Comparison of Tensile Strength of Garbage Bags

Researched by Carmen L.
2002-03


PURPOSE

The purpose of this experiment was to compare the tensile strength of various garbage bags. 

I became interested in this idea because product manufacturers are always advertising that their product will hold the most weight, and I wanted to see which was actually strongest. 

The information gained from this experiment will help consumers who purchase those products to make good purchasing decisions.


HYPOTHESIS

My hypothesis was that the more garbage bags cost on average the higher the tensile strength would be. 

I based my hypothesis on the information I gathered from the Internet about the products tensile strength compared to its average price.  In addition Rick Kondel from Plastic Technology Labs stated, "As the cost goes up, the thickness (or tensile strength) increases."  He wrote this to me in an email response, dated 11/6/2002. (See appendix.)


EXPERIMENT DESIGN

The constants in this study were:
* Temperature of room (21° C)
* Machine used (Tensile Tester)
* Size of plastic tested (2.54x2.54 cm.)
* The age of the bag (unused)
* Way of cutting plastic into 2.54x2.54 cm. squares
* Stress on plastic when put into jaws (.30 -.40 psi.)

The manipulated variable was the brand of garbage bags I measured.

The responding variable was the tensile strength.

To measure the responding variable I conducted an elongation test, with a Tensile Tester machine.


MATERIALS

QUANTITY 
ITEM DESCRIPTION
1
Tensile Tester machine
1
Die Cut (2.54x 2.54 cm.)
1
 Brand A Bag
1
 Brand B Bag
1
 Brand C Bag
1
Red Pen (for labeling machine direction test strips)
1
Black Pen (for labeling transverse direction test strips)
1
Thickness Tester machine
3
Pieces of scrap paper
6
Large bag clips


PROCEDURES

1. Look at bag "A" very closely, and try to find out which is transverse direction and machine direction
2. Label the machine direction with the red pen
3. Label the transverse direction with the black pen
4. Carefully fold bag "A" in half, while leaving the red and black marks you have made showing
5. Carefully fold bag "A" in half again, while leaving the red and black marks you have made showing
6. Clip two clips on the top of the folded bag
7. Label bag "A" by taking a small piece of paper, and writing the brand of bag on it, and clip he paper with one of the two clips
8. Cut the folded bag "A" into 2.54x2.54cm.  Test strips in transverse direction with die cut. Do this twice
9. Label the top test strip of bag "A" transverse direction with the black marker
10. Put the transverse direction pieces clipped to label
11. Cut the folded bag "A" into 2.54x2.54cm. Test strips in machine direction with die cut. Do this twice
12. Then label the top test strip of bag "A" machine direction with red marker
13. Put the machine direction pieces clipped to label, but do not get them confused with the transverse direction ones
14. With thickness tester machine, measure thickness of bag "A" 
15. Input thickness of bag "A" into computer
16. Place one test piece of bag "A" into the jaws of the tensile tester with around .30 to .40 psi
17. Donít forget to check if the piece is lined up strait when you lock the jaws
18. Press the lock jaws button
19. Press button on computer to start test
20. When test is complete, unlock the jaws and allow tested piece to fall
21. Repeat steps 14-20 until all pieces of "A" have been tested
22. Repeat steps 1-21 only instead of using bag a use bag "B"
23. Repeat steps 1-21 only instead of using bag a use bag "C"


RESULTS

The original purpose of this experiment was to compare the tensile strength of various garbage bags.

The results of the experiment were that the cost of the garbage bag was higher when the tensile strength was higher. 

See the tables and graph.


CONCLUSION

My hypothesis was that the more garbage bags cost on average the higher the tensile strength would be.

The results indicate that this hypothesis should be accepted, because I was rite, the higher the price of the bag, the stronger it was. 

Because of the results of this experiment product consumers will be able to understand that the price that they pay results to what they will get.

If I were to conduct this project again I would probably plan out a day in which I could do all my testing, and get it completed at once, instead of testing over a long amount of time. Other then that I think that my experiment was great.
RESEARCH REPORT

INTRODUCTION

Plastic has changed the way we have lived, and many people donít realize how hard our lives would be without it. It is used in a variety of ways from health matters such as tooth fillings and medication bottles, to commercial industries such as garbage cans and juice machines.

USES

Plastic is used in many different ways. It is used to replace metal on cars, because it does not rust. It is used in building structures, and in surgeries. Itís used to replace leather, fur, clothing, stuffing, wood, stone, glass, metal, and fiberglass. 

HISTORY

Plastic has been around for a very long time. Back in the late 1700ís and early 1800ís natural resins were made of tortoise shells, and animal horns. It was also found in the Gutta Percha Malaya tree sap. These natural resins were placed over fires, made by Native Americans, and were brushed or poured over various things to preserve and water proof these items. It has also been said that the ancient Egyptians created natural plastic, and covered their dead with it to preserve them during the mummification process.

Alexander Parkes created the first man made plastic, in 1862.  He was at the Great International Exhibition in London, when he claimed that his great invention would do anything that rubber could do but at a much lower price. "It can be transparent, and can mold into 1000+ shapes", he claimed.  Thanks to him, now we have what we know as plastic.

In 1866, John Wesley Hyatt spilled celluloid all over the floor in his workshop and discovered when it dried it became very flexible. This was considered the first thermoplastic and was used in the first flexible photo film. 

Rayon was first developed in Paris, 1891, by Louis Marie Hibire Bernigaunt. At the time, he was looking for a way to make manmade silk, after a recent study of the silk worm. He made the rayon, but then found out it was highly flammable. In 1892 Charles Topham used Louis Marie Hibire Bernigauntís idea but made some changes to his original idea, and fixed the factor that it was highly flammable.

The 1920ís were considered the plastic craze. Cellophane was invented and everyone wanted it. Then in 1933 polyethylene was invented. 

In 1957, James Wright discovered that when silicone oil and boric acid were mixed it created an incredibly bouncy and stretchy mixture. It could bounce 25% higher than a bouncy ball, and was then named silly putty. George de Maestral also created Velcro this year. 

CHEMISTRY

Plastic consists of long, chain like molecules called polymers. The polymers are made of small molecules called monomers, which contain hundreds of thousands of alcanes, which are found in crude oil. The plastic will have a higher tensile strength due to the way the polymers are aligned. They can be aligned to make structures that are sturdier than others.

TYPES

Plastic is sorted into two major groups, thermosetting, and thermo plastic. 

The difference is that thermosetting plastic can only be heated once, and then it can never again be reshaped. When this type of plastic is heated for the first time it undergoes chemical reaction that causes the polymers to link and bind together. When this type of plastic is reheated, it doses not become runny and watery like thermoplastic, but instead it burns. This type of plastic is used in places where there may be high amounts of heat, such as light fixtures, and for some medical devices. When products that are made out of this type of plastic are unable to be used, they are ground down into a fine dust and are then disposed of. 

The other type of plastic is called thermoplastic. This is the type of plastic that will become soft when it comes in contact with heat. It can be melted and reshaped over and over again.

There are many types of plastic procedures that are smaller then thermoplastic, and thermosetting. 

Polyethylene is used in bottles, packaging, and carpet. It will break with scissors, has some bend, floats, and will soften when heated. When put over a flame it will turn yellow/blue, and will smell like wax. 

Polystyrene can be broken with a hammer, does not bend, floats in water, and will soften in heat. An example of a product made of this is toys. 

PVC can be broken with scissors, does not bend, does not float in water, and will soften when heated. 

Allcylic is a strong plastic material that is used outdoors, and in electrical plug-ins.

Epoxy is a type of plastic resistant to water and weather. It hardens quickly, and is a protective coating.

Phenoliclis resistant to heat and cold, it is used often on appliance handles.

ABC is a type of plastic that is strong, lasts long, and resists stain. 

PROCESS

There are 7 main processes of shaping plastic. They are molding, casting, extrusion, calendaring, laminating, foaming, and thermoforming.

The molding process is the 1st procedure. During this procedure, the resin is put into a mold, heated, and then is released. Some of the products made this way are boats, and car bodies and so much more. 

Another process is casting. During this process, the melted resin is poured into a mold, and there is no external pressure. So products made this way are paperweights, and other solid objects.

Extrusion is another process used on plastic. During this procedure, the melted resin is pushed through a hole, and creates long, continuous, sameshaped products. Some of these products are pipes, tubing, and wire covers. 

Calendaring is the 4th procedure. During this procedure, plastic is pushed between rollers to create long sheets of plastic. Table clothes are usually made this way. 

Laminating is a process where two separate pieces of plastic are bound together; this creates a protective layer over the product. The sheets are coated and covered with resin. 

Foaming is a process where gas is used to blow plastic bubbles. Some products made this way are plastic cups. 

Thermoforming is an inexpensive way to mold sheets. In this process plastic is secured over the object, then it is heated, and then the air, is sucked out of the mold by a pump. Then it hardens to the molds shape. 

Blow molding is the process in which water bottles are made. The plastic is placed in a mold, and then blown into so hard that the plastic sticks too the sides of the mold to recreate a copy of the mold.

Injection molding is a process in which plastic is injected into a mold, and then once the mold is full and cooled, the mold is opened, and the product is done. Products made this way are rulers, and steering wheels. 

RECYCLE

Plastic is not biodegradable, and is a very big problem with recycling, but now there is a new type of plastic called TDPA, or Totally Degradable Plastic Additive.  When it is in contact with heat, or humidity, it starts to disintegrate.  It does this because they add chemicals to the plastic that create these effects.  It has helped the environment tremendously and now junkyards, and dumps, are less full of plastic products.

CONCLUSION

Plastic may not be something you think about every day, but it is something you use every day. Plastic affects our lives.
BIBLIOGRAPHY

Ardley, Neil. Dictionary of Science. New York, New York: Dorling Kindersley Publishing Inc, 1994. Pp. 162-163.

Beisenberger, Joseph A. "Plastic." The World Book Encyclopedia. 1991.

Cash, Terry. Plastics. Limited, London: A&C Black, 1989. Pp.  8,9,16,24.

Chisholm, Jane and Johnson, Mary. Chemistry. London England: Usborn Publishing LTD, 1983.

Dempsley, Donna. "The Society of Plastic Industry Inc." October 30, 2002 <http://www.plasticindustry.org/>.

"GladďTrash Bags." October 30, 2002 <http://www.glad.com/trashbags.html>.

"History of plastic." October 30, 2002 <http://www.americanplasticscouncil.org/benefit/about_plastic/history.html?src=over>.

"Major Plastic Materials." Microsoft Encarta Encyclopedia Deluxe. 2001 Ed.

Richardson, Terry L. "Plastics and Environments." Microsoft Encarta Encyclopedia Deluxe.2001 Ed.

"Tensile Test." November 6, 2002 <http://www.enged.com/students/matpro/matprosl.html>.

Warriers, Gopikrishna S. "Scottish Co. Offers Tech." <http://proquest.umi.com/pqdweb?did=000000207932351&fmt=3deli=1&mtd=1&1dx=1&sid=2&rqt=309>.
 

ACKNOWLEDGEMENTS

I could never be able to conduct this experiment without all of the help I received from many people. I would like to thank my mom for all of the car rides back and forth from Shields, for buying my board, journal, page covers, and the garbage bags. Thank you also for encouraging me to keep going, and for helping me when I got stressed. A big thank you to Scott McGreggor for helping me prep my test pieces, and the actual testing. Thank you for all the explaining, phone calls/ emails, and all of his time! Thank you Mr. Newkirk, for all of the spelling adjustments, the proofreading, the time, sitting down and helping me with my graphs, and for all the suggestions. Thank you to Mrs. Helms for all the answers to the questions Mr. Newkirk could not answer because he was to busy, and for the opinions she gave me about my display colors. 


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