HIGH PERFORMANCE FIBRES Naveed Ahmed Fassana
Jan 21, 2018
HIGH PERFORMANCE FIBRES
Naveed Ahmed Fassana
INTRODUCTION
Definition
The fibre having tenacity greater than 20 g/denier are known as high performance fibres.
High-performance fibers are those that are engineered for specific uses that require exceptional strength, stiffness, heat resistance, or chemical resistance.
These fibers are driven by special technical functions that require specific physical properties unique to these fibers.
CONT….
Major applications for the highperformance fibres are transportation,aerospace, protective clothing, marine(ropes and sails), hostile thermal andchemical environments (replacement forasbestos) and leisure activities industries(golf clubs and tennis rackets).
INTRODUCTION CONT….
Commodity fibres
Volume driven Price oriented Large scale line-
production
High performance fibres
Technically driven Speciality oriented Smaller batch type
production
BASIC PROPERTIES
Strength
modulus
Heat resistance
Chemical resistance (acids, alkalies, solvents)
GENERAL APPLICATIONS
Antiballistic
Insulation batting
Fire resistant fabrics
Marine ropes
Hot gas filtration
ARAMIDS.
Para Aramids ( cut resistant )
Kevlar (Du Pont),Technora (Teijin), Twaron (Teijin)
Meta Aramids ( Fire Retardant )
Nomex (Du Pont) , Teijin conex (Teijin)
High Performance Fibers
All fibres except the cheapest commodity fibres are high performance fibres.
The natural fibres (cotton, wool, silk . . .) have a high aesthetic appeal in fashion fabrics (clothing, upholstery, carpets . . .)
100 years ago, they were also the fibres used in engineering applications –which are called industrial textiles.
High Performance Fibers
The maximum strengths of commercial nylon andpolyester fibres approach 10 g/den (~1 N/tex), with breakextensions of more than 10%.
The combination of moderately high strength andmoderately high extension gives a very high energy tobreak, or work of rupture.
Good recovery properties mean that they can stand repeated high-energy shocks.
.
High Performance Fibers
In the last quarter of the twentieth century, a second generation of manufactured fibres became available.
these high-performance fibres showed a step change in strength and stiffness.
They are high-modulus, high-tenacity (HM-HT) fibres.
Types Of Spinning
There are typically four types of spinning for polymers.
wet spinning.
dry spinning.
melt spinning.
gel spinning.
Wet Spinning
Wet spinning is the oldest process.
It is used for polymers that need to be dissolved in asolvent to be spun.
The spinneret remains submerged in a chemical baththat leads the fiber to precipitate, and then solidify,as it emerges out of the spinneret holes.
The name of the process i.e. wet spinning has got itsname from this "wet" bath only.
Acrylic fiber, rayon fiber, modacrylic fiber, and spandex fibers, all are manufactured through wet spinning.
MELT SPINNING
Melt Spinning is used for the polymeric fibers or thepolymers that can be melted.
The polymer is melted and then pumped through aspinneret.
The cooled and solidified molten fibers get collected on atake-up wheel.
The fibers, when stretched in both, the molten and solidstates, facilitate orientation of the polymer chains along thefiber axis.
Melt spun fibers can be forced through the spinneret indifferent cross-sectional shapes
DRY SPINNINGDope is fed from the feed-tank through pipes to the spinning cabinets
A metering pump is used for constant flow of dope and then it is fed to the spinning jet. But between the pump and spinning jet there is a candle filter which is used to give a final filtration and avoid trouble due to solid particles
The spinneret consists of a metal plate on which a number of small holes are drilled
The number of holes in the jet determines the number of filaments in the yarn
DRY SPINNING
In the cabinet, hot air is fed in near the bottom at a temperature of 100°C. This evaporates all the solvent in the dope emerging from the jets, and the solvent-laden air is withdrawn near the top of the cabinet and taken away to a recovery plant, where the solvent may be recovered.
Then the filaments passes through the feed roller from which it is guided onto a bobbin.
When the yarn has been collected on the bobbin it is ready for textile use and this method of spinning is called “dry spinning”.
GEL SPINNING
Gel spinning is used to make very strong fibershaving special characteristics.
The polymer here is partially liquid or in a "gel" state,which keeps the polymer chains somewhat boundtogether at various points in liquid crystal form.
GEL SPINNING
This bond further results into strong inter-chainforces in the fiber increasing its tensile strength.
The polymer chains within the fibers also have alarge degree of orientation, which increases itsstrength.
The high strength polyethylene fiber and aramidfibers are manufactured through this process.
GEL SPINNING
ARAMIDSNaveed Ahmed Fassana
Aramids-Nomex
Aromatic polyamides became breakthroughmaterials in commercial applications as early asthe 1960s, with the market launch of the metaaramid fiber Nomex® (Nomex® is a DuPontRegistered Trademark), which opened up newhorizons in the field of thermal and electricalinsulation.
Aramids (Kevlar & Twaron)
A much higher tenacity and modulus fiber wasdeveloped and commercialized, also by DuPont,under the trade name Kevlar® (Kevlar® is a DuPontRegistered Trademark) in 1971.
Another Para-aramid, Twaron® (Twaron® is aregistered product of Teijin), similar to Kevlar®, andan aromatic copolyamide, appeared on the markettowards the end of the 1980s.
TECHNORATechnora® (Technora® is a registered product ofTeijin) fibre. It is more flexible, high tenacity fibre.
The manufacturing process of Technora, reactsPPD and 3,4-diaminodiphenylether withterephthaloyl chloride,in an amide solvent such asN-methyl-2-pyrrolidone/CaCl2 to complete thepolycondensation.
The reaction mixture is neutralised and subjectedto spinning into an aqueous coagulation bath
The spun fibre is then brought to extraction ofsolvent,superdrawn at high temperature, andpassed through finishing to give the final product.
Polymer Preparation
Basic synthesis
Aramids are the fibers in which the fiber-formingsubstance is a long chain synthetic polyamide inwhich at least 85% of the amide (—CO—NH—)linkages are attached directly to two aromaticrings’.
Aramids are prepared by the generic reactionbetween an amine group and a carboxylic acidhalide group.
P-phenylene Terephthalamide(PPTA)
Aromatic polyamides of the PPTAtype are usually synthesized via alow-temperaturePolycondensation reaction basedon p- Phenylene diamine (PPD)and terephthaloyl chloride (TCl),
The Aromatic Polyamide Polymerization Process
NOMEXThe earliest representative of this class which was commercialized by
DuPont in 1967 was Nomex® aramid fiber. Its chemical formula is
Step 1: Dissolve PPD in mixture of HMPA (hexamethylphosphoramide) and NMP (N-methyl pyrrolidone)
Step 2: Cooling in an ice/acetone bath at -15oC in nitrogen atmosphere.
Step 3: Add TCL (terephthaloyl chloride) and stirrrapidly – paste like gel
Step 4: Discontinue stirring and allow the reaction mixture to stand for gradual warming to room temperature
Step 5: Agitate the reaction mixture with water to wash away solvent and HCL
Step 7: Collect the polymer by filtration
SYNTHESIS OF META ARAMIDS
Spinning of AramidFibers
Polymer Solution
Rigid chain macromolecules such as the aromatic polyaramids exhibit low solubility in many common solvent systems utilised in polymer technology
if the chains are relatively stiff and are linked to extend the chain in one direction, then they are ideally described in terms of a random distribution of rods.
CONT…
Now, as the concentration of rod-likemacromolecules is increased and thesaturation level for a random array of rodsis attained, the system will simply becomea saturated solution with excess polymer;or more interestingly, if thesolvent/polymer relationships are right,additional polymer may be dissolved byforming regions in which the solvatedpolymer chains approach a parallelarrangement. These ordered regions definea mesomorphic or liquid crystalline state.
SPINNING PROCESS OF ARAMIDS
Production of fibres initially involvesheating the spinning solution up to asuitable processing temperature, which isof the order of 80 °C for the highlyconcentrated solutions in 100% (water-free) sulphuric acid.
Polymer spinning solutions are extruded through spinning holes and are subjected to elongational stretch across a small air gap.
SPINNING PROCESS OF ARAMIDSAt this temperature, above a polymerconcentration of about 10wt% the solutionstate corresponds to a nematic liquidcrystalline phase. The concentration limitfor the polymer in spinning solution is20wt%. If concentrations above thiscritical limit are used, spinnability isaffected due to un-dissolved material;therefore the resulting fibre has inferiormechanical properties. Because theserod-like polymers are rigid, they orientatethemselves with respect to each other,forming a nematic phase
SPINNING PROCESS OF ARAMIDS
The spinning holes fulfill an importantfunction. Under shear, the crystaldomains become elongated andorientated in the direction of thedeformation.
In the air gap, elongational stretchingtakes place.
DRAW RATIO
This is the ratio of velocity of the fibreas it leaves the coagulating bath tovelocity of the polymer as it emergesfrom the spinning holes.
‘draw ratio’ can be fine-tuned to obtainhigher tenacities and moduli with lowerelongations and denier.
The resulting stretch in the air gapfurther perfects the respectivealignment of the liquid crystal domains.
CRYSTALLINITY AND ORIENTATION Overall, a higher polymer orientation inthe coagulation medium corresponds tohigher mechanical properties of thefibre.
The crystallinity and orientation of thesolution are translated to the fibre.
These factors allow the production ofhigh strength, high modulus, as-spunfibres. Fibres can exhibit three possiblelateral or transverse crystallinearrangements
EFFECT OF HEAT AND ORIENTATION ON TENACITY
Present para-aramid products have need of a very high molecular orientation (less than 12°), which has an almost directly proportional relationship to fibremodulus.The tenacity of a particular fibre material is also, but not only, governed by this molecular orientation angle. The modulus of the as-spun yarn can be greatly affected by the drying conditions, temperature and tension. Additional orientation inside the solid phase occurs during drying.
CONT…
Fibres prepared by a dry-jet wet-spun processhave a noteworthy response to very brief heattreatment (seconds) under tension. Thesefibres will not undergo drawing in theconventional sense, showing an extension ofless than 5% even at temperatures above500°C,but the crystalline orientation and fibremodulus is increased by this short-termheating under tension.As-spun fibre has anorientation angle of 12–15°; this decreases toabout 9°or less after heat treatment,with thefibre modulus increasing from 64GPa to over150GPa.The applications of these principles led
GENERAL CHARACTERISTICS
Good resistance to abrasionGood resistance to organic solvents but sensitive to Chlorine, Some Acids and Bases
Good thermal insulation Nonconductive under regular conditions, but can absorb water and salt water
No melting point, degradation starts from 500oC
Low flame-ability Good fabric integrity at high temperaturesSensitive to some acids and salts
The properties of aramid fibres depend on theparticular spinning and post-treatingconditions. In Table list the forms that arecommercially available, together with theirTEM (tenacity, elongation, modulus) properties.
Aramid Types
Type Tenacity
(mN/tex
Initial
modulus
(N/tex)
Elongation
at break
(%)
Kevlar ® 29 2030 49 3.6
Kevlar ® 49 2080 78 2.4
Kevlar ® 149 1680 115 1.3
Nomex ® 485 7.5 35
Twaron ® 2100 60 3.6
Twaron ® high modulus 2100 75 2.5
Technora ® 2200 50 4.4
PROPERTIES OF ARAMIDS FIBER
Aramid fibres have unique properties that setthem apart from other fibres. Aramid fibretensile strength and modulus are significantlyhigher than those of earlier organic fibres, andfibre elongation is lower.Aramid fibres can bewoven on fabric looms more easily than brittlefibres such as glass, carbon or ceramic. Theyalso exhibit inherent resistance to organicsolvents, fuels, lubricants and exposure toflame.
the tensile modulus of a fibre will be largelydetermined by the details of the molecularorientation about the fibre axis, and the effective
CONT…
For instance, in poly(pphenyleneterephthalamide), the polymer chains are verystiff, brought about by bonding of rigidphenylene rings in the para position.Incontrast, for Nomex® fibres, the phenyleneand amide units are linked in the metaposition, which results in an irregular chainconformation and a correspondingly lowertensile modulus. Also in PPTA, the presenceof amide groups at regular intervals along thelinear macromolecular backbone facilitatesextensive hydrogen bonding in a lateraldirection between adjacent chains.This, inturn, leads to efficient chain packing and high
WHY KEVLAR FIBER IS STRONGA single Kevlar polymer chain could haveanywhere from five to a million segments bondedtogether. Each Kevlar segment or monomer is achemical unit that contains 14 carbon atoms, 2nitrogen atoms, 2 oxygen atoms and 10 hydrogenatoms.
A Kevlar fiber is an array of molecules orientedparallel to each other like a package of uncookedspaghetti. This orderly, untangled arrangement ofmolecules is described as a crystalline structure.Crystallinity is obtained by a manufacturingprocess known as spinning, which involvesextruding the polymer solution through smallholes. The crystallinity of the Kevlar polymerstrands contributes significantly to its unique
CONT…
The individual polymer strands ofKevlar are held together by hydrogenbonds that form between the polaramide groups on adjacent chains.
The aromatic components of Kevlarpolymers have a radial orientation,which provides a high degree ofsymmetry and regularity to the internalstructure of the fibers. This crystal-likeregularity is the largest contributingfactor in the strength of Kevlar.
You can see that there are many similarities and differences between polymers. One of the similarities that seems related to strength is the presence of aromatic amides.
Mechanical Properties
Mechanical Properties Of Aramids
The mechanical properties of aramid materials underlietheir significant commercial utilisation in many areas.For instance, the as-spun Kevlar® aramid fibre exhibitsover twice the tenacity and nine times the modulus ofhigh strength nylon. On a weight basis it is strongerthan steel wire and stiffer than glass. Both creep and thelinear coefficient of thermal expansion are low and thethermal stability is high. The latter properties resemblethose of inorganic fibres and, of course, can beattributed to the extended chain morphology, highmolar mass and excellent orientation in a thermallystable structure that does not melt. Para-aramid fibreshave utility due to a combination of superior propertiesallied with features usually associated with organicfibres such as low density, easy processibility and rather
Creep
Creep is measured either by the lengthvariation under tension or by the stressdecrease at constant gauge length. Para-aramids, which exhibit little creep, differsignificantly from other highly orientedpolymeric fibres, such as HMPE fibres,whichcan break after several days underintermediate load due to their high creepproperties associated with a stress slip ofmolecules (compared to a structure-tightening in the case of para-aramids).Creep is affected by the temperature,theload relative to the fibre ultimate strength,
PROPERTIES OF COMMERCIALLY REPRESENTATIVE REINFORCEMENT FIBRES
Material Density
(g/m3)
Decomposition
melt
(Co)
Tenacity
(mN/tex)
Initial
Modulus
(N/tex)
Para-aramid standard 1.44 550 2065 55
Para-aramid H.M 1.45 550 2090 77
Nomex ® 1.46 415 485 7.5
Technora ® 1.39 500 2200 50.3
PA 66 1.14 255 830 5
Steel cord 7.85 1600 330 20
Carbon HT 1.78 3700 1910 134
Carbon HM 1.83 3700 1230 256
E-Glass 2.58 825 780 28
PROPERTIES AND END USES
The p-aramid fibres have a very highstrength, 5 times stronger than steel,little loss of strength during repeatedabrasion, flexing and stretching. It hasan excellent dimensional stability. Bothcreep and the linear coefficient ofthermal expansion are low and thethermal stability is high. The m-aramid fibres are used for theirexcellent heat resistance.
CONT…
Some of the main end-uses for meta-aramids are protective clothing, hot gasfiltration and electrical insulation. Para-aramids are used to replace asbestos inbrake and clutch linings, as tyrereinforcement, and in composites suchas materials for aircraft, boats, high-performance cars and sports equipment.Members of police forces and armedforces wear anti-ballistic aramidapparel.
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End Use End Use System Key Attribute
Composition Fabric for aircraft &
containers
Pressure vessels
Ship building
Sport goods
Plastics additive
Civil engineering
Light weight
High strength
High modulus
Good impact
strength
Wear resistance
Protective
apparels
Heat resistance work-wear
Fire blankets
Flame retardant textiles
Cut protective gloves
Cut protective seat cover
layers
Heat resistance
Flame retardation
Cut resistance
End Use End Use System Key Attribute
Tyers Truck & aircraft tyers
High speed tyers
Motorcycle tyers
Bicycle tyers
Low density
Weight saving
High tenacity
Dimensional
Low shrinkage
Puncture resistance
Mechanical
rubbers goods
Conveyor belt
Transmission belt
Hoses for automotive
Hydraulic hoses
Hoses in off -shore
Umbilical
High strength
High modulus
Dimensional
stability
Thermal resistance
Chemical
resistance
End Use End Use System Key Attribute
Friction
products and
gaskets
Brake linings
clutch facing
Gaskets
Thixotropic Additives
industrial paper
Fibre fibrillation
Heat resistance
Chemical resistance
Low flame ability
Mechanical
performance
Rope and
cables
Aerial optical fibre cable
Traditional optical fibre
cable
Electro cable
Mechanical cable
Mooring ropes
High strength
High modulus
Dimensional
stability
Low density
Corrosion resistance
Good dielectric
properties
Heat resistance
End Use End Use System Key Attribute
Life
protection
Bullet proof vests
Helmets
Property protection
panels
Vehicle protection
Strategic equipment
shielding
High tenacity
High energy
dissipation
Low density and
weight reduction
Comfort