C15 Flashcards
What do the properties of polymers depend on ?
-the monomer used to make it
-the conditions used to carry out the reaction
What are the conditions to make low density poly(ethene) ? And what are the properties
Using very high pressures and a trace of oxygen, ethene forms LD poly(ethene). The polymer chains are randomly branched and cannot pack closely together, hence it’s lower density
What are the conditions needed to make high density poly(ethene) ?
Using a catalyst at 50°C and a slightly raised pressure, ethene makes
HD poly(ethene). This is made up of straighter poly(ethene) chains.
They can pack more closely together than branched chains, hence its higher density of HD poly(ethene). It also has a higher softening temperature and is stronger than LD poly(ethene).
What’s a thermosoftening plastic ? And what is it made out of ?
They can be heated and reheated
They are made up of individual polymer chains that are tangled together
What’s a thermosetting plastic ? And what is it made out of ?
They do not melt when you heat them
They have strong covalent bonds forming ‘cross-links’ between their polymer chains
In thermosoftening polymers why does the polymer melt when heated ?
In thermosoftening polymers, the forces between the polymer chains are weak. When you heat the polymer, these weak intermolecular forces are broken. The polymer becomes soft. When the polymer cools down, the intermolecular forces bring the polymer molecules back together. Then the polymer hardens again. This type of polymer can be remoulded.
Why wont thermosetting polymers melt ?
However, thermosetting polymers are different. Their monomers make covalent bonds between the polymer chains when they are first heated in order to shape them. These covalent bonds are strong, and they stop the polymer from softening. The covalent ‘cross-links’ between chains do not allow them to separate. Even if heated strongly, the polymer will still not soften. Eventually, the polymer will char at high enough temperatures.
What are the most common glass made out of ?
Soda-lime glass is the most common glass
-sand
-sodium carbonate
-calcium carbonate
What is Borosilicate glass made from and what are the properties ?
Made from:
-sand
-boron trioxide
It melts at a higher temperature than soda-lime glass
What are clay ceramics and how are they made and what are the properties ?
wet clay is baked in kiln/furnace
e.g. crockery, bricks
clay ceramics are hard, unreactive, resistant to heat
What are composites and what is it made from ?
• made from 2 or more materials
• has REINFORCEMENT (fibres or fragments) in MATRIX (binds then together)
• properties of composite different to each separate material
Whats the fibre glass made off?
Reinforcement Matrix = glass fibres
Matrix = polymer
What is the reinforcment and matrix for natural wood ?
Reinforcement = cellulose fibres
Matrix = lignin
What is the reinforcement and matrix of plywood / mdf ?
Reinforcment = wood fibres
Matrix = adhesives
What are the reinforcments and matrix of carbon fibre ?
Reinforments = C fibres / nanotubes
Matrix = polymer
