When plastic is recycled, it is melted down and reformed. If a student investigates the label of a plastic container, he will find a number that indicates the type of plastic a particular container has been classified as. A container labeled with a "1" is a PET container, with examples being a 1-liter bottle or many plastic wrappers. A number 2 container is HDPE. HDPE containers include soap and detergent bottles, bottled water and plastic bags. These are the most common types of plastics. Others include PVC, LDPE, PP and PS.
Students should be given one of each type of the six plastics to analyze. It may be helpful to give them a chart to fill out with listings such as color, clarity, texture and flexibility. Using a pair of tongs and a burner or candle, allow students to watch the effects of subjecting each type of plastic to fire. Ask them to note the color of both the flame and the smoke that appears when the plastics are burned.
Now place all of the plastic types together in a heat-safe container. Place the container over a hot plate or a burner and allow the plastics to melt. Let students observe the results of attempting to melt the plastics together. Ask them to note the colors and appearance of the melted plastic when they are combined together in one container. Ask volunteers to come up and attempt to stir together the melted plastic while observing proper safety precautions.
Students should have observed the differences between all of the plastics when they were subjected to direct heat. Because each of the plastic types reacted differently, it should illustrate to students that there is a reason behind the numbering system in place for plastics. This reason is further elaborated on when the plastics are melted in the same container but cannot be stirred together or combined. Let this be a starting point for students to discuss the difficulties associated with recycling plastics and why plastics must be sorted before they can be recycled.