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Fantastic Plastic

Spring is here and there are a host of clean-up projects going on in elementary classes in my city. We did help at a local lake and the volume of plastic we collected filled 3 trucks. Several years back that prompted me to create a unit on recycling plastics. That morphed into a study of the chemistry of the different types of plastics. I can reload all the supplies I need for the unit each year at the clean up by keeping some samples of each recycling code before we bag and truck them off to the local recycling plant.

Each plastic type has specific physical and chemical characteristics that can be a great lab investigation. The key is in the recycling code. For a key to those codes check out this site.

http://www.ides.com/resources/plastic-recycling-codes.asp

Plastics with bisphenol A and phthalates have been linked to some health issues particularly when the plastics are heated as in baby bottles.  A government panel suggested that folks avoid these in any plastics you heat in the microwave or drink water or hot liquids from. These two chemicals are only found in plastics with the recycling codes 3, 6 and 7. My reusable water bottle needed to be replaced as it was one of those types. Now many bottles that are reused are made of BPA free plastics. To read about that government report (a good idea for a class science and society discussion) this site has the whole report and then some.

http://www.thedailygreen.com/environmental-news/latest/bisphenol-a-47091707

If you want a plastics unit all laid out with activities and objectives the American Chemical Society has a great site.

http://www.americanchemistry.com/s_plastics/sec_content.asp?CID=1123&DID=4277

The site above will have links to all sorts of plastics information, activities, technical and manufacturing and testing.

If you are into the relatively short history of plastics (they were first introduced in the 1860’s there are two sites that do a good job of telling the invention story of plastics.

http://inventors.about.com/od/pstartinventions/a/plastics.htm

http://www.mindfully.org/Plastic/Plastics-History.htm

National Public Radio has an amazing timeline of the invention from start to today.

http://www.npr.org/templates/story/story.php?storyId=114331762

OK, with all that web based information where do you start? I like to begin with cups of the different types of plastics cut into small pieces. If you have a plastic manufacturing plant (or one that forms things out of plastics…most mid-size and larger cities have one) they will give you samples of the small plastic pellets (resins) that are used to make different plastics. Some of these float in water (are less dense than H2O) and some sink. Some burn with a characteristic black smoke (test in a room with good ventilation and in really small quantities), and some give off white smoke or none. Some will drip and some will flow when heated above an open flame. We took various types of plastics and tried a density in water test. We tried the density in other liquids as well. If we knew the density of the liquid and the plastic sank we knew this plastic had a density above that of the liquid. We looked at the appearance to see if the plastic was shiny or dull, opaque or clear and flexible or brittle. This chart became a great tool to test unknown plastics and place them in a known category.

This inquiry activity was a doorway to teaching about monomers (the tiny parts that make up plastics (also called polymers) and the chemistry of plastics. There are lots of great issue links to this topic as well. We increased school recycling, changed our water bottle use and cleaned up around the lake…again. It is a good time to look at the chemistry of the things we use every day and the materials are free for the clean-up.

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