Polymers are everywhere.
You find them used in virtually every electronic device and from the ubiquitous (nice word there!!) polythene supermarket bag to the bearings of the decking of the Humber Bridge.
Polymer clothing is common too.
The point being of course is that the properties of polymers can be tuned to fit the use required.
And there has been massive investment in the development of polymers for sports and outdoor use.
So we are thinking about the versatility of polymers like nylon and materials like GORE-TEX.
But first a simple interesting thing about polythene bags.
Now every tried to rip a polythene bag apart?
If you stop now and find an old bag and try to rip it up you will find it easier to do this in one direction rather than the other.
Which is the stronger direction and why?
This is the reason why:
The polymer fibres and to a large extent the polymer molecules themselves are aligned one way in the bag that is from the handle to the bottom of the bag.
So it is stronger in the direction that it needs to be to carry a large weight of shopping.
But at right angles to this direction the plastic is much weaker.
The strength comes from the forces within as opposed to the forces between the polymer fibres and molecules.
There are comparatively weaker forces between the polymer chains in polythene.
But there are really strong forces within the polymer chains themselves because the carbon atoms are held together with strong covalent bonds.
Polymer like polythene and other addition polymers like PVC, polystyrene and polypropene are called thermo softs or thermoplastics.
The test comes when they are gently heated because they can be deformed and be remoulded at relatively low temperatures into a different shaped object.
Thermosplastic polymers can be easily stretched because the polymer chains can easily slide over each other.
Now chemists can strengthen the links between polymer chains adding what are called crosslinks and create a a stronger plastic but sacrifice a great deal of flexibility like this:
The strong covalent bonds between the polymer chains now add rigidity to the plastic.
It will char on heating rather than softening and being remoulded.
It cannot be stretched.
It will have a high melting point
Examples of thermosets are in this table:
Thermosoftening plastics are in the table below:
Pages on the "Mole" and "Using the Mole" in chemical calculations are here
You find them used in virtually every electronic device and from the ubiquitous (nice word there!!) polythene supermarket bag to the bearings of the decking of the Humber Bridge.
Polymer clothing is common too.
The point being of course is that the properties of polymers can be tuned to fit the use required.
And there has been massive investment in the development of polymers for sports and outdoor use.
So we are thinking about the versatility of polymers like nylon and materials like GORE-TEX.
But first a simple interesting thing about polythene bags.
Now every tried to rip a polythene bag apart?
If you stop now and find an old bag and try to rip it up you will find it easier to do this in one direction rather than the other.
Which is the stronger direction and why?
This is the reason why:
The polymer fibres and to a large extent the polymer molecules themselves are aligned one way in the bag that is from the handle to the bottom of the bag.
So it is stronger in the direction that it needs to be to carry a large weight of shopping.
But at right angles to this direction the plastic is much weaker.
The strength comes from the forces within as opposed to the forces between the polymer fibres and molecules.
There are comparatively weaker forces between the polymer chains in polythene.
But there are really strong forces within the polymer chains themselves because the carbon atoms are held together with strong covalent bonds.
Polymer like polythene and other addition polymers like PVC, polystyrene and polypropene are called thermo softs or thermoplastics.
The test comes when they are gently heated because they can be deformed and be remoulded at relatively low temperatures into a different shaped object.
Thermosplastic polymers can be easily stretched because the polymer chains can easily slide over each other.
Now chemists can strengthen the links between polymer chains adding what are called crosslinks and create a a stronger plastic but sacrifice a great deal of flexibility like this:
The strong covalent bonds between the polymer chains now add rigidity to the plastic.
It will char on heating rather than softening and being remoulded.
It cannot be stretched.
It will have a high melting point
Examples of thermosets are in this table:
Thermosoftening plastics are in the table below:
Pages on the "Mole" and "Using the Mole" in chemical calculations are here
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