Biodegradability
The Elusive Disappearing Act

Developers:

Sister John Ann Proach, OSF
Bishop Conwell High School
Levittown, PA t

Robert M. Amici
Richard A. Einhorn
Rohm and Haas Company
Bristol, PA

Grade Levels:

Grades 7 through 12

Discipline:

Environmental Science, Chemistry, Physical Science

Goal:

The students will be able to explore the concept of degradability and biodegradability and study its effects on the environment.

Objectives:

1. To study the effects of water, salt water and heat on common household materials.
2. To separate an emulsion and show that the materials are completely recoverable.
3. To observe the effect of acetone and water on polystyrene.

Background:

Today, there is great concern for the environment, and a current environmental issue that confronts the scientists, politicians and educators is biodegradability. Where are all the materials that we hope to dispose of really going? What happens when we throw something away?

Years of research in chemisty, polymer science and technology have produced new plastics which have made life easier and more convenient. Polymers have been developed which are able to retain their strength by resisting the break down of their molecular composition caused by light, air and water . This enabled consumer products made of these polymers to be very effective in many applications. Because of their light weight and durability, plastics have become a commonplace material in the lives of the consumer.

Since many plastics are used in 'throw-away' packaging applications, an environmental issue has arisen concerning the use, recycling, and disposal of these materials. Can we reduce our landfill needs by reducing the amount of plastics that we discard? For any material to decompose, chemical bonds must be broken by bacteria, fungi, microorganisms, water in the soil, sunlight or by some other means. From studies so far we see that this process takes time, and time seems to be running out for Planet Earth. What are some possible answers to the problems of disposal? Is degradability and biodegradability the answer?

Materials:

Part I - per team

8 pieces ( 5 cm square) of materials to be tested ex. paper cup, plastic milk container, newspaper, paper bag, poly (vinyl chloride) (PVC), plastic bottle, aluminum foil, etc.

16-250-mL beakers

1 hot plate

1 pair of beaker tongs

1balance (reading to two decimal places)

13% salt solution or simulated sea water

water

marking pen or pencil

goggles

aprons

hot pads or gloves

Part II A-- per team

2 grams of calcium chloride dihydrate, CaCl2 2H2O

100 mL water

Latex paint (not oil based)

thermometer

hot plate

glass stirring rod

2-250-mL beakers

balance ( reading to two decimal places)

1-100-mL graduated cylinder

goggles

aprons

hot pads or gloves

Part II B - per team

1-250-mL beaker

glass stirring rod

weighing dish

pipette

hot plate

balance (reading to two decimal places)

goggles

aprons

hot pads or gloves

Part III - Demonstration

balance (reading to two decimal places)

2- 400-mL beaker

1-100-mL graduated cylinder

100 mL of acetone

400 mL of water

polystyrene packing peanuts

glass stirring rod

Procedures:

Part I - Solid - Non-Degradable - Here to Stay

1. Obtain 16 250-mL beakers and label 8 beakers "water" and 8 beakers "salt water."
2. Obtain 2 pieces each (5cm square) of the materials to be tested such as paper plates, paper cups, newspaper, aluminum foil, PVC bottle, milk container plastic.
3. Weigh each piece of material and record the mass in Data Table 1.
4. Fill 8 beakers with 100 mL of water and 8 beakers with 100 mL salt water.
5. Place one piece of each material selected in a beaker of salt water and one in a beaker of water.
6. Place the beakers on the hot plate and heat to boiling. Continue heating for 15 minutes.
7. Note any changes in each of the materials as they are heating.
8. After 15 minutes of heating, remove the beakers from heat and with your forceps remove each piece of material from the beakers and place the materials on a paper towel to dry.
9. The materials may have to dry overnight.
10. Reweigh the materials and record the masses in Data Table #1.
11. Compare your results and answer the questions for Part 1.
    

Part II A - Plastic Dispersion - Gone But Not Forgotten

1. Weigh 2 grams of CaCl₂ 2H₂O and place in a 250-ml beaker. Add 100 mL of water. Stir and place on a hot plate.
2. Heat the CaCl₂ solution to between 85�C to 90�C .
3. While the solution is heating, obtain another 250-mL beaker and place 20 grams of latex paint in the beaker. Add 10 mL of water to the beaker and stir until homogeneous .
4. When the CaCl₂ solution reaches between 85�C to 90�C , slowly add the diluted paint to the CaCl₂ solution while on the hot plate.
5. Continue to heat the mixture for 10 to 15 minutes, stirring constantly.
6. Remove from the hot plate and allow to cool.
7. Observe the material in the beaker and complete the questions for Part II A.
   

Part II B -Determination of the Percent Solids of a Latex Paint

1. In a 250-ml beaker, dilute 10 grams of paint with 20 mL of water.
2. Record the mass of a weighing dish in Data Table 2B.1
3. Add 1.5 to 2.0 grams of the diluted paint to this weighing dish.
4. Place the weighing dish on a hot plate and begin heating it at a low setting. Do not let the suspension splatter.
5. Record your starting time .
6. At one-minute intervals, remove the weighing dish from the hot plate and reweigh it. Record your reading in the proper place on Data Table 2B.2.
7. Place the weighing dish on the hot plate and continue heating and reweighing the material at one minute intervals until the mass of the dish remains constant for two consecutive readings.
8. Remove the dish from the heat and allow to cool. Take the final reading of the dish and calculate the percent solids.
9. Graph your data from Data Table 2B.2 on Graph 2B.2 Refer to Sample Data Table 2B.2 and Sample Graph 2B.2
10. Complete your observations and answer the questions from Part II B
    

Part III - Demonstration- You Think I'm Gone But I'm Not

1. Take a 400-mL beaker and fill it with 200-mL of water.
2. Add a few packaging "peanuts" to the water.
3. Observe the reaction of the water and the "peanuts."
4. Fill another 400-mL beaker with 100 mL of acetone.
5. Weigh a few packaging "peanuts" and record their mass.
6. Take approximately 50 - 100 packaging "peanuts" and continually add them to the beaker with the acetone.
7. Observe what happens to the "peanuts" as each is added to the acetone.
8. Estimate the total weight of the "peanuts" added to the acetone.
9. Predict what would happen to the contents of the beaker when you would add 200-mL of water.
10. Add 200-mL of water to the contents of the beaker.
11. Filter the contents of the beaker and weigh the material.
12. Make your observations and answer the questions to Part III.

Questions:

Part I

1. What was the purpose of heat in this experiment?
2. What were the changes observed in the water and salt water?
3. What do the changes in the water mean for the environment?
4. If these materials were degradable, what would you expect to see? If these materials were biodegradable, what would you expect to see?
   

Part II A

1. Describe the appearance of the CaCl₂ solution and the paint emulsion upon mixing.
2. Describe the final appearance after heating the solution for 15 minutes between 85�C and 90�C.
3. Do you think you have the same material that you began with? Why?
4. Where do you think the precipitate came from?
5. What does this tell you about paint?
6. Is this a qualitative or quantitative observation? Why?
7. If a plastic disperses in a liquid, does this mean it is degradable?
8. If a plastic disperses in a liquid, does this mean it is biodegradable?
   

Part II B

1. While heating the dish with the paint, what was given off?
2. From your calculations in the experiment, what would be the percent of solids obtained for a solution of 10 grams of paint and 30 grams of water? 40 grams of water?
3. Why did you weigh the dish at one minute intervals?
4. What percent water was in your sample of paint solution?
5. From this experiment, what general conclusion can you make about degradability? biodegradability?
   

Part III

1. What happens to the packaging "peanuts" when added to the beaker with water?
2. What was the approximate mass of 5 packaging "peanuts."
3. What was your prediction of the number of peanuts that could be placed into the acetone in the beaker?
4. What is the approximate mass of all the packaging "peanuts" that were added to the acetone?
5. As the peanuts are placed in the acetone, describe what is happening?
6. What do you think causes the "fizzing" heard?
7. Does the acetone degrade the peanuts?
8. What role does the water play in the experiment?
9. If the plastic disperses in the liquid, does it mean that it is degraded? biodegraded?
10. After you filtered the contents of the beaker, what was the approximate mass of the material?
11. What can you conclude about the material you isolated inrelationship to the starting material?

Table Data:

Data Table I

Sample Identfication	Water Exposure			Salt Water Exposure
	g	g	g	g	g	g
	g	g	g	g	g	g
	g	g	g	g	g	g
	g	g	g	g	g	g
	g	g	g	g	g	g
	g	g	g	g	g	g
	g	g	g	g	g	g
	g	g	g	g	g	g
	g	g	g	g	g	g
	g	g	g	g	g	g
	g	g	g	g	g	g
	g	g	g	g	g	g
	g	g	g	g	g	g

Data Table 2B.1

Mass of Paint and Dish	g
Mass of Dish	g
Mass of Paint
Percent Solids	%

Sample Data Table 2B.2

Time (Minutes)	Mass (grams)
0	2.87
1	2.48
2	2.16
3	1.86
4	1.61
5	1.40
6	1.32
7	1.31
8	1.30
9	1.30
10	1.30

Data Table 2B.2

Time (Minutes)	Mass (grams)
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15

Data Graphs

Procedure For Calculations:

Discussion Questions:

1. What does degradability mean?
2. What does the term biodegradability mean?
3. Is biodegradability good for all materials? Why?
4. What things would you not want to be biodegradable?
5. What are the conditions required for biodegradability?
6. What are some ways in addition to biodegradability that will help the environment?

References:

Part III Demonstration was adapted from "Project LABS" Rohm and Haas Co. 1990, pg. 27-28.

Extension Activities:

1. Many companies are trying to capitalize on the biodegradability theme by offering "green" materials, i.e. their product as biodegradable. But are they really? Go through the supermarket and stores and list all of the products that claim to be biodegradable. Design possible ways to test their claim.
2. As part of the extension activity in #1, select materials that you could subject to a long term exposure study. These materials could be buried, or put in a water-filled trash can for months, weighing the materials every so often to determine if they degrade.

Teacher Notes:

If CaCl₂ is not available in Part II A of the experiment acetic acid may be substituted. Two mL of acetic acid may be added to 100 mL of water. The results would be the same. Please Note: When heating the acetic acid place the hot plate in a hood or heat the solution in a well ventilated room. The fumes created from heating acetic acid can be irritating to the respiratory tract and eyes.

In Part IIA milk could be tried instead of paint with the acetic acid. This could be filtered at the end and other activities could be developed.

In Part IIB of the activity, Determination of the Percent Solids, Elmer's Glue� can be substituted in the place of latex paint.