Polymers

Age

Elementary, Middle School, High School

Format

Stage Show, Hands-on

Materials

   Clean HDPE containers (recycling label #2, your typical milk jug)
   Laboratory heat gun 

Safety Precautions: The heat gun can get very hot very fast, make sure to NOT touch the barrel of the gun while and shortly after use. After you are done using the heat gun, run it on cold for a few seconds, until the barrel is cool enough to grasp without irritation.

Demonstrators should wear goggles and lab coats, and the ST general safety box should be available to them.

Preparation

Make sure all of the milk jugs are clean.

Demonstration

Grasp milk jug in one hand, heat gun in other

Turn the heat gun onto heat and slowly wave in on one side of the milk jug

When the plastic on that side becomes clear, turn off the heat gun, give the heat gun to your partner, he/she should run it on cold until it reaches a safe temperature

Quickly blow into the top of the milk jug, the melted side should blow up like a balloon. Sometimes the balloon will pop as soon as you start blowing it, but when you're lucky it gets really big (see diagram)! The trick is to blow slowly and constantly.

If the milk jug is cool enough, you can have the kids feel both the regular milk jug and the side that has been melted.

What to Say

Polymers have become an essential part of our lives, you may not realize it, but we encounter polymers throughout our entire day.

In general, polymers consist of small molecules bonded together in extremely long repeating chains. Basically, you have these really tiny units. These units get hooked together to form a chain. This chain gets longer and longer and longer, until it forms a huge polymer. You can compare this to one car versus an entire train.

Many of the foods we eat contain polymers. Starch in plants is a polymer.

Polymers can have many different properties. Some are very rigid, like football helmets or bowling balls, while others are very flexible, like our milk jug. Some are heat resistant; those used as adhesives on a space shuttle, while others melt fairly easily, like our milk jug. The milk jug is made of HDPE, which stands for high density polyethylene.

Tons of manmade materials are polymers. Styrofoam is a polymer known as polystyrene. Various acrylic paints are made of polymers. Nylon is also a common polymer. Many types of adhesives are polymers.

When you make the balloon from the milk jug, mention that polymers which melt when heated, can be reshaped, and then harden when cooled (like the milk jug) are called thermoplastics. Not all polymers possess this property. Ask the students why we might want milk jugs to be thermoplastics. Make sure they understand that it is easier to mold something into a particular shape if it’s melted. In fact, many plastic bottles are made by “blow molding” melted thermoplastics. Make sure they understand that the particular polymer in the milk jug is made from petroleum, a non-renewable resource, so we want to be able to recycle the plastic in the milk jug. We can do this by melting it, forming the melt into a new product, and letting it cool to harden.

Thanks to their varied properties, polymers are used in the equipment of just about every sport. Thick layers of a certain type of polyethylene, the same plastic polymer used in the milk jug, can be shock-absorbing and so are used for gymnastics mats. Similar materials are used in running tracks to help sprinters lose less energy each time their feet hit the ground. Nike has even used a recycled plastic polymer in their track suits that helps reduce air resistance. In recent years, golf balls have been developed to maximize the distance they go when they are hit. These golf balls contain many layers of all sorts of polymers. Many basketballs are made of polymers. The outside layer of leather is a natural polymer, while the inside lining is composed of polyisobutylene, a special synthetic polymer that is impermeable to gas.

Why It Is

Heat makes HDPE melt, simply because of the nature of the polymer. After it melts, it can be molded into various shapes easily.

Real Life Examples

Nylon, adhesives, starch, milk jugs, bowling balls, football helmets