Aramid FibresMukesh Kumar Singh

High PERFORMANCE FIBREA fibre that is specially designed and manufactured to give some specific performance characteristics under some specific ambient conditions Example HM-HT Fibre Kevlar, UHMWPE Fibre, PBO Thermal resistant Nomex, Kevlar, PBO, Carbon

History Nomex -1960Kevlar- 1971Twaron (by Teijin ) 1980 by Ozawa &MatsudaLast 20 years: structure and properties of Aramid

Definition United States Federal Trade Commission 1974Aramid ia 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.p-phenylene terephthalarnide (PTA), of which Kevlar fibres are made

Aramid manufacturingBy reaction between amine and carboxylic acid halide group to synthesize AB homopolymer

Similarly AABB homopolymer can also be synthesized

Polymerization Polycondensation

ProcessDissolve PPD in a mixture of hexamythylphosphoramide (HMPA) and N-methylpurrolidone (NMP)

Cooling in ice/ecetone to -15C in N2 atmosphere

Add TCL with rapid stirring: paste like gelStand overnight with gradual warming to room temp

Resultant mixture is agitated with water to wash solvent and HCLPolymer is collected by filteration

History of AramidAromatic polyamides were first introduced in 1960s, with a meta-aramid fiber produced by DuPont under the tradename Nomex. Meta-aramid is also produced Teijin: Conex Kermel France: Kermel

ProductionWorld capacity of para-aramid production is estimated at about 41,000 tons/yr in 2002 and increases each year by 5-10%. In 2007 this means a total production capacity of around 55,000 tons/yr.

Aramid Fibre Production Polymer solvent for spinning PPTA is generally 100% (water free) sulfuric acid (H2SO4).The aromatic polyamide solution processing temperature is of the order of 80C for the highly concentrated solution in 100% sulphuric acid.At this temperature, the solution state corresponds to a pneumatic crystalline phase. The degree of orientation of these polymer chains depends on solution temperature and polymer concentration. The radial crystalline orientation can only be brought about using the dry-jet wet spinning process. Kevlar fibres have a very high molecular orientation, which has an almost directly proportional relationship to fibre modulus and is highly dependent on drying conditions, temperature and tension. By applying the above parameters properly high tenacity Kevlar fibres can be obtained

Monomers are made up of fourteen Carbon atoms, two Nitrogen atoms, two Oxygen atoms and ten Hydrogen atoms.

A single Kevlar polymer chain could possibly have anywhere from one to five million monomers bonded together.

Kevlar Kevlar is the trade name (registered by DuPont Co.) of aramid (poly-para-phenylene terephthalamide) fibers. Kevlar fibers were originally developed as a replacement of steel in automotive tiresKevlar is high impact resistance and low density fibre

SpinningSolution is prepared by using H2SO4 as solvent (100% free from water)Solution is heated to 80CSolution solid content 10%

Gel spinning

Liquid crystalline solution

Semi-crystalline polymer like nylon 6Kevlar

Atomic configuration

Properties of Kevlar FibreHigh tensile strength (five times stronger per weight unite than steel)High modulus of elasticityVery low elongation up to breaking pointLow weightHigh chemical inertnessVery low coefficient of thermal expansionHigh Fracture Toughness (impact resistance)High cut resistanceTextile processibilityFlame resistance (burning starts at 427C

051015201234Elongation (%)Specific stress (N/tex)PolyamidePolyesterSteelS-GlassAramidCarbon-HSHDPE

Moisture attraction by KevlarX-ray data have shown that the water molecules from moisture uptake do not enter the unit cell of the crystal lattice. Hence, the amide-water molecular interactions are likely to be confined to the polymer chains on the surface. Secondly, the presence of microvoids on the surface

Limitations of Kevlar FibreVery low moisture regain Very difficult to cutLow compressive strength

Physical properties of materials

MATERIALUltimate Strength MPaDensity g/cm3Spectra fiber (UHMWPE)2300-3500.97Kevlar (ARAMID)27571.44Carbon Fibre41371.75Carbon laminate16001.5E Glass Fibre34502.57E Glass laminate15001.97Polypropylene19.7-80.91S Glass Fibre47102.47Spider Silk10001.3Steel alloy ASTM A364007.8Epoxy12-301.23Nylon751.15

Modulus of materials

MaterialYoung's Modulus GPaPTFE (Teflon)0.5Rubber (small strain)0.010.1PTFE (Teflon)0.5Low density polyethylene0.2UHMWPE (such as Dyneena or Spectra).7Polypropylene1.5-2 Nylon24Pine wood (along grain)8.963Glass-reinforced plastic (70/30 by weight fibre/matrix, unidirectional, along grain)4045Carbon fiber (depends on direction and type)300-400Carbon fiber reinforced plastic (70/30 fibre/matrix, unidirectional, along grain)181Steel200Single-walled carbon nanotube1,000+

Molecular requirement of Aramids

Improvement Polymeric composition Thermal resistance Wholly aromatic polyamide, absence of unstable linkage (urethane, urea, alkylene etc.) Solubility Copolymer with dissymmetrical units inclusion of O-, -CO-, -SO2- etc., amides rather than estersDrawing potentialHigh molecular weightEnhanced chain flexibility by incorporating -O-, -CO-, -SO2-, etcDimensional stabilityRigid molecular chain, crystallinity

Chemical properties of KevlarAramid Fibers are Chemically quite ResistantAramids are not sensitive to organic solvents or oil.Kevlar, Twaron and other Aramids are sensitive to strong acids, bases, and certain oxidizers, like chlorine bleach* (sodium hypochlorite). Exposure to these cause degradation of the fiber. Regular chlorine bleach (e.g. Clorox) cannot be used with Kevlar, oxygen bleaches such as sodium perborate (e.g. OxiClean) can be used without damaging the Aramid fiber. Hydrogen Peroxide cannot be used to whiten Aramid though.This is important for anyone cleaning boat ropes or sails containing Kevlar. Polyester (Dacron) is not particularly sensitive to bleach but Kevlar's strength will be destroyed! Nylon is also attacked by bleachMost organic solvents (oil) have little effect on the material, and most salt solutions (sodium chloride) have no effect on Kevlar fiber. However, strong acids and bases (hydrochloric acid and sodium hydroxide) at high concentrations or elevated temperatures are able to attack Kevlar fiber.

Types of Kevlar fibreKevlar 29 high strength (3600 MPa), low density (1.44 g/cc3), used for bullet-proof vests, composite armor reinforcement, helmets, ropes, cables, asbestos replacing parts

Kevlar 49 high modulus (131 GPa), high strength (3800 MPa), low density (1.440 g/cm) used in aerospace, automotive and marine applications

Kevlar 149 ultra high modulus (186 GPa), high strength (3400 MPa), low density (1.470 g/cm) highly crystalline, used as reinforcing dispersed phase for composite aircraft components.

All trans polyamide stretches fully to form a wonderful Aramid fibre, Kevlar

Applications of KevlarKevlar may protect carbon fibers and improve their properties: hybrid fabric (Kevlar + Carbon fibers) combines very high tensile strength with high impact and abrasion resistance The most popular matrix materials for manufacturing Kevlar (aramid) Fiber Reinforced Polymers are Thermosets such as Epoxies (EP), Vinylester and Phenolics (PF)

Kevlar Fiber Reinforced Polymers are manufactured by open mold processes, closed mold processes and Pultrusion method

Aramid BrandsNomexAramid fibre reinforced for sealing friction

Conveyor beltsTechnoraSulfronAramid fibre: Kevlar

Aramid BrandsAramid /PVC: Clad for optical fibreAramid fibre honeycombAramid fibre braided sleeve Sharx

Ultra-High-Molecular-Weight-Polyethylene (UHMWPE) fibers

CCHHHHnN=40,000

Solvent for UHMWPE: Decaline

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