Thermoplastic matrices

Question 1

What is the function of the matrix?

Answer 1

1. Binds reinforcements together
2. Maintains shape
3. Transfers stress onto reinforcement
4. Protects reinforcement
5. Adds properties

Question 2

What are the considerations when choosing a matrix

Answer 2

• Cost
• Mechanical properties
• Service temperaturs
• Compatibility with reinforcement
• environmental resistance
• Abrasion resistance
• Heat and electrical conductivity
• Appearance
• Processing

Question 3

What is a thermosetting polymer?

Answer 3

polymers that cannot be melted

Question 4

How can you process thermosetting polymers?

Answer 4

• polymerise them in situ
• Start with monomers and react them to form polymer
• forms an amorphous crosslinked or highly crosslinked polymeric structure

Question 5

How can thermosetting polymer parts be made?

Answer 5

• Combine monomers with reinforcements
• shape and cure to solidify

Question 6

What is a thermoplastic polymer?

Answer 6

one that can be melted

Question 7

how can you process thermoplastics?

Answer 7

Melt them

Question 8

How can you make thermoplastic parts?

Answer 8

Melt polymer
combine with reinforcements
Shape and solidify

Question 9

What are the advantages of thermosets?

Answer 9

• Low viscosity reactants
• Good adhesion with reinforcement
• Thermal stability
• Chemical resistance
• Low creep

Question 10

What are the disadvantages of thermosets?

Answer 10

• Limited shelf life
• Long cure time
• Low strain to failure

Question 11

What are the advantages of thermoplastics?

Answer 11

• High impact strength
• High fracture toughness
• High strain to failure
• Good shelf life
• Short ‘cure’ time

Question 12

What are the disadvantages of thermoplastics?

Answer 12

• High melt viscosity
• Low creep resistance
• low thermal stability

Question 13

How does molecular weight affect thermoplastics?

Answer 13

Higher molecular weight gives improved properties

Question 14

What about amorphous thermoplastics gives improved properties?

Answer 14

entangled chains

Question 15

What about semi-crystalline thermoplastics gives improved properties?

Answer 15

aligned chains

Question 16

What is the order of common thermoplastic in terms of cost, modulus and strength?

Answer 16

Polypropylene
Polyamides(Nylons)
Polysulfones
Thermoplastic polyimides
Polyketones

Question 17

What is the structure and properties of polypropylene (PP)?

Answer 17

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

Question 18

What is the structure and properties of polyamides (Nylons)?

Answer 18

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

Question 19

What is the structure and properties of polysulfones?

Answer 19

aromatic contains SO2
backbone phenylene results in excellent performance
inflexible
strong stiff
tough
chemical +thermal resistance
polyphenylene sulfone too stiff

Question 20

What is the structure and properties of polyimides?

Answer 20

aromatic high performance
high temp performance
contain imide linkages
300*C

Question 21

What is the structure and properties of polyketones?

Answer 21

aromatic high performance containing ketone groups -C(O)-
Not as goog as polyimides but good heat resistance 250*C
EXPENSIVE

Question 22

What temperature are amorphous thermoplastics processed at?

Answer 22

above Tg (glass transition temp)
heating lead to disentanglement

Question 23

What temperature are semicrystalline thermoplastics processed out?

Answer 23

above Tm melting temp
melting of crystalline phase

Question 24

How does pultrusion work?

Answer 24

fibres and polymers pulled through heated die.
constant cross section
impregnation difficult

Question 25

How does extrusion and injection moulding work?

Answer 25

High shear polymer to melt and homogenise
Short fibres
properties limited by the amount of attrition the fibres experience

Question 26

How does sheet moulding work?

Answer 26

long fibres and thermoplastic powder tumbled together
Co-mingling thermoplastic fibres with reinforcing fibres
Component stamped out using hot press

Question 27

How does thermoplastic Pre-preg work?

Answer 27

Best properties
continuous unidirectional or woven fibres

Question 28

How does liquid processing of thermoplastics work?

Answer 28

short molecules that can be polymerised during the processing step using heat to cause polymerisation step