Thermoplastic matrices Flashcards
What is the function of the matrix?
- Binds reinforcements together
- Maintains shape
- Transfers stress onto reinforcement
- Protects reinforcement
- Adds properties
What are the considerations when choosing a matrix
- Cost
- Mechanical properties
- Service temperaturs
- Compatibility with reinforcement
- environmental resistance
- Abrasion resistance
- Heat and electrical conductivity
- Appearance
- Processing
What is a thermosetting polymer?
polymers that cannot be melted
How can you process thermosetting polymers?
- polymerise them in situ
- Start with monomers and react them to form polymer
- forms an amorphous crosslinked or highly crosslinked polymeric structure
How can thermosetting polymer parts be made?
- Combine monomers with reinforcements
- shape and cure to solidify
What is a thermoplastic polymer?
one that can be melted
how can you process thermoplastics?
Melt them
How can you make thermoplastic parts?
Melt polymer
combine with reinforcements
Shape and solidify
What are the advantages of thermosets?
- Low viscosity reactants
- Good adhesion with reinforcement
- Thermal stability
- Chemical resistance
- Low creep
What are the disadvantages of thermosets?
- Limited shelf life
- Long cure time
- Low strain to failure
What are the advantages of thermoplastics?
- High impact strength
- High fracture toughness
- High strain to failure
- Good shelf life
- Short ‘cure’ time
What are the disadvantages of thermoplastics?
- High melt viscosity
- Low creep resistance
- low thermal stability
How does molecular weight affect thermoplastics?
Higher molecular weight gives improved properties
What about amorphous thermoplastics gives improved properties?
entangled chains
What about semi-crystalline thermoplastics gives improved properties?
aligned chains
What is the order of common thermoplastic in terms of cost, modulus and strength?
Polypropylene
Polyamides(Nylons)
Polysulfones
Thermoplastic polyimides
Polyketones
What is the structure and properties of polypropylene (PP)?
low cost and reasonable properties
low performance
single C-C bonds along chain
increased crystallinity improves properties and solvent resistance
used for household and machine parts
What is the structure and properties of polyamides (Nylons)?
contain amide groups
good performance despite aliphatic structure
extensive hydrogen bonding
excellent wear resistance
used for gears/bearing, housings
very susceptible to water
add short glass fibre to minimise
What is the structure and properties of polysulfones?
aromatic contains SO2
backbone phenylene results in excellent performance
inflexible
strong stiff
tough
chemical +thermal resistance
polyphenylene sulfone too stiff
What is the structure and properties of polyimides?
aromatic high performance
high temp performance
contain imide linkages
300*C
What is the structure and properties of polyketones?
aromatic high performance containing ketone groups -C(O)-
Not as goog as polyimides but good heat resistance 250*C
EXPENSIVE
What temperature are amorphous thermoplastics processed at?
above Tg (glass transition temp)
heating lead to disentanglement
What temperature are semicrystalline thermoplastics processed out?
above Tm melting temp
melting of crystalline phase
How does pultrusion work?
fibres and polymers pulled through heated die.
constant cross section
impregnation difficult
How does extrusion and injection moulding work?
High shear polymer to melt and homogenise
Short fibres
properties limited by the amount of attrition the fibres experience
How does sheet moulding work?
long fibres and thermoplastic powder tumbled together
Co-mingling thermoplastic fibres with reinforcing fibres
Component stamped out using hot press
How does thermoplastic Pre-preg work?
Best properties
continuous unidirectional or woven fibres
How does liquid processing of thermoplastics work?
short molecules that can be polymerised during the processing step using heat to cause polymerisation step
