Modern Fibres

MODERN FIBRES
WOOL RESEARCH ASSOCIATION
By ,
SUDEEP SHAW

Man made fibers
• Nylon Polyester Olefin PAN
• Rayon Elastomeric (Spandex)

The step change in strength and stiffness from first generation to
second generation manufactured fibres.

A fibre that is specially designed and
manufactured to give some specific
performance characteristics under some
specific ambient conditions.
Such as : HM-HT Fibres
- Kevlar, PBO, UHMWPE, Carbon.
Thermally Resistant Fibres.
- Nomex, Kevlar, PBO, Carbon.
Definition of High-Performance Fibre

 Linear Polymers
- Kevlar, PBO, UHMWPE, etc.
 Two Dimensional Networks
- Carbon Fibres
 Three Dimensional Networks
- Glass & Ceramic Fibres
HM-HT Fibres fall into three groups :

• Sufficiently high polymer chain lengths.
• High degree of orientation among the
polymer chains.
• High degree of crystallinity.
A diagram drawn by Staudinger, which is the ideal form of a linear-
polymer fibre with high strength & stiffness
Requirements of a linear polymer to act as
a HM-HT Fibre :

Very high chain flexibility in polymer melt / solution
Leads to high degree of entanglements of the polymeric chains
Extremely difficult to remove / open-up these entanglements
during drawing process
Thus such a structure with high strength & high modulus can not be
achieved.
The main constraint towards achieving
such a structure

• Using polymeric chains of rigid in nature, so
that their flexibility will be low and it will be
easy to orient them and chances of formation
of entanglements will be low.
• Using flexible polymeric chains, but by some
means preventing the formation of
entanglements right at the polymeric-melt /
solution state.
Two ways to solve the problem

Classification of Linear HM-HT Fibres

Rigid rod-like polymers shows a particular
state, which is known as liquid crystalline
polymer state , and therefore sometimes
called LCP.
Liquid crystals are of two types –
 Lyotropic liquid crystal ( KEVLAR, VECTRAN ).
 Thermotropic liquid crystal ( PBO ).
Liquid Crystalline Polymer ( LCP )

Polymer Solvent
Increase in polymer concentration
( Viscosity increases )
Isotropic solution
Lyotropic Liquid Crystalline Solution(Viscosity starts
decreasing and reaches a lowest
value)
Solid
Lyotropic liquid crystal

Polymer ( Chip-form /
Δ T Direct from polymerisation Reactor )
Viscosity decreases
Isotropic polymer melt
Δ T
Viscosity decreases
Thermotropic Liquid Crystalline Melt ( Vicosity reaches
lowest value and then starts
increasing )
Δ T
Viscosity increases
Isotropic polymer melt
Thermotropic liquid crystal

 A manufactured fiber in which the fiber-forming
substance is a long-chain synthetic polyamide in which at
least 85% of the amide (-CO-NH-) linkages are attached
directly between two aromatic rings .
• Invention
• DuPont – Morgan, Kwolek et. al.
Aromatic Polyamides
“Aramids”

• Diamine and diacid chloride – DuPont
• Low temperature
• Monomer purity and concentration
• Amide solvent (NMP, HMPA, DMA)
 A lot of structural diversity can be introduced into these polymers by
changing the identity of the aromatic groups in the monomers.
Solution Polycondensation

Dry-jet Wet Spinning
• Spinning Solution
– 10-20 wt% polymer
– 100% H2SO4(H2O free)
• Elongation aligns
crystalline domains
• Precipitates out of
coagulation bath
• Crystallinity of solution
is translated to fiber
• paraaramids show LC due to the rigidity of their chains which comes
from the para linkages between all the aromatic groups
Aramid Fiber Spinning (p-Aramids)

• Poly(m-phenylene isophthalamide) Nomex®
• First commercial aromatic polyamide.
• spun from isotropic solutions (not liquid
crystalline like Kevlar) so it has greater
flexibility than Kevlar fibers.
NOMEX

• Poly(p-phenylene terephthalamide) (PPTA)
Kevlar®
• DuPont – Bair, Blades, Morgan, Kwolek
• AKZO – Leo Vollbracht, Twaron®
KEVLAR

 Positive Attributes :
• High tensile strength (five times stronger per
weight unit than steel);
• High modulus of elasticity;
• Very low elongation at breaking;
• Low weight;
• High chemical inertness;
• Very low coefficient of thermal expansion;
• High Fracture Toughness (impact resistance);
• High cut resistance;
• Flame resistance
Properties of Kevlar Fibre

 Negative Attributes :
• very low resistance to axial compression
typically around 20% of the corresponding
tensile strength
• fibres break into small fibrils (fibres within the
fibre)
• fibres are hygroscopic (they absorb water)
• fibre surfaces are susceptible to degradation
by ultraviolet light.
Properties of Kevlar Fibre
( contd. )

KEVLAR
NOMEX
Applications of Aramids

• Thermoset polurethane synthetic material.(aromatic hetrocylic polymer).
• Trade name: Zylon, produced by Toyobo Corpn, japan since 1998.
• Condensation polymerisation of 4,6-diamino-1,3- benzenediol
dihydrochloride (DABDO) or Diamino resorcinol with terephthalic acid
(TA).
• Dry-jet Wet Spinning
• 15-18 wt% polymer
• Spinning Solution
• 77% PPA at 60-80°C
High degree of polymerisation (between 82–84%)
PBO
Poly(p-phenylene benzobisoxazole)

Characteristics
•The poor compressive strength of these fibres restricts their use in composites.
• Characterised by high rigidity and form highly ordered structures.
• PBO fibres exhibit very high flame
resistance and have exceptionally
high thermal stability.
•Extremely high tensile strength, an
extremely high modulus.
•Uses: •Fire fighting , bullet proof vest , race yacht sail , aero space etc.
•Ideal for heat and flame resistant work-wear such as for fire
fighters, Motorcycle suits, gloves, hot gas filtration media etc.
•General applications for reinforcement include those for tyres,
belts, cords, etc.

The backbone of polyethylene is highly
flexible, because of the possibility of rotation
around “C – C’’ bonds and because the only
other element present is light hydrogen.
- Thus a high degree of entanglement is
present in normal industrial grade PE.
UHMWPE

• In ‘ C ’- axis direction, diamond is composed of
fully aligned zig-zag chains of carbon just like those in
polyethylene.
• Young modulus of diamond is 1160 GPa and the
cross-sectional area per chain is 0.0488 nm2
• While for polyethylene it is 0.182 nm2
, i.e.- four
times higher.
• From this analogy we can expect a modulus of 285
GPa for fully aligned polyethylene, well above that of
steel.
- But, the normal industrial grade HDPE has a
modulus of only 5 GPa.
Frank has offered an elegant explanation of the physical basis
for this high modulus offered by UHMWPE

1) Theoretical modulus of this polymer is very
high.
2) Availability of high molecular weight
material.
3) It has high crystallinity and fast crystallizing
property.
4) The structure of the polymer chain is zig-zag
linear, without any bulky side-groups.
5) Low intermolecular interactions.
Then, why PE was chosen for preparing
HM-HT Fibre ?

UHMWPE HDPE
Macromolecular Orientation
- Therefore we are required to prevent the formation of
entanglements at the polymer- melt / solution state.
Macromolecular structure of UHMWPE &
HDPE

• First , in the well-known melt-spinning and hot
drawing route ( followed for PET, Nylon ); by
which a maximum modulus of 60 GPa and
tenacity of 1.3 GPa was achieved.
• Second, through Gel-Spinning and subsequent
drawing.
This process was first invented and patented
by Smith & Lemstra ( DSM High-Performance
Fibres ). The fibre they had produced had a
modulus of 200 GPa and tenacity of 7 GPa .
The earlier research work was carried out
in two different directions

GEL SPINNING
Thus the prevention of the formation of
entanglements at the solution state is possible
through -----

a ) Dissolution, b) Spinning, c) Drawing
Steps involved in GEL Spinning

Solution of UHMWPE of Mol. Wt.- 30 to 60 Lacs, for
polymer concentration of 0.65 to 0.40 g/100 ml. , using
Decalin / Paraffin oil as solvent
Heated to 100 – 130 °C, with continuous stirring for
proper dissolution
Cooled down to room temerature which forms
spherulites, and gets precipitated
( contd. )

spherulites are separated and mixed with proper amount of
decalin / paraffin with rigorous stirring to obtain 10 % wt
solution
At the point , where spinning stress is applied, the
temerature is increased to 130 – 140 ° C, so that the
spherulites are destroyed
Water is used as the non-solvent in the extraction bath and
a draw-ratio of upto 100 – 200 is applied during subsequent
drying, to achieve high orientation.
( contd. )

 Density - ≈ 0.90-0.93 g/cc
 Moisture Regain - ≈ 0 %
 Tenacity - ≈ 3 GPa or 22-24 g/den
 Modulus - ≈ 120-180 GPa or 900-1400 g/den
 Elongation - ≈ 2.5-3.5 %
 High Abrasion Resistance ( Inspite of having high modulus )
 Chemically inert to most acids & alkalis upto
100 ° C.
 Impact resistance very high.
Properties of UHMWPE

 Creep High
 Thermal properties not good.
Melting Temp - ≈ 160-165 °C
Has to be used in an atmosphere where the
temperature does not increase above 120 °C
 Poor adhesion properties
Properties of UHMWPE ( contd. )

Specific strength vs Specific modulus of various fibres
Comparison of some of the properties :

Abrasion & Flex life of various fibres
Comparison of some of the properties :

 Ballistic Protection :
Dyneema UD & Spectra Shield are used for ballistic
protection. These are made of unidirectional layers, in which
yarns are not woven but lie parallel to each other and are
bonded by various thermoplastic matrices.
Construction of Dyneema UD & Spectra shield
Applications of UHMWPE

 Why UHMWPE is most suitable for ballistic
protection ?
1) Very high strain wave propagation rate ( 12300 m/sec; for KEVLAR it is
7000 m/sec ), due to low fibre density.
R = K.W.C
= K.W. √ ( Ef / ρf )
[ R = Energy applied by the bullet/ Energy that can absorbed by the
substrate.
K = Constant depending on various parameters.
W = Energy required to break per unit fibre length.
C = Starin wave propagation velocity.
Ef = Modulus of the fibre.
ρf = Density of the fibre. ]
Applications of UHMWPE ( contd )

2 ) Very high impact resistance
- It’s glass transition temp ( - 10 ° C ) is below the
room temperature, therefore in room temperature the
material is in rubbery state and thereby giving a high impact
resistance.
3 ) UHMWPE has the highest rate of increase in modulus , with
increase in rate of loading.
- Thereby showing very high modulus at the
moment of impact.

 Damage Tolerent Radar Domes :
UHMWPE has very low dielectric constant ( 2.25
at 22 °C and 10 6
Hz ), thereby being more or less
transparent to the waves. Thus loss due to reflection
is low.
Moreover, high degree of structural intigrity,
high impact tolerence are the essential properties of
radar domes.

 Ropemaking :
Where the number of contact points are
very high, there the rope that is being used,
should have high strength & modulus; as well
as very high abrasion resistance.
Moreover light-weight, floatability,
flexibility, low moisture absorption and
outstanding flex fatigue performance makes
UHMWPE most suitable for this purpose.

 Composites :
UHMWPE fibres in non-ballistic composites are mainly
used to improve the impact resistance and the energy
absorption of glass or carbon fibre reinforced products.
Hybrid fabrics with glass or carbon can be used and the
fibre or the fabric can be plasma treated to improve the
adhesion of the matrix to the fibre. The matrix material is
normally an epoxy or polyester resin.
The basic limitation here is that the curing temperature
should not exceed 140°C.

 Medical Application :
Sutures, artificial ligaments, medical
transplants .

Schematic structure of graphite
CARBON FIBRE

In late 1950s & early 1960s three groups were involved in
serious efforts to produce high strength carbon fibre.
 Research group at Wright Patterson Air Force Base in Dayton,
Ohio, USA ;using viscose rayon as the precursor.
 Shindo in the Industrial research Institute in Osaka, Japan, using
PAN as the precursor.
 Watt, Johnson and Phillips in the Royal Air crafts Establishment
in Farnborough, England, using PAN as the precursor.
Early Research-Works

1) During pyrolysis the precursor material should not melt, and
maintain it’s filament form.
2) Precursor material should give high amount of carbon yield.
3) A stabilization step is required to make the material thermally
stable and infusible.
4) A step involving preferential orientation of the graphitic layers ,
i.e- carbonization step is required to be carried out.
5) The hexagonal structure formation that starts at carbonization
step , must be completed perfectly & properly; for which
graphitization process need to be carried out.
Important requirements for the Production
of carbon fibre :

 PAN-Based Precursor Process
 Rayon-Based Precursor Process
 Pitch-Based Precursor Process
Commercially used Precursor Processes :

 Most widely used ( 90 % market share).
 Comparatively higher carbon yield than
the rayon process.
 PAN in filament form is used for this
purpose.
 Most cost effective process.
PAN-Based Precursor Process :

1) Stabilization : First two steps that are involved in stabilization
of PAN are cyclization and dehydrogenation which is carried out
at a temperature of 200 - 220°C.
Steps involved in PAN-Based Precursor
Process :

The third step involved in stabilization is oxidation, which is
carried out at a temperature of 220 – 300°C in the presence of
air and thereby forming hydroxyl, carbonyl and carboxyl
groups on the ladder polymer.
In this process the material gets fully stabilized and becomes
infusible.
Process : ( contd. )

2 ) Carbonization ( under tension ) :
The black oxidized fibre is heated slowly to a temperature
of 1000 – 1500°C in an inert atmosphere ( N2 ) under tension
resulting in elimination of low molecular wt. gaseous products
( HCN, NH3 , H2 , CO, CO2 ).

3 ) Graphitization ( under stretch ) :
The carbonized filaments are heat treated at 1500 – 2700°C
in an inert atmosphere ( Ar ) under 30 % stretch, when the
structure becomes more ordered and turns towards a true
graphitic form, with the elimination of nitrogen ( N2 ).

 Almost an obsolete process (2 % market share ).
 Rayon in filament form is used for this purpose.
 Carbon yield is very low ( ≈ 20 % ).
 Resultant product has many defects &
imperfections.
 During graphitization almost 300 % stretch is
required, which makes the process costlier &
difficult.
Rayon-Based Precursor Process :

Pitch-Based Precursor Process :
 Comparatively newly developed process ( 8 % market share).
 No tension is required to be applied in this process.
 The final material has very high degree of purity ( upto 99.9 %).
 The resultant carbon fibre ( Ultra High Modulus ) has very high
modulus .
 Meso-Phase pitch is converted into filament form for
further processing.
 Costlier process.

Comparison of carbon fibres produced from
different precursors :

Comparison of different types of carbon
fibres
Carbon-fibre
type
Tensile
Strength
( GPa )
Tensile
Modulus
( GPa )
Breaking
Elongation
( % )
Density
( g/cm3
)
Carbon
Content
( wt % )
Electrical
Resistivity
(x 10– 4
Ω cm)
Low Strength 2.5 – 3 240 – 270 1.2 – 1.4 1.7 – 1.8 92 – 93 15 – 16
High
Strength
3.8 – 4.3 240 – 270 1.2 – 1.4 1.7 – 1.8 92 – 93 15 – 16
Ultra-High
Strength
4.7 – 4.9 250 – 270 1.2 – 1.4 1.7 – 1.8 93 – 94 15 – 16
Intermediate
Modulus
5.7 – 6.0 ≈ 300 1.2 – 1.4 1.7- 1.8 95 – 96 17 – 18
High
Modulus
2.5 – 3.0 380 – 400 0.6 – 0.7 1.8 – 1.9 > 99.0 9 – 10
Ultra-High
Modulus
3.8 – 4.0 530 - 540 0.3 – 0.4 1.9 – 2.1 > 99.9 6 – 7

 High strength & high modulus.
 High temperature resistance ( upto 2400 –
2500°C )
 Not subjected to creep or fatigue failure.
 Good electrical conductivity.
 Chemical & biological inertness.
Properties of carbon fibre :

 Low impact strength / compressive strength.
 Carbon fibres are expensive.
Properties of carbon fibre :
( contd. )

 Carbon fibre rarely used alone.
 Major use is reinforcement in composites.
 Crabon fibre surface is very smooth, due to
graphitization and relative chemical inertness of
carbon atoms.
 Thus resin bonding in case of carbon fibre
composite production becomes difficult;
resulting in low Interlaminar Shear Strength
( ILSS ).
 Plasma treatment and different chemical
treatments are applied to modify the fibre
surface.
Surface treatment of carbon fibres :

Surface treatmet of carbon fibres :
( contd. )

 Aerospace & Aviation :
 Booster rocket casing of US Space
Shuttles
 Satellite antennas
 Rocket nosel cone
 Air-craft main-wings
& tail-units
 Helicopter blades
Applications of Carbon fibre :

 Industrial :
 Shuttles in textile machinery
 Machinery items such as turbine,
compressor, bearings, gears, etc.
 Windmill blades
 Industrial high pressure gas cylinder
 Concrete reinforcement composites
( contd. )

 Sports & Leisure :
 Tennis & badminton racquet handles
 Pole vaulting pole
 Golf-club shafts
 Skis
 Fishing rods
 Bi-cycle frames, wheels
 Racing car & bike components
( contd. )

 What is Glass?
Glass is an amorphous solid, with isotropic three –
dimensional network.
“ American Society for Testing
and Materials ’’ ( ASTM ) defines glass
- as an inorganic product of fusion
which has been cooled to a rigid
condition without crystallizing .
Glass Fibre

• A: high alkali grade ( Soda-lime glass )
– originally made for window glass
• C: chemical resistance or corrosion grade
– for acid environments
• D: low dielectric
– good transparency to radar: Quartz glass
• E: electrical insulation grade
- the most common reinforcement grade (E ~70 GPa)
• M: high modulus grade
• R: reinforcement grade
– European equivalent of S-glass
• S: high strength grade (a common variant is S2-glass)
– fibre with higher Young’s modulus and temperature resistance
– significantly more expensive than E-glass
Different classes of Glass Fibre

Glass forming Oxides
Oxide % in E-
glass
% in S-
glass
Effect on Fibre Properties
SiO2
54 65 very low thermal expansion
Na2
O trace trace high thermal expansion, moisture sensitivity
K2
O - - high thermal expansion, moisture sensitivity
Li2
O - - high thermal expansion, moisture sensitivity
CaO 17.5 trace resistance to water, acids and alkalis
MgO 4.5 10 resistance to water, acids and alkalis
B2
O3
8.0 trace low thermal expansion
Al2
O3
14 25 improved chemical durability
Fe2
O3
trace trace green colouration
ZnO - - chemical durability
PbO - - increased density and brilliance (light transmission)
and high thermal expansion
BaO - - high density and improved chemical durability
TiO2
improved chemical durability especially for alkali

Steps involved in Glass-Fibre
manufacturing :

 Density : ( 2.48 – 2.55 ) g/cm3
 Tenacity : ( 11 – 21 ) gpd
 Modulus : ( 320 – 390 ) gpd
 Elongation : ( 3 – 5.3 ) %
 Maximum usable temperature : ( 300 – 350 )°C
 Low thermal & electrical conductivity.
 Being a three-dimensional isotropic structure, the
mechanical properties along the fibre axis are the
same as transverse to the axis, resulting in good
compressive strength; which is ideal for use in
composites.
Properties of Glass Fibre

 Composites : Glass fibre reinforced plastics
for industrial & automotive applications, in
various components of lightweight aircrafts, in
sports & leisure activities.
 Thermal & Electrical Insulation
 Optical Fibres
Applications of Glass Fibre

 Advantages of Optical fibre compared to
conventional copper-wire for telecommunication :
1) High information carrying capacity.
2) Low electromagnetic interference.
3) Higher chemical & thermal stability.
4) Light weight.
 Applications :
Telecommunication, Medical application ( Laser ballon
angioplasty ), etc.
Optical Fibre

 The working principle of optical fibre is based
upon Total Internal Reflection of light.
Optical Fibre
( contd. )

Optical Fibre
( contd. )
Commercially Silica-Glass Ge- doped optical
fibres are used.[ Normal SiO2 in the cladding
and Ge-doped SiO2 in the core ]
 Different doping agents are used to increase
or decrease refractive index.
Ge, P, Cl Increases R.I.
F, B Decreases R.I.

Types of Optical Fibre
( contd. )

Fibre type Density
(g/cm3
)
Strength
(gpd)
Elongation
( % )
Modulus
(gpd)
Maximum
Use temp.
( °C )
Kevlar 1.43-1.47 20-26 1.5-3.6 430-1100 200
Nomex 1.38 5 22 140 200
Vectran 1.47 25 2-2.25 700 150
PBO 1.54-1.56 42 2.5-3.5 1300 300
Spectra 0.97 32 3.5 1800 120
Carbon 1.7-2.1 16-40 1.2-1.4 1510-3200 2400-2500
Glass 2.48-2.55 11-21 3-5.3 320-390 300-350
steel 7.8 11 4.8 220 500
Summary

Modern Fibres

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