United States
Environmental Protection
Agency
Environmental Sciences Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S3-84-021 Feb. 1984
v>EPA Project Summary
Characterization of Carbon
Fiber Emissions from Current
and Projected Activities for the
Manufacture and Disposal of
Carbon Fiber Products
J. A. Gieseke, R. B. Reif, and E. W. Schmidt
Carbon and graphitic fibers emitted
during fiber or composite manufacture,
handling, and disposal were character-
ized according to mass concentrations,
number concentrations, and size distri-
butions; chemical, optical and morpho-
logical properties; and electrical and
physical properties that cause problems
in electrical and electronic devices.
Samples were collected from air streams
that controlled fiber release from manu-
facturing operations, or near such oper-
ations when no air flow control existed.
Operations studied included fiber wind-
ing, prepregging, and weaving, as well
as composite cutting, grinding, drilling,
machining, sanding, and incineration.
The rate of fiber mass released per
unit of material processed in the opera-
tion ranged over several orders of magni-
tude, with the largest releases associ-
ated with weaving and incineration. In
most cases, control of emissions seemed
to be effective.
This Project Summary was developed
by EPA's Environmental Sciences Re-
search Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering in-
formation at back).
Introduction
Carbon and graphitic fibers are chemi-
cally inert, resistant to high temperatures
and thermal shock, light weight, good
electrical conductors, and have good
mechanical strength. Because of these
properties, composites formed from the
fibers combined with a binder material
(such as epoxy or various plastics) are
being used in an increasing number of
aerospace, military, commercial, and
industrial applications. Carbon fibers are
made by heating organicfibersfnatural or
synthetic) at high temperatures without
oxygen. The long lengths of synthetic
fibers make them adaptable for lay-up
and woven products.
Whenever carbon fibers are produced,
handled, woven, or impregnated with a
binder, the manufacturing operations
provide some opportunity for the fibers to
break off and to be released into the
ambient air. In manufacturing operations
with the composite materials such as
cutting, sanding, or machining, oppor-
tunities again exist for fibers to be re-
leased. Finally, release of fibers can occur
during the use of composites or more
significantly during disposal of the prod-
ucts through incineration.
Because of their physical properties,
carbon fibers released to the ambient air
may pose special problems, such as the
potential for carbon fiber interference
with or shorting out of electrical and
electronic devices. Although much is
known about the carbon fibers as used in
manufacturing operations, the release
rates or characteristics of the released
fibers are not well established. Manu-
facturers, processors, and end-product
users are usually aware of problems
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associated with carbon fiber release and
in most cases use good housekeeping
practices and protective or removal tech-
niques to eliminate excessive carbon
fiber emissions.
The original fiber diameters were main-
tained in the emitted material to improve
control methods and to determine typical
release incineration where fiber diam-
eters were reduced slightly by burning.
Fiber lengths varied over wide ranges
from tens of thousands of micrometers.
Incineration experiments suggested that
mechanical agitation and air flow in the
incinerator would strongly affect releases.
Chemical characterization indicated
that, as expected, the fibers were com-
posed almost entirely of carbon with only
a few percent or less by weight being
hydrogen and nitrogen. Analyses of sam-
ples collected from the manufacturing
operations indicated that particles other
than the fibers were characteristic of
materials normally present in the ambient
atmosphere. Electrical characterization
of the fibers demonstrated that fibers will
move and form chains in electrical fields
and that for low power electronic equip-
ment, the intrusion of fibers could cause
significant damage or disruption of nor-
mal operation.
Conclusions
Based on the sampling and analyses of
carbon fibers, experimental evaluation of
their electrical properties, and studies of
their burning characteristics, the follow-
ing conclusions have been reached:
1. Of the manufacturing operations or
processes investigated, drilling and
weaving release the most carbon
fibers
2. Tne a mount of carbon fiber released
and the distribution of fiber lengths
are highly dependent upon the
particular machining or manufac-
turing operation. Fiber diameter is
not significantly affected by any
operation except incineration.
3. Releases of carbon fibers during
incineration of composites will de-
pend on the degree of mechanical
agitation of the burning material
and on the air flow rate in the
combustion region. Atypical emis-
sion rate of carbon fibers from the
burning zone in a municipal incin-
erator would be approximately one
percent of the composite being
burned.
4. Composites made with epoxy binder
materials are expected to give a
greater fiber release during combus-
tion than those made with phenolic
binder materials.
5 The burning rate for carbon fiber
composites is a sensitive function
of temperature with the burning
rate increasing rapidly with temper-
atures ranging from 500 to 700°C
(1,000 to 1,250°F).
6. The resistance of graphitized carbon
fibers ranges between about 1 x 103
and 25 x 103 ohms per centimeter
of fiber length, and fibers between
0.6 and 1.25 cm long will conduct
currents of about 5 to 1 5 ma befc
burning with power inputs of 0.2
0.5 W
7 Fibers orient in electrical fields a
will form chains to bridge gaps th
are longer than individual fibers.
8. Carbon fibers will move in t
direction of increasing field streng
in nonuniform electrical fields, a
in uniform fields will move back a
forth between plate electrodes
the fibers are charged, attracte
and discharged successively with
the field and on contact with t
electrodes.
9. The risk to electrical and electror
equipment increases as the a
borne concentration and carb<
fiber length increase and as t
distance between circuit elemer
decreases.
10. Only sudden infusion of large nui
bers of fibers would cause any ri
to most electrical systems operati
at 110 V and greater than 1 \
however, electronic equipment opt
ating at low power levels could
damaged or be made unreliab
perhaps insidiously, by only a sing
critically located fiber.
J. A. Gieseke, R. B. Reif. and E. W. Schmidt are with Battelle-Columbus
Laboratories, Columbus, OH 43201.
Kenneth T. Knapp is the EPA Project Officer (see below).
The complete report, entitled "Characterization of Carbon Fiber Emissions from
Current and Projected Activities for the Manufacture and Disposal of Carbon
Fiber Products," (Order No. PB 84-149 632; Cost. $10 00, subject to change]
will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Sciences Research Laboratory
U. S Environmental Protection Agency
Research Triangle Park, NC 27711
Umtec S:ates
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45260
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