Chemistry Everyday for Everyone
A Polymer “Pollution Solution” Classroom Activity Terry L. Helser Chemistry Department, SUNY College at Oneonta, NY 13820-4015 While thinking about how to present polymer chemistry to undergraduate nonmajors using the “Chemistry in Context” approach (1), I remembered that acetone can deflate polystyrene foam (Styrofoam) leaving a residue that can be recycled (2). In addition, several companies are now shipping materials cushioned with foam “peanuts” made from water-soluble starch, rather than the environmentally troublesome Styrofoam nuggets.1 Finally, a recent paper in this Journal (3) described using water- soluble plastic bags made from poly(vinyl alcohol) (PVA) to produce Slime®.2 Together these materials can be used to create a very interesting and instructive classroom activity. Materials Each team of students will need a multiwell plate or beakers, glass rod, and waste containers, one of which should be designated for acetone. Having available three sets of 100-mL squirt bottles filled with acetone, ethyl or methyl alcohol, and water works well for a class of 24 students. The packing peanuts are provided by the storeroom. I mix four types: shiny white, “S”-shaped and gray, “8”shaped Styrofoam nuggets, and two types of cylindrical starch nuggets. Testing four types with three solvents is easily completed in about half an hour, even by the teams that do each one individually, instead of testing all four at once, with each solvent. The nuggets are brought to the room in the PVA bag.3 Safety Precautions As in any activity involving solvents, providing eye protection and a warning about flammability is prudent. Use of ethanol is preferable to methanol because ethanol is less toxic and is disposable down the drain. To remove any temptation to ingest it, you can warn students that the alcohol is denatured, even if it isn’t. The small volumes used prevent problems with inhalation or ventilation, and covering the solvent containers helps even more. Indeed, getting the students to link the odor of acetone with nail-polish remover can be used to prompt a warning that spills be avoided, or, failing that, absorbed and immediately rinsed with water, since acetone will dissolve some furniture finishes. The water-soluble wastes (starch and PVC) can be washed down the drain, as can the small amount of acetone, since all are biodegradable. However, the acetone used to treat the Styrofoam is best left in a hood to evaporate, and any residue put with the solid waste. Of course, your students might invent a more ingenious method of disposal! 1 For example, Carolina Biological Supply Co., 2700 York Road, Burlington, NC 27215; Wm. C. Brown Publishers, Dubuque, IA; and Amway® use starch foam packaging. 2 Slime® is a registered trademark of Mattel, Inc., Hawthorne, CA 90250. 3 M.D. Industries, Inc., PO Box 1355, 3100 Dundee Road, Suite 308, Northbrook, IL 60065-1355 (800/421-8370), provided a 10-bag sample package of their #1-342 “Melt-A-Way” cold-water-soluble PVA bag when informed that they would be used to make Slime®.
Procedure The instruction sheet that describes the problem is shown in Figure 1. It can be given to the students the day before or just prior to the exercise. As Figure 1 states, students are instructed to work in teams of two to four to determine the solubility of the various types of packing materials, and then to develop a plan for recycling and/or disposing of them. During each stage, I meet with individual teams to ensure that they are working on a reasonable plan to test the nuggets. They are not told the chemical composition of the different nuggets, but most already assume they are Styrofoam. The blank stares that result when they are asked what Styrofoam is, chemically, provide the perfect opportunity to send them to their textbook (1) to find out. While the students are testing solubility, I help them realize there are two fundamentally different materials
Your Name: __________________ Partner’s: ____________________
Chemistry 100: CHEMISTRY for EVERYDAY LIFE
Pollution Solution Studies have shown that plastics take up more space in landfills than anything else except paper. Of particular concern because of their bulk are the packing “peanuts” used to cushion things during shipping. How could you eliminate, or at least reduce, the volume and possibly recycle these environmental irritants? Working with someone near to you, take about 5 minutes to plan how to test inexpensive solvents (H2 O, an alcohol and acetone will be available) for their effect on a variety of foam packing materials. • Caution: The alcohol and acetone are flammable and volatile. Be careful. Your plan should minimize the amount used a nd your exposure to the solvents. (Why?) 1. Describe and/or diagram your solvent-testing plan : (Space provided for answer) Then do the testing. 2. Describe and/or diagram your solvent-testing results: (Space provided for answer) Next, develop a recycling/disposal plan to be implemented in your community. (Include suggestions at all stages from receipt of the packaging by homeowners, institutions and industries through collection, recycling and disposal.) You must state how all solvents and residues will be recycled or disposed! 3. Describe your plan to eliminate foam-peanut pollution: (Space provided for answer) 4. What objections might be raised to your proposal? Explain how you would answer each. (Space provided for answer)
Figure 1. Classroom handout.
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Chemistry Everyday for Everyone
used in the nuggets. I carry I2/KI(aq) solution with me to see if they can deduce the presence of starch in the watersoluble nuggets. The solid starch peanuts turn black and the dissolved starch turns blue in the I2 test, whereas Styrofoam peanuts neither absorb the I2 test solution nor change color. Interestingly, the commonly available tincture of I2 does not give a positive test with the solid Styrofoam or the starch peanuts, since neither is soluble in ethanol. It does produce the blue complex with the dissolved starch, however. When most students are nearly finished, we discuss the results and the implications for disposal. Most realize that water could be used to dissolve the starch peanuts, leaving the Styrofoam ones floating. The resulting starch solution could be flushed or composted or even used as feedstock for ethanol production. The Styrofoam peanuts can then be deflated with relatively small amounts of acetone. To illustrate this point you can challenge the students to fill a beaker with Styrofoam peanuts (2). Get a “volunteer” to fill a dry beaker with these peanuts and then empty them into a beaker with 0.1 volume of acetone in it. You can continue this as long as your Styrofoam supply and time permits without filling the beaker. This is a good place to ask them how they would handle the residual polystyrene and dirty acetone. (Solar distillation could recover the acetone, for example.) This and the question about objections to their plan (see Figure 1) are excellent opportunities for a writing assignment outside of class. Finally, I hold up the bag of nuggets and ask how they would handle the plastic in the bag itself. If time permits, you can cut off samples (it is quite tough and nearly impossible to rip) for them to test with the solvents. If time is short, I cut off a 10-cm2 piece of bag and dissolve it in about 10 mL of water. I ask them the advantages and disadvantages of using PVA for bags, and describe their use in hospitals to contain contaminated bedding (3). To end the class, I squirt in about 2 mL of 4% borax (Na2B4O7·10 H2O) and stir up some Slime® to show them another way to recycle these bags. Judging from the participation and comments during and after this activity, the students love it. A question
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on an exam asking how they would solve this packaging problem effectively separates those who understood and learned from the exercise from those who had no clue, which not surprisingly correlates closely with class attendance. Evaluating this activity with a graded writing assignment makes it an even more effective learning experience. Requiring accurate references to their book (1) may also prepare them for subsequent classes on this topic. Furthermore, the information gained from this exercise can be used in subsequent classes to illustrate several concepts about chemistry and polymers. Polystyrene is a good example of a hydrophobic hydrocarbon that is not biodegradable, making it both a disposal problem and an excellent structural material for park benches. The gray 8-shaped Styrofoam nuggets seem to contain a plasticizer that turns the acetone yellow. This is apparently what makes these nuggets softer and more flexible than the white ones, a good example of this concept. The starch and PVA are examples of hydrophilic polymers, showing the effect of multiple hydroxyl groups. Not only are they polar and water-soluble, but they are biodegradable because of these functional groups. The starch/I2 test is a good introduction to branched and helical macromolecules (1, p. 336) because the black color is the result of a red I2 complex with amylopectin and a blue complex within the amylose helix, respectively. Finally, as suggested above, the starch solution that results can be seeded with yeast and sealed in a plastic bag to test if fermentation will inflate the bag with CO2 and produce ethanol. It will not, since yeast lack the amylases necessary to digest starch into fermentable sugars, but you could add commercial amylases or saliva (guess how!) to simulate the malting process in brewing (4). Surely other concepts could be related to this project as well. Give it a try and let me know what you and your students discover. Literature Cited 1. Schwartz, A.; Bunce, D.; Silberman, R.; Stanitski, C.; Stratton, W.; Zipp, A. In Chemistry in Context; ACS & Wm. C. Brown: Dubuque, 1994; Chapter 10. 2. Shakhashiri, B. Z. Chemical Demonstrations: A Handbook for Teachers of Chemistry, Vol. 3; U. of Wisconsin Press: Madison, 1989; p 348. 3. Katz, David A. J. Chem. Educ. 1994, 71, 891–892. 4. Bering, C. L. J. Chem. Educ. 1988, 65, 519–521.
Journal of Chemical Education • Vol. 73 No. 9 September 1996
