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.

1)

2)

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