The Fibre Phase Flashcards

1
Q

What is the diameter of whiskers?

A

10-100nm

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2
Q

What is the diameter of fibres?

A

5-15μm

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3
Q

What is the diameter of wires?

A

0.1-1mm

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4
Q

What are some aspects of whiskers?

A

-highly crystaline
- low flaws
- high strength
- high AR
- difficult to combine into a matrix
- expensive
- health concerns

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5
Q

What is the cost, modulus and strength of glass fibres

A

Low
Medium
Medium-hig

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6
Q

What is the cost, modulus and strength of carbon fibres

A

high
high-veryhigh
high-veryhigh

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7
Q

What is the cost, modulus and strength of Polymeric fibres?

A

medium-high
for all

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8
Q

Are glass fibreanisotropic or isotropic?

A

Isotropic
same proterties parallel to fibre direction as perpendicular

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9
Q

What is the chemical structure of glass fibres?

A

series of interconnected tetrahedral SiO2 groups repeated in 3D
- silicon at centre
- Oxygen at vertices
- strong covalent bonds

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10
Q

What are the 3 types of glass fibre used in composites and there properties?

A

E-glass(electrical) - good strength, stiffness, electrical and weathering properties CHEAP

C-glass(corrosion) - better corrosion resistance but lower strength

S-glass(strength) - Expensive but higher strength, tensile modulus and temp resistance

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11
Q

Applications of glass fibres

A

Marine
Automotive
Military
Construction
Storage
Baths

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12
Q

How are glass fibres manufactured?

A
  1. weigh and dry oxide powders
  2. refractory furnace, melt and homogenise @1370*C
  3. refiner to complete homogenisation and remove bubbles @1340*C
  4. Forehearth @1250*C for extrusion through platinum bushings
  5. Draw fibres at 60m/s
  6. Quench fibres using air or water
  7. Sizing
  8. Process
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13
Q

How is the diameter of glass fibres controlled?

A
  • Viscosity of the melt
  • Size of bushing holes
  • Drawing speed
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14
Q

What are different processing options of glass fibres?

A

Continuous strand - >100mm (long)
Chopped strand 3-100mm (short)
Hammer milled 30μm-3mm (particulate)

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15
Q

What does sizing do to glass fibres?

A
  • protect fibres
  • binds fibres together
  • lubricate fibres to reduce abrasion
  • impart anti static properties
  • Chemical link between fibres and matrix
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16
Q

What does a typical sizing consist of?

A
  1. Protective polymeric film (PVA)
  2. Small molecule acts as lubricant
  3. Coupling agent to promote adhesion (organosilane)
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17
Q

What happens when glass fibres readily absorb water?

A

Na and Ca are leached out leaving it porous and weak

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18
Q

What would an ideal sizing prevent for glass fibres?

A

water affecting surface whilst providing chemical link to matrix phase
Strong covalent chemical bonds 350kJ/mol

19
Q

What happens to the surface energy of the glass fibres in water?

A

reduces surface energy
if surface energy drops below liquid matrix, wettability of fibre is reduced and fibre-matrix is weakened

20
Q

What R group should be used for epoxy and phenolics?

A

Use γ-Aminopropyl Triethoxy Silane (GAPS)

21
Q

What R group should be used for unsaturated polyesters?

A

Use Methacryloxy Propyl Trimethoxy Silane

22
Q

What R group should be used for polyethylene and polypropylene?

A

Use Vinyl Trimethoxy Silane + peroxide

23
Q

What R group should be used for polycarbonate nylons

A

GAPS

24
Q

What is the chemical structure of carbon fibres?

A

hexagonal arrangement of carbon atoms into a flat basal plane or layer
- strong covalent bonds
van der waals interations

25
Q

what is the physical structure of carbon fibres?

A
  • outer skin more ordered graphitic carbon
  • inner skin less ordered turbostratic carbo
  • turbostratic moslty orientated along fibre acis but folds.
26
Q
A
27
Q

Are carbon fibres anisotropic or isotropic?

A

highly anisotropic
much stronger forces in fibre direction

28
Q

What are the 3 types of Carbon fibre

A

HM - high modulus
IM - intermediate modulus
HS - high strength

29
Q

Applications of carbon fibres?

A

Aerospace
Automotive
Sports

30
Q

How are most carbon fibres manufactured?

A

Polyacrylonitrile PAN
1. Textile fibre
2. Stretch
3. thermoset
4. carbonise 1000C inert atomsphere ( rid of O)
5. graphitize 2000-3000
C inert atmosphere (Removes any non carbon)
6. surface treatment
7. sizing

31
Q

What is a second way to manufacture carbon fibers?

A

Pitch
- stiffer but weaker

32
Q

What are 2 surface treatment options for carbon fibres?

A

Oxidative process (oxygenate surface)
Non-oxidative

33
Q

What are the oxidative surface treatments for carbon fibres?

A

Gas phase - O with inert carrier @high temp over time

Liquid phase - Strong liquid phase oxidising agents (nitric acid) or potassium permanganate

Electrolytic - similar to liquid oxidising agents used in electrolyte solution with fibres as 1 electrode

Plasma - plasma created from oxygen or air

34
Q

What are the non-oxidative surface treatments?

A

Whiskerisation - Grow small whiskers of SiC perpendicular to fibre surface

Sizing
- coat fibres in polymer emulsion (solution deposition)
- Deposit ionised polymer using fibre as electrode. initiate polymerisation within monomers (electro-deposition)

35
Q

How can polymeric fibres obtain high modulus and strength?

A

High performance rely on alignment of polymer chains

Extend chains when polymer is flexible

Align chains when polymer rigid

36
Q

How are Ultra High Molecular Weight Polyethylene (UHMWPE) made?

A

Gel-spinning hot drawing method
1. Dissolve PE in 0.5-5% decalin solution 150*C (removes chain entanglements)

  1. Spin fibres (extrude) 130*C (forms fibre, removes entanglement and orientation)
  2. Draw fibres under tension 155*C (provides most orientation)
37
Q

How are aramid fibres made?

A

Dry-jet-wet-spinning method

  1. dissolve in 15-20% conc H2SO4 solution ( forms crystal solution so rigid polymer chains align
  2. Spin fibres (extrude) 80*C (Forms fibre)
  3. Drawing needed only to reorient on exiting spinneret air gap
38
Q

Applications of UHMWPE

A

Ballistic protection personal/vehicles

39
Q

Application of aramids

A

kevlar
ballistics

40
Q

Properties of UHMWPE

A

High modulus and strength
low density, tough, chemically inert
low max usage temp

41
Q

Properties of aromatic polyamides?

A
  • high specific modulus and specific strength
  • low density and very tough
  • Poor in compression
  • Degrade in UV and absorb moisture easily
42
Q

Why is it hard to surface treat polymeric fibres?

A
  • fibres are highly aligned, stable polymer chains which depend on strong inter-chain interactions
  • Therefore difficult to bond to surface without compromising fibres
43
Q

How can the adhesion of polymeric fibres be improved?

A

Oxidative plasma surface treatment
short - oxidises surface improving wetability

Intermediate - crosslinking @ surface eliminates weak material

Long - pitted surface to be penetrated by resin (strength reduction)