Favorite Polymer Demonstrations
for Middle School Teachers
by Wayne Goates, from Goddard, KS and "Booger Hollow Science"

A. Shell Game

Materials: sodium polyacrylate (diaper absorber powder), water, 3 opaque cups, sodium chloride

Sodium polyacrylate can be used to do a revised version of the old shell game where students must pick the cup that has the pea under it. Have three cups (right side up) on the demo table. One cup should contain a couple of scoops of sodium polyacrylate. Tell your students to watch carefully. Pour about 100 mL of water into that cup and then switch the cups around and have students guess which cup contained the water. When students guess the correct cup, turn the cup upside down and show that no water runs out. Add salt to show students that in fact there was water but it was in a gel form as the chemical absorbed the water. Sodium chloride releases the water from the gel.

B. Magic Sand

Materials: fine white sand, Scotch-Guard water-repellent (spray), oven or Toaster Oven

Magic Sand or Mystic Sand is sand that has been treated with a colored dye and coated with finely divided hydrophobic silicon coating. Due to the coating, it can be used to form underwater towers or columns or designs, and then be removed. The sand will be completely dry. Spraying oven-dried sand one hour at 250° F with a water-repellent material such as Scotch-Guard will make a magic sand type of material.

C. Melting Money

Materials: Melting Money (Flinn AP8678), water, container

Melting Money and Melting Memos, marketed by So Much Fun, are paper items that dissolve when placed in water. The paper is composed of carboxymethylcellulose (starch) with 20% or less cellulose. This material has been used by organizations such as the CIA for secret or sensitive documents that can easily be destroyed by wetting with water. A number of toys using this are Trash Bag Bunch, the wrapper of Hot Wheels Revealers, Magic Nursery Dolls, and their Bye-Bye Diapers.

D. Density of HDPE and LDPE

Materials: large glass cylinder, alcohol and water solution, samples of HDPE and LDPE

Since its accidental discovery in 1933, polyethylene (PE) has become the world’s largest poundage plastic. The difference in density can be easily, quickly, and clearly demonstrated in the classroom by the use of a large glass cylinder. Fill the cylinder with alcohol-water solution. A one-liter cylinder filled with 50-50 volume of 95% ethyl alcohol (or methyl alcohol) and water works well. When two half-dollar sized pieces of high density polyethylene (HDPE) and low density polyethylene (LDPE) are added to the solution in the cylinder, the HDPE will sink while the LDPE will remain floating. (HDPE is used to make plastic grocery sacks and butter containers and LDPE is used to make fresh produce bags at the grocery store or squeezeable bottles. Check the recycle codes.) The PE samples can also be cut to the form the letters "H" and "L" for high and low. Make sure you cut the width of the letters to be about the diameter of the cylinder so that the letters will remain upright as they position themselves in the cylinder. The solution can be kept indefinitely in a closed container and reused many times. The HDPE molecules are linear and can be packed closely together making the plastic opaque and non-waxy. The LDPE molecules are branched chains with less packing and so the plastic has greater transparency, flexibility and waxiness.

E. The Fireproof Balloon                 Materials: round balloons, water, long matches or Booger Hollow Light Stick or candle on a meter stick Balloons are fragile and must be kept from sharp objects and flames! A fire can weaken the rubber and cause it to burst. However, in this demonstration, one will find that a flame held directly under a balloon will not break it. Inflate one balloon with air and tie it closed. Place 60 ml of water in the other balloon and then inflate it with air and tie it closed. Activate the flame to touch the air filled balloon. What happens? The balloon breaks because the rubber becomes hot and the bonds break as the hot air inside the balloon increases the pressure on the rubber. Activate another flame and hold it directly under the water filled balloon. Allow the flame to touch the balloon. What happens? The balloon does not break because the water is absorbing heat and not the rubber. Water is a good absorber of heat or it has a high heat capacity. It takes 10 times as much heat to raise the temperature of one gram of water 1° C than it does to raise the temperature of one gram of iron by the same amount. This is why it takes so long to bring a teakettle of water to the boiling point. However, when water cools, it releases all that stored heat. Land areas near oceans and lakes stay warmer in the winter than areas at the same latitude further inland for this same reason.

F. The Booger Hollow Light Stick Materials: one meter stick, two meters of surgical hose, BBQ butane lighter with trigger, electrical tape

Assembly: Using the electrical tape, secure the lighter to one end of the meter stick. Thread the surgical hose through the trigger mechanism of the lighter. Tie the ends of the hose together to make a loop that can be stretched to hook onto the end of the meter stick. Turn the lighter to the "on" position. Push (or pull) of the trigger mechanism to activate a flame. Keep your finger on the trigger while you stretch the surgical hose over the end of the meter stick. This keeps the trigger depressed and allows you to control the flame at a maximum distance of one meter.