論 文 An Evaluation of Naphthalene-Based Mesophase as a ...

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素TANSO 1992 [No.155] p.417-425 An Evaluation of Naphthalene-Based Mesophase as a Carbon Fiber Precursor J.J. McHugh, G.Z. Liu and D.D. Edie (Received February 28, 1992) Center for Advanced Engineering Fibers Clemson University, Clemson, SC 29634-0909, USA Naphthalene-based mesophase, supplied by Mitsubishi Gas Chemical Co., Inc., (under the commercial name "AR" mesophase) and a heat-soaked mesophase pitch were melt-spun into fiber- form using a pilot-scale extruder. The oxidation conditions of the as-spun fibersformed from each mesophase were optimized (based on tensile strength), and all fibers were graphitized at 2400•Ž. The naphthalene-based mesophase was found to be more spinnable, despite the fact thatits viscosity was more temperature-dependent than that of the heat-soaked mesophase. Also, fibers formed from the naphthalene-based mesophase were found to stabilize more rapidly than those formed from the heat- soaked mesophase. After carbonization, the naphthalene-based mesophase fibers exhibited much higher tensile strengths and moduli than equal-sized fibers produced from heat-soaked mesophase. The naphthalene-based mesophase fibers also exhibited lower electrical resistivities. Wide angle X-ray diffraction showed that the naphthalene-based mesophase fibers developed a smaller average interplanar spacing of the graphite basal planes and a larger average crystallite size than the heat-soaked mesophase pitch-based fibers. KEYWORDS: Mesophase, Melt-spinning, Petroleum pitch, Carbon fiber 1. Introduction Since the stiffness and thermal conductivity of a carbon fiber is a direct result of its graphite-like crystallinity, the precursor for products such as high thermal conductivity fibers must be capable of forming a highly-ordered graphitic structure. Because of this requirement, mesophase pitch is the preferred precursor for this variety of carbon fibers. Mesophase pitch is a liquid-crystalline material, and thus, it tends to orient in a shear field (e.g. during extrusion). During fiber formation, draw down creates additional orientation, yielding large, crystalline domains that extend essentially parallel to the fiber axis. Because of this peculiarity, carbon fibers produced from mesophase pitch precursors can exhibit outstanding stiffnesses and thermal conductivities, significantly higher than those produced from polyacrylonitrile. These mesophase pitch precursors can be produced by heat-soaking a raw petroleum or coal tar-based pitch, or synthetically by polymerizing pure compounds such as naphthalene. 2. Formation of Mesophase Pitch Raw pitch, a high molecular weight by-product formed during petroleum or coal refining operations, is comprised of a rather broad mixture of organic species. Many of these species are heterocyclic and contain highly aromatic components. Often, pitch is classified into four general fractions: saturates, naphthalene aromatics, polar aromatics, and asphaltenes1). The saturates are the lowest molecular weight fraction and are aliphatic. Naphthalene aromatics consist largely of low molecular weight aromatic species. Polar aromatics are larger molecules ―417―

Transcript of 論 文 An Evaluation of Naphthalene-Based Mesophase as a ...

炭 素TANSO 1992 [No.155] p.417-425

論 文

An Evaluation of Naphthalene-Based Mesophase as a Carbon Fiber Precursor

J.J. McHugh, G.Z. Liu and D.D. Edie

(Received February 28, 1992)

Center for Advanced Engineering Fibers

Clemson University, Clemson, SC 29634-0909, USA

Naphthalene-based mesophase, supplied by Mitsubishi Gas Chemical Co., Inc., (under the

commercial name "AR" mesophase) and a heat-soaked mesophase pitch were melt-spun into fiber-

form using a pilot-scale extruder. The oxidation conditions of the as-spun fibersformed from each

mesophase were optimized (based on tensile strength), and all fibers were graphitized at 2400•Ž. The

naphthalene-based mesophase was found to be more spinnable, despite the fact thatits viscosity was

more temperature-dependent than that of the heat-soaked mesophase. Also, fibers formed from the

naphthalene-based mesophase were found to stabilize more rapidly than those formed from the heat-

soaked mesophase. After carbonization, the naphthalene-based mesophase fibers exhibited much higher

tensile strengths and moduli than equal-sized fibers produced from heat-soaked mesophase. The

naphthalene-based mesophase fibers also exhibited lower electrical resistivities. Wide angle X-ray

diffraction showed that the naphthalene-based mesophase fibers developed a smaller average interplanar

spacing of the graphite basal planes and a larger average crystallite size than the heat-soaked mesophase

pitch-based fibers.

KEYWORDS: Mesophase, Melt-spinning, Petroleum pitch, Carbon fiber

1. Introduction

Since the stiffness and thermal conductivity of a

carbon fiber is a direct result of its graphite-like

crystallinity, the precursor for products such as high

thermal conductivity fibers must be capable of forming

a highly-ordered graphitic structure. Because of this

requirement, mesophase pitch is the preferred precursor

for this variety of carbon fibers. Mesophase pitch is

a liquid-crystalline material, and thus, it tends to orient

in a shear field (e.g. during extrusion). During fiber

formation, draw down creates additional orientation,

yielding large, crystalline domains that extend

essentially parallel to the fiber axis. Because of this

peculiarity, carbon fibers produced from mesophase

pitch precursors can exhibit outstanding stiffnesses and

thermal conductivities, significantly higher than those

produced from polyacrylonitrile. These mesophase

pitch precursors can be produced by heat-soaking a raw

petroleum or coal tar-based pitch, or synthetically by

polymerizing pure compounds such as naphthalene.

2. Formation of Mesophase Pitch

Raw pitch, a high molecular weight by-product

formed during petroleum or coal refining operations,

is comprised of a rather broad mixture of organic

species. Many of these species are heterocyclic and

contain highly aromatic components. Often, pitch is

classified into four general fractions: saturates,

naphthalene aromatics, polar aromatics, and

asphaltenes1). The saturates are the lowest molecular

weight fraction and are aliphatic. Naphthalene

aromatics consist largely of low molecular weight

aromatic species. Polar aromatics are larger molecules

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Fig. 1 Typical molecule of a heat-soaked mesophase6).

and may be heterocyclic. Lastly, the asphaltenes are

large, plate-like, aromatic molecules and often possess

aliphatic side-groups. Since the asphaltene fraction

already has a high molecular weight and is highly

aromatic, raw petroleum pitches which contain a high

percentage of asphaltenes (e.g., A-240, A-260) are

usually selected as the feedstock for the formation of

mesophase.

A mesophase, or an optically anisotropic fluid

phase, can be produced by the heating of a highly

aromatic pitch in an inert atmosphere for an extended

period of time. Singer2) developed a process for

converting 50% of Ashland 240 to mesophase by

heating the pitch to 400-410•Ž for approximately 40

hours. During this heat-soak, mesophase tends to

collect at the bottom of the vessel, due to its greater

density. Lewis3) discovered that a more uniform (and

thus, more spinnable) product could be obtained by

agitating the pitch during the pyrolysis. Chwastiak and

Lewis4) were able to produce a 100% mesophase

product by using an inert gas to agitate the reactive

mixture and remove the more volatile components.

Otani and Oya5) have reported that a lower softening

product may be obtained if a hydrogenation step is

added either before or after mesophase formation.

While the mesophase produced by this heat-soaking

technique has a relatively broad molecular weight

distribution, a typical molecule6) is illustrated in Fig. 1.

The formation of mesophase also can be induced

by a solvent extraction technique. Diefendorf and

Riggs7 have shown that a carbonaceous pitch, like

Ashland 240, may be converted to mesophase by first

extracting the pitch with a solvent, such as benzene,

toluene, or heptane. If the insoluble portion then is

pyrolyzed for only ten minutes, a 100% mesophase

product results. The benefit of the huge savings in time is offset, however, by the potential handling hazards and

the high costs of these organic solvents. Furthermore,

if the volatile components are not completely removed,

spinning can be difficult.

The above processes involve the production of

mesophase from a raw (petroleum) pitch. Their primary

advantage is that the raw pitch feedstock is inexpensive,

since it has little other practical value. However, there

are three significant drawbacks to its use as a carbon

fiber precursor. First, the composition of the raw pitch

feedstock may vary from day to day, since it is a by-

product of a very complex process and is, itself, refined from a variable feedstock (crude oil). Also, since the

mesophase produced from raw pitch is comprised of a

wide range of molecular weights, melt spinning can be

difficult to control. Finally, in every step of pitch

production, refining, and subsequent mesophase

formation, the heavy ends are collected. This means

that impurities, which are inevitably present, are

sequentially concentrated. The result is a reduction in

tensile strength of pitch-based fibers due to inclusions,

even after extensive filtration.

These problems have encouraged research into

alternate methods of mesophase production.

Hutchenson et al.8 have reported that supercritical fluid

extraction can be employed to fractionate pitch. By

continuously varying pressure or temperature (and thus,

solvent strength), selective fractions of pitch may be

isolated. Such a process has the potential of producing

a uniform product from a changing feedstock.

Mochida et al.9) have developed a process whereby

mesophase can be produced by the polymerization of

naphthalene or methyl naphthalene, with the aid of a

HF/BF3 catalyst. This catalyst has been studied as a

Bronsted acid "super catalyst" in applications such as

coal liquefaction and aromatic condensation. Its ability

to polymerize aromatic hydrocarbons, however, has

only recently been utilized to produce mesophase.

Mitsubishi Gas Chemical Co., Inc., now utilizes this

technique to produce a commercial naphthalene-based

product, termed AR mesophase, which is reported to

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Carbon Fiber Precursor

Fig. 2 Several benzene-soluble fractions of naph-

thalene-based mesophase10).

be quite spinnable and easily oxidized. Furthermore,

Mitsubishi Gas Chemical Co. has reported that the

properties of the final carbonized fibers formed from this precursor are comparable to the best commercial

mesophase fibers.

The unusual processing characteristics of the

naphthalene-based mesophase are likely due to a

narrower weight distribution, as well as fewer impuri-

ties, compared to mesophases formed by the thermal

polymerization (or heat-soaking) of a natural pitch. Furthermore, the molecular structure of the several

mesogenic species in naphthalene-based mesophase

which have been isolated (see Fig. 2) appears less-

circular than the structure of a typical molecule found

in heat-soaked mesophase, shown in Fig. 1. This dif-

ference in structure certainly could impact the

rheological behavior of the naphthalene-based meso-

phase. In addition, the presence of aliphatic side chains would seem to be favorable for spinning and oxidation.

For this reason, methyl naphthalene may be a better

choice as a starting material than naphthalene for

producing a mesophase precursor for pitch-based carbon fibers11).

3. Rheology of Mesophase

Because of numerous difficulties in modeling

mesophase pitch as a liquid crystalline material, in most

studies a single viscosity is measured, as a function of

shear rate, time, and/or temperature, using a rheometer

of some standard geometry. Although a single viscosity

provides little insight into structural development during

fiber formation, such information can prove very useful

in qualitatively characterizing the spinnability of a

pitch, as well as predicting the approximate temperature

at which an untested pitch may be melt-spun.

Previous research12) has indicated that mesophase

pitch exhibits shear-thinning behavior at low shear rates

and, essentially, Newtonian behavior at higher shear

rates. Since isotropic pitch is highly Newtonian over

a wide range of shear rates, it may be postulated that

the observed pseudoplastic behavior is due to shear-

induced orientation of liquid crystalline domains.

Others have reported that mesophase pitch can show

thixotropic behavior13),14). Thus, the duration of shear

also may influence development or orientation of the

domain structure.

4. Experimental Procedure

In the present study, naphthalene-based AR 824

mesophase pitch, produced by Mitsubishi Gas Chemical

Co., Inc., and a heat-soaked, petroleum-based

mesophase precursor, produced according to the method

of Singer2), were melt-spun into circular fibers. The

time of oxidation was optimized for fibers formed from

each precursor. After being carbonized at identical

conditions, the fibers were characterized by scanning

electron microscopy (SEM), electrical resistivity

measurement, single filament tensile testing, and wide

angle X-ray diffraction. The following procedures were

used to melt-spin, thermally treat, and evaluate these

carbon fibers.

4.1 Rheology

The apparent viscosities, as a function of shear rate

and temperature, of the two mesophase pitches were

measured using an Instron Model 3211 Capillary

Rheometer. In addition, the viscoelastic properties

(storage modulus and loss modulus) of the two mesophase pitches were determined by dynamic

analysis, using a Rheometrics RDSII Dynamic

Spectrometer with parallel plate fixtures.

4.2 Melt-Spinning

The mesophase pitches were melt-spun using a

pilot-scale Akron extruder, shown schematically in

Fig. 3. The system was purged with nitrogen during all

spinning trials. Zone 1 of the extruder conveyed the

solid pitch into the melting zone (zone 2), and zone

3 pumped the molten pitch from the extruder to the

die head. Within the die head, the molten pitch was

forced through a 18 ƒÊm screen filter and, subsequently,

through a 24-hole spinnerette. For the naphthalene-

based mesophase a melt-spinning temperature of 299•Ž

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Fig. 3 Schematic diagram of pilot-scale melt-spinning

process.

was employed, but for the heat-soaked mesophase a

melt-spinning temperature of 343°C was necessary to

obtain a proper extrusion viscosity. Pressures in the die

head ranged from 2.4 to 6.6 MPa, depending upon the

exact extrusion temperature and flow rate of the trial.

Upon exiting the capillaries, the fibers were drawn

down and collected under ambient conditions on a

Fincor variable speed winder. Windup speeds ranged

from approximately 5 to 10 m/s.

4.3 Oxidation

As-spun fibers were cut into lengths of

approximately 15 cm, weighed, and placed in a

nichrome wire-wound furnace. Air was heated to a

controlled temperature and circulated through the fiber

bundle throughout oxidation. Fibers formed from the

heat-soaked mesophase were heated at 5•Ž/min to

180•Ž and at 1•Ž/min to the final temperature of 280•Ž.

This final temperature was considered an appropriate

balance between minimizing the total time of oxidation

without softening the pitch and, thus, sacrificing

structure and properties. The holding time at 280•Ž was

varied from 20 to 120 min. Fibers formed from the

naphthalene-based mesophase were heated at 5•Ž/min

to 270•Ž, and the holding time was varied from 0 to

30 min. This temperature, to which the naphthalene-

based mesophase was heated, was that suggested in the

literature supplied by Mitsubishi Gas Chemical Co. The

fibers oxidized for the various times were carbonized

Fig. 4 Four-point-probe technique for fiber electrical

resistivity determination.

and their tensile strengths were evaluated to determine

the optimum holding time for each precursor.

4.4 Carbonization

Carbonization was performed in two separate steps

for all fibers used in this study. First, fibers were placed

in a graphite boat and inserted into an Astro(R) graphite

resistance furnace which was purged with industrial

grade argon. The furnace was heated at 20•Ž/min to

1000•Ž and held at this temperature for 15 minutes.

A subsequent heat treatment at a higher temperature,

but in the same graphite resistance furnace, served to

graphitize the fibers under flowing ultra-high purity

helium. For this final heat treatment, the fibers were

heated at 60•Ž/min to 2400•Ž and held at this

temperature for 15 minutes.

4.5 Testing

SEM Examination of Transverse Texture. To qualita-

tively examine the transverse texture of the carbonized

fibers, representative samples of the fibers were cut into

approximately 1 cm lengths and attached with copper

tape to aluminum stubs. To prevent charging, the fibers

were coated with a 600 nm layer of gold. After coating,

the stubs were placed into the stage chamber of an

ETEC Autoscan(R) scanning electron microscope and

were scanned at an accelerating voltage of 20 kV.

Measurement of Electrical Resistivity. The electrical

resistivities of the fibers were determined using a four-

point-probe technique, similar to that described by

Coleman15). The apparatus, shown in Fig. 4, consists

of four parallel, 50 ƒÊm diameter, copper wires, with

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1992[No.155] An Evaluation of Naphthalene-Based Mesophase as a

Carbon Fiber Precursor

(a)

(b)

Fig. 5 Apparent viscosity versus shear rate at various

temperatures for (a) heat-soaked mesophase

and b) naphthalene-based mesophase.

Fig. 6 The dependency of viscosity on temperature for

heat-soaked mesophase, naphthalene-based

mesophase, and a typical polymeric fiber

precursor.

the two inner wires separated by 2.5 cm and the two

outer wires by 3.5 cm. Prior to testing, the cross-

sectional area of each fiber was measured. Then, a

measured length of the fiber was placed perpendicular

to, and in contact with, the four copper wires and was

fixed in place using silver conducting paint. Finally,

leads from the four copper wires were connected to the

terminals of a Keithley model 580 micro-ohmmeter.

The two outer copper wires carry a precise, known DC

current, allowing the electrical potential to be measured

across the two inner wires.

Single Filament Tensile Testing. The mechanical prop-

erties of the as-spun and carbonized fibers were

determined by standard single filament testing (ASTM

D3379-75) using a Instron universal testing machine.

Forty filaments of each fiber sample were tested, and

a constant 10 mm gauge length was used for all tests.

Fiber cross-sectional areas were determined optically

via a Zeiss light microscope equipped with a Micro-

Image(R) analysis system. From these test results, fiber

tensile strength, elastic modulus, and strain-to-failure

were calculated.

Wide Angle X-ray Diffraction. Structural parameters

of carbonized fibers produced from the two mesophase

precursors were obtained by wide angle X-ray diffraction. First, small bundles of each sample were

impregnated with a polyester resin and then cured,

yielding a unidirectional composite strand. Next, a 2.54 cm length of the strand was cemented to a circular

aluminum ring. Finally, the assembly was placed in the

azimuthal stage of a Scintag XDS 2000 diffractometer,

and a Bragg scan, using a diffraction angle of the

graphite basal plane peak, was conducted. The resulting diffraction pattern permitted the average interlaminar,

or d002, spacing and the average crystalline stack height,

Lc, to be determined.

5. Results and discussion

Figs. 5a and b illustrate the effect of shear rate on

the apparent viscosity of the two mesophase pitches,

as determined by the capillary rheometer. While both

mesophases exhibit nearly Newtonian flow behavior

over this moderately-high range of shear rates, the

viscosities of both mesophase pitches were extremely

temperature-dependent. This is shown more clearly in

Fig. 6. If one compares the slopes of the viscosity-

temperature curves for these two mesophase pitches

with that of Nylon-6, a typical melt-spun polymer, it

is apparent that the temperature dependence is much

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(a)

(b)

Fig. 7 Master curves of (a) loss modulus and (b)

storage modulus for various fiber precursors

obtained by time-temperature superposition to

their respective spinning temperatures.

stronger for the mesophases. Normally, fluids with

highly temperature-dependent viscosities are difficult to

melt-spin. During melt-spinning the fiber is extruded

from the spinnerette and cools as it is drawn to its final

diameter by the winding device. Thus, the temperature-

dependency of viscosity and the rate of draw down of

the fiber are directly related. When a fluid with a highly

temperature-dependent viscosity is melt-spun, draw

down occurs in a very short distance. The rapid draw

down generates high stress in the spinline, increasing

the number of filament breaks. Note that the viscosity

of the naphthalene-based mesophase has an even

stronger temperature-dependence than that of the heat-

soaked mesophase. Thus, based on its viscosity-

temperature behavior, one might expect the

naphthalene-based mesophase to be more difficult to

spin than the heat-soaked mesophase.

Dynamic mechanical evaluation provides additional

information relating to the flow behavior of the two

mesophase pitches. If a sinusoidal strain is applied to

a viscoelastic material, the in-phase, or storage modulus

measures the elastic response, while the out-of-phase,

or loss modulus represents the viscous component. As

Fig. 7a shows, the viscous behavior of the two pitches

was quite similar (as was indicated by the capillary

rheometer measurements), however their elastic

responses were quite different (see Fig. 7b). These data

were collected at several temperatures, and were

subsequently shifted to each material's spinning

temperature using the time-temperature superposition

principle.

After studying their rheological behavior, the two

mesophase precursors were extruded into fiber-form

using the pilot-scale extruder. Table 1 lists the con-

ditions used during these melt-spinning evaluation

trials. Most materials are spun at a melt viscosity

ranging from 20 to 500 Pa•s. Thus, the spinning

temperatures were chosen to ensure that the viscosities

of the two mesophases were comparable and within this

viscosity range. Note the difference in spinning tem-

peratures, as dictated by the lower softening point of

the naphthalene-based mesophase. One measure of

spinnability, the maximum winder speed at which fibers

could be collected without substantial breakage, was

significantly higher for the naphthalene-based meso-

phase, indicating this material to be the more spinnable.

Table 1 Comparison of spinning conditions of heat

soaked and naphthalene-based mesophase

pitch-based carbon fibers.

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1992 [No.155] An Evaluation of Naphthalene-Based Mesophase as a

Carbon Fiber Precursor

Table 2 Mechanical properties of as-spun mesophase

pitch-based carbon fibers, obtained from single

filament testing (•} indicates the standard

deviation for 40 filaments).

Fig. 8 Mass increase during stabilization for 10 pm

round fibers in air (heating rate = 5•Ž/min).

Based on the viscosity-temperature behavior of the two

mesophases, this result was surprising (recall the

viscosity-temperature relationships of the pitches).

However, as Table 2 illustrates, the as-spun

naphthalene-based fibers have a noticeably higher

tensile strength. This was apparent during all spinning

trials and may account for their improved spinnability.

However, to quantify this effect, samples 14 gm in

diameter (relatively large fibers, because of the

weakness of the mesophase fibers before carbonization)

were melt-spun and tested, in order to obtain a more

reliable force reading.

The as-spun naphthalene-based fibers are more

reactive during oxidation as can be seen in Fig. 8. Even

more striking, however, is the fact that carbonized

naphthalene-based fibers achieve a maximum tensile

strength (Fig. 9a) after only 20 minutes of stabilization,

even though the mass increase is still quite low. Fibers

formed from the heat-soaked precursor require 60

(a)

(b)

Fig. 9 Tensile strength and modulus versus oxidation

time of carbonized (a) naphthalene-based fibers

oxidized at 270•Ž and (b) heat-soaked fibers

oxidized at 280•Ž.

minutes of oxidation to reach a maximum tensile

strength (see Fig. 9b). Note that in the tensile testing

of carbonized fibers, samples of fibers of 7 gm diameter

formed from each precursor were employed. These

fibers were approximately 9-10 gm before heat

treatment.

After carbonization, the transverse microstructures

of the round fibers melt spun from heat-soaked and

naphthalene-based mesophase fibers are quite similar,

as shown in Fig. 10; although, qualitatively, the

naphthalene-based mesophase fibers appear to exhibit

a more-subtle radial texture.

When the mechanical and electrical properties of

heat-soaked and naphthalene-based mesophase pitch-

based carbon fibers are compared (Table 3), it is

apparent that the naphthalene-based fibers are superior

to the heat-soaked fibers in terms of tensile strength,

modulus, and electrical resistivity. Both sets of fibers

were stabilized under optimum conditions, as defined

previously. It should be noted that the naphthalene-

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(a)

(b)

Fig. 10 Scanning electron micrographs of transverse

microstructures of carbonized (a) heat-soaked

and (b) naphthalene-based mesophase pitch-

based carbon fibers.

Table 3 Comparison of mechanical and electrical

properties of heat-soaked and naphthalene-

based fibers carbonized at 2400•Ž (•} indicates

the standard deviation for 40 filaments).

based fibers were able to develop an extremely high

tensile modulus (nearly 80% of the theoretical value of

crystalline graphite) at a relatively moderate

carbonization temperature (2400•Ž).

The superior properties of the naphthalene-based

Table 4 X-ray diffraction data for heat-soaked and

naphthalene-based mesophase fibers after

carbonization at 2400•Ž.

fibers may he traced to structural data obtained by

X-ray diffraction, as Table 4 indicates. The disc spac-

ing of the naphthalene-based fibers is approaching the

graphite value of 0.315 nm. In addition, the average

crystallite site in the naphthalene-based fibers is

significantly larger than that of the fibers produced

from the heat-soaked mesophase.

6. Conclusion

The acid-catalyzed, naphthalene-based mesophase

proved to be more spinnable than the beat-soaked

mesophase. even thought its viscosity is more

dependent on temperature than that of the heat-soaked

mesophase. Not only were fewer filament breaks

observed at any given windup speed. but smaller fibers

could be collected when the naphthalene-based meso-

phase was melt-spun. This improved spinnability may

be the result of the higher measured tensile strength

of the as-spun naphthalene-based mesophase fibers. In

addition, the fibers melt-spun using the naphthalene-

based mesophase could be oxidized more easily than

those formed from the heat-soaked mesophase.

particularly when carbonized tensile strength is used as

the gauge of the sufficiency of oxidation.

Naphthalene-based fibers which were carbonized at

2400•Ž developed a higher tensile strength and

Young's modulus, lower electrical resistivity, smaller

average interplanar spacing. and larger crystallite site

than heat-soaked mesophase pitch-based fibers

carbonized at the same temperature. Thus, the HF/BF3-

catalyzed. naphthalene-based AR mesophase seems to

provide a promising alternative to the classical heat-

soaked mesophase pitches, both from a processing and

a performance standpoint.

7. Acknowledgments

The authors wish to thank the U.S. Department of

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1992 [No.155] An Evaluation of Naphthalene-Based Mesophase as a

Carbon Fiber Precursor

the Navy, Manufacturing Technology Program (Steve

Linder, technical monitor), for supporting this work.

Also, the authors thank D.K. Rogers for his assistance

with carbonization and X-ray diffraction measurement

and K.E. Robinson for her work on the scanning

electron microscope. Finally, the supply of

naphthalene-based AR 824 mesophase pitch,

generously provided by Mitsubishi Gas Chemical Co.,

is greatly appreciated.

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pp. 196-271.2. L.S. Singer, U.S. Patent 4,005,183 (1977).

3. I.C. Lewis, U.S. Patent 4,032,430 (1977).

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5. S. Otani and A. Oya, Petroleum-Derived Carbons,

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