Kevlar® Aramid Fiber Technical Guide

KEVLAR

ARAMID FIBER

TECHNICAL GUIDE

TABLE OF CONTENTS

Contents

Section I: Introduction to DuPont

™

Kevlar

Aramid Fiber

What Is Kevlar

? ..................................... 3

Development and Molecular Structure of Kevlar

......... 3

Section II: Properties of DuPont

™

Kevlar

Typical and Comparative Properties of Kevlar

........... 5

Effect of Chemical Agents on Kevlar

................... 8

Effect of Water and pH on Kevlar

..................... 11

Hydrolytic and pH Stability ........................ 11

Moisture Regain ................................. 11

Thermal Properties of Kevlar

........................ 12

Decomposition Temperature ....................... 12

Effect of Elevated Temperatures on

Tensile Properties ............................... 13

Effect of Elevated Temperatures on

Dimensional Stability ............................. 13

Heat of Combustion ............................... 14

Speciﬁc Heat .................................... 14

Effect of Arctic Conditions ......................... 14

Effect of Cryogenic Conditions ...................... 14

Flammability, Smoke and Off-Gas Generation

Properties of Kevlar

............................... 15

Effect of Electron Radiation on Kevlar

................. 16

Effect of UV Light on Kevlar

. . . . . . . . . . . . . . . . . . . . . . . . . . 16

Section III: DuPont

™

Kevlar

Short Fibers

Kevlar

Pulp ....................................... 18

Precision-Cut, Short Fibers .......................... 19

Kevlar

Staple ................................... 19

Kevlar

Floc ...................................... 19

Kevlar

M/B Masterbatch ............................ 20

Section IV: Glossary ........................... 21

Ordering Information for DuPont

™

Kevlar

............... 23

Technical Guide for Kevlar

Aramid Fiber 3

WHAT IS KEVLAR

Kevlar® is an organic fiber in the aromatic polyamide family.

The unique properties and distinct chemical composition of wholly

aromatic polyamides (aramids) distinguish them—and especially

Kevlar®—from other commercial, man-made fibers.

Kevlar® has a unique combination of high strength, high modulus,

toughness and thermal stability. It was developed for demanding

industrial and advanced-technology applications. Currently, many types

of Kevlar® are produced to meet a broad range of end uses.

This guide contains technical information primarily about Kevlar®

industrial yarns, as well as some basic information on Kevlar® short

fibers. If you require any additional information including, information

on the various applications and special forms of Kevlar®, please contact

your DuPont Representative or call 1-800-931-3456. From outside the

United States, call (302) 999-3358.

DEVELOPMENT AND MOLECULAR STRUCTURE

OF KEVLAR

In the mid-1960s, nylon and polyester represented the state of the

art in man-made fibers. However, to achieve maximum tenacity

(break strength) and initial modulus, the polymer molecules had

to be in extended-chain configuration and almost perfect crystalline

packing. With flexible-chain polymers, such as nylon or polyester,

this could be accomplished only by mechanically drawing the fiber after

melt spinning. This required chain disentanglement and orientation

in the solid phase, so tenacity and modulus levels were far from the

theoretically possible values.

In 1965, scientists at DuPont discovered a new method of

producing an almost perfect polymer chain extension. The polymer

poly-p-benzamide was found to form liquid crystalline solutions due to

the simple repetitiveness of its molecular backbone. The key structural

requirement for the backbone is the para orientation on the benzene

ring, which allows the formation of rod-like molecular structures.

These developments led us to our current formulation for Kevlar®.

To illustrate the difference between liquid crystalline polymers and

flexible, "melt" polymers, consider what happens when rod-like polymer

molecules are dissolved, as opposed to molecules with flexible chains.

With flexible chain polymers, random coil configuration is obtained

in solution, and even increasing the polymer concentration cannot

generate a higher degree of order. In contrast, with rigid polymers,

as the concentration increases, the rods begin to associate in parallel

alignment. Randomly oriented domains of internally highly oriented

polymer chains then develop.

Figure 1.1 Rod-Like Fiber Structure by the

Radial Stacking of Hydrogen-Bonded Sheets.

Figure 1.2 Differences in Behavior During

Spinning Between Flexible and Rigid Polymers.

SECTION I: INTRODUCTION TO DUPONT™ KEVLAR® ARAMID FIBER

Hydrogen-Bonded Sheet Sheets Stacked Together

Flexible

Rod-like

Dilute

Solution

Dilute

Solution

Higher

Concentration

Higher

Concentration

Spin

Draw

Spin

Orient

Partially Extended

Chains

Fully Extended

Chains

Technical Guide for Kevlar

Aramid Fiber 4

SECTION I: INTRODUCTION TO DUPONT™ KEVLAR



ARAMID FIBER

Liquid crystalline polymer solutions display a unique behavior

under shear. This unique aspect opened up new dimensions in fiber

manufacturing and processing. Under shear forces, as the solutions

pass through a spinneret (orifice), the randomly oriented domains

become fully oriented in the direction of the shear and emerge with

near perfect molecular orientation.

The supramolecular structure is almost entirely preserved in the

as-spun filament structure due to very slow relaxation of the

shear-induced orientation. This process is a novel, low-energy way to

highly orient polymer molecules and to achieve very strong fibers.

DuPont utilized this technology to develop a fiber of

poly-para-phenylene terephthalamide, which was introduced

as high-strength Kevlar® aramid fiber in 1971.

Technical Guide for Kevlar

Aramid Fiber 5

SECTION II: PROPERTIES OF DUPONT™ KEVLAR®

This section lists and describes the typical properties of Kevlar®.

The data reported are those most often observed, and are representative

of the particular denier and type indicated. The properties are reported

in both U.S. and S.I. units.

For information on safety and health, refer to the Kevlar® Material

Safety Data Sheet.

TYPICAL AND COMPARATIVE PROPERTIES

OF KEVLAR

Table II-1 lists the typical yarn, tensile and thermal properties of

Kevlar® 29 and Kevlar® 49 yarns.

Additional products in the Kevlar® family of fibers are available

with different combinations of properties to meet your engineering

design needs.

Please contact your DuPont Representative or call 1-800-931-3456 to

discuss your specific application and determine the optimum

Kevlar® fiber for you.

Table II-1 Typical Properties of DuPont

™

Kevlar

29 and Kevlar

49 yarns

Property Unit Kevlar

29 Kevlar

Yarn

Type denier

(dtex)

# of filaments*

1,500

(1,670)

1,000

1,140

(1,270)

768

Density lb/in.

(g/cm

)

0.052

(1.44)

0.052

(1.44)

Moisture Levels

As Shipped** % 7.0 3.5

Equilibrium from

Bone-Dry Yarn***

% 4.5 3.5

Tensile Properties

Straight Test on Conditioned Yarns

†

Breaking Strength lb

(N)

76.0

(338)

59.3

(264)

Breaking Tenacity g/d

(cN/tex)

23.0

(203)

23.6

(208)

psi

(MPa)

424,000

(2,920)

435,000

(3,000)

Tensile Modulus g/d

(cN/tex)

555

(4,900)

885

(7,810)

psi

(MPa)

10.2 x 10

(70,500)

6.3 x 10

(112,400)

Elongation at Break % 3.6 2.4

Resin Impregnated Strands

††

Tensile Strength psi

(MPa)

525,000

(3,600)

525,000

(3,600)

Tensile Modulus psi

(MPa)

12.0 x 10

(83,000)

18.0 x 10

(124,000)

NOTE: The data in this table are those most commonly observed and are representative of the particular denier and type indicated; they are not product specifications.

Properties will vary with denier and type. For Kevlar

29, the basis weight used to calculate denier is zero finish and 4.5% moisture. For Kevlar

49, the basis weight

used to calculate denier is zero finish and 0% moisture.

* Filament diameter is 0.00047 inches (12 microns).

Typical moisture levels on yarn as shipped; they reflect values reached at normal, moderate temperature and humidity levels following fiber production, which is a wet process.

***Equilibrium values are determined by bone drying the fiber and conditioning at 75°F (24° C), 55% relative humidity (RH).

† ASTM D885-85, tested at 1.1 twist multiplier.

†† Epoxy-impregnated strands, ASTM D2343.

Technical Guide for Kevlar

Aramid Fiber 6

SECTION II: PROPERTIES OF DUPONT™ KEVLAR®

Table II-1 Typical Properties of DuPont

™

Kevlar

29 and Kevlar

49 yarns (continued)

Property Unit Kevlar

29 Kevlar

Thermal Properties

Shrinkage

In Water at 212°F (100°C) % <0.1 <0.1

In Dry Air at 351°F (177°C) % <0.1 <0.1

Shrinkage Tension

In Dry Air at 351°F (177°C) G/D

(cN/tex)

<0.1

(0.88)

<0.2

(1.77)

Specific Heat

At 77°F (25°C) cal/g x °C

(J/kg x K)

0.34

(1,420)

0.34

(1,420)

At 212°F (100°C) cal/g x °C

(J/kg x K)

0.48

(2,010)

0.48

(2,010)

At 356°F (180°C) caJ/g x °C

(J/kg x K)

0.60

(2,515)

0.60

(2,515)

Thermal Conductivity

BTU x in./(h x ft

x °F)

(W/(m x K)]

0.3

(0.04)

0.3

(0.04)

Decomposition

Temperature in Air

†††

°F

(°C)

800–900

(427–482)

800–900

(427–482)

Recommended Maximum

Temperature Range for

Long-Term Use in Air

°F

(°C)

300–350

(149–177)

300–350

(149–177)

Heat of Combustion BTU/lb

(Joule/kg)

15,000

(35 x 10

)

15,000

(35 x 10

)

Poisson’s Ratio 0.36

††† Varies with rate of heating.

Technical Guide for Kevlar

Aramid Fiber 7

SECTION II: PROPERTIES OF DUPONT™ KEVLAR®

Table II-2 compares the properties of Kevlar® 29 and Kevlar® 49 to

other yarns, such as glass, steel wire, nylon, polyester, polyethylene and

carbon. Compared to Kevlar®, nylon and polyester have relatively low

moduli and intermediate melting points. Polyethylene has a high initial

modulus, which is offset by its relatively low melting point.

Table II-2 Comparative Properties of Dupont

™

Kevlar

vs. Other Yarns

“Customary” (inch-pound) Units

Specific

Density,

lb/in.

Tenacity,

psi

Modulus,

psi

Break

Elongation,

Specific

Tensile

Strength,*

in.

CTE,**

-6

/°F

Decomposition

Temperature,

°F °C

Kevlar

29 0.052 424 10.2 3.6 8.15 -2.2 800–900 427–482

Kevlar

49 0.052 435 16.3 2.4 8.37 -2.7 800–900 427–482

Other Yarns

S-Glass 0.090 665 12.4 5.4 7.40 +1.7 1,562

†

850

E-Glass 0.092 500 10.5 4.8 5.43 +1.6 1,346

†

730

Steel Wire 0.280 285 29 2.0 1.0 +3.7 2,732

†

1,500

Nylon 66 0.042 143 0.8 18.3 3.40 – 490

†

254

Polyester 0.050 168 2.0 14.5 3.36 – 493

†

256

HS Polyethylene 0.035 375 17 3.5 10.7 – 300

†

149

High-Tenacity Carbon 0.065 450 32 1.4 6.93 -0.1 6,332

†

3,500

*Specific tensile strength is obtained by dividing the tenacity by the density.

**CTE is the coefficient of thermal expansion (in the longitudinal direction).

†

Melt temperature.

Technical Guide for Kevlar

Aramid Fiber 8

SECTION II: PROPERTIES OF DUPONT™ KEVLAR®

EFFECT OF CHEMICAL AGENTS ON KEVLAR

Kevlar® is chemically stable under a wide variety of exposure conditions;

however, certain strong aqueous acids, bases and sodium hypochlorite

can cause degradation, particularly over long periods of time and at

elevated temperatures. Table II-3 summarizes the effect of chemical

agents on the breaking strength of Kevlar®.

Table II-3 Chemical Resistance of DuPont

™

Kevlar

Aramid Yarn

Chemical

Concentration,

Temperature,

Time,

hours

Effect on

Breaking Strength*°F °C

Acids

Acetic 99.7 70 21 24 None

Acetic 40 70 21 1000 Slight

Acetic 40 210 99 100 Appreciable

Benzoic 3 210 99 100 Appreciable

Chromic 10 70 21 1000 Appreciable

Formic 90 70 21 100 None

Formic 40 70 21 10000 Moderate

Formic 90 210 99 100 Degraded

Hydrobromic 10 70 21 1000 Appreciable

Hydrochloric 37 70 21 24 None

Hydrochloric 10 70 21 100 Appreciable

Hydrochloric 10 160 71 10 Degraded

Hydrofluoric 10 70 21 100 None

Nitric 1 70 21 100 Slight

Nitric 10 70 21 100 Appreciable

Nitric 70 70 21 24 Appreciable

Oxalic 10 210 99 100 Appreciable

Phosphoric 10 70 21 100 None

Phosphoric 10 70 21 1000 Slight

Phosphoric 10 210 99 100 Appreciable

Salicylic 3 210 99 1000 None

Sulfuric 10 70 21 1000 Moderate

Sulfuric 10 70 21 100 None

Sulfuric 10 212 100 10 Appreciable

Sulfuric 70 70 21 100 Moderate

* None ................ 0 to 10% strength loss Appreciable .............41 to 80% strength loss

Slight ............... 11 to 20% strength loss Degraded ................. 81 to 100% strength loss

Moderate .........21 to 40% strength loss

Technical Guide for Kevlar

Aramid Fiber 9

Table II-3 Chemical Resistance of DuPont

™

Kevlar

Aramid Yarn (continued)

Chemical

Concentration,

Temperature,

Time,

hours

Effect on

Breaking Strength*°F °C

Bases

Ammonium Hydroxide 28.5 70 21 24 None

Ammonium Hydroxide 28 70 21 1000 None

Potassium Hydroxide 50 70 21 24 None

Sodium Hydroxide 50 70 21 24 None

Sodium Hydroxide 40 70 21 100 None

Sodium Hydroxide 10 70 21 1000 Appreciable

Sodium Hydroxide 10 210 99 100 Degraded

Sodium Hydroxide 10 212 100 10 Appreciable

Sodium Hypochlorite 0.1 70 21 1000 Degraded

Salt Solutions

Copper Sulfate 3 70 21 1000 None

Copper Sulfate 3 210 99 100 Moderate

Ferric Chloride 3 210 99 100 Appreciable

Sodium Chloride 3 70 21 1000 None

Sodium Chloride 10 210 99 100 None

Sodium Chloride 10 250 121 100 Appreciable

Sodium Phosphate 5 210 99 100 Moderate

Miscellaneous Chemicals

Benzaldehyde 100 70 21 1000 None

Brake Fluid 100 235 113 100 Moderate

Cottonseed Oil 100 70 21 1000 None

Formaldehyde

in Water

10 70 21 1000 None

Formalin 100 70 21 24 None

Lard 100 70 21 1000 None

Linseed Oil 100 70 21 1000 None

Mineral Oil 100 217 99 10 None

Phenol in Water 5 70 21 10 None

Resorcinol 100 250 121 10 None

Water, Ocean

(Ocean City, NJ)

100 — 1 year None

Water, Salt 5 70 21 24 None

Water, Tap 100 70 21 24 None

Water, Tap 100 212 100 100 None

Water, Tap 100 210 99 100 None

* None ................ 0 to 10% strength loss Appreciable .............41 to 80% strength loss

Slight ............... 11 to 20% strength loss Degraded ................. 81 to 100% strength loss

Moderate .........21 to 40% strength loss

Technical Guide for Kevlar

Aramid Fiber 10

Table II-3 Chemical Resistance of DuPont

™

Kevlar

Aramid Yarn (continued)

Chemical

Concentration,

Temperature,

Time,

hours

Effect on

Breaking Strength*°F °C

Organic Solvents

Acetone 100 70 21 24 None

Acetone 100 Boil 100 None

Amyl Alcohol 100 70 21 1000 None

Benzene 100 70 21 1000 None

Benzene 100 70 21 24 None

Carbon Tetrachloride 100 70 21 24 None

Carbon Tetrachloride 100 Boil 100 Moderate

Chlorothene 100 70 21 24 None

Dimethylformamide 100 70 21 24 None

Ethyl Ether 100 70 21 1000 None

Ethyl Alcohol 100 170 77 100 None

Ethylene Glycol/Water 50/50 210 99 1000 Moderate

Freon

™

11 100 140 60 500 None

Freon

™

22 100 140 60 500 None

Jet Fuel

(Texaco “Abjet” K-40)

100 70 21 24 None

Kerosene 100 140 60 500 None

Suva

™

Centri-LP

(HCFC-123)

100 70 21 1000 None

Gasoline, Leaded 100 70 21 1000 None

Gasoline, Leaded 100 70 21 24 None

Methyl Alcohol 100 70 21 1000 None

Methylene Chloride 100 70 21 24 None

Methylene Ketone 100 70 21 24 None

Perchloroethylene 100 210 99 10 None

Toluene 100 70 21 24 None

Trichloroethylene 100 70 21 24 None

* None ................ 0 to 10% strength loss Appreciable .............41 to 80% strength loss

Slight ............... 11 to 20% strength loss Degraded ................. 81 to 100% strength loss

Moderate .........21 to 40% strength loss

Technical Guide for Kevlar

Aramid Fiber 11

SECTION II: PROPERTIES OF DUPONT™ KEVLAR®

EFFECT OF WATER AND PH ON KEVLAR

Hydrolytic and pH Stability

Degradation can occur when Kevlar® is exposed to strong acids and

bases. At neutral pH (pH 7), the filament tenacity remains virtually

unchanged after exposure at 149°F (65°C) for more than 200 days.

The further the pH deviates from pH 7, the greater the loss in tenacity.

Acidic conditions cause more severe degradation than basic conditions

at pH levels equidistant from neutral.

Similar behavior is seen in saturated steam generated from water at

various pH levels. The results of the 16-hour exposure at 309°F

(154 °C) show maximum strength retention in pH 6 to pH 7,

with a sharper drop-off on the acidic side (Figure 2.1).

Figure 2.1 Hydrolytic Stability of Kevlar

in 309°F (154°C) Steam vs. pH of Water.

The resistance of Kevlar® to hydrolysis in saturated steam is measured in

a sealed tube ("bomb") test. Kevlar® yarn (1,500 denier) in a skein form

is held at 280°F (138°C) for various lengths of time in the presence

of sufficient water (pH 7) to form saturated steam. The strength loss

results are determined by comparing strength data measured at room

temperature for control and exposed yarns (Figure 2.2).

Figure 2.2 Hydrolytic Stability of Kevlar

in Saturated Steam at 280°F (138°C) vs. Exposure Time.

Moisture Regain

Moisture regain is the tendency of most fibers to pick up or give off

ambient atmospheric moisture until they reach an equilibrium moisture

content at a given temperature and humidity level. Relative humidity

(RH) has a significant effect on the rate of moisture absorption by

Kevlar® and the equilibrium level reached. The higher the RH,

the faster Kevlar® absorbs moisture during the initial phase of

moisture gain, and the higher the final equilibrium level.

(control)

1,500 denier

Strength Loss, %

Exposure Time, hours

0 10 20 30 40 50 60 70 80 90 100

Exposure: 16 hours

% Break Strength

Remaining

3 4 5 6 7 8 9 10

100

Technical Guide for Kevlar

Aramid Fiber 12

SECTION II: PROPERTIES OF DUPONT™ KEVLAR®

Bone-dried Kevlar® will reach a slightly lower equilibrium moisture

level than fiber that has never been bone dried. Figure 2.3 illustrates

this effect for Kevlar® 29. Figure 2.4 illustrates the effect of RH on the

equilibrium moisture content obtained from a bone-dry yarn of

Kevlar® 49. This relationship is linear throughout the entire RH range.

The tensile properties of Kevlar® are virtually unaffected by

moisture content.

Figure 2.3 Moisture Regain of Kevlar

(After Various Preconditionings).

Figure 2.4 Equilibrium Moisture Content of Kevlar

49 vs.

Relative Humidity (RH) at Room Temperature.

THERMAL PROPERTIES OF KEVLAR

Decomposition Temperature

Kevlar® does not melt; it decomposes at relatively high temperatures

(800°F to 900°F [427°C to 482°C] in air and approximately

1,000°F [538°C] in nitrogen), when tested with a temperature rise

of 10°C/minute. Decomposition temperatures vary with the rate of

temperature rise and the length of exposure.

Figures 2.5 and 2.6 show typical thermogravimetric analyses (TGAs)

of Kevlar® 49 in air and nitrogen, respectively. TGAs are generated

by an instrument that measures weight loss as a function of temperature

rise over time. The analyses can be performed in air

or in a variety of other atmospheres.

For Kevlar®, as temperature increases there is an immediate weight

reduction, corresponding to water loss. The curve then remains

relatively flat until decomposition, where a significant weight loss

is observed.

Figure 2.5 Typical Thermogravimetric Analysis (TGA) of

Kevlar

49 in Air at a Temperature Rise of 10°C/Minute.

Moisture Regain, %

(from the dry side)

Relative Humidity (RH), %

0 10 20 30 40 50 60 70 80 90 100

Weight, %

Temperature, °C

0 100 200 300 400 500 600 700

120

100

Moisture Regain, %

Time, hours @ 65% Relative Humidity (RH)

and 72°F (22°C)

0 20 40 60 80 100 120 140

12.0

10.0

8.0

6.0

4.0

2.0

Preconditioned @ 85% RH/75°F

(24°C) for 3 days

Bone-dried, then preconditioned

@ 85% RH/75°F (24°C) for 3 days

Bone-dried @ 221°F (105°C) for 4 hours

Technical Guide for Kevlar

Aramid Fiber 13

SECTION II: PROPERTIES OF DUPONT™ KEVLAR®

Figure 2.6 Typical Thermogravimetric Analysis (TGA) of

Kevlar

49 in Nitrogen at a Temperature Rise of 10°C/Minute.

Effect of Elevated Temperatures on Tensile Properties

Increasing temperatures reduce the modulus, tensile strength and break

elongation of Kevlar® yarns and other organic fibers. This should be

taken into consideration when using Kevlar® at or above 300°F to 350°F

(149°C to 177°C) for extended periods of time.

Figures 2.7 and 2.8 compare the effects of exposure to elevated

temperatures on the tensile strength and modulus, respectively,

of Kevlar® and other yarns.

Figure 2.7 Effect of Elevated Temperatures on

the Tensile Strength of Kevlar

29.

Figure 2.8 Comparative Effect of Elevated Temperatures

on the Modulus of Various Yarns.

Effect of Elevated Temperatures on

Dimensional Stability

Kevlar® does not shrink like other organic fibers when exposed

to hot air or hot water. Most other fibers suffer significant,

irreversible shrinkage.

Kevlar® has a very small, negative coefficient of thermal expansion

(CTE) in the longitudinal direction. The value of the CTE of

Kevlar® is dependent on measuring technique, sample preparation

and test method (Table II-4).

Tested at Temperature After 5-Minute Exposure in Air

Kevlar

Polyester

Nylon

Modulus, gpd

Modulus, cN/tex

Test Temperature

0 100 200 300 400°F

38 93 149 204°C

1000

900

800

700

600

500

400

300

200

100

8000

7000

6000

5000

4000

3000

2000

1000

250°C

482°F

Dry, Twist-added Yarn Test

10” Gauge Length

10%/Minute Extension

Tested at Room Temperature

160°C

320°F

180°C

356°F

200°C

392°F

Time, hours

Tensile Strength, gpd

Tensile Strength, 10

psi

400

350

300

250

200

150

0 100 200 300 400 500

Table II-4 Coefficient of Thermal Expansion (CTE)

of DuPont

™

Kevlar

29 and Kevlar

49*

Type of

Kevlar

Denier

Temperature Range

CTE

in./in./˚F

(cm/cm/˚C)˚F ˚C

Kevlar

29 1,500 77–302 25–150 -2.2 x 10

(-4.0 x 10

)

Kevlar

49 1,420 77–302 25–150 -2.7 x 10

(-4.9 x 10

)

*Tested with zero twist and 0.2 gpd tension at 72˚F (22˚C), 65% relative humidity (RH).

Weight, %

Temperature, °C

0 100 200 300 400 500 600 700

120

100

Technical Guide for Kevlar

Aramid Fiber 14

SECTION II: PROPERTIES OF DUPONT™ KEVLAR®

Heat of Combustion

The heat of combustion of Kevlar® is measured by an Emerson oxygen

bomb calorimeter. Table II-5 compares the heat of combustion of

Kevlar® to that of other polyamides and to an epoxy used in making

rigid composites.

Speciﬁc Heat

The specific heat of Kevlar® is markedly influenced by temperature.

It more than doubles when the temperature is raised from 32°F (0°C)

to 392°F (200°C), as seen in Figure 2.9. Further increases are

more gradual.

Figure 2.9 Effect of Temperature on the

Specific Heat of Kevlar

49.

Effect of Arctic Conditions

Exposure to arctic conditions (-50°F [-46°C]) does not adversely

influence the tensile properties of Kevlar® (Table II-6). The increase

in modulus and the small decrease in break elongation at this low

temperature can be attributed to a slight increase in molecular rigidity.

Effect of Cryogenic Conditions

Kevlar® shows essentially no embrittlement or degradation at

temperatures as low as -320°F (-196°C).

Table II-6 Tensile Properties of DuPont

™

Kevlar

29 at

Room and Arctic Temperatures

Property Unit

Test Temperature,

75˚F

(24˚C)

-50˚F

(-46˚C)

Tenacity gpd

(cN/tex)

19.1

(169)

19.8

(175)

Tensile Strength 10

psi

(MPa)

352

(2,430)

365

(2,510)

Elongation at Break % 4.1 3.9

Modulus gpd

(cN/tex)

psi

(MPa)

425

(3,750)

7.82

(53,900)

478

(4,220)

8.81

(60,800)

A 30-inch sample cord twisted to 6.5 twist multiplier was tested, of which 18 inches were

exposed to the cold chamber at a 10%/minute strain rate.

Specific Heat, BTU/lb, °F

Temperature, °F

0.7

0.6

0.5

0.4

0.3

0.2

0.1

32 122 212 302 392 482 572

Table II-5 Heat of Combustion of DuPont

™

Kevlar

and Other Materials

Material

Heat of Combusion

BTUlb Joule/kg

Kevlar

49 14.986 34.8 x 10

Nylon, Type 738 15.950 37.1 x 10

Nomex

aramid 13.250 30.8 x 10

Shell Epon

828/NMA/BDMA 12.710 29.5 x 10

Technical Guide for Kevlar

Aramid Fiber 15

SECTION II: PROPERTIES OF DUPONT™ KEVLAR®

FLAMMABILITY, SMOKE AND OFF-GAS

GENERATION PROPERTIES OF KEVLAR

Kevlar® is inherently flame resistant, but can be ignited

(limiting oxygen index of 29). Burning usually stops when the

ignition source is removed; however, pulp or dust, once ignited,

may continue to smolder. In laboratory testing (Table II-7),

fabrics of Kevlar® do not continue to burn when the source of

ignition is removed after 12 seconds of contact. Although the glow

time increases with the thickness of the fabric, the burn length does

not. No "drips" are experienced, which can cause flame propagation,

a common problem with other organic fibers.

Kevlar® is not intended to be used as fuel, nor should it be deliberately

burned under any circumstances. The laboratory data shown in

Table II-8 were generated to provide important information in case

Kevlar® is accidentally burned.

Burning Kevlar® produces combustion gases similar to those of

wool—mostly carbon dioxide, water and oxides of nitrogen.

However, carbon monoxide, small amounts of hydrogen cyanide

and other toxic gases may also be produced, depending on burning

conditions. The composition of off-gases from Kevlar® and other

fibers under poor burning conditions is shown in Table II-8.

For more detailed information, please refer to the Material Safety

Data Sheet (MSDS) for Kevlar®.

Table II-7 Smoke Generation and Vertical Flammability of Fabrics of DuPont

™

Kevlar

Fabric Smoke** Vertical Flammability

Style

Number*

Fabric

Weight Thickness

Maximum

Specific Optical

Density

Burn

Time Drips Glow Time Burn Length

After-

Burn Time

oz/yd

mil mm sec sec in. cm sec

120 1.7 4.5 0.11 0 12 none 3.0 1.55 3.94 0

281 5.1 10 0.25 7 12 none 5.3 0.97 2.46 0

328 6.8 13 0.33 4 12 none 6.5 0.96 2.44 0

Z-11

††

1.5 12 0.29 0 12 none 1.0 2.50 6.35 0

* Selected fabric constructions commercially available at the time of test.

** National Bureau of Standards Smoke Chamber; Flaming Mode.

† Federal Aviation Administration Part 24, Sections 25, 833 (A) and (B).

†† Kevlar

Z-11 is a nonwoven fabric.

Table II-8 Composition of Off-Gases of DuPont

™

Kevlar

and Other Fibers Under Poor Combustion Conditions*

Combustion Products in mg/g of Sample

CO C

O HCN NH

HCl SO

Kevlar

1,850 50 — 1 — 10 14 0.5 — —

Acrylic 1,300 170 5 2 17 45 40 3 — —

Acrylic/Modacrylic (70/30) 1,100 110 10 1 18 17 50 5 20 —

Nylon 66 1,200 250 50 5 25 20 30 — — —

Wool 1,100 120 7 1 10 30 17 — — 3

Polyester 1,000 300 6 5 10 — — — — —

* The sample is placed in a quartz tube through which air is drawn at a controlled flow and heated

externally with a hand-held gas-oxygen torch. Air flow and heating are varied to give a condition of

poor combustion (i.e., deficiency of oxygen). Combustion products are collected in an evacuated tube

and analyzed by infrared.

Technical Guide for Kevlar

Aramid Fiber 16

SECTION II: PROPERTIES OF DUPONT™ KEVLAR®

EFFECT OF ELECTRON RADIATION ON KEVLAR

Electron radiation is not harmful to Kevlar®. In fact, filaments of

Kevlar® 49 exposed to 200 megarads show a very slight increase in

tenacity and modulus (Figure 2.10).

Figure 2.10 Effect of Electron Radiation on the Tenacity,

Elongation, Modulus and Toughness of Filaments

of Kevlar

49.

A G.E. resonant transformer is used at 0.5 milliamps and 2 megavolts to generate

1 megarad every 13.4 sec. The filament distance from the radiation source is

30 cm [11.8 in.]. The filament is wrapped in aluminum foil and kept over dry ice.

EFFECT OF UV LIGHT ON KEVLAR

Like other polymeric materials, Kevlar® is sensitive to UV (ultraviolet)

light. Unprotected yarn tends to discolor from yellow to brown after

prolonged exposure. Extended exposure to UV can also cause loss

of mechanical properties, depending on wavelength, exposure time,

radiation intensity and product geometry. Discoloration of fresh yarn

after exposure to ordinary room light is normal and is not indicative

of degradation.

Degradation, which occurs only in the presence of oxygen, is not

enhanced by moisture or by atmospheric contaminants, such as sulfur

dioxide. Two conditions must be fulfilled before light of a particular

wavelength can cause fiber degradation:

• Absorption by the polymer; and

• Sufficient energy to break the chemical bonds.

Figure 2.11 shows the absorption spectrum of Kevlar®, along with that

of sunlight. The overlap region of these two curves—especially between

300 nm to 450 nm—should be considered when specifying outdoor

use of unprotected Kevlar®. This range includes the so-called near

UV and part of the visible region. For effective protection of

Kevlar® from UV degradation, this kind of light must be excluded.

Figure 2.11 Overlap of the Absorption Spectrum of Kevlar

with

the Solar Spectrum.

Only small amounts of this light occur in artificial light sources, such as

ordinary incandescent and fluorescent bulbs, or in sunlight filtered by

window glass. However, to avoid possible damage, yarn should not be

stored within one foot of fluorescent lamps or near windows.

Tenacity, Elongation and Toughness

Modulus

Exposure, megarads

0 100 200

1,100

1,000

900

800

700

Tenacity (g/d)

Modulus (g/d)

Elongation (%)

Toughness (g•cm/cm•denier)

≈

Near

Visible

Critical

Wavelength

Region for

Kevlar

Midsummer

Sun & Sky Light

Energy Intensity,

Cleveland, OH

Absorption

of Kevlar

Absorption, arbitrary units

Energy, micro-watts/cm

Wavelength, nanometers

300 400 500 600 700 800

1.0

0.8

0.6

0.4

0.2

1,000

800

600

400

200

Technical Guide for Kevlar

Aramid Fiber 17

SECTION II: PROPERTIES OF DUPONT™ KEVLAR®

Kevlar® is intrinsically self-screening. External fibers form a protective

barrier that shields interior fibers in a filament bundle or fabric.

UV stability increases with size—the denier of a yarn, the thickness

of the fabric or the diameter of a rope.

Extra UV protection can be provided by encapsulation:

• By overbraiding with other fibers; or

• By applying an extruded jacket over ropes and cables.

Whenever a coating, extrudate or film is used, it should not be

UV-transparent. Rather, it should have the proper pigmentation

to absorb in the 300-nm to 450-nm range.

Figure 2.12 shows the UV stability of Kevlar® obtained with a

"Fade-Ometer" equipped with a xenon arc.

Figure 2.12 Ultraviolet (UV) Stability of Kevlar

Yarns.

% Tensile Strength Retained

Exposure

100

450 Hours

900 Hours

Kevlar

4,500 Denier

Kevlar

3,000 Denier

Kevlar

1,500 Denier

Kevlar

1,500 Denier

Kevlar

3,000 Denier

Kevlar

4,500 Denier

Technical Guide for Kevlar

Aramid Fiber 18

Kevlar® is available in several short forms, including staple and floc

(precision cut) and pulp (fibrillated).

KEVLAR

PULP

Kevlar® pulp (Figure 3.1) is a highly fibrillated form of the fiber that

can be dispersed into many different matrix systems. The fibrillation

(Figure 3.2) results in a high surface area of 7 m

/g to 10 m

(170 yd

/oz to 240 yd

/oz).

Figure 3.1 Photograph of Kevlar

Pulp.

Figure 3.2 Photomicrograph of Kevlar

Pulp.

Kevlar® pulp is non-brittle, so standard mixing and dispersion

equipment will not affect the fiber size. Kevlar® pulp is available in wet

form (approximately 50% moisture)* for dilute, aqueous dispersions

and dry form (6% moisture) for solvent-based dispersions and dry

mixes. Various fiber lengths are available to meet your engineering

design needs.

Kevlar® pulp enhances the performance of elastomers, thermoplastics

and thermoset resins, especially where high-temperature performance

is required.

Kevlar® UltraThix™ is available for use as a thixotrope in adhesives,

sealants and coatings (Figure 3.3). Kevlar® UltraThix™ disperses

easily and provides both viscosity control and reinforcement

in most resin systems.

Figure 3.3 Viscosity vs. Shear Rate of Kevlar

Pulp in Epoxy.

SECTION III: DUPONT™ KEVLAR® SHORT FIBERS

0.4% Kevlar

Pulp in Epoxy

Epoxy

Gravitational

Sag

Agitated

Tank

Centrifugal

Pump

Brushing Spraying

Temperature 25°C

Viscosity, cp

Shear Rate, s

-1

⁄ ⁄

-2

-1

*Moisture specifications vary with fiber length and merge.

Technical Guide for Kevlar

Aramid Fiber 19

SECTION III: DUPONT™ KEVLAR® SHORT FIBERS

PRECISION-CUT, SHORT FIBERS

Kevlar

Staple

Kevlar® staple (Figure 3.4) consists of precision-cut, short fibers,

¼ inch or longer. It is used to manufacture spun yarns, which

provide enhanced wear resistance and comfort vs. filament yarns.

Because spun yarns are discontinuous fibers, their applications

generally take advantage of the barrier properties of Kevlar®,

rather than the tensile and modulus properties.

Figure 3.4 Photograph of Kevlar

Staple.

Kevlar® staple is also used in felts and nonwovens to increase

thermal insulation and vibration-dampening properties.

Other applications include thermoset and thermoplastic

resin systems where Kevlar® increases strength and wear

resistance over a wide range of temperatures.

Kevlar

Floc

Kevlar® floc (Figure 3.5) refers to precision-cut short fibers,

shorter than staple, down to 1 mm in length. It can be used as a

reinforcement in a wide variety of resin systems. In thermoplastics,

it provides increased wear resistance with minimal abrasion on

opposing surfaces. In thermoset resins, it provides increased strength

without significantly affecting the viscosity of the system.

Figure 3.5 Photograph of Kevlar

Floc.

Technical Guide for Kevlar

Aramid Fiber 20

SECTION III: DUPONT™ KEVLAR® SHORT FIBERS

KEVLAR

M/B MASTERBATCH

Short Kevlar® pulp is available in a masterbatch form for easy,

uniform dispersion in viscous elastomers. When Kevlar® pulp is

blended with various elastomers it gives enhanced tensile strength

(Table III-1) at elevated temperatures. It also increases the modulus

(Figure 3.6), tear resistance, wear resistance and puncture resistance

of the resulting compounds. To make it easier to incorporate pulp into

elastomers, DuPont offers Kevlar® M/B a masterbatch concentrate.

Kevlar® M/B can also be blended with other elastomers to give

desired end-use properties.

Figure 3.6 Stress-Strain Curve.

Kevlar

M/B more than triples the modulus in the machine direction vs.

an unreinforced elastomer.

2,000

(13.8)

1,500

(10.3)

1,000

(6.9)

500

(3.4)

Fiber

• Natural rubber

• Pull parallel to fibers

10 phr

Kevlar

Pulp

0 100 200 300

Stress, psi (MPa)

Elongation, %

Table III-1 Typical Improvements in Properties of Elastomeric Compounds with DuPont

™

Kevlar

3 phr Kevlar

Pulp in Viton

™

Machine Direction

(MD)

Cross Machine Direction

(CMD)

Room Temperature

Modulus at 50% Elongation 7X 1.4X

Tensile Strength 1X 1X

Tear Strength 1.7X 1.3X

300°F (149°C)

Modulus at 30% Elongation 6X —

Modulus at 50% Elongation — 1.5X

Tensile Strength 1.6X 1.3X

20 phr Kevlar

Pulp in Nordell** 1040/Neoprene FB (80/20)

(MD) (CMD)

Room Temperature

Modulus at 20% Elongation 9.4X 3.3X

Tensile Strength 1X 0.6X

Tear Strength 1.5X 1.4X

300°F (149°C)

Modulus at 8% Elongation 15X —

Modulus at 20% Elongation — 3.9X

Tensile Strength 2.3X 1.3X

Tear Strength 1.9X 1.5X

Technical Guide for Kevlar

Aramid Fiber 21

Break Strength

The force needed to cause failure in a material, irrespective of the cross-sectional area of the sample.

The most commonly used units are "pounds [force]" (lb); "grams [force]" (g); "kilograms [force]" (kg);

and "Newtons" (N).

Bobbin

Smallest production unit of yarn or roving, including its appropriate (usually cardboard tube) support.

Sometimes also referred to as a "package."

Coefficient of Thermal

Expansion (CTE)

Describes the length change per unit of temperature based on the original length of the sample. Its units

are either °F

-1

or °C

-1

, because the length units appear in both the numerator and the denominator:

CTE =

length

length x temperature

Count

Cross section or thickness of yarn or roving expressed as "denier" or "(deci)tex."

Denier

Property unique to the fibers industry to describe the fineness (and, conversely, the cross-sectional

area) of a filament, yarn, rope, etc. It is defined as the weight in grams of 9,000 meters of the material.

An alternative unit is "dtex" (decitex): 1 dtex = 0.9 denier.

Density

The denseness of a material is expressed as mass per unit volume, either as "pounds per cubic inch"

(lb/in.

) or as "grams per cubic centimeter" (g/cm

dtex

Standard abbreviation for "decitex." This is a property unique to the fibers industry to describe the

fineness (and, conversely, the cross-sectional area) of a filament, yarn rope, etc. It is defined as the

weight in grams of 10,000 meters of the material. Its U.S. equivalent is "denier:" 1 dtex = 0.9 denier.

Elongation at Break

Also called "break elongation," it is the change in length of the specimen compared to its no-load length

at the moment of failure under load. It is usually expressed as percent (%).

Equilibrium

Moisture Content

Maximum moisture attained after long exposure.

Filament

Smallest component of a yarn.

Finish

Mixture or emulsion often consisting of oil(s), which is applied to the fiber surface primarily to reduce

friction and to improve processing and/or end-use performance.

Heat of Combustion

The amount of heat released when one gram molecule of a substance is burned in oxygen.

LASE

"Load At Specified Elongation." The load required to produce a given elongation of a yarn or cord.

Its units are lb, kg or g force, etc., at X% elongation. A related property is SASE, "Stress At Specified

Elongation." Its units are "pounds per square inch" (psi), "grams per denier" (gpd), "kilograms per

square millimeter" (kg/mm

), "pascals" (Pa), "Newtons per square meter" (N/m

) etc., at X% elongation.

Merge

Identification code assigned to a specific product with its corresponding production process and

quality control parameters. Usually only shipments with identical merge numbers can be mixed during

subsequent processing, although in some cases merge-mixing is permissible. Check with your DuPont

representative before mixing different merges.

Metered Length

Standard yarn length on a package, controlled within narrow tolerances. This permits matching the

length to your process needs and significantly reduces waste.

SECTION IV: GLOSSARY

Technical Guide for Kevlar

Aramid Fiber 22

SECTION IV: GLOSSARY

Modulus

The property describing a material's resistance to extension. Young's modulus or modulus of elasticity

represents the stress required to produce a given strain or change in length. Modulus is area-specific,

that is, it is expressed based on a unit of the original (i.e., no-load) cross section. Modulus units are

the same as those for "tenacity." The most common examples are "pounds per square inch" (psi);

"grams per denier" (gpd); "Newtons per tex" (N/tex); and "pascals" (Pa).

Moisture Regain

The tendency of most fibers to pick up or give off ambient atmospheric moisture until they reach an

equilibrium moisture content at a given temperature and humidity level.

Poisson's Ratio

The ratio of the strain perpendicular to the loading direction to the strain along the loading direction;

relevant to composites.

SASE

"Stress At Specified Elongation. "The stress required to produce a given elongation of a yarn or cord.

Its units are "pounds per square inch" (psi), "grams per denier" (gpd), "kilograms per square millimeter"

(kg/mm

), "pascals" (Pa), "Newtons per square meter" (N/m

), etc., at X% elongation.

Specific Heat

The ratio of the amount of heat required to raise the temperature of a given mass of a substance one

degree to the amount of heat required to raise the temperature of an equal mass of water one degree.

Strain

In fibers terminology, it is synonymous with elongation and expressed in % (i.e., % change in

original length).

Stress

The force exerted on a material, expressed per unit of the original (i.e., no-load) cross section.

The units are the same as those for "tenacity." The most common examples are "pounds per

square inch" (psi); "grams per denier" (gpd); "Newtons per tex" (N/tex); and "pascals" (Pa).

Tenacity/Tensile

Strength

The ultimate strength exhibited by a material at the moment of failure based on a unit of the original

(i.e., no-load) cross section. The most commonly used units are "pounds per square inch" (psi);

"grams per denier" (gpd); "Newtons per tex" (N/tex); and "pascals" (Pa). Frequently, the term tensile

strength is used synonymously with ultimate stress.

Tex

The basic property, unique to the fibers industry, to describe the fineness (and, conversely, the cross-

sectional area) of a filament, yarn, rope, etc. It is defined as the weight in grams of 1,000 meters of the

material. Its U.S. equivalent is "denier:" 1 tex = 9 denier. In many instances, "decitex" (dtex) is used to

keep fineness numbers about the same as the "denier" values.

Throwster

Company that specializes in putting twist and/or texture into yarns.

Twist (Noun)

The number of turns about its axis per unit length of yarn. The most common units are "turns per inch"

(tpi) and "turns per meter" (t/m): 1 tpi = 39.37 t/m.

Twist Multiplier

A property defined by a mathematical formula to describe the helix angle in a twisted structure.

Twisted bundles with the same twist multiplier (TM) have the same theoretical helix angle,

regardless of their cross-sectional area. The mathematical formula of the twist multiplier is:

TM =

twist [tpi] x denier

twist [t/m] x dtex

73 3,000

Yarn

Bundle (assembly) of individual filaments.

Yield

Length of yarn, rope, etc. contained in a unit weight of package. The most common units are

"yards per pound" (yd/lb) and "meters per kilogram" (m/kg).

Technical Guide for Kevlar

Aramid Fiber 23

SECTION IV: GLOSSARY

ORDERING INFORMATION FOR DUPONT

™

KEVLAR

DuPont produces and sells Kevlar® filament, pulp, staple and floc,

as well as specialized forms, including: Kevlar® M/B masterbatch

and Kevlar® Wearforce™ injection moldable composites.

Please note that all Kevlar® yarns are sold with zero twist.

For more information on DuPont products, call your DuPont

Representative. For additional information, including source lists for

fabrics, other products made from Kevlar®, and for throwsters,

to add twist to yam, call 1-800-931-3456. Outside the United States,

call (302) 999-3358.

To place an order call:

Kevlar

Yarn

1-800-344-8986 or 1-800-441-2767

Kevlar

Pulp, Kevlar

Staple,

Kevlar

Floc, Kevlar

1-800-441-0969

TERMS

• Net 30 days from date of invoice

• FOB shipping point, freight prepaid our route within continental

limits of United States, excluding Alaska.

• All prices subject to change without notice.

Table IV-1 Conversion Table for Yarn Length to Weight

Denier

Number of

Filaments

Yield

yd/lb

Yield

m/kg

55 25 81,175 163,636

195 90 22,895 46,155

195 134 22,895 46,155

200 134 22,320 44,997

380 180 11,749 23,684

380 267 11,749 23,684

400 267 11,160 22,500

720 490 6,200 12,500

750 490 5,952 12,000

840 534 5,314 10,714

1,000 666 4,464 9,000

1,140 768 3,916 7,895

1,420 1,000 3,144 6,338

1,500 1,000 2,976 6,000

2,160 1,000 2,097 4,228

2,250 1,000 1,984 4,000

2,840 1,333 1,572 3,169

2,840 1,000 1,572 3,169

3,000 1,333 1,488 3,000

4,320 2,000 1,048 2,110

4,560 3,072 979 1,974

6,000 744 1,500

7,100 5,000 630 1,268

8,640 4,000 524 1,057

10,800 5,000 413 833

11,400 391 789

15,000 10,000 298 600

The information in this guide was prepared as a possible aid to using Kevlar

aramid fiber. Anyone intending to use recommendations contained in this publication concerning equipment, processing

techniques and/or products should first be satisfied that the information is suitable for their application and meets all appropriate safety and health standards. Refer to other DuPont publications

for safe handling and use instructions for all types of Kevlar

aramid fiber before using product. Both manufacturing and end-use technologies may undergo further refinements; therefore, DuPont

reserves the right to modify fiber properties and to change current recommendations as additional knowledge and experience are gained.

DuPont makes no guarantee of results and assumes no obligation whatsoever in connection with these recommendations. This information is not a license to operate under, or intended to suggest

infringement of, any existing patents.

™

, Kevlar

Wearforce

™

, Kevlar

UltraThix

™

and Nomex

are trademarks or registered trademarks of

E.I. du Pont de Nemours and Company or its affiliates. K-XXXXX (07/18)

Freon

™

, Suva

™

and Viton

™

are trademarks of The Chemours Company FC, LLC.

Epon

is a registered trademark of The Shell Oil Company.

Nordel

is a trademark of The Dow Chemical Company or an affiliated company of Dow.

FOR MORE INFORMATION OR TO REQUEST A PRODUCT SAMPLE,

CALL OR CONTACT:

DuPont

Advanced Fibers Systems

Customer Inquiry Center

5401 Jefferson Davis Highway

Richmond, VA 23234

Tel: (800) 453-8527

(804) 383-4400

Fax: (800) 787-7086

(804) 383-4132

E-Mail: afsc[email protected]

kevlar.com