Metalwork - Materials - Plastics
Plastics is the general name applied to a range of "organic polymeric materials" that demonstrate the Property of being Plastic. In other words what people generally refer to as "Plastics" should properly be called Polymers, and that is how they will be reffered to from now on. Polymers are involved in every area of industry nowadays, from the Food Industry to the Space Program. Since the production of Polymers really took off, after World War 2, they have infiltrated every aspect of our everyday lives. Just walk around your house and notice how many items are either made from or have parts made from Polymers; food and liquid containers, the kettle, cables, furniture, floor coverings, bins, maybe the bath, the list is endless.... Did you notice the variety of shapes, the differing uses, the varying colours, softness, elasticity....
Polymer is a Greek word. We can understand it better when we break it in two : Poly means many, and mer means parts. Polymers are made up of long chain like Molecules, where each molecule is a part or mer. These mers are joined together by Chemical Bonds. Look at the picture of the paper clips to the right. Imagine each paper clip represents a molecule or mer, and when they are joined together they form long chains. Polymers are made up of similar long chains.
Take a look at the bowl of spaghetti to the left. This is what a Polymer might look like under a microscope, magnified many, many times.
Below you can see a diagram of the Polymer called Polythene. You can see what one mer looks like and when a number of these mers are joined together you have a Polymer. Carbon and Hydrogen are the basis of Polythene, and most other types of Polymers.
Use the links below to learn more information about Polymers in terms of the types, history, characteristics, uses, recycling, and much much more.
Polymers are divided into 3 main categories, depending on how the are obtained :
Polymers are sub-divided into two classification based on their Chemical Bonds, which determines how they react to heat and / or pressure.
The reason that Polymers are affected by heat has to do with their Chemical Bonds.
Thermoplastic Polymers make up 80% to 90% of the worlds Polymers. A Thermoplastic Polymer can be reheated and reshaped over and over again. When enough heat is applied to a Thermoplastic Polymer it softens allowing you to reshape it. It hardens again when it cools. You can learn more about reshaping Polymers in Working with Acrylic . Thermoplastic Polymer's mers are joined by Secondary Bonds. Secondary Bonds break when heated as they are weak and so a Thermplastic Polymer can be reshaped. When the Polymer cools down again tghe Secondary Bond reforms between the mers. Generally Thermoplastic Polymers cannot be used in temperatures much above 100°C as the heat resoftens them.
Candle wax is good for a demonstration of Thermoplastic Properties. When you burn the candle the wax melts and then solidifies when it cools. If you heat up the wax again, it will resoften, and can be shaped. You can keep doing this over and over again.
Thermosetting Polymers, although not as common as Thermoplastic Polymers, are still an important part of the Polymer industry. Thermosetting Polymers undergo a chemical change called curing when they are moulded and hardened. What happens here is that Primary Bonds form between the molecules. Primary Bonds do not break up under heating, so Thermosetting Polymers cannot be resoftened and reshaped. Take the example of boiling an egg. After the egg has been boiled and cooled down, it is solid. If you reheat it the egg will not soften. And that is basically how Thermosetting Polymers operate.
Natural Polymers have been in use for thousands of years, however it is really only in the last 140 years that the Polymer Industry has grown.
In 1862 the first modified polymer was unveiled by Alexander Parkes at the 'Great International Exhibition' in London. The material was called Parkensine and Alenander Parkes claimed that it could do everything that Rubber could do but it was cheaper to produce.
Rubber had been used by Native South Americans, who used it for shoes,coats and capes, long before Christopher Columbus set off in 1492. In 1770 a British chemist called Joeseph Priestley discovered that Rubber could rub out pencil marks on paper, and this is where the name came from.
In 1839 an American called Charles Goodyear, (yes the tyres), introduced a process called Vulcanisation. This was a major break through. Vulcanisation made Rubber more elastic, stronger, and mor resistant to abrasion and weathering.
Nowadays the Rubber Industry is hugh with Bridgestone, Goodyear, Michellen, and Pirelli at the forefront. If you watch a Formulae One motor car race you will notice how additives to the Rubber produce many different Rubber compounds so that the cars will have maximum grip in a wide varity of conditions.
In 1909, when Leo Baekeland from Belgium created Bakelite, polymers came into their own and started to be recognised as 'real' materials. However the real big break for Polymers took place because of World War II. Because of the War all of the countries involved lost their easy access to raw materials, such as fabrics and metals, from other countries. Scientists then set about really investigating Polymers to see what could be done to solve the problem. Nylon became a major source of textile fibres, and Polyester was used in making armor and other materials.
After the War the study and production of Polymers rapidly increased to get us where we are today.
Most people take Polymers for granted... they all
look the same, they feel the same... etc. Click on Types
of Polymers if you would like to find out more
information about the many common Polymers that
surround you, in terms of discription, properties and uses.
All Polymers are different, and are made in this
way so that they can be used for so many different purposes.
However most most Polymers have the following
charasteristics in common :
Polymers have a lot of advantages as their availability and variety of uses prove. However they have one major problem which is very evident in this age of conservation and being friendly to the enviornment. All Polymers have additives included to increase their range of uses and to improve their physical properties. Some additives are :
Some of these additives make the Polymers enviornmentally undegradeable, that is they won't rot like paper or wood in a landfill. As a result Recycling has emerged as the most practical solution to the problem. In 1988 a special code system was introduced by the Americans to help with recycling. On some Polymer food or solvent containers you can see the symbol to the right with a number in the centre. The number tells the recycler what material the Polymer product is made from. You can investigate this yourself by using this handy Chart.
Goto the Polymer Experiment Page to see how you can differentiate between different types of Polymers in the school workshop. You will need a number of different types of Polymers, and you could even bring some used household products with you to experiment with.
The use of Polymers is becoming more and more popular in the Metalwork room. Acrylic or "Perspex" as it is more commonly known is probably the most common. To learn more about workshop techniques with Polymers goto the Working with Acrylic page