Learning about polymers
What words do you know that start with Poly-?
Polygon, Polyester (responses I received from eight 3-5 graders)
Poly-"many" in Greek
Mer - "parts" in Greek
Polymer- a large Molecule made up of long chains of repeating units called monomers.
Water Storing Crystals are the polymer, polyacrylamide. This chemical polymer was first used to absorb water in places where a pump could not be used. It is also used in agriculture to keep soil moist.
These creepy crawlers or Gro-beasts are also made of polyacrylamide. It is also found in super absorbent diapers.
The package of "creepy crawlers" comes with a spider, a scorpion, a cockroach and a centipede. You could talk about Arthropods here!
The experiment: Does your grobeast "grow" 600%? We measured the length using a ruler (centimeters ) and we used an electric balance in grams.
You could discuss why scientists use the metric system (it helps to use the same system of measurements if you are sharing your experiment) and why scientists use mass instead of weight ( I did have one student in my group tell me it's because of gravity!)
I had the students calculate how big their arthropod would get if it "grew" 600%. This could be a hard concept, but once one student said the 600% is just 6 times the size of it, they were able to calculate it. In the case of the spider, it was 4 cm at start and 9.4 cm after 3 days in water. If it had grown to 600% it would have been 24 cm ( the diameter of the plate). Its mass after 3 days went from 2.1 g to 17.8 g, which is more than 600% by mass.
Some students in the class had made "slime" before. It is an example of a cross-linked polymer made from polyvinyl acetate (found in Elmer's glue) and sodium tetraborate ( borax).
Here is the recipe for slime:
Slime Recipe
- Prepare Borax Solution: 2 Tablespoons of borax into 2 cups of water, stir until dissolved. ( more than enough for 30 students)
- Mark a plastic cup at the 20 ml mark by pouring 20 ml of water from graduated cylinder. ( you do not want to get glue out of a graduated cylinder!)
- Pour glue to the 20 ml mark and add 20 ml of water.
- Stir. You could add food coloring here.
- Add drop wise the borax solution, stirring until a mass of "slime " is formed.
- Carefully rinse under running water to get rid of excess borax.
Students can test the properties of their "slime" for:
Stretch-ability
Bounce-ability
Ability to make a puddle
Print-ability ( use water soluble markers or newspaper print like silly-putty)
*** Please don't let children take home the "slime" unless it is in a plastic baggie and has a warning label taped to it. You could decide as a group what should be written on the label.
Example:
Warning: Do not eat or throw. Do not place on furniture. May cause discoloration on clothes. Not suitable for kids under 4.
If the students are not going straight home, I take the slime back and make one big ball for observation in the classroom. This especially goes for high school students who have other classes to go to. Their teachers will appreciate this rule.
We also looked at these grow capsules made out of synthetic sponge material.
I included "Magic Sand" in this class because it is hydrophobic, it is not a polymer. The polyacrylamide is hydrophilic.
The polymer, polystyrene can take many forms. Many students were familiar with styrofoam. But polystyrene can be hard plastic like for a computer casing, as well as a clear plastic top at the salad bar.
experiment
Does # 6 plastic (salad lids) shrink just as much as the "Shrink-it" you can buy in the store?
The package claims it shrinks 60%.
Obtain a piece of "shrink-it". Sand the entire piece with a medium to fine sandpaper. We used colored pencils, but you could experiment with "sharpies" and crayons too. Trace around your piece and measure its width in centimeters. Place in a toaster oven on a piece of cardboard or Al foil (that is just used for experiments) at 250 degrees and watch very carefully. (Adults only handling plastic) Remove after transformation (no more than 5 minutes). Measure the "after" and do the math! Estimation could also be used here! Repeat again using a piece of # 6 plastic from a salad top. Compare!
Recycling plastic could be discussed here!
We are examples of Natural Polymers! DNA I also passed around some of my Pygora goat's fiber and sheep's wool as examples too!
Polymers are everywhere!