Enhancing/Testing a Natural Polymer
Enhancing a Polymer
Gelatin is a natural polymer. We know how it acts every time we eat Jello or fruit squares made with gelatin. We can treat gelatin with a chemical agent that helps connect molecules into longer chains.
In this exploration students will compare the natural gelatin polymer that was created in the previous exploration (A) with a new one. The idea here is to have a "control." A “control” is a concept we use in science experimentation as a way to compare any changes with a known. For example, if we want to test fertilizers effect on the growth of a tomato plant we should have at least two plants, one which we put the fertilizer on (the experimental plant) and one we leave alone (the control). We should otherwise treat the plants in exactly the same way: the same amount of water, the same sunlight, pot, soil, etc. In this experiment we need a control gelatin to see how it compares to our new polymer.
Follow the directions below:
Control:
1) Mix the gelatin and hot water (5 ml each as in the first exploration)
2) Pour out the composite on an aluminum foil “mold”.
Experimental Polymer
1) Mix another batch of the gelatin and hot water (5 ml each as in the first exploration)
2) This time add 2.5 ml Borax to the water before you add the gelatin. Mix and stir well.
3) Pour out the composite on an aluminum foil “mold” as before.
4) Allow both polymers a few minutes to gel and then hang them on the close line to dry.
Testing the Polymers
How do these two polymers compare? Brainstorm how one could develop a way to measure the behavior of the polymer. How far can it stretch without breaking? How well does it bounce back after being compressed?
Make a data table in the STEM/Engineering Notebook:
Why are these different? What did the borax do to the gelatin? Have students think about what it looks like inside the gelatin if you could see the atoms and molecules? Allow students to discuss their ideas about what they think is going on inside the gelatin.
Now offer an analogy. When we add hot water to gelatin, the molecules line up like the magnets we demonstrated in the first lesson. We could magnetize paper clips so they stick together. Can we take the magnets apart? Yes, we can shake them or heat them and the gelatin would come apart easily again. The polymer is not very permanent or tightly bonded.
Now arrange a simple chain of paper clips. Manipulate the chain by bending shaping and returning it to its original form. Strong polymers are chains of individual molecules that are linked together with stronger bonds.
Borax provides borate ions to cross-link the gelatin polymer chains.
Allow students an opportunity to think about the characteristics of their polymer in terms of the idea of linked molecules. How can they explain how their gelatin polymer stretches? Returns to it original form?
