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 700C
            (1,000 to 1,250F).
         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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