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Classes of Polymeric MaterialsChapter 3: Thermosets

Professor Joe Greene

CSU, CHICO

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Thermosetting Resins (thermosets)• Introduction

– Thermoplastics are supplied as pellets, powders, or granules and do not undergo a chemical reaction.

• Thermoplastics have large molecular weights & long molecules• The high viscosities are reduced by high temperatures

– Thermoset resins are supplied as liquid chemicals (low MW and low viscosity) and undergo a chemical reaction that features polymerization and crosslinking.

• Liquid chemicals have short chains that polymerized into long chains and high molecular weights and high viscosity.

• The chains are crosslinked (attached) to each other to make a stiff molecule• Rubbers involve cross-linking of already polymerized molecules to stiffen the

molecules together in Vulcanization• Heat is needed to cause polymerization to build MW and to cause stiffening of

molecule through cross-linking• Heat reduces the viscosity of the chemicals until the reaction occurs and then

causes the viscosity to get very large during crosslinking.

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Thermosetting Resins (thermosets)• Types of thermosets

– Temperature activated– Catalyst activated– Mixing-activated

• Temperature activated Fig 3.84– All thermosets require heat to undergo chemical reaction

• Lower temperature thermosets (room temperature cure) react to a more rubbery polymer that gets stiffer upon additional heat.

• Pot life: time that it takes for the thermosets to react to a solid after mixed.• Gel time: time it takes for two liquid thermoset polymers that are mixed to form a gel

or skin (and stop flowing)

– Several thermosets are supplied as powder or granular form.• Heat reduces the viscosity and melts the polymer to allow it to flow & mold• Additional heat triggers a chemical reaction which forms a cross-linked 3D

– Common heat activated polymers• Formaldehyde (FOR), phenoplasts (PF), amnioplasts (UF), polyester, vinyl ester,

alkyd, allyl, furan, some epoxies, and polyimides

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Thermosetting Resins (thermosets)• Catalyst activated: Fig 3.85

– Some thermosets supplied as stable liquid form• Small amount of liquid (catalyst) is added which starts a

chemical reaction and leads to formation of 3D structure.

• Chemical type and amount of catalyst controls the extent of reaction and the speed of polymerization.

• Many systems can set at room temperature.

• Useful for casting resins and for glass fiber reinforced composites.

• Common polymer is unsaturated polyester resin (UPR)

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Thermosetting Resins (thermosets)• Mixing activated systems: Fig 3.86

– Some thermosets supplied as two stable liquids.• When the two are added together, a chemical reaction starts and

forms a 3D structure.

• Ratio of the two chemicals and temperature controls the extent of reaction and the speed of polymerization.

• Many systems can set at room temperature.

• Useful for casting resins and for glass fiber reinforced composites.

• Common polymers are polyurethane and epoxies.

• Polyurethane can be mixed at high speeds in a Reaction Injection Molding (RIM) process.

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Commercial Thermosets• Formaldehyde Systems: Functional Groups

– Formaldehyde plus one of the three hydrogen containing chemicals to form a 3D molecular network

• Phenol,• Melamine, or• Urea.

– Condensation reaction involving the oxygen and two hydrogens from two different molecules, Phenol, Urea, or formaldehyde.

– One stage systems with resols– Two stage systems with novolacs prepolymers, or precursers– Usually have large amounts of filler, e.g., wood flour, cellulose fibers and

minerals.– Supplied as powder or granual form or pills (compacted preforms)

• Molding temperatures (125°C – 200°C) and molding pressures of 2000 to 8,000 psi for compression molding and 18,000 psi for injection molding

O = CH

H

OHC N

N

N

HNH

NNCC H

HH

HHN- C- NH

O

HH

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Commercial Thermosets• Formaldehyde Systems: Functional Groups

– Phenoplasts (phenolics) are based on phenol and formaldehyde and were one of the first commercial polymers, Bakelite, and were used for billiard balls.

– Used with other materials to act as a binder, adhesive, coatings, surface treatments, etc.

– Applications• Temperature resistant insulating parts for appliances (handles,

knobs), electrical components (connectors, distributor caps) and bottle closures.

• Abrasive binder for grinding wheels and brakes.• Decorative laminates (counter tops or table tops)• Fire resistant rigid foams.

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Commercial Thermosets• Formaldehyde Systems: Functional Groups

– Aminoplasts (amino resins) are based on urea and formaldehyde or melamine and formaldehyde.

• Can be made translucent or in light colors for aesthetics

– Urea-formaldehyde resins are used for many of the same applications as phenolics if have color requirements

• Castable foam system is used for home insulation

– Melamine-formaldehyde resins are based on melamine and formaldehyde

• Noted for their excellent water resistance.• Used for dishwater safe dinner ware which can be decorated with molded-in

paper overlays.• Form the surface layer for decorative laminates (Formica)• Used as an adhesives for water resistant plywood.

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Commercial Thermosets• Furan Systems

– Feature a ring structure which can be opened cleaved to yield polymeric molecules which have 3-D molecular networks.

– Combined with fomaldehyde related thermosets.• Used as binder for sand and foundry work or abrasive particles in grinding wheels.• Used as adhesives and matrix for reinforced plastics where corrosion resistance is

important.

• Allyl systems (Pg 171)– Manufacture involves the reaction of a monofunctional unsaturated

alcohol, allyl alcohol (AA) with a difunctional acid.• Ester linkages are formed though not a polymer• 2 unsaturated C=C per monomer permits formation of 3-D molecule with the use

of catalysts and elevated temperatures.• DAP (diallylphthalate) is most common allyl monomer• Thermoplastic pre-polymers are available that are cured with little shrinkage• Applications include high performance molding compounds for electrical

O

C C

H

H

C CH

H

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Commercial Thermosets• Alkyd Systems

– Alkyd comes from alcohol (alk) and acid (yd)– Reaction of difunctional alcohol and difunctional acids or

anhydrides forms a polyester which is what alkyd is.– Used as coatings (paints, coatings, varnishes)

• Unsaturated Polyesters– Thermoset reaction between a difunctional acid (or anhydride) and

a difunctional alcohol (glycol)

– At least some of the acid (or anhydride) features double bonds between adjacent carbon atoms for unsaturation.

– Characteristic ester linkages are formed, hence the name Polyester

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Polyester Chemistry • Unsaturated Polyesters

– Thermoset reaction between a difunctional acid (or anhydride) and a difunctional alcohol (glycol)

C6H4(COOH)2 + (CH2)2(OH)2 -[(CH2)2 -O- C - C-O]-

terephthalic acid + ethylene glycol Polyethylene terephthalate (PET)

– Acids include: maleic, fumaric, isophthalic, terphthalic, adipic, etc.– Anhydrides include: maleic, phthalic– Glycols include ethylene glycol, diethylene glycol, propylene glycol

O O

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Polyester Chemistry• Heat or radiation can trigger the cross linking reaction

– Catalyst is used• Starts reaction but is not consumed and is retrieved at end of reaction.

– Initiator• Methyl ethyl ketone (MEK) peroxide, benzoyl peroxide, and cumene hydroperoxide• Starts reaction, then is consumed in reaction.

– Accelerators (or promoters) speed up the reaction. – Inhibitors extend shelf life (hydroquinone, tertiary butyl catechol)

• Condensation Reaction results in CO2 and H2O – Monomer required to polymerize, e.g., Styrene, to react with the unsaturations in the

polyester molecules to form 3-D network. • Styrene at 30% to 50% in commercial polyester systems for polyester• vinyl toluene for vinyl ester resins• methyl methacrylate

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Polyester Chemistry• Step 1: Create polymer and build MW of polymer

chain – Condensation Polymerization of Di-ACID and Di-

ALCOHOL• Fig 2.: Condensation reaction

– Connects one end of acid with one end of alcohol to form polyester bond.

– The opposite end of acid reacts with another free end of alcohol, and so on .

– Have water as a by-product means condensation.

– Still have unsaturated polymer. The Carbon atom has double bonds:

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Polyester Chemistry• Step 2: Crosslink polyester polymer with unsaturated styrene.

– Addition (free radical) reaction to connect polyester with styrene• Use a peroxide (free radical) to open the unsaturated bond to form

saturation• One reaction starts, the other unsaturated bonds open up and react with the

styrene to form a saturated polymer.• The ends of the polyester-styrene crosslinked polymer has peroxide end-

groups.• Peroxide is an initiator and not a catalyst since it is consumed in reaction.

Catalysts are not consumed in the reaction and can be retrieved at the end of it.

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Sheet Molding Compound (SMC)• SMC is the paste that is compression molded

– 33% polyester resin and stryrene, which polymerizes and crosslinks

– 33% glass fibers (1” fibers)

– 33% Calcium Carbonate

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Epoxy Chemistry• Epoxy: O H H

C C H + H2N (C) N (C) NH2

H H H H

epoxide group + amines (DETA) epoxy

• Other epoxy resins– diglycidyl ether of bisphenol A (DGEBRA)

– tetraglycidyl methylene dianiline (TGMDA

– epoxy phenol cresol novolac

– cycloaliphatic epoxies (CA)

• Curing agents (hardeners, catalysts, cross-linking agents)– aliphatic or aromatic amines (DETA, TETA, hexamethylene tetramine,etc.)

– acid anhydrides (phthalic anhydride, pyromellitic dianhydride, etc.)

– Active hydrogen react with epoxide groups.

– As much as 15% hardener is needed

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Polyurethane Chemistry• Reaction between isocyanate and alcohol (polyol).• Crosslinking occurs between isocyanate groups (-NCO) and the polyol’s

hydroxyl end-groups (-OH)• Thermoplastic PU (TPU) have some crosslinking, but purely by physical means.

– These bonds can be broken reversibly by raising the material’s temperature, as in molding or extrusion.

– Ratio between the two give a range of properties between a flexible foam (some crosslinking) to a rigid urethane (high degree of crosslinking).

– In PUR foams density can range from 1 lb/ft3 to 70 lb/ft3.– Foams are produced by chemical blowing agents.– Catalyst are used to initiate reaction.– RIM process is used to produce fenders and bumper covers

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Other Thermosets• Polyimides

• Bismaleimide

• Polybenzimidazoles

• Phenolics

• Carbon Matrices

• Thermoplastic matrices– Polyamides

– Polypropylene

– PEEK

– Polysulfone

– PPS

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Polyimides

• For temperature stability up to 600 F– Polyimides or polybenzimidazole (PBI) rather than

epoxy– Aerospace applications due to high cost– Chemical Structure

• Polyimides– Characterized by cyclic group containing a nitrogen and two carbonyl

groups (C with double bond with oxygen)

• PBI– Characterized by a five member ring containing two nitrogens and is

attached to a benzene ring.

• Polyimids and PBI are structurally planar and very rigid. Large aromatic groups are added into polymer to make stiffer.

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Polyimides

• Formed with two step condensation. Fig 2-5– First step: An aromatic dianhydride is reacted with an

aromatic diamine to form polyamic (polamide) acid. – Second step: Curing of the polyamic acid.

• Formation of imide group by closing of 5-member ring• Condensation step of solvent molecules: water, alcohol,

solvents• Chain extension• Cross-linking

– High viscosities of polyamid acids require use of prepregs.

• Impregnating the fiber mat with monomer solutions of diamines and diester acids.

• Long times and gradual increase in temperature are needed.

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Polyimides• Major condensation polyimids, Dupont’s Avimid N &

K– are marketed as Prepreg polyimids

• Avimid N Tg = 675F (360C), and • Avimid K: Tg = 490F (254C)

– Linear polyimids are produced which have thermoplastic behavior above the Tg.

– They process like thermoplastics for a few heat cycles.– Advantages of thermoplastic nature

• Tractable nature of resins when hot facilitates the removal of volatiles.• Voids, formed as result of the evolution of gases, can be eliminated by

applying pressure while heating the resins above Tg.

– Applications• Wing skins for high performance aircraft.

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Polyimides• Addition Polyimides

– Many polyimids are cross linked with an addition reaction• Two general cross-linking reactions are widely used

– End group reactions– Bismaleimide reactions

• Reactive End Group Resin Fig 2-6– First phase (imidization): results in the formation of the oligomeric (small

polymer) imide– Second phase (consolation): is when the oligomer melts and flows to fill voids

that were created from volatiles depart.– Third phase (crosslinking): oligomer builds MW & crosslinks

» MW = 1500– Shorter polymer chains gave lower viscosity and better wet-out

» Wet-out is defined as uniform coating and soaking of resin in fiber.– Commercial end group resin (PMR) is PMR 11, PMR 15 and PMR 20

» PMR-11 has more end groups and higher cross-linking density and higher stiffness

» PMR-20 gave better thermal stability.» PMR-15 has the best physical properties balanced.

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Polyimides• Second type of endgroup crosslinking has acetylene

endgroups and is called Thermid 600– Crosslinking

• First step: joining two polyimid oligomers to form a butadiene linkage which results in chain extension. Each double bond can react with double or triple bonds to form highly crosslinked.

• Addition reaction

• Problems is with too fast a cure and chain extension competing with cross-linking mechanism thus causing MW to build too fast.

– Alleviated with proper solvents.

• Disadvantage is the loss of tackiness in prepregs as the solvent evaporates.

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Polyimides• Bismaleimide (BMI) resins

– Addition polymerization• Reactions involving bismaleimide (BMI) derivatives: Fig 2-8

• Case 1– Carbon-Carbon double bond in the maleimide group reacts with the

carbon-carbon double bond in the olefin co-reactant (similar to maleic acid is crosslinked with styrene in polyester)

• Case 2– An aromatic diamine adds to the carbon-carbon double bond of the

maleimide in what is called Michaels Reaction.

• Both cases: the coreactants (olefin or diamine) form bridges between the imide molecules to form a crosslinked structure

– Commericial products• Ciba-Geigy uses an olefinic compound with two olefins

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Polyimides• Bismaleimide (BMI) resins

– Advantages• Low processing temperature versus polyimides (Cured

at 350F)• Standard epoxy processing equipment can be used

since same T.• Postcure of 475 F is required to complete

polymerization.• BMI are fully formed polyimides when reacted to form

composite• Thus, no volatiles are removed and no consolidation

problems• Tack and drape are quite good because of the liquid

component of the reactants

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Polyimides• Polybenzimidazole (PBI) resins

– Less prevalent than the polyimides, PBI have equivalent and sometimes superior physical and thermal properties

– Formation reaction- fig 2-9• Five member ring containing two nitrogens is formed with

accompanying aromatic groups.• Groups are flat and stiff leading to good physical properties

and aromatics result in high thermal.

– Problems are expensive, difficult process, toxicity• Some have been alleviated and is commercially available• Resin is thermoplastic with a Tg over 800F (427C)

• It does not burn, contribute fuel to flames or produce smoke• Forms a tough char• Resins are toxic and need to be handles with care.

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Phenolics• Phenolics is an old thermoset resin

– Used for general purpose, unreinforced plastic

• electrical switches

• junction boxes

• automotive molded parts

• consumer appliance parts, handles, billiard balls

– Fillers are required due to high shrinkage and brittle nature.

• Sawdust, nut shells, talc, or carbon black

– Fiber reinforced Phenolics have aerospace applications

• Rocket nozzles, nose cones due to ablative nature (Goes from solid to gas during burning)

• High temperature aircraft ducts, wings, fins, and muffler repair kits

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Phenolics• Phenolic chemical structure-

– Formed by reaction between phenol and formaldehyde• Condensation reaction releases water as a byproduct.• Initially low molecular weight, soluble and fusible, A-Stage resin• Condensation reaction involves more and more phenol molecules that

causes the resin to pass through a rubbery, thermoplastic state that is only partially soluble phase called B stage.

• Resin is cured and cross-linked thermoset resin, C- Stage.– Other terms describing phenolic formation

• Resole: If phenol/formaldehyde reaction is carried out in excess formaldehyde and base catalyst is called resole at low molecular weight stage. Requires just heat to convert to C-stage (1 step)

• Novolac: If phenol/formaldehyde reaction is carried out in excess phenol with an acid catalyst is called novolac.

– Requires addition of a hardener (hexamethylenen tetramine) to achieve C- Stage in 2 steps. It provides acid to both reactants which speeds up reaction.

– Reinforcements are mixed with novolacs for composites. Bstaging is when any other resin is cured to an intermediate stage and cured by heating

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Thermoplastic Composites• Plastics are reinforced with glass and a few with carbon fiber

• Nylon, PP, PBT, PEEK and PEK, and Polysulphone

• Advantages– Requires less processing time since it is heated and not cured.– Thermoplastic pre-preg sheets have infinite shelf life versus thermoset

• Disadvantages– Have lower thermal resistance than most thermoset composites– Have lower strength and modulus than some thermoset composites– Have difficulty wetting out high fiber loading composites.

Property

Thermoset (Fiberite 931 Epoxy)

Thermoplastic (ICI APC-2P)

Melt Viscosity Low HighFiber Impregnation Easy DifficultPrepreg Tack Good NonePrepreg Drape Good PoorPrepreg Stability at 0F 6mos -1yr InfiniteProcessing Cycle 1-6hrs 15sec-6hrsProcessing Temp 350F 700FMechanical Props Good GoodEnviron Durability Good ExceptionalDamage Tolerance Average GoodDatabase Large Average

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Thermoplastic Matrices• Two types of thermoplastic composites: Discontinuous and

continuous reinforcements– Discontinuous fiber- Conventional thermoplastics and short (3mm) or long

fibers (6mm)• Polypropylene, nylon, PET, PBT, Polysulphone, PE, ABS, PC, HIPS, PPO

– Short Glass or Carbon fiber increases• Tensile strength, modulus, impact strength, cost, thermal properties

– Short Glass or carbon fiber decreases • Elongation, • CLTE, • Moisture sensitivity

Nylon 6,6 Nylon 6,6 with30% short glass

Nylon 6,6 with30% long glass

Nylon 6,6 with30% carbon fiber

Density, g/cc 1.13-1.15 1.4 1.4 1.06-1.10

Tensile Strength,psi

14,000 28,000 28,000 32,000

Tensile Modulus,psi

230K – 550K 1,300K 1,400 K 3,300 K

TensileElongation, %

15%-80% 3% 3% 4%

Impact Strengthft-lb/in

0.55 – 1.0 1.6-4.5 4.0 1.5

CLTE (in/in/Cx10-6)

55 18 18 15

Moisture % 1.0-2.8% (24h)8.5% (Max)

0.7-1.1 (24h)5.5-6.5 (Max)

0.9 (24h)5.5-6.5 (Max)

0.7 (24h)5 (Max)

Cost $/lb $1.40 $1.70 $2.00 $2.70

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Thermoplastic Matrices• Several types of resin types

– Conventional plastics: Less expensive (< $2 per pound)• Commodity plastics : PP, PE, PVC, PS, etc. (<$1 per pound)• Engineering resins: PC, PET, PBT, Nylon, ABS etc. (>$1pp)

– High Performance Plastics: High Costs (> $10 per pound) and High Thermal Properties

• PEEK, PEK, LCP, PPS, Polyaryle Sulfone, Polysulfone, Polyether sulfone, Polyimid

• PEEK and PEK = $30 per pound

– Polyarylesters

• Repeat units feature only aromatic-type groups (phenyl or aryl groups) between ester linkages. Called wholly aromatic polyesters O

n

O O CO

n

O C

PolyEther-Ether-Ketone (PEEK) PolyEther-Ketone (PEK)

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Properties of Reinforced PEEK Mechanical Properties Reinforced

PEEK PEEK 30%glass fibers

PEEK with 30%carbon fibers

Density, g/cc 1.30-1.32 1.52 1.43

Tensile Strength,psi

10,000 – 15,000 23,000 – 29,000 31,000

Tensile Modulus,psi

500K 1,300K – 1,600K 1,900K – 3,500K

TensileElongation, %

30% - 150% 2%-3% 1% - 4%

Impact Strengthft-lb/in

1.6 2.1 – 2.7 1.5 – 2.1

Hardness R120 R120

CLTE10-6 mm/mm/C

40 - 47 12-22 15-22

HDT 264 psi 320 F 550F -600F 550F -610F

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Advantages and Disadvantages of Polyketones• Advantages

– High continuous use temperature (480F)– High toughness, especially at high temperatures.– Outstanding wear resistance– Excellent water resistance and better than thermoset composites– Excellent mechanical properties– Very low flammability and smoke generation– Resistant to high levels of gamma radiation– Higher Elongation (30%-100%) versus thermosets (1%-10%)

• Disadvantages– High material cost and long processing times– High processing temperatures due to high viscosities (1 Million poise) versus thermoset composites (Epoxy = 10 poise). Syrup = 1000 poise– Moderate or poor resistance to hot oils– Difficult to have high fiber loadings due to high viscosity– Need special processing techniques; comingle plastic powder with fiber sheet and consolidate (impregnate resin in fiber bundle) through

heated rollers.

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Thermoset Reacting Polymers• Process Window

– Temperature and pressure must be set to produce chemical reaction without excess flash (too low a viscosity), short shot (too high a viscosity), degradation (too much heat)

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Compression Molding of Polyesters• Compression molding was specifically developed for replacement

of metal components with composite parts. • Materials can be either thermosets (SMC) or thermoplastics (GMT)

– Most applications today use thermoset POLYESTER polymers, e.g., SMC or BMC. In fact,compression molding is the most common method of processing thermosets.

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Resin Transfer Molding of Polyester or Epoxy• In the RTM process, dry (i.e.,unimpregnated )

reinforcement is pre-shaped and oriented into skeleton of the actual part known as the preform which is inserted into a matched die mold.

• The heated mold is closed and the liquid resin is injected

• The part is cured in mold.

• The mold is opened and part is removed from mold.

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Open Mold Processing of Composites• Open Mold processes of Polyester or Epoxy

– Vacuum bag, pressure bag, SCRIMP – Autoclave: Apply Vacuum Pressure and Heat in an oven

which can be 5 feet to 300 feet long

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Polyurethane Processing• Polyurethane can be processed by

– Casting, painting, foaming– Reaction Injection Molding (RIM)

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Structural RIM for Urethanes (Fast RTM)

• Fiber preform is placed into mold.

• Polyol and Isocyanate liquids are injected into a closed mold and reacted to form a urethane.

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Composite Reinforcement Classifications• Reinforcement Type

– Discontinuous (fibers are chopped and dispersed in matrix resin)• Short fibers: fiber lengths 3mm or less (glass filled plastics, GF-Nylon)

• Long fibers: fiber lengths greater than 6 mm. (Some injection molded materials with 6mm fibers, Sheet Molding Compound (SMC) with 1” fibers, DFP Directed Fiber Preforms for RTM and SRIM)

• Particulates: fibers is forms as spheres, plates, ellipsoids (some injection molded materials reinforced with mineral fibers)

– Continuous (fibers are throughout structure with no break points)• Glass roving: glass bundles are wound up in a packet similar to yarn.

• Roving is woven into several weaves using a loom machine like in apparel.

– Mat products: random swirl glass pattern.

– Woven product: roving is woven into machine direction (warp) and cross direction (weft)

– Uni product: roving is woven in one direction with a cross thread given to hold mat together.

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Processing of Fiber Reinforcements• Carbon fiber or glass fiber

– Hand lay-up and Spray-up

– Filament winding

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Injection Molding Glass Reinforced Composites

• Plastic pellets with glass fibers are melted in screw, injected into a cold mold, and then ejected.

Glass filled resin pellets

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Composites Can Have a Fiber Preform• Fiber type

– Roving form that can be sprayed into a 3-D preform– Roving form that is woven into a glass sheet and then

formed to shape (preform)

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Glass Fibers• Properties of Glass Fibers: (Table 3-1)

Type of GlassProperty C E SDensity 2.49 2.54 2.48Tensile Strength, ksi 460 500 665

Tensile Modulus, Msi 10 10.5 12.4CLTE (in/in/ F) x10-6 4 2.8 3.1Specific Heat @72F 0.2 0.195 0.176Softening Point, F 1381 1550 1778Dielectric Constant 0.008 0.002 0.003Chemical Resistance (% wt gain after 24hrs)In H20 1.1 0.7 0.7In 10%HCl 4.1 4.2 3.8In 10% H2SO4 2.2 3.9 4.1In 10% Na2CO3 2.4 2.1 2

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Carbon/Graphite Fibers• Need for reinforcement fibers with strength and moduli

higher than those of glass fibers has led to development of carbon

• Thomas Edison used carbon fibers as a filament for electric light bulb

• High modulus carbon fibers first used in the 1950s• Carbon and graphite are based on layered structures of

hexagonal rings of carbon

• Graphite fibers are carbon fibers that – Have been heat treated to above 3000°F that causes 3 dimensional

ordering of the atoms and – Have carbon contents GREATER than 99%– Have tensile modulus of 344 Gpa (50Mpsi)

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Carbon Fiber Mechanical PropertiesCarbon Fiber Mechanical Properties

PAN Based PITCH Based Rayon Based Tensile Modulus (Mpsi) 33 - 56 23 -55 5.9Tensile Strength (Msi) 0.48 - 0.35 0.2 - 0.25 0.15Elongation (%) 1.4 - 0.6 0.9 - 0.4 25Density (g/cc) 1.8 - 1.9 1.9 - 2.0 1.6Carbon Assay (%) 92 - 100 97 - 99 99

Note: 1Mpsi = Mpa

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Organic Fiber- Kevlar Properties• Properties- Table 3-3

– Kevlar has high heat resistance, though less than carbon fiber.– Kevlar has exceptional exposure limits to temperature

• No degradation in properties after 7 days at 300 F.• 50% reduction in properties after 7 days at 480F.• 50% reduction in properties after 12 months of sunlight exposure in

Florida– Kevlar are hygroscopic and are susceptible to moisture and need to

be dried– Aramids do not bond well to matrices as do glass and carbon fibers

• The ILSS (interlaminar Short beam shear) values are lower.Properties of Kevlar Kevlar

29 49 149Tensile Mod MPa 83 131 186Tensile Strength MPa 3.6 3.6 3.4Elongation % 4 2.8 2Density g/cc 1.44 1.44 1.47