Polymer Milk Jug: Difference between revisions

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== Materials ==
== Materials ==


* Clean HDPE containers (recycling label #2, your typical milk jug)
* Clean HDPE Containers (#2 Plastics)
* Laboratory heat gun
* Laboratory Heat Gun


==Safety Precautions==  
==Safety Precautions==  
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== Demonstration ==
== Demonstration ==


Grasp milk jug in one hand, heat gun in other
# Hold the container in one hand and the heat gun in the other. Turn the heat gun on and slowly wave it back and forth over one side of the container.
# While heating the container, explain to the audience or students present that the plastic is starting to melt, and the bonds are getting weaker. Point out to them when the side of the container turns clear, and continue to heat it until the clear spot is several inches wide.
# Turn off the heat gun, and put the mouth of the container to your lips with the now-clear side facing upwards. Blow into the container gently and in a controlled fashion, and watch as the clear side expands and becomes a bubble! If you blow too quickly, the bubble will pop and be less impressive. Continue to blow into the container until the clear plastic all turns foggy again.
# After a minute, the bubble will be cool enough for students to touch and feel. It is very different from the rest of the container!
# After making the first bubble, you can make up to three more bubbles by using the other three sides of the container. Don't try to use the bottom of the container; The seam will break open once you start blowing into it.


Turn the heat gun onto heat and slowly wave in on one side of the milk jug
== Why This Works ==


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
Polymers have become an essential part of our lives. We encounter polymers throughout our entire day, from the food we eat to the clothes we wear and the toys we play with. ''Polymers'' are strings of molecules bonded together in extremely long repeating chains. These chains connect end to end, and can stretch, bend or warp to resist breaking or separating. This demonstration focuses on what we call ''Thermoplastics'', which are plastic polymers that can be altered by heating them.


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.
Our milk jug is a plastic, and plastics are usually numbered from #1 to #7. There are seven types of plastics, and each one has different properties to them. Each type of plastic can be recycled, but when they are recycled they might be transformed from one type to another, depending on what type is needed. Our container is a #2 plastic, which is high density polyethylene or HDPE. HDPE has a rigid polymer, which is why it is stiff and doesn't bend easily. When we heat the wall of the container, we are making the polymer melt, making it less stiff. By blowing air into the container, we then are stretching out the melted polymer, which will stretch as far as it can to resist breaking. Polymers don't like to separate, so the wall will stretch out a LOT before it cools down and re-solidifies. Once cooled, it is now a #4 plastic, a low density polyethylene or LDPE!


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.
==Additional Information==
 
* All kinds of things are made with polymers! Some examples are:
== What to Say ==
** Leather in footballs, rubber in basketballs, and plastics in golf balls and soccer balls.
 
** Nylon and polyester, both of which are often used in clothing.
Polymers have become an essential part of our lives, you may not realize it, but we encounter polymers throughout our entire day.
** Acrylic, such as in paint or nail polish.
 
** Starch in potatoes and corn, carbohydrates in bread, and proteins in meat are all types of polymers!
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.
* This demonstration pairs well with the [[Vanishing Peanuts]].
 
* This demonstration is a part of the [[Environmental Show]].
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

Latest revision as of 20:01, 7 June 2016

Chemistry, Biology: Polymers, Recycling Plastics
Grade Range: Elementary School, Middle School, High School
Format: Stage, Hands-on

This demonstration is a thought-provoking example on how we recycle plastics. Students are likely familiar with the idea to recycle, but this will intrigue them as an example of how it can be done.

Materials

  • Clean HDPE Containers (#2 Plastics)
  • Laboratory Heat Gun

Safety Precautions

Please read the Fire Safety section of the Demonstration Safety Page. Although this demonstration does not use fire, the Heat Gun does get very hot and can burn things.

Demonstration

  1. Hold the container in one hand and the heat gun in the other. Turn the heat gun on and slowly wave it back and forth over one side of the container.
  2. While heating the container, explain to the audience or students present that the plastic is starting to melt, and the bonds are getting weaker. Point out to them when the side of the container turns clear, and continue to heat it until the clear spot is several inches wide.
  3. Turn off the heat gun, and put the mouth of the container to your lips with the now-clear side facing upwards. Blow into the container gently and in a controlled fashion, and watch as the clear side expands and becomes a bubble! If you blow too quickly, the bubble will pop and be less impressive. Continue to blow into the container until the clear plastic all turns foggy again.
  4. After a minute, the bubble will be cool enough for students to touch and feel. It is very different from the rest of the container!
  5. After making the first bubble, you can make up to three more bubbles by using the other three sides of the container. Don't try to use the bottom of the container; The seam will break open once you start blowing into it.

Why This Works

Polymers have become an essential part of our lives. We encounter polymers throughout our entire day, from the food we eat to the clothes we wear and the toys we play with. Polymers are strings of molecules bonded together in extremely long repeating chains. These chains connect end to end, and can stretch, bend or warp to resist breaking or separating. This demonstration focuses on what we call Thermoplastics, which are plastic polymers that can be altered by heating them.

Our milk jug is a plastic, and plastics are usually numbered from #1 to #7. There are seven types of plastics, and each one has different properties to them. Each type of plastic can be recycled, but when they are recycled they might be transformed from one type to another, depending on what type is needed. Our container is a #2 plastic, which is high density polyethylene or HDPE. HDPE has a rigid polymer, which is why it is stiff and doesn't bend easily. When we heat the wall of the container, we are making the polymer melt, making it less stiff. By blowing air into the container, we then are stretching out the melted polymer, which will stretch as far as it can to resist breaking. Polymers don't like to separate, so the wall will stretch out a LOT before it cools down and re-solidifies. Once cooled, it is now a #4 plastic, a low density polyethylene or LDPE!

Additional Information

  • All kinds of things are made with polymers! Some examples are:
    • Leather in footballs, rubber in basketballs, and plastics in golf balls and soccer balls.
    • Nylon and polyester, both of which are often used in clothing.
    • Acrylic, such as in paint or nail polish.
    • Starch in potatoes and corn, carbohydrates in bread, and proteins in meat are all types of polymers!
  • This demonstration pairs well with the Vanishing Peanuts.
  • This demonstration is a part of the Environmental Show.
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