Becoming Familiar with Polymers
Getting Started
It is important at this point to show a direct link between the students’ questions and this exploration. Teacher language such as “You had questions about polymers.... So, let’s explore that area first.”
Depending on the experience of the students, a variety of possibilities may arise. Having materials handy as visual props may stimulate student idea-making.
The teacher can then ask the class how they might suggest finding out about polymers. In this curriculum we want students to think about what they could do experimentally to find out and to read and listen about the scientific information that helps explain the theory and detail behind their observations.
Lead students to an initial encounter with a natural polymer, gelatin. Gelatin is a safe, non-toxic, natural polymer that we can use without worry of toxicity. (Most polymers are highly toxic and are not pleasant smelling.)
Exploration
Offer the students a simple process for exploring a polymer. Model the following process for the class:
1) Add 5 ml hot water to 7.5 ml gelatin. Gelatin is a natural substance in granular form that is rendered from the gummy connective tissue of animals. See the definitions section for a description of gelatin. Students can read or listen to this background before or after they prepare this first polymer experiment.
5 ml 7.5 ml
Gelatin Mix Hot Water
2) Stir the mixture until the gelatin begins to thicken, then pour onto a smooth surface (table or tray or aluminum foil--See diagram below). It is best to pour strips in inch wide by three or four inch long.
3) Allow the ribbon to set undisturbed for about 3 minutes. Then carefully loosen and lift gelatin ribbon.
4) Hang the gelatin on a clothesline to complete the setting-up process. Be sure to label the composition of this material (pure gelatin).
One set-up idea. Fill two water bottles with water. Tape a wooden skewer to the lids of each bottle.
Use close pins to hang gelatin to dry. Mark each test/trial with an index card below.
5) Allow students time to create an additional gelatin Allow them to vary the amount of water used to less than or more than the 7.5 ml recommended amount. Having two examples to test can be a good way to both practice the process and to compare which ratio is the more favorable formula.
6) After the gelatin has set and ceases to become sticky to the touch, it can be manipulated and examined. Have students make notes on this first process by recording data in their STEM/engineering notebook. Simple observations can be made about the gelatin polymers How sticky is it? How stretchy? If it is twisted or rolled does it return to its original position? Compare the test trials of the gelatin. Which gelatin to water ratio has more desirable characteristics?
Concluding
Offer students an opportunity to discuss what they think might be happening at the molecular level. They may not have a sense of the vocabulary or the specific details of a chemical reaction, but may have ideas about what is happening to the unseen components inside these materials. What is happening to this mixture when warm water it added to the gelatin molecules?
After some theorizing, offer students an analogy that will help them understand how these molecules act. Each molecule is like a weak magnet that can attract another molecule. In the video below we place individual magnets (monomers) on a sheet of paper. We add energy (in the case of gelatin hot water). The magnets form chains.
Polymers are molecules that become chained together to form long threads or mats. Depending on the building block of these polymers, the results can be very different. A very basic introduction to polymers can be found at http://www.pslc.ws/macrog/kidsmac/basics.htm
Assessment
Students should record their procedures and observations in the STEM/Engineering Notebook. Assessment of the notebook can follow a rubric for science process such as note taking and observation, data recording, or appropriate use of ELA requirements.
Alternatively, students can report on an oral or written assessment a recollection of the process required to make a simple polymer and their understanding of what happens to the molecules in polymer formation.
Follow-up
The gelatin polymer will slowly lose water over the next hours of drying. In a day or so the polymer will be completely dry. The nature of the polymer changes and it becomes hard, like plastic. Further exploration can be done on the completely dry substance.