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Let's move on to another synthetic polymer known as plastic.
Plastic is a type of synthetic polymer which consist of carbon and non-metallic elements such as hydrogen, oxygen, fluorine and chlorine.
Raw materials for making plastic are usually obtained from petroleum as well as natural gas.
Plastic can be divided into two types depending on the action of heat.
So the two types of plastic are thermoplastic as well as thermosetts.
In this lesson, we will discuss both of these types.
Thermoplastic as well as thermosetts.
Now, let's begin with thermoplastic.
What is thermoplastic?
Thermoplastic consist of linear polymer chains, so the polymer chains are linear like this and they are linked together by weak attraction force.
So this is a polymer. How is it linked to the other polymer?
Well, there is attraction but the linkage is very weak.
So we can guess that this type of plastic is not very tough.
Upon heating, polymer chains will slide easily over one another because of this weak attraction force, right?
So this contributes to the softness of the plastic.
So thermoplastic is soft and when we heat it up, it will actually becomes soft and when we cool it down, the polymer chains will become closer again and attract each other making the plastic hard again.
So, thermoplastic can actually be melted and moulded repeatedly.
So we can heat it up, change its shape and then it hardens again and we can heat it up, it changes shape, we can harden it again.
Thermoplastic is easy to burn and bend because plastics are non-metallic, right?
They do not contain electricity and plastic is also inert to most chemicals.
This means it does not react with chemicals.
The examples of thermoplastic includes PVC - polyvinyl chloride.
What is the use of polyvinyl chloride?
Well, you can see them in your house or even in school where we use it to make plastic pipes.
Before this, pipes are made up of metals but nowadays we have PVC pipes.
We also make them into bottles.
Now another example is nylon.
Nylon is actually a type of plastic that can also be used as textile.
For example nylon shirts and the likes of it.
Then we have polythene. Polythene is used to make plastic bags.
When you 'tapau' food from the shop, we use polythene as food containers.
Another example will be perspex.
Perspex is used in aeroplane windows.
It is transparent.
We also can use it in our roof if we want transparent roof.
Other examples include polypropene.
Polypropene is made into plastic bottle.
Besides polypropene, we have terylene.
Terylene is also another type of synthetic fibre that we can use in the production of textiles and last but not least, polystyrene.
Polystyrene is used in packaging materials.
It is also used in toys, to produce plastic toys and so on.
So these are some of the examples of thermoplastics.
Now let's move on to thermosetts.
Thermosett are actually made from polymer chains but this type of linkages are much stronger than termoplastic.
So we have polymer chain but the forces of attraction between them is much stronger.
So they have a much stronger attraction force between them and when we heat it up the first time, cross linkages will be formed.
This cross linkages makes the thermosett hard and heat resistant.
This makes it very difficult to change its structure by heating after it has been moulded.
So this type of plastic cannot slide anymore, so we cannot re-mould it anymore because it is not soft.
They are not easily flammable and since they are plastic, they do not conduct electricity and among the type of thermosetts that we have is bakelite.
Bakelite is used to make switch and also plugs that we have in our house.
It is also used to make buttons, computers, telephones and even television sets.
Another type is melamine.
Melamine is used in making plastic plates and also cups.
So the one that is used in your school canteen is melamine and last but not least epoxyl glue.
Epoxyl glue is used to make glue and it is also used to make electric insulator.
So these are the examples of thermoplastics as well as thermosetts.
Before we end the lesson, let's take a look at the differences between thermoplastics and thermosetts.
What are the differences between both of them?
Well, both of them are synthetic polymer and both of them do not conduct electricity.
But what is thermoplastic in regards of the actions of heat?
Well, thermoplastic cannot withstand heat.
It becomes soft when heated and hard when cooled.
It does not withstand heat.
While on the other side, thermosett can withstand high heat.
Now, how about the number of times it can be moulded?
For thermoplastic it can be remoulded a lot because when it is heated it becomes soft and that is why we can remould it.
But for thermosett, it cannot be remoulded.
So if we heat it up and it melts, after it cools down, that will be its final shape.
How about the ability to slide?
Well, thermoplastic can slide but thermosett are held together by strong cross linkages, right?
So they will not be able to slide.
Therefore, for thermoplastic, there will be no cross linkages.
But for thermosett, there are lot of strong cross linkages, right, and there you go...plastic.
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