1. A level Product Design Unit 2
Polymers
A level Product Design
Unit 2

2. Whats the difference between a plastic & a polymer ?
Plasticity is a material property & not a material
“the ability to be shaped or formed”
Plastic Materials
Bone
Horn
Clay
Concrete
A polymer is a certain type of material
There are natural & synthethic polymers
We are only interested in synthetic polymers
Whats the difference between a plastic & a polymer ?

3. an individual chemical molecule is called a monomer
When many monomers are linked together to form a chain, a polymer molecule is formed
A plastic consists of many large polymer molecules
What is a Polymer ?

4. A chemical reaction forms the polymer molecule (makes the chain)
polymerisation
Normally, chains are randomly arranged and form a 3d pattern
Imagine a piece of string scrunched up into a ball
What is a polymer ?

5. Fully uncoiled, one polymer molecule’s chain length may be 10,000 times the diameter of the chain
The length of the chain gives the material flexibility
Many other material properties are dependent on the chain length
Tg = glass transition temperature
Temperature at which polymer moves from a hard glass like state to a softer rubbery state
Polymer Properties

6. Plastic Additives Polymer molecules Reinforcement Plasticizer Filler
Added to improve material strength properties
Plasticizer
Added to change natural material properties
Makes material easier to process
Filler
Added to replace polymer
Cost reduction measure
Stabilizers
Stop deterioriating over time
Heat, UV, Biodegradation
Foamants
Increases volume
Gives more elasticity
under compression
Plastic Additives
Typical PVC Content

7. Synthetic Polymer Categories
Long chain polymers
Crosslinked polymers
Thermoplastics
Thermosetting
Plastics
Elastomers
Semi-crystalline
amorphous
Synthetic Polymer Categories

8. Crosslinked Polymers Very strong Level of crosslinking determines Tg
Strong bonds between chains (crosslinks) and intra-chain
Level of crosslinking determines Tg
Thermosetting plastics (eg Araldite) are highly linked
Chemical reaction forms the links
One way process – cannot be reversed
Will not soften with heat - very high Tg
Araldite is a tradename for a resin based polymer
The resin is mixed with an activator to start curing
Materials like rubbers are lightly crosslinked
Tg is below freezing ie. Is in a rubbery state at all temperatures above 0
Below Tg, material is hard & brittle (useless)
Crosslinked Polymers

9. Thermoplastics Strong covalent bonds Weak bonds between chains
Bonds between individual chain elements
Weak bonds between chains
These bonds can be easily broken with heat
Breaking all bonds causes return to original shape
Recyclable by re-heating
Energy cost !
Contamination is a big issue
Thermoplastics

10. Thermoplastics Amorphous thermoplastics Semi-crystaline thermoplastics
Chains are randomly entangled
Generally transparent
Eg. PolyCarbonate (CDs)
Glass transition temperature (Tg) is a key property
Semi-crystaline thermoplastics
Cooling causes molecules to fold in a regular structure and form a crystal
Crystal is dense and so plastic is opaque
Eg. Polyethylene (gas and water pipes)
Have a definate meting point (Tm)
Thermoplastics

11. Semi-Crystalline Thermoplastics
The more crystalline a material is:
The stronger it gets
It has more resistance to solvents
Solvents need to dissolve into a material
Amorphous plastics have greater free space
Higher density
Higher modulus (stiffness)
Higher melting point (Tm)
The lower its transparency
Reduced impact resistance (brittle)
Reduced ductility
Ability to be deformed without cracking
Semi-Crystalline Thermoplastics

12. Interesting, right?
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