&EFK
United States
Environmental Protection
Agency
Environmental Sciences Research EPA 600 279196
Laboratory November 1979
Research Triangle Park NC 27711
Research and Development
Dusts and
Residues from
Machining and
Incinerating
Graphite/Epoxy
Composites
A Preliminary Study
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution-sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-79-196
November 1979
DUSTS AND RESIDUES
FROM MACHINING AND INCINERATING GRAPHITE/EPOXY COMPOSITES
A Preliminary Study
by
Jack Wagman, Henry R. Berger, John L. Miller, and William D. Conner
Emissions Measurement and Characterization Division
Environmental Sciences Research Laboratory
Research Triangle Park, North Carolina 27711
ENVIRONMENTAL SCIENCES RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U. S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711
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DISCLAIMER
This report has been reviewed by the Environmental Sciences Research
Laboratory, U. S. Environmental Protection Agency, and approved for publica-
tion. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
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PREFACE
Environmental protection depends on efforts to detect, identify and
quantify specific pollutants and to assess their effects. As part of this
Laboratory's research to determine the relationships between emissions of
pollutants from all types of sources and air quality, the Emissions Measure-
ment and Characterization Division conducts studies to identify and elucidate
the chemical and physical nature of pollutants emitted to the atmosphere and
develops methods and instrumentation for their measurement.
Projections of greatly increased use of carbon fiber composites in
aerospace, automotive and industrial applications and in a variety of con-
sumer products give rise to concern about future environmental problems that
may be posed. Releases of carbon fibers that may occur in large scale
manufacturing and in the ultimate disposal of carbon composite materials
could constitute significant hazards because of the susceptibility of elec-
tronic and electrical power equipment to damage from exposure to these
highly conducting fibers. The potential health hazard of these fibers is of
less concern at this time. This preliminary study of dusts and debris from
the machining and incineration of graphite/epoxy composites is intended as a
prelude to the research program being conducted by the U. S. Environmental
Protection Agency to characterize carbon fibers released during manufacturing,
handling and disposal of carbon fiber products, develop measurement technology
needed for source and ambient air monitoring of released carbon fibers, and
develop safe methods for disposal of discarded consumer goods and industrial
scrap.
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ABSTRACT
Preliminary laboratory experiments were carried out to obtain some
information on the nature of potential carbon fiber emissions resulting from
the machining and incineration of graphite/epoxy composites. Examination of
residues by scanning electron microscopy following exposure of graphite
fiber products in a laboratory furnace showed the high resistance of graphite
fibers to combustion at temperatures up to 1000°C. Resins and binders in
the composites are destroyed rapidly at elevated temperatures, but one can
predict that the disposal of composite waste materials by conventional
refuse incineration would result in the release of large amounts of both
intact and partly degraded and thinned graphite fibers. In other experiments,
dusts generated by sawing and drilling of graphite/epoxy composites contained
large numbers of fibers free of the resin matrix and generally about 50 to
100 urn in length. There was also evidence of longitudinal cleavage of some
fibers by sawing; the potential thus exists for the formation of more respir-
able fiber fragments with diameters smaller than those (about 6 to 8 ym)
established in the fiber manufacturing process.
IV
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INTRODUCTION
The development of high strength carbon and graphite fibers in the
1950's followed by their embedment in resin matrices resulted in the pro-
duction of materials called composites with highly desirable properties.
Attracted by their light weight and high strength, the aircraft industry has
found steadily increasing applications for these composites in various
structural components of military and commercial aircraft. The necessity
for achieving improved fuel economy in passenger cars is expected to induce
the automotive industry to become by far the largest user of graphite
composites, and projected decreases in graphite fiber production costs are
expected to lead to increased use of fiber composites in industrial appli-
cations, sporting goods and other consumer products.
Evidence has been obtained that carbon fibers such as those used in
advanced composites can cause failures in exposed electrical, electronic,
and power equipment. For example, the burning of carbon composites can
release carbon fibers to the environment and may result in damage to elec-
tronic or electrical equipment. While current usage of carbon composites
poses only a very limited hazard, projected increases in usage could result
in significant hazard. A NASA Technical Memorandum (1) outlines the Federal
Government's plan involving many agencies to study all aspects of this and
other potential problems associated with carbon fibers. As its part of
this plan, the U. S. Environmental Protection Agency has initiated a^program
with the following objectives: (a) to determine the concentration and size
distribution of carbon fibers released during manufacturing, handling, and
disposal of carbon fiber products; (b) to develop measurement technology for
monitoring carbon fiber emissions; (c) to assess the transport and deposition
of carbon fibers in the atmosphere and relate ambient concentrations to
source emission rates; (d) to assess the likelihood of damaging releases of
carbon fibers from conventional solid waste processing, resource recovery,
and disposal technologies; and (e) to modify these technologies or develop
new technology to safely dispose of carbon fiber containing materials.
The program outlined above will be carried out primarily through
contracts, grants and/or interagency agreements. Since extramural research
programs require significant lead times before they can be implemented, some
preliminary experiments were carried out in this Laboratory, using available
facilities and instrumentation, with the objective of obtaining a rough
characterization of dusts and other debris resulting from the machining and
incineration of graphite/epoxy composites. While these experiments involved
only labortory simulations of actual or projected operations, it was felt
that they could yield some useful information on the nature of potential
carbon fiber emissions.
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SUMMARY AND CONCLUSIONS
Examination of residues after exposure of graphite fibers and fiber/
epoxy composites to elevated temperatures in a laboratory furnace demon-
strate the high resistance of graphite fibers to combustion at temperatures
up to 1000°C. Resins and binders in composites are destroyed rapidly but
the fibers remain intact for significant periods even at 1000°C. Resistance
of fibers to damage varies from product to product and probably depends on
degree of graphitization. Damage is first observed in the form of dimpling
and thinning of the fibers after exposure for some minutes at 1000°C. One
can predict from these results that the disposal of graphite/epoxy composite
waste materials by conventional refuse incineration would result in the
release of large amounts of both intact and partly degraded graphite fibers.
Dusts generated by sawing or drilling of graphite/epoxy composites
contain significant numbers of fibers free of the resin matrix. These
fibers generally have lengths of about 50-100 ym. There is also evidence
that sawing can cause longitudinal cleavage of the fibers, thereby making
possible the generation of more respirable fiber fragments with diameters
less than that (about 6-8 ym) determined in the fiber manufacturing process.
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MATERIALS AND METHODS
Assorted samples of carbon fiber and carbon fiber composite materials
were kindly provided by several manufacturers. The types of samples obtained
are listed in Table I including the trade designations and some specifications
given by the manufacturers. It can be seen that these samples included
fibers with a broad range of physical properties in terms of tensile strength
and elasticity, thus reflecting varying degrees of graphitization. Pro-
perties of composites are dependent not only on fiber characteristics but
also on fiber surface treatment, type of resin matrix, proportions and
geometry of the fiber-matrix combination, and resin curing procedure.
Scanning electron micrographs of typical carbon fiber production
samples are shown in Figure 1. The fibers appear to be smooth circular
cylinders with diameters varying from about 5 to 8 pm, though the actual
cross-sectional morphology of different samples vary and include circular,
elliptical and dogbone shapes. Some manufacturers expose fiber surfaces to
a roughing etch to improve inter!aminar sheer strength in the composite.
Also, a sizing or coating of resin is often added to enhance the bonding
capability of the fibers in the composite medium.
Our laboratory-simulated incineration process consisted of the use of
a single-zone tube furnace, shown in Figure 2, to heat carbon fiber and
fiber composite samples to temperatures up to 1000°C. Samples were placed
in ceramic combustion boats which were inserted and heated within a quartz
combustion tube. Temperature was monitored with a thermocouple. Following
various combustion intervals, fibers were collected on glass fiber filters
for microscopic analysis after becoming airborne by purge air circulated
through the quartz tube. In some instances residues remaining in the combus-
tion boats were also analyzed.
In other tests, samples of composite were subjected to cutting with a
hacksaw blade and drilling with carbide-tipped drills in a press. Settled
dust samples thus generated were collected for microscopic analysis.
Fiber residues and dusts were examined with a Bausch and Lomb light
microscope and with an AMR-900 scanning electron microscope (SEM).
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TABLE 1. TENSILE STRENGTH AND MODULUS OF CARBON FIBER SAMPLES9
Tensile Tensile
Product
Designation
GY-705E
Celion 6000
Panex 1/4 CF
Panex 30
Panex PWB-6
Magnamite ASS
Magnamite
A370-8H/3501-6
Thornel 300
WYP 30 1/0
Fortafil 3U
(fiber)
Fortafil 3U
(composite)
Fortafil 5
(fiber)
Fortafil 5
(composite)
Manufacturer
Celanese
Celanese
Stackpole
Stackpole
Stackpole
Hercules
Hercules
Union Carbide
Great Lakes Carbon
Great Lakes Carbon
Great Lakes Carbon
Great Lakes Carbon
Strength
(103 psl)
270
400
325
225b
360
90b
360
360
190b
400
160b
Modulus
(106 psi)
75
34
30
18b
30
10. 5b
34
27
16b
48
23. 5b
Remarks
surface treated,
sized
surface treated,
sized
chopped form,
sized for
nylon resins
epoxy composite
cloth, for
high heat
resistance
sized with
epoxy resin
8-harness satin-
weave composite
surface treated,
sized
no surface
treatment
60% fiber
volume in epoxy
no surface
treatment
60% fiber in
epoxy
Manufacturer's data
Composite properties
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RESULTS
INCINERATION EFFECTS
Exposure of raw carbon fiber samples to temperatures of 200° to 220° C
for 30 to 60 minutes caused little or no damage. As shown in Figure 3,
there were no discernible changes in the appearance of the fibers when
observed in the SEM. At a temperature of 1000° C, however, the fibers
showed definite signs of degradation after a short period. Dimples or pits
in the fibers appeared after 1 minute (Figure 4) and were deep and numerous
after 3 1/2 minutes (Figure 5). A general thinning of the fibers even in
undimpled portions was also noted.
When samples of carbon fiber composite in epoxy resin matrices were
subjected to elevated temperatures, the epoxy matrix material was incinerated
first, leaving the fibers virtually intact at temperatures of 300 - 600° C
and delaying the degradation of fibers at 1000° C. Examination of composite
samples after 5 minutes at 1000° C showed some charred remains of the epoxy
matrix adhering to apparently unaffected fibers (Figure 6), as well as some
fiber clusters completely free of epoxy residue with little, if any, signif-
icant damage to the fibers (Figure 7).
Another type of carbon fiber product subjected to incineration was a
woven cloth (Panex PWB-6 manufactured by Stackpole) designed for high heat
resistance. After exposure for 23 minutes at 1000° C, the cloth fibers
were still in remarkably good condition (Figure 8) though showing very
definite signs of damage including thinning and pitting.
MACHINING EFFECTS
Microscopic examination of dust generated by drilling a sample of
composite (Fortafil 3U manufactured by Great Lakes Carbon) showed (Figure
9) the presence of free fibers in lengths mainly from about 50 to 100 ym in
addition to particles of epoxy debris.
Dust from sawing another sample of composite (Magnamite A 370-84/3501-6
manufactured by Hercules) also contained free fiber fragments (Figure 10).
These were generally shorter than those seen in drill dusts, and the micro-
graphs also show evidence that some were cleaved longitudinally, probably
along the graphitic planes.
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DISCUSSION
This preliminary laboratory study has demonstrated the high resistance
of graphite fiber products to combustion at temperatures up to 1000° C.
There is no doubt that the disposal of graphite fiber composite waste materi-
als by conventional refuse incineration would result in the release of air-
borne graphite fiber residues. Released fibers will be intact in some
instances and partly degraded and thinned in others. The resistance of carbon
fibers to incineration is dependent on their degree of graphitization. It
is clear that the control of carbon fiber emissions from the incineration of
waste composite materials will require either high efficiency fiber trapping
or incinerator designs that permit more complete combustion of fibers.
Although free graphite fibers may be released by the sawing or drilling
of composite materials, these generally have lengths less than 100 ym and
are therefore likely to have a very low potential for causing electrical
equipment failure. On the other hand, fibers released by these and other
types of machining operations (cutting, grinding, etc.) are in a size range
that requires an assessment of potential health hazards. Since most of the
fibers generated have diameters (about 6-8 ym) that are predetermined in
the fiber manufacturing process, their health effects are likely to be limited
to skin, eye, and upper respiratory tract irritation. However, the evidence
that longitudinal cleavage of fibers can occur requires that due consideration
be given to the possible generation, during manufacturing operations, of
significant numbers of smaller diameter fibers which can penetrate more
deeply into the lungs and therefore constitute a greater respiratory hazard.
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REFERENCES
1 Carbon Fiber Study. Technical Memorandum 78718, National Aeronautics
and Space Administration, Washington, D. C. 20546, May 1978.
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lOpn
(b)
5pm
Fig. 1
SEN! micrographs of carbon fiber samples:
(a) Panex 1/4 CF (Stackpole); (b) Magnamite
AS3 (Hercules).
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Fig. 2 Laboratory quartz tube combustion furnace.
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10 [in
Fig. 3
SEM micrograph of carbon fiber [Thornel 300 (Union Carbide)]
sample after exposure for 30 minutes at 200-220°C.
Fig. 4 SEM micrograph of carbon fiber [Thornel 300 (Union Carbide)]
sample after exposure to a temperature of 1000°C for 1 minute.
10
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Fig. 5 SEM micrograph of carbon fibers [Thornel 300 (Union Carbide)] after
exposure for 3.5 minutes at 1000°C.
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(a)
10|JfT
f
(b)
Fig. 6 Micrographs of residues after exposure of graphite/epoxy
composite sample [Fortafil 5 (Great Lakes Carbon)] for
5 minutes at 1000°C: (a) SEM micrograph; (b) optical
micrograph.
1
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10 ^n
Fig. 7 SEM micrograph of fiber residue following exposure
of graphite/epoxy sample [Fortafil 5 (Great Lakes Carbon)]
for 5 minutes at 1000°C.
13
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1 Opm
Fig. 8
Woven cloth sample [Panex PWB-6 (Stackpole)] after
exposure for 23 minutes at 1000°C: SEM micrographs
at two different magnifications.
::
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•
(a)
(b)
1 0 t- f
Fig. 9 SEM micrographs of dust particles from drilling a sample of
graphite/epoxy composite: (a) large particle containing
fibers still bound in resin; (b) free fibers.
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3 pm
Fig. 10 SEM micrographs of dust particles from sawing a
graphite/epoxy composite sample.
16
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TECHNICAL REPORT DATA
(rlease read instructions on the reverse before completing)
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
IUSTS AND RESIDUES FROM MACHINING AND INCINERATING
iRAPHITE/EPOXY COMPOSITES
Preliminary Study
5. REPORT DATE
November 1979
6. PERFORMING ORGANIZATION CODE
AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
ack Wagman, Henry R. Berger,
nd William D. Conner
John L. Miller,
i. PERFORMING ORGANIZATION NAME AND ADDRESS
:nvironmental Sciences Research Laboratory
Dffice of Research and Development
I. S. Environmental Protection Agency
Research Triangle Park, N. C. 27711
10. PROGRAM ELEMENT NO.
1AD712B BE-009 (FY-79)
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Sciences Research Laboratory-RTP, NC
Jffice of Research and Development
J. S. Environmental Protection Agency
Research Triangle Park, N. C. 27711
13. TYPE OF REPORT AND PERIOD COVERED
Tn-hnuse in/7ft-Q/7Q
14. SPONSORING AGENCY CODE
EPA/600/09
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Preliminary laboratory experiments were carried out to obtain some information
the nature of potential carbon fiber emissions resulting from the machining and
incineration of graphite/epoxy composites. Examination of residues by scanning
electron microscopy following exposure of graphite fiber products in a laboratory
furnace showed the high resistance of graphite fibers to combustion at temperatures
jp to 1000°C. Resins and binders in the composites are destroyed rapidly at elevated
temperatures, but one can predict that the disposal of composite waste materials by
:onventional refuse incineration would result in the release of large amounts of both
intact and partly degraded and thinned graphite fibers. In other experiments, dusts
generated by sawing and drilling of graphite/epoxy composites contained large numbers
)f fibers free of the resin matrix and generally about 50 to 100 ym in length. There
vas also evidence of longitudinal cleavage of some fibers by sawing; the potential
thus exists for the formation of more respirable fiber fragments with diameters
smaller than those (about 6 to 8 ym) established in the fiber manufacturing process.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
COSATI Field/Group
''Carbon fibers
Epoxy resins
Machining
Incinerators
''Dust
*Residues
*Electron microscopy
HE
111
13H
13B
116
14B
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
21. NO. OF PAGES
21
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE
17
,.,-nent Printinq office: 1979- fi39-?M/ •
Reqion ^o. 3-II
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