The Fibre Phase Flashcards
What is the diameter of whiskers?
10-100nm
What is the diameter of fibres?
5-15μm
What is the diameter of wires?
0.1-1mm
What are some aspects of whiskers?
-highly crystaline
- low flaws
- high strength
- high AR
- difficult to combine into a matrix
- expensive
- health concerns
What is the cost, modulus and strength of glass fibres
Low
Medium
Medium-hig
What is the cost, modulus and strength of carbon fibres
high
high-veryhigh
high-veryhigh
What is the cost, modulus and strength of Polymeric fibres?
medium-high
for all
Are glass fibreanisotropic or isotropic?
Isotropic
same proterties parallel to fibre direction as perpendicular
What is the chemical structure of glass fibres?
series of interconnected tetrahedral SiO2 groups repeated in 3D
- silicon at centre
- Oxygen at vertices
- strong covalent bonds
What are the 3 types of glass fibre used in composites and there properties?
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
Applications of glass fibres
Marine
Automotive
Military
Construction
Storage
Baths
How are glass fibres manufactured?
- weigh and dry oxide powders
- refractory furnace, melt and homogenise @1370*C
- refiner to complete homogenisation and remove bubbles @1340*C
- Forehearth @1250*C for extrusion through platinum bushings
- Draw fibres at 60m/s
- Quench fibres using air or water
- Sizing
- Process
How is the diameter of glass fibres controlled?
- Viscosity of the melt
- Size of bushing holes
- Drawing speed
What are different processing options of glass fibres?
Continuous strand - >100mm (long)
Chopped strand 3-100mm (short)
Hammer milled 30μm-3mm (particulate)
What does sizing do to glass fibres?
- protect fibres
- binds fibres together
- lubricate fibres to reduce abrasion
- impart anti static properties
- Chemical link between fibres and matrix
What does a typical sizing consist of?
- Protective polymeric film (PVA)
- Small molecule acts as lubricant
- Coupling agent to promote adhesion (organosilane)
What happens when glass fibres readily absorb water?
Na and Ca are leached out leaving it porous and weak
What would an ideal sizing prevent for glass fibres?
water affecting surface whilst providing chemical link to matrix phase
Strong covalent chemical bonds 350kJ/mol
What happens to the surface energy of the glass fibres in water?
reduces surface energy
if surface energy drops below liquid matrix, wettability of fibre is reduced and fibre-matrix is weakened
What R group should be used for epoxy and phenolics?
Use γ-Aminopropyl Triethoxy Silane (GAPS)
What R group should be used for unsaturated polyesters?
Use Methacryloxy Propyl Trimethoxy Silane
What R group should be used for polyethylene and polypropylene?
Use Vinyl Trimethoxy Silane + peroxide
What R group should be used for polycarbonate nylons
GAPS
What is the chemical structure of carbon fibres?
hexagonal arrangement of carbon atoms into a flat basal plane or layer
- strong covalent bonds
van der waals interations
what is the physical structure of carbon fibres?
- outer skin more ordered graphitic carbon
- inner skin less ordered turbostratic carbo
- turbostratic moslty orientated along fibre acis but folds.
Are carbon fibres anisotropic or isotropic?
highly anisotropic
much stronger forces in fibre direction
What are the 3 types of Carbon fibre
HM - high modulus
IM - intermediate modulus
HS - high strength
Applications of carbon fibres?
Aerospace
Automotive
Sports
How are most carbon fibres manufactured?
Polyacrylonitrile PAN
1. Textile fibre
2. Stretch
3. thermoset
4. carbonise 1000C inert atomsphere ( rid of O)
5. graphitize 2000-3000C inert atmosphere (Removes any non carbon)
6. surface treatment
7. sizing
What is a second way to manufacture carbon fibers?
Pitch
- stiffer but weaker
What are 2 surface treatment options for carbon fibres?
Oxidative process (oxygenate surface)
Non-oxidative
What are the oxidative surface treatments for carbon fibres?
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
What are the non-oxidative surface treatments?
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)
How can polymeric fibres obtain high modulus and strength?
High performance rely on alignment of polymer chains
Extend chains when polymer is flexible
Align chains when polymer rigid
How are Ultra High Molecular Weight Polyethylene (UHMWPE) made?
Gel-spinning hot drawing method
1. Dissolve PE in 0.5-5% decalin solution 150*C (removes chain entanglements)
- Spin fibres (extrude) 130*C (forms fibre, removes entanglement and orientation)
- Draw fibres under tension 155*C (provides most orientation)
How are aramid fibres made?
Dry-jet-wet-spinning method
- dissolve in 15-20% conc H2SO4 solution ( forms crystal solution so rigid polymer chains align
- Spin fibres (extrude) 80*C (Forms fibre)
- Drawing needed only to reorient on exiting spinneret air gap
Applications of UHMWPE
Ballistic protection personal/vehicles
Application of aramids
kevlar
ballistics
Properties of UHMWPE
High modulus and strength
low density, tough, chemically inert
low max usage temp
Properties of aromatic polyamides?
- high specific modulus and specific strength
- low density and very tough
- Poor in compression
- Degrade in UV and absorb moisture easily
Why is it hard to surface treat polymeric fibres?
- fibres are highly aligned, stable polymer chains which depend on strong inter-chain interactions
- Therefore difficult to bond to surface without compromising fibres
How can the adhesion of polymeric fibres be improved?
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)
