Lecture 2 - Structure of thermoplastics Flashcards
What are some advantages of designing in plastics?
Freedom of design
Weight reduction
Cheap
Resistant to corrosion
Insulating
What are some disadvantages of designing in plastics?
Fire hazard and high temperatures
Tight tolerances
If mass is desired
How are thermoplastics represented?
Entanglements
How are elastomers represented?
Entanglements (many) & Cross-links (some)
What is an attribute of single chains?
Low stiffness due to weak interaction
What is an alternative for low stiffness due to weak interaction?
Multiple entangled chains
What is polymerization?
Polymerization is a chemical process that combines small molecules (monomers) into larger, chain-like molecules known as polymers.
What is condensation polymerization?
Two monomers with different reactive groups react to form a polymer releasing small molecules (such as water)
What is a saturated bond?
Single bonds between carbon atoms
What is an unsaturated bond?
Have one or more double or triple bonds between carbon atoms
What are side groups in chain configuration?
Check slides
How does the chain length influence the properties of polymers?
Increasing the number of monomers can create phase changes from gas to brittle solid.
Further increasing the length can increase the toughness and wear resistance of the material.
What is Pi?
Degree of polymerization
What is Ni?
Number of chains
What is Mi?
Mass of chain - 28 two C and four H - multiplied by the number of monomers in the chain
What is the Wi?
Weight of chain
Ex: 4x3000x28/ 1000
- 4 - no of chains
- 3000 - degree of polymerization
- 28 - mass of one chain
- divided by 100 to transform into kg
When are Mn and Mw equal?
When the lengths of the chains are equal
What is the degree of dispersity (D)?
A measure of the width of the molar mass (or chain length) distribution and is defined as Mw/Mn
What is Mn?
Average strength
Short chains - no entanglements - low strength
Longer chains - more entanglement - stronger material
What is Mw?
Melt viscosity
Higher viscosity - due to increase in entanglements
What is Mz?
Melt elasticity
Highest molecular - elasticity in the melt
When are Mn = Mz = Mw?
If the lengths of the chains are equal
What is the consequence of irregularly branched chains?
Low density
What is the consequence of no branches?
High density
