Plastics are everywhere – from airplanes to drinking bottles to sports equipment. They are most commonly derived from petrochemicals but many are partially natural. Typically, plastics are organic polymers (or chains of carbon atoms with hydrogens hanging off), but they often contain other substances.
Each plastic is chemically unique and has distinct properties that make it suitable for certain products. These different characteristics (weight, durability, stacking, and even consumer appeal) are taken into consideration when packaging is considered for new products.
Plastics Lab Activity
Plastics can provide hands-on, inquiry based lab activities with which students can investigate materials that are common to your everyday lives. To begin our initial plastics lab activity, I asked the kids to name as many things as they could that are made of plastic. Are all plastics the same? How are they different?
I then displayed a number of plastic materials I had collected and we talked about the characteristics of each. [Alternatively, you could do this lesson in two parts and ask the students to bring in samples themselves.]
I explained that plastics are classified #1 through #7 and I showed them how to check the bottom of the object to locate the number inside the recycle symbol. Even though some recycling centers only accept certain numbers, all plastics with this symbol are recyclable. Markets just don’t exist for all recycled products.
After our discussion, students were asked to sort the plastic bottles and containers according to their numbers. Then, students were asked to brainstorm different physical properties that are characteristic of each type of plastic and test them. The students were encouraged to make a table in their science notebook and record the physical properties of each type of plastic. This data table would then be used to help them classify a set of unknown plastic pieces.
- Density – Does the plastic float or sink in water? (Cut plastics into pieces before dunking in water. #2, #4, and #5 float while #1 and #6 sink.)
- Transparency – Is the plastic clear or opaque?
- Luster – Is the plastic dull or shiny?
- Brittleness – Does the plastic break when bent?
- Rigidness – Is the plastic flexible or tough?
- Color – Is the color the same for every sample number?
In advance, samples of #1, #2, #3, #4, #5, and #6 plastics were cut into small pieces (about 1 to 2 in.). As many were not distinguishable by sight, I cut each number into a different shape. For example, I cut #1 plastic into squares, #2 into triangles, and so on. I made a key that identified each plastic by its number. A mixture of all types of plastics were then placed into a bag for each group.
When the students’ data tables were complete, I gave a bag of mystery plastics to each group and challenged the kids to identify the different plastics by their physical properties. Could they assign a number to each sample? Once a group was finished, they could check their predictions with the key.
Take it Further
During the testing process, one of the students made an interesting discovery in class – he had pulled on a strip of plastic cut from a bread bag and discovered it stretched quite a distance before breaking. Another plastic (a sandwich zip baggie) took significantly more force before breaking. This lead us to talk a little about tensile strength.
I encouraged the kids to pursue this further by cutting strips (approximately 2.5cm by 12cm) from a variety of different plastics (freezer bags, food wrap, microwave wrap, trash bags, grocery bags, or any other type of similar plastic) and developing a test to determine the weight needed to break each of the plastic strips. As you slowly pull the ends apart (stress), you can feel the resistance of the material as you pull it (strain).
Note: If you choose to pursue this, be certain to cut out plastic strips that are consistent in size and either parallel or perpendicular to the grain of the material. [By holding the bag to the light, the lines you see indicate the general direction of the polymer chains. The direction in which these chains are lined up is also known as the anisotropic nature of the material, or the direction of extrusion.]
March 5, 2014 at 1:28 pm
Great ideas for exploring plastics, Eva! Thanks for sharing the post with me.
March 25, 2014 at 3:42 pm
Don’t you love it when kids want to explore a subject further? This gives me an idea for a recycling unit study. Thanks!
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