with UV light boxes for more than a few seconds.
Be sure to protect your arms and hands by wearing a long-sleeve lab coat and gloves.
Photodegradation is the most important process for destroying chemicals in atmosphere. source
Also search the internet for photodegradation, photolysis, photo chemistry.
Need more information?
You may need more “information” about organic materials (mainly polymers) such as paper, paint, glue, plastic and rubber.
Try the chemistry “polymer” section of your local library for some related books. Focus on paper and rubber.
Use a low hazard UV lamp
UV lamps provide a continuous and constant level of UV radiations. They are not affected by cloud or bad weather condition. Most researchers use UV lamps for faster and more reliable results.
If you want to use UV lamp, try using a blacklight UV lamp with the wave length of 320 nm – 400 nm.
Picture above shows the UV18F1 that we used in this experiment.
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 purpose of this experiment is to identify the effects of sunlight on paper, ink and rubber. We focus on physical effects such as color, strength and elasticity.
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.
Independent variable is the sunlight exposure time. In an experiment using UV light instead of sunlight, independent variable is the UV exposure time. This is the number of hours that an object is exposed to the sunlight or UV light.
Dependent variables are color, strength, and elasticity of a sample.
Constants are the type of test material, the size of the test material and the type of radiation (UV or sunlight).
Controlled variable is the temperature. (Make sure all your experiment runs are performed at the same time or in the same ambient temperature. Record the temperature to show that there has not been a significant change from one trial to the other.)
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.
This is a sample hypothesis:
Sunlight and UV radiation have no effect on polymers such as rubber, paint and paper. My hypothesis is based on my observation of many paper and rubber products that are exposed to the sunlight and show no obvious sign of change. Among such products are automobile tires, wall papers and automobile paints.
This is another sample hypothesis:
I think UV radiation has strong photochemical properties, causing decomposition in all test subjects. If we increase the exposure time to UV radiation, then the polymer will decompose faster and show more signs of discoloration and physical change.
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.”
Preparation:
The effect of sunlight on material can be tested with natural sunlight or synthetic lights such as UV lights or visible light bulbs that produce a wide spectrum of frequencies including UV.
If you are planning to use sunlight, use multiple reflectors or mirrors to reflect a high intensity light in a small spot. In this way you can get your results much faster. Cardboards covered by aluminum foil, mirrors and steel trays can be used as reflectors. This is almost like a solar cooker.
Higher intensity of light, produces a faster effect.
If you are using UV lamps, get the strongest one and place the test samples as close as possible to the light. Place the lamp and sample in an aluminum covered carton box and close it while the light is on. Make sure there is no fire hazard caused by overheat in the box. If the box is getting hot you need to replace it with a metal box.
Bellow is a sample setup (Home made UV cabinet) using two UV18F1 lamps. In this example I am using two UV lamp fixtures, aluminum foil and two empty boxes (that might be substituted by a few books or other items you may have at home.)
Place two boxes or wood blocks about 18″ apart to support the UV lights. Then cover the blocks and the distance between them with aluminum foil.
The purpose of the blocks is to hold the UV lamp fixtures elevated about 3 inches above the samples.
Alternatively you may use a box about 18″ wide and 3 inches deep, and cover that with aluminum foil.
Place you samples on the aluminum foil and place the UV lamp fixture faced down like a bridge between the two blocks. Test the Off/On button and starter to make sure that UV light comes on.
If you have a second UV lamp, place that also faced down next to the previous UV lamp fixture. Position them so that the UV lamp tubes will stay next to each other (in the center of your setup).
To make sure that no UV radiation will be wasted, lift the aluminum foil from both sides and tape them to the top of the lamp fixtures. This will make a closed UV cabinet for your experiments.
Before closing the second side, make sure the lights are on and the samples are positioned properly in the center.
Uses of UV lamps
UV lamps have many other uses. Use this link to learn about some of them.
Among the uses of UV lamps are in the mineralogy. Many minerals are in white or gray color in natural light, but they become colorful and radiant under UV light.
If you don’t need your UV lamp after completing your experiments, consider donating it to your school.
Experiment 1:
Introduction: In this experiment you will test the effect of sunlight on the rubber bands. (This experiment is relatively easier and provides faster results in compare with the next two experiments.)
Procedure:
Use 15 identical rubber bands for this experiment. Put aside 5 rubber bands in an envelop and do nothing with them. Label the envelop as “CONTROL”. Place 10 other rubber bands under high intensity sunlight (or UV light) for 40 hours. Remove 5 rubber bands from the set and place them in an envelop and label it 40 hours exposure. Continue the sunlight exposure with the other 5 rubber bands for additional 40 hours. Place this set in an envelop and label it 80 hours exposure.
Note: You could use latex balloons or latex gloves instead of rubber bands.
Open all 3 envelops and compare the rubber bands that have been exposed to sunlight with each other and with control.
Observe and record the color of rubber bands in 3 groups.
Compare and record the feel in touch of rubber bands in 3 groups. (rough, smooth, sticky, dry, wet, soft, hard, …)
Compare and record the odor of the rubber bands in 3 groups
Compare the elasticity of rubber bands in all 3 groups. Pull them and see how much they will be stretched before they break. You need to repeat the elasticity test for all 5 samples in each group and then take the average.
Record the results in a table like this:
| CONTROL | 40 hours Exposure | 80 hours exposure | |
| Color | |||
| Feel in touch | |||
| Odor | |||
| Elasticity | |||
Experiment 2:
In this experiment you will test the effect of sunlight on ink. There are a large variety of printing inks used by printers of magazines and newspapers and other publications. There are also inks used in pens, fountain pens and markers. To test printing inks, use printed publications such as magazines and newspapers. To test pen and marker inks, use such pens and markers to draw lines on a white paper and use them for test.
Procedure:
Collect small samples (10 cm x 10 cm) of printed material such as newspaper, book, magazine. Cover half of each sample with black construction paper or a sheet of metal.
Place the sample under intense sunlight for 40 hours. Uncover the half covered by construction paper or sheet of metal.
Compare the color of ink in exposed half with the color of ink in covered half.
Compare smearing properties of exposed half with smearing properties of covered half.
Drop the sample in water and compare the water solubility of exposed half with the water solubility of covered half.
Record the results in a table like this:
| Sample Ink | Rate of color change | Change in rate of smearing | Change in solubility |
| Newspaper | |||
| Book | |||
| Wall paper | |||
| Gift Wrap paper |
Estimate the rate of color change visually.
Change in the rate of smearing and solubility may also be tested and estimated visually. In advanced laboratories, devices such as colorimeters and spectrophotometers are used to measure color change.
Need a graph?
Make a bar graph to show your results. Use one bar for each type of ink that you test. The height of each bar will represent the rate of color change of that specific ink.
You may need a control for this experiment. Although we don’t really need it here, scientific method requires us to have a control. For example someone may claim that the discoloration of ink in exposed area has nothing to do with the sunlight. It could happen even if you wouldn’t expose it to sunlight. Then you will say “The area covered by construction paper did not lose color, so that means that sunlight removed the color of the exposed half”. The critic will then argue that maybe construction paper has color preservation properties, and that is why the covered area did not lose color.
To avoid such arguments, keep another piece of the same printed material away from the experiment area and do nothing with that. Call it CONTROL and just look at it at the end of the experiment and compare it with your experimental sample.
Experiment 3:
In this experiment you will test the effect of sunlight on paper.
Procedure:
Get a sheet of A4 size copy paper. Cut it in long strips of 1″ wide. You will get 8 strips and a narrow strip (1/2″ wide) that will not be used in your experiment.
Place four strips of 1″ x 11″ under intense sunlight for 40 hours. Keep the other four strip unexposed. These will also serve as control. At the end of experiment compare the exposed papers and control (un-exposed) group.
Visually observe and record the color of paper in two groups.
Test tensile strength of all samples in all groups. Take the average of tensile strength of the samples in each group. Record the results.
Compare and record the feel in touch of paper strips in two groups. (rough, smooth, sticky, dry, wet, soft, hard, …)
Compare and record the odor of the paper in two groups.
How can I measure the tensile strength?
There is a machine that can measure the tensile strength. If you have access to such a machine, connect two ends of the paper strip to the machine and press the start button. Machine starts to pull the paper from both ends until it breaks. The final force used to break the paper is the tensile strength of the sample.
If you don’t have access to a machine, you can still do it in a different way.
Use paper glue or wood glue and cover one inch of one end of the paper with a very thin layer of glue. Then connect this end to the opposite end to make a ring. The edges of paper where you connect them must be fully aligned.
Place a short wood dowel into the ring and connect the wood dowel to a horizontal bar using masking tape. Horizontal bar can be any wood or metal bar secured such that it can carry some weight.
Place another short wood dowel in the ring to be used for hanging a weight. Use a string to hang a weight to the lower wood dowel. String can be a 2 feet nylon or cotton string. Connect the ends of the string using a knot. That makes a circle or a ring from the string. Pass the ring through any weight and hang it to the wood dowel from both sides.
If you have a spring scale strong enough for this test, use it to pull the string down. Do it slowly and watch the weight that spring scale shows. Continue to increase the pressure until the paper breaks. Use the final weight as the tensile strength. (Since you have made a ring from the paper, half of that value is the actual tensile strength.). The spring scale that you want to use must be able to show about 10 kg for a 1″ wide paper. If you don’t have access to a 10 kg spring scale, you may reduce the with of your paper strip.
If you don’t have a spring scale, attach an empty bucket to the string. Start adding sands to the bucket until the paper breaks. Then you can use any scale to weight the bucket of sand.
Note that you don’t want the bucket fall a long distance. Place something under the bucket so the falling distance will be about 1 inch. None of these methods are as safe and as easy as a machine designed for testing the tensile strength.
Be careful while performing experiments and use goggles and protective gloves.
Materials and Equipment:
List of material can be extracted from the experiment section.
Following is a sample list of material:
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.
Your experiment results and the way that you present them may vary. For example you may test the elasticity of rubber bands that have been exposed to UV light (or sunlight) different amounts of time. To test these rubber bands you can simply pull them until they break. You will record the maximum length at which the bands break. Your results table may look like this:
| Exposure Time | Elasticity to break |
| 0 (control) | |
| 5 hours | |
| 10 hours | |
| 20 hours | |
| 30 hours | |
| 40 hours | |
| 50 hours |
You can use the above results table to draw a line graph. Show the hours on X axis and elasticity on Y axis.
If you are doing such a test on paper, you must measure the tensile strength instead of elasticity. Your results table however will be similar to the above table.
Calculations:
You will need to calculate the average of tensile strength and elasticity of the samples in each group.
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:
I could not find any book or reference directly related to this subject. However there are many books that have something about photochemistry and photodegradation. Also there are books about material strength that tell you about tensile strength. Please visit the chemistry and mechanics section of your local library to see some samples.
You may also find Journals with related articles in your local public library. If not, you have to go to larger libraries such as libraries of big cities or libraries of colleges.
Search articles archive for stabilizer or UV stabilizer.
Did you know that automobile tires are black because carbon black is used in them as a stabilizer. Without that tires wouldn’t last more than a few weeks or a few months.
Following are some related links:
http://www.natmus.dk/cons/tp/fading/light_i.htm
http://sedac.ciesin.columbia.edu/ozone/UNEP/chap7.html
http://www-classes.usc.edu/engr/ms/125/MDA125/polymers_files/frame.htm#slide0037.htm
http://chemed.chem.purdue.edu/genchem/topicreview/bp/1polymer/types.html
