Developers:

Sister Frances Boyle RSM
West Catholic High School
Archdiocese of Philadelphia

Dr. Eugene Dougherty
Rohm and Haas Company
Bristol, PA

Grade Levels:

Grades 10 through 12

Disciplines:

Chemistry, Physics

Goals:

To give students the opportunity to see that plastics can be separated and identified by their different physical properties

Specific Objectives:

The student will:

1. participate in a demonstration of the different densities of plastics.
2. use density to identify an unknown plastic.
3. suggest a method by which municipalities could separate the plastic waste collected.

Background:

On TV, plastics from milk, soda and other food containers are shown recycled into park benches and plastic posts. However, for plastics to be recycled for some uses, the plastics must be the same type. A chemical company producing plastics, such as Rohm and Haas, knows the identity of its plastic waste. The waste may not meet their color specifications but it can be sold for manufacturing where color is not critical.

Introduction:

Many municipalities have days when they pick up scrap metal, glass and plastics . Some communities are urged to put the three in separate containers, but even then some objects appear in the wrong category of waste. How is the waste separated for recycling? Trash on a conveyer belt allows magnets to remove some metals. Other metals and glass of various colors are sorted by hand.

How can the plastics be separated? Magnets cannot be used. Visual inspection, even with the aid of recycling codes is tedious. Can DENSITY help?

Teacher Demonstration:

Apparatus:  seven (7) 250-mL beakers, graduated cylinders, stirring rod, long forceps

Material:  Listed in the following chart.

Prepare the seven (7) beakers with the liquids in the following chart. Demonstrate how samples of plastic sink or float in the appropriate liquids.

After a discussion of solution proportions and %, students made up the solutions. The separation worked well.

Densities of Polymers and Separating Liquids*

Kenneth E. Kolb and Doris K. Kolb,Bradley University, Peoria, IL 61625
Journal of Chemical Education

Apparatus:

Materials:

Procedure:

Student Laboratory Procedures: (DONE IN GROUPS OF 4)

250-mL beaker, forceps

distilled water
two (2) plastic samples (with coded identity) for each group
access to beakers previously used in demonstration

1. Assign one (1) piece of plastic to each pair in group of four (4).

2. Examine the plastic and record its code and its appearance.

Sample Code __________________ Sample Code __________________

Appearance ___________________ Appearance ___________________

3. Plan how to use what you learned from teacher demonstration and he apparatus and materials you have been assigned to identify the pieces of plastic. Students have access to all beakers from previous demonstration. Also they have access to distilled water and normal laboratory equipment.

4. Each team executes the identification plan for the piece of plastic you have been given. Have the other pair verify your identification. Fill in the identification below.

Sample Code _________________ Sample Code __________________

Sample Identify _______________ Sample Identify________________

5. Using words, pictures or a physical model, show how a municipality could separate the large volume of waste plastics it collects.

Additional Information:

Chemical companies such as Rohm and Haas are working on processes that would reduce various plastic waste to original monomers. Therefore, separation before recycling would be unnecessary.

Petroleum refineries, such as Amoco Chemical Co. (Naperville, IL) convert plastic waste into basic chemicals. Some efforts to reuse plastic waste have focused on burning the waste for energy.

Plastics can also be separated by differences in solubilities. Several articles in the Journal of Chemical Education are helpful here. In Volume 60, No. 2, February 1983, Joseph H. Ross of Indiana University at South Bend, IN 46634 wrote "Demonstration of Solvent Differences by Visible Polymer Swelling." In Volume 62, No. 9, September 1985, Helene Cloutier and Robert E. Prud'homme of Laval University, Quebec 10, P.Q. Canada G1K7P4 included the following chart in their article "Rapid Identification of Thermoplastic Polymers":

The table below is taken from SHOPPING FOR PLASTICS developed by Lisa Ann Jones et al for PROJECT LABS and published in the fall of 1990.

Here is a sample list of items which bear the plastics recycling symbol and code.

1-PETE	2-HDPE	3-V	4-LDPE
mouthwash Pepto BismolÆ soda spices peanut butter salad dressing seltzer coffee bacon bits	Cool WhipÆ lemonade grated cheese Hershey syrupÆ detergents mini-juices water bottles bath cleaners milk bottles	car wax peanut oil Ajax LiquidÆ CremoraÆ clear shampoo RitÆ dye	mustard diapers (package)
5-PP	6-PS	7-OTHER
RubbermaidÆ salsa alfredo sauce solid detergents syrup yogurt	salad containers cheese containers cottage cheese petroleum jelly	ketchup plastic cups juice bottles cat food