Physical, morphological, and chemical studies of dusts derived from the machining of composite-epoxy materials

ENVIRONMENTAL RESEARCH 45, 242--255 (1988)

Physical, Morphological, and Chemical Studies of Dusts Derived from the Machining of Composite-Epoxy Materials E. S. B O A T M A N , D. COVERT, D. K A L M A N , D. LUCHTEL, AND G. S. OMENN Department of Environmental Health, School of Public Health and Community Medicine, University of Washington, Seattle, Washington 98195 Received August 12, 1987

This work (in three parts) inquires into whether respirable dusts derived from the machining of six composite-epoxy materials (e.g., aircraft industry) may pose a health risk to the operators. Dust samples representative of a variety of composites and structural components were aerodynamically sized and fractionated. Bulk and fractionated samples were examined by light and electron microscopy and analyzed chemically by thermogravimetry (TGA), gas chromatography (GC) and mass spectrometry (MS). Relative fractions of respitable to total mass of bulk samples were <3%; aerodynamic diameters of fractionated particles ranged from 0.8 to 2.0 p.m. By microscopy, bulk particles ranged from 7 to 11 txm in diameter, with mean aspect ratios from 4 to 8:1. Mean diameter of fractionated particles was 2.7 p.m. By TGA, weight losses were negligible below 250°C and variable but elevated at temperatures up to 860°C. In assays of vapors released at 250°C, GC/MS indicated a variety of compounds in different amounts for each sample. We conclude that under the present machining protocols, dusts at the tool face contained few particles of respirable size with no evidence of splitting of fibers longitudinally and were of a low volatilizable chemical content. Overall, composites were judged to be well cured and thermally stable. © 1988 AcademicPress, Inc.

INTRODUCTION The use of carbon, graphite fibers, or fiberglass combined with a binder derived from an assortment of plastics or epoxy resins has become a prominent feature in the design and manufacture of components for the aerospace, military, automobile, and sporting goods industries. The term "carbon fiber" applies to carbonaceous fibrous material pyrolyzed at 1200°C and consists essentially of amorphous carbon. Graphite fibers are carbon fibers heated to between 2200 and 2700°C, resulting in a crystalline fiber structure often referred to as graphite yarn (Zumwalde and Harmison, 1980). The derived fibers are chemically inert, are resistant to high temperatures, have good mechanical strength, are light in weight, and are good electrical conductors. When combined with a binder, the composite material can be molded and machined in a variety of ways (Saracco et al., 1981; Jones et al., 1982). At most stages during manufacture, opportunities exist for the release of fibers into the ambient air; during the machining stage, released particles will be coated with residues of binder chemicals which, if become heated to above 400°C, will vaporize and generate condensation aerosols (Mazumder et al., 1982) often in the form of spheroids (unpublished observations, Boeing Co.). In light of these releases, and of recommendations that toxicologic characterization be incorporated into early stages of materials development (COSEPUP, 1984), we have investigated the possibility of hazards to health from these mate242 0013-9351/88 $3.00 Copyright © 1988by AcademicPress, Inc. All rights of reproductionin any form reserved.

STUDIES OF COMPOSITE-EXPOXY DUSTS

243

rials. Our studies address the question of whether the level of risk from carbon/ graphite fibers might approach that of known fibrogenic/carcinogenic airborne particulates or fibers, such as a-quartz, cotton dust, and asbestos (Ziskind et al., 1976; Nicholson et al., 1981; Imbus, 1986). Although a great deal is known about the constituents and production of carbon-graphite composite materials (Saracco, 1981; Jones et al., 1982; Chou et al., 1986) only scanty data exist on the characteristics of the airborne fibers that are released during manufacturing processes (Connor, 1981; Peters et al., 198I; Mazumder, 1982) and their possible effects on human health (Kowalska, 1982) or in experimental animals (Fedyakina, 1984; Troickaja, 1984). There are no studies employing the multi-disciplinary approach reported here. In the workplace under investigation, graphite dust (primarily particulates) are dealt with in lay-up work, curing, sanding, sawing, cutting, grinding, casting, and machining. Many of these steps were being evaluated in the company development laboratory at the time our studies were initiated, and machine tools were being designed to facilitate work with these new materials. Toxicologic and industrial hygiene information at this stage could influence the tooling and the engineering processes themselves. The present work, in three parts, describes (1) aerodynamic, morphological, and chemical features, (2) cytotoxicological evaluation, and (3) effects on rodents following intratracheal administration of dusts derived from graphite-epoxy and fiberglass-epoxy composite materials as machined in the aerospace industry. The present communication is Part I of the work. MATERIALS AND METHODS

(a) Collection o f Samples Samples of prefabricated graphite fiber-epoxy and fiberglass-epoxy composite components of differing composition were subjected to routine machining operations, and the dusts were collected at the tool face by use of a Nilfisk GS 80 industrial vacuum cleaner device equipped with a bag filter and a Gore-tex 0.3-1~m microfilter (99.95% collecting efficiency) positioned at the exhaust end. Samples were selected as representative of a variety of key structural forms, as well as materials most commonly used by this manufacturer. Sample identification number, materials composition, and machining operation are listed in Table 1. On average, about 800-1000 g of dust/sample was required from a batch of identically machined components to ensure adequate material to complete the full series of analyses. The vacuum collection system was cleaned and new filters were installed prior to each sample collected.

(b) Aerodynamic Sizing Visual examination of the bulk samples of composite-epoxy dust indicated a large fraction of gross particulate matter in some of the samples. Such samples required initial sieving through a 250-p~m screen, after which all bulk samples were redispersed to the aerosol phase by use of a fluidized bed aerosol generator (TSI, Model 93 I0) connected to a 10-cm-diameter cyclone (Fig. 1). The entire unit was

244

BOATMAN ET AL. TABLE 1 MATERIAL COMPOSITION AND TRIMMING OPERATION OF COMPOSITE-EPoxY COMPONENTS

Sample No.

Graphite or fabric type

1 2

Graphite-p a Fiberglass

3

Graphite-PAN/Kevlar

4

Graphite-PAN c

5

Graphite-Pitch a

6

Graphite-PAN

Epoxy system composition

Trimming operation(s)

PEEK b Epoxy + amine curing ~ agent Epoxy + amine curing ~ agent Epoxy + aromatic amind curing agent Epoxy + aromatic amine r curing agent Epoxy + amine curing agent

Spindle shaper: 10,000 rpm Spindle shaper: 3,450 rpm Hand router: 23,000rpm Saber saw Spindle shaper: 3,450 rpm Hand router: 23,000rpm Spindle shaper: 3,450 rpm Hand router: 23,000 rpm

Note. All systems are preimpregnated, i.e., resin impregnation of bundled continuous filaments to form a continuous tape or fabric which is later plied in layers of the same or different alignments. a Proprietary material. b Non-epoxy polyetheretherketone thermoplastic. c Polyacrylonitrile graphite precursor. a Pitch graphite precursor. Two products having similar epoxy and curing agent chemical composition. f Two products having similar epoxy and curing agent chemical composition.

vacuumed, washed, and air-dried between use with each sample. The generator output flow and total cyclone flow were adjusted to achieve a size segregation such that at least 90% by mass and more than 90% by number were particles less than 10 ~zm in aerodynamic diameter (Due). Particle number-size distributions and mass concentration of the resultant aerosol were determined with an aerodynamic particle size analyzer (TSI, APS-33) and filter deposit, respectively. Surface and volume distributions were calculated from the number distribution. Samples of aerodynamically defined material were collected on 25-ram-diam., 2.0:~m-pore-size Nuclepore filters in open-faced cassettes at a flow of 4 liters/rain for morphological analysis, and on 37-ram-diam., 3.0-txm-pore-size Teflon filters

ditution/cyclone drive air 0 to 500 I/m

outpLJtflow 290 tO 500 I/m TSI model 9310 fluidized bed aerosol generator

co particle collection

cyco ll open-faced / I exhaust filter | °l cassette / ° I - - ' ~ ports _~

TSI model 33 aerodynamic particle analyzer

FIG. 1. Schematic of aerosol generating system.

STUDIES OF COMPOSITE-EXPOXY DUSTS

245

(Membrana, Inc.) with fiber backup disks at a flow of 20 liters/min for chemical and biological analysis.

(c) Morphology Material from the bulk samples was examined by light microscopy (LM) with transmitted illumination, Nomarski differential interference optics, and phasecontrast. Random fields were photographed at 205x, prints were enlarged to 656x, diameter and length of the particles were measured by use of a Zeiss Interactive Digitizing System (ZIDAS), and aspect ratios were calculated. Aliquots of the samples were distributed on double-sided sticky tape on aluminum stubs, sputtered with gold-palladium, and observed with a JEOL 35U scanning electron microscope (SEM). Other aliquots were placed on carbon-coated grids and examined with a JEOL 100S transmission electron microscope (TEM). Random fields by SEM (at 0° tilt) and TEM were photographed and printed, and dimensions of the deposited material were estimated by use of the ZIDAS system. Similar procedures were used for fractionated material retained on Nuclepore filters; however, because the fractionated material deposited on the filters was quite fine and not firmly bound to the filter surface, it was necessary to examine them by light microscopy virtually in situ, i.e., by cutting out a quadrant of the filter and mounting directly between a slide and a cover glass. The deposits were photographed by transmitted light at 205x and enlarged photographically to 2563 x on 11 x 14 in. paper.

(d) Chemical Analysis The methods used for survey analysis of chemical vapors released from plastics have been reported previously (Kalman, 1986). Weight loss versus temperature profiles of each composite material obtained by use of thermogravimetric analysis (TGA) were used to establish the quantity of vaporous products produced under controlled heating. This component of the composite dust is comparable to the soluble (non-polymeric) organic material adsorbed to or incorporated in the dust, as confirmed by parallel analysis of solvent extracts and thermal desorption assays. The volatilizable organic fraction was then collected under isothermal conditions by dynamic headspace sampling with cryogenic focusing on fused silica capillary gas chromatographic columns for quantitative and qualitative gas chromatography/mass spectrometry (GC/MS) analysis. Although solvent extracts and dynamic headspace vapor samples showed peak-for-peak correspondence, the latter samples showed higher quantities of all components detected and, specifically, an improved recovery for the more volatile components. Other advantages of this procedure are absence of extraction solvent interference, minimal sample mass requirement (a key consideration when using size-fractionated samples), and minimal handling with less opportunity for chemical decomposition during sample preparation. Weight loss over a temperature range of ambient to 860°C was determined for each sample by use of a Fischer 260F thermogravimetric analyzer driven by a Fischer 360 linear temperature programmer. Vapors evolved by isothermal desorption in an inert atmosphere (nitrogen) were trapped and analyzed by GC-

246

BOATMAN ET AL.

MS (Fig. 2). For characterization of analytical variability and extent, 2.0 txl of an internal standard solution of deuterated naphthalene was spiked into each weighed sample. The vehicle, methylene chloride, was allowed to evaporate before insertion of the sample into the injection port. Sample component spectra were matched against an NBS Mass Spectral Reference Library containing approximately 35,000 entries by searching using an automated survey program.

RESULTS

Aerodynamic Sizing All dust samples contained respirable fractions, defined as a measurable particle number concentration below 10 ixm Dae. The output of the generator was stable over an 8-hr period and generated dust concentrations that were on the order of 20-30 mg/m 3 at flow rates of 200-400 liter/rain. The relative fraction of respirable to total mass of the bulk samples ranged from less than 1% in the case of sample 2, to a few percentages for sample Nos. 4, 5, and 6. Precise quantitative determinations were considered inappropriate because of the large nonrespirable particles present. All samples yielded respirable fractions with number modes that were of a size that could penetrate to the alveolar region of the lung if inhaled. Figure 3 shows the relative number-size distributions of the fractionated dusts; the size statistics are presented in Table 2. Samples 1, 3, and 4 were similar in number distribution. They had a singular mode with a model size of about 1.2 p.m and a significant larger-size tail on their distributions up to 10 txm. Samples 5 and 6 had similar distribution to those above but with a smaller modal size between 0.8 and 1.0 txm. Sample 5 had relatively fewer particles in the mode than the others, whereas sample 2 had a bimodal distribution with modes of approximately equal magnitude at 1.1 and 3.5 ~xm. Due to the non-gaussian form of the distributions it is not valid to express them in terms of simple mean and standard deviation parameters.

Microscopy By light microscopy, the basic graphite yarn (filament winding material) consisted of fibers of 4--8 ~m in width. Following processing with epoxy resins, OVEN INJECTION PORT

G•C - - ~ / / ~

CRYOGENIC k ~'~'~l

T.A.

F

GAS FLOW

I

?

DATA SYSTEM Fro. 2. Instrument configuration for dynamic headspace--GC/MS.

247

STUDIES OF COMPOSITE-EXPOXY DUSTS Sample #2

Relative number

concentration d[N]/dFog Dp

:""," •

0.5

#6

":..

1 2 4 110 Aerodynamicdiameter,Dp, Fm

FIG. 3. Relative number-size distributions of fractionated dusts.

fabrication, and machining of the components, the composite materials released at the tool face ranged in width from 7 to 11 ~m (Table 3). Measurement of width by SEM supported the LM findings (Fig. 4). As expected, particle length varied markedly within each sample (Fig. 5) and between samples; the fiberglass containing sample No. 2 contained the longest "fibers." Aspect ratios varied widely according to fiber length (Table 3). By TEM, all samples contained a small fraction of particles below 0.2 ~m in diameter, and unresolvable by LM. Evaluation of photographs of random fields of fractionated material showed only an occasional particle with obvious fibrous morphology and an aspect ratio greater than 3:1 (Fig. 6). The remaining particles were particulate in form, either square or irregular, and therefore, size determinations were estimated in terms of equivalent circle diameter by a digtizing board and cursor (ZIDAS). Preliminary measurements of bulk material indicated equivalent circle diameter to be a quick TABLE 2 NUMBER-SIzE DISTRIBUTIONS OF SIZE-FRACTIONATED COMPOSITE-EPoxY DUSTS

Aerodynamic diameter (p~m)

Geometric diameter b (p~m)

Sample No.

Modal size

Mean Size

Mean size

6 5 1 4 3 2

0.8 0.9 1.0 1.2 1.2 1.1,3.5"

0.9 1.3 1.3 1.4 1.5 2.1

1.1 1.6 1.6 1.8 1.9 2.6

a Bimodal distribution. b Correcting for density and shape factors.

248

BOATMAN ET AL. TABLE3 AVERAGE FIBERa LENGTHS AND WIDTHS OF BULK COMPOSITE-EPOXY MATERIALS

Sample number

Machine operation

l

Spindle shaper ~0,000 b Spindle shaper 3,450 Hand router 23,000 Saber saw Spindle shaper 3,450 Hand router 23,000 Spindle shaper 3,450 Hand router 23,000

2 3

4 5 6

LM (~m) Length Width 38 (106-22) 295 (624-50) 68 (340-8)

53 (132-16) 27 (61-12) 29 (76-4)

Aspect ratio

10

4:1

11

26:1

8

8:1

7

8:1

8

4:1

7

4:1

SEM 0xm) Length Width 71 (342-23) 262 (2500-32) 109 (340-28)

87 (264-28) 63 (120-34) 210 (1307-26)

7 10 9

8 10 8

Note. LM, light microscopy; SEM, scanning electron microscopy.

" On average, these dimensions do not conform to the definition of a fiber in asbestos usage because fiber widths exceed 3.0 ~m. b Machine speed in revolutions/minute.

appropriate measurement for particles <10.0 ~m in length and about 8 ~xm in width, and for particles of a square or irregular shape. In fractionated material, the mean particle size (equivalent circle diameter) ranged from about 1.7 to 6.0 rxm, with about 74% of particles less than 3.0 ~xm (Table 4). In the original nonfractionated samples, fiber length ranged from 4 to 624 ixm with fiber widths 7 to 11 jxm (Table 3).

Chemical Analysis By TGA, each sample of aerodynamically defined respirable material demonstrated multiple stages of weight loss over a temperature range from ambient to 860°C. Table 5 summarizes the weight lost during each temperature range. Negligible losses were seen below 250°C. Vapor samples obtained from a known weight of unfractionated bulk material subjected to isothermal desorption in an inert atmosphere at 250°C and analyzed by GC/MS (Fig. 2) corresponded to mass loss percentage in the bulk sample of 2 to 3% (Table 5). Although the percent weight-loss variation between samples was small, a variety of different compounds in different amounts was found for each type of sample. There are summarized according to chemical class in Table 5. Oxygen-containing compounds including phthalates and phenols predominated in all samples. Two samples evolved large proportions of chlorinated compounds, and two evolved high percentages of alkanes and alkenes. As an example, Table 6 lists in detail the 14 identified compounds and their quantitative amounts for sample 4. Carbon dioxide, carbon monoxide, and water vapor could also have

STUDIES OF COMPOSITE-EXPOXY DUSTS

249

Fx6.4. Scanning electron micrograph of bulk sample 4. The three large fibers are 47 x 8 ~m; these, with fragments of varying size, are representative of the other graphite-epoxy samples. 1350 x. Marker = 10 t~m.

been evolved, but were not detected by this method. A quantitative comparison of yields of selected compounds of possible concern to health for all six samples is shown in Table 7. DISCUSSION

Due to their remarkable mechanical properties, carbon/graphite fibercomposites are finding rapidly expanding uses. Thus, it is timely to use our knowledge of methods to characterize environmental and industrial derived particulate materials to determine the respirability, chemistry, and potential toxicity of carbon or graphite dusts in order to decide whether stringent controls of workplace exposures should be recommended. Certain questions had to be resolved in designing the study and collecting the samples. Could we expect the chemical composition of a particular material by name to be consistent from batch to batch? and, is the processing, from preimpregnation to the completed formed structure consistent and reproducible? We were assured that the manufacturing of these products, although beyond our control, were within the tolerances demanded by the design/performance specifications. The next question concerned the representativeness of the samples for various kinds of operations. Since the same operator, cutting tool, operating speed, and dust collecting device was used for a batch of identically formed

250

B O A T M A N ET AL.

J

4'

f

J

Fro. 5. Light micrograph of bulk sample 4. In this field, the longest fiber m e a s u r e s 308 x 8 ~xm. 180x. M a r k e r = 50 ~tm.

components, it as likely that any sample from a particular batch would yield comparable analyses. Intrasample variation was not determined. The purpose of the redispersion and size segregation of the bulk dust samples was to provide respirable-sized samples for chemical and morphological analysis and for biological assays. The generator method described here met that need. Furthermore, the stability and output of the generator would yield samples appropriate for inhalation exposures, should these be considered desirable. The combined data on the aerodynamic size of the redispersed, segregated dusts showed the presence of particles between 0.8 and 2.0 ~xm in all of the materials tested. Particles of this size may deposit in the upper and lower respiratory tract by impaction and sedimentation, respectively. Thus, such dusts may have the potential for producing short-and long-term effects on the respiratory system. It should be noted that the proportion of particles of respirable dimensions on a mass basis was only a few percentages of the whole. The range of dimensions of the bulk material in our study was similar to the size range of airborne composite dusts collected in industrial settings by Jones et al. (1982) of 0.5 to 10 rxm diam and by Gieseke et al. (1983) of 6 to 8 fxm. In the latter work, the quantity of fibers released and their lengths varied according to the particular machining operations, which was not the case in our study. For fiberglass, the length of the released dusts depended more on the characteristics of the composite material than the tool used to do the cutting (2 fiberglass vs 5 graphite-pitch, Table 3). For composites

STUDIES OF COMPOSITE-EXPOXY DUSTS

251

I

2

%

Fro. 6. Light micrograph of sample 4 after fractionation. Except for an occasional fiber (arrow; 29 × 7 txm), the material is particulate. 230x. Marker = 50 p~m.

4 and 6, composition and trimming operation were identical, and yet fiber lengths were different. Fiber diameters appeared not to be affected significantly by any operation, in agreement with the findings of Gieseke et al. (1983). Constancy in fiber diameter is probably due to the fracturing of fibers crosswise rather than longitudinally, which occurs with asbestos fibers. In terms of fiber diameter, carbon and graphite fibers are presently the largest in the man-made mineral fibers (MMMF) range, second only to certain types of ceramic fiber. Reported airborne dust levels of carbon/graphite composite materials in various manufacturing plants vary somewhat (e.g., 0.4 mg/m3, Jones et al., 1982; < 1 mg/m 3, Saracco et al., 1.5 to 81 mg/m3, Fedyakina, 1984), presumably depending upon the processes involved, and the ventilation and sampling procedures in force. Of these dusts, the respirable fractions varied from 40 to 70% by weight. In our study, the respirable fractions derived from dusts collected at the tool face were only 2 to 3% by weight. However, it should be stressed that this low fraction of respirable particles is not representative of concentrations in the breathing zone of the machine operators (in our study), since our method of sampling collected all material, including large particles that would settle rapidly and not normally reach the breathing zone. Thus, comparison with personal sampling results is inappropriate. The key aspects of the chemical composition of graphite-epoxy composite dusts that would be expected to account for greater or lesser toxicity would be the completeness of the cure (amount of residual prepolymer and catalysts present),

252

BOATMAN ET AL. TABLE 4 EQUIVALENT CIRCLE DIAMETERS OF COMPOSITE-ExPoxY MATERIALS FOLLOWING FRACTIONATIONa (LM Prints at 2563 ×; ZEISS DIGITIZER) Diameter (t~m)

% Particles with Ixm diam <5.0 <3.0

Sample No.

Range

Mean

Particles counted

1 2nd aliquot 2 3 4 2nd aliquot 5 6 2nd aliquot

9.5-0.7 10.3-0.5 11.3-1.0 9.0--0.9 12.2-0.5 7.8-0.6 6.6-0.6 I0.1-0.5 8,7-0.4

3.1 3.0 6.0 2.8 2.1 1.8 2.2 1.8 1.7

200 227 44 200 206 232 216 227 240

87 78 40 91 92 97 96 94 95

61 64 18 85 83 88 86 90 89

9.5-0.6 0.57 0.07

2.7 0.45

1792

86

74

x SE

a Mean diameter of all particles 2.7 i~m. Percentage less than 5.0 p~m diam, 86%. Percentage less than 3.0 ~m diam, 74%.

the chemical stability of the polymerized material, and the presence or absence of desorbable (nonepolymeric) components in the dust. The last of these could result from the use of coolants or lubricants during machining, from sorption of vapors from the atmosphere where the dust was generated, or from polymer modifiers (plasticisers, stabilizers, etc.) present in the original composite material. As has TABLE 5 THERMAL AND CHEMICAL ANALYSIS OF COMPOSITE DUSTS Sample No,

1

2

3

4

Thermal gravimetric analysis Sample weight (rag) 6.6 4.2 0.68 8.4 T°C at first weight loss 478 235 250 233 T°C at final weight loss 773 695 810 860 Number of AM/AT maxima 2 5 6 5 Weight losses (rag (%)) First 0.2(3.0) 0.1(2.4) 0.03(4.4) 1.6(19.1) Final 6.4(97.0) 0.3(7.2) 0.03(4.4) 2.0(23.8) Chemical composition of emitted vapors at 250°C Mass loss (%) 3.1 2.5 2.4 2.1 Percentage makeup of identified constituents Oxygenated 40.1 36.6 29.7 95.4 Chlorinated 13.7 59.8 48.5 3.4 Aromatics 8.7 2.3 2.6 BD Nitrogen-containing 0.1 0.7 BD BD Alkenes/alkanes 37.4 0.6 19.2 1.2 Number of components identified 117 29 39 14 BD, below level of detection,

5

6

7.4 233 835 5

4.3 233 733 2

0.4(5.4) 4.3(58.1)

1.1(25.6) 3.2(74.4)

2.1

2.6

46.5 7.3 1.7 BD 55.5

89.3 BD a BD BD 10.7

44

17

STUDIES

OF COMPOSITE-EXPOXY

253

DUSTS

TABLE 6 INVENTORY ( M S ) OF ORGANICS RELEASED FOLLOWING ISOTHERMAL DESORPTION (E.G., SAMPLE N o . 4)

Sample N o .

(~xg/g)

% Total identified compounds

167 209 209 5320 192 154 150 73 571 797 300 96 1514 355

0.4 0.5 0.5 84.7 0.5 0.4 0.4 0.6 1.4 1.9 0.7 0.2 3.6 0.9

Name Ethane, c h l o r o Sydnone, 3-phenyl2H-Azepin-2-one, Hexahydro1,2-benzenedicarboxylicacid 1-Decene 3,5-Decadiyne,2,2-DimethylPhosphoricacidtributyle ster 1 , 2 - B e n z e n e d i c a r b o x y l i c a c i d , Butyl-2-Methylpropylester Hexadecanoicacid 1 , 2 - B e n z e n e d i c a r b o x y l i c a c i d , Dibutylester 1H-Isoindole- 1,3(2H)-dione, 2-phenyl4-Undecen-6-one

1,2-Benzenedicarboxylicacid, Diisooctylester Phosphine oxide, Triphenyl

been noted elsewhere (Kalman, 1986), material data safety sheets and manufacturers' specifications or product descriptions are frequently insufficient to permit these factors to be evaluated without chemical analysis. The chemical and thermal analyses indicate that the material has a very high degree of cure, is thermally quite stable, and does not contain a high loading of desorbable material. Specifically, the low percentage of mass loss, particularly at temperatures comparable to machining temperatures, and the absence of detectable prepolymer or catalyst in the chemical analysis support these favorable conclusions. Among the detected agents are compounds widely used as plastic modifiers (phthalate ester, hexadecanoic acid, phosphate esters) while other compoTABLE 7 QUANTITATIVE YIELDS OF COMPOUNDS CONSIDERED TO BE OF PRINCIPAL CONCERN

Sample N o . Compound

1

2

3

----379 . 80 95 162 542 --

-8250 ----

142 5340 22 147 58 . . . . . --

4

5

6

---150 --

------

---9 -78

--

--

(P~g/g) Chloroaniline Dichloroaniline Dichloronitrobenzene Tributyl phosphate Diphenylphosphine oxide Dibenzofuranamine Benzofuran Biphenyl Diphenyl hydrazine Benzothiazole Triphenylphosphine oxide

.

. . . . . 155

. . . .

. . . . .

. . . . 355

254

BOATMAN ET AL.

nents are probable degradation or conversion products of plastic components (eg., alkylphosphine oxides, diphenylhydrazine). There are considerable difficulties in trying to identify in such chemically diverse samples the components that are likely to give rise to health effects or toxicity. Thus, an absolute assessment of chemical hazard from present information is a complex undertaking. What can be said is that this polymeric dust is lower in desorbable and/or reactive chemistry than many or most other plastic products (Kalman, 1986). These findings do not indicate a need for a standard more restrictive than the present nuisance dust standard. However, the biological response(s) to the mixtures represented by these dusts must be evaluated before firm conclusions regarding potential health effects can be drawn. Materials with the least generation of respirable-fraction particles under real manufacturing conditions and with the least hazardous overall chemical releases should be chosen so long as they still meet the design and performance specifications. Such a choice is facilitated when toxicologic characterization occurs early in the materials development process for specific applications. Our studies of the dusts taken at the source indicate the respirable component as particulate and of a few percentages and the fiber portions of typically large diameter. Based on this information, hazard evaluation of work operations might typically include gravimetric analysis of respirable fractions of graphite-epoxy material rather than chemical analysis or fiber counting. Future work will undoubtably focus on characterizing the chemistry, morphology, and potential toxicity of yet newer composite materials of diverse composition. ACKNOWLEDGMENTS We thank the Boeing Company, Michael Stewart, Dr. Barry Dunphy, Dr. Denis Bourcier, and Nicholas Novak for their cooperation and supply of dust samples.

REFERENCES Chou, T. W., McCullough, R. L., and Pipes, R. B. (1986). Composites. Sci. Amer. 255, 192-203. Conner, W. D. (1981). "Monitoring Techniques for Carbon Fiber Emissions: Evaluation A." EPA600/$2-81-145. Environ. Sci. Res. Lab., NC. COSEPUP (1984). "Research Briefing on Polymer Composites." National Academy Press, Washington, DC. Fedyakina, R. P. (1984). Experimental study of the biological effects of the dust of carbon fibrous materials on the organism. Gig. Tr. Prof. Zabol. 7, 30-32. (In Russian). Gieseke, J. A., Reif, R. B., and Schmidt, E. W. (1983). "Characterization of Carbon Fiber Emissions from Current and Projected Activities for the Manufacture and Disposal of Carbon Fiber Products Contract." EPA-68-02-3230. Environ. Sci. Res. Lab., NC. Imbus, H. R. (1986). Cotton dust. Amer. Ind. Hyg. Assoc. J. 47, 712-716. Jones, H. D., Jones, T. R., and Lyle, W. H. (1982). Carbon fibre: Results of a survey of process workers and their environment in a factory producing continuous filament. Ann. Occup. Hyg. 26, 861-868. Kalman, D. A. (1986). Survey analysis of volatile organics released from plastics under thermal stress. Amer. Ind. Hyg. Assoc. J. 47, 270-275. Kowalska, M. (1982). Carbon fibre reinforced epoxy prepregs and composites--Health risks aspects. S A M P E Q. (January, 1982) Sweden, pp. 13-19.

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Mazumder, M. K., Chang R. J., and Bond, R. L. (1982). Aerodynamic and morphological properties of carbon-fiber arosols. Aerosol Sci. Technol. 1, 427-440. Nicholson, W. J., Perkel, G., Selikoff, I. J., Seidman, H, (1981). "Quantification of Occupational Cancer." Banbury Report, 9, Vol. pp. 87-111. Cold Spring Harbor Laboratory, NY. Peters, E, T., Mengies, K. T., Cook, E. J., and Rossetti, M. (1981). "Monitoring Techniques for Carbon Fiber Emissions: Evaluation B." EPA-600/S2-81-145. Environ. Sci. Res. Lab., NC. Saracco, G. B., Scolaris, M., Rubino, G. F., Scansetti, G. (1981). Manufacturing of articles with carbon fiber reinforced plastics (C.F.R.P.) within the Aerospace Industry. G. Ital. Med. Lav. 3, 141-147. Troickaja, N. A., Velickovskij, B. T., Kogan, F. M., and El'vicnyh, L. N. (1984). Comparative fibrogenicity of carbon fibre and asbestos. Gig. Sanit. 6, 18-20. (In Russian). Wagner, J. C. (Ed) (1980). "Biological Effects of Mineral Fibers," 2 Vols., Int. Agency for Research on Cancer, Lyon, France. Ziskind, M., Jones, R. B., and Weill, H. (1976). Silicosis. Amer. Rev. Resp. Dis. 113, 1-23. Zumwalde, R. D., and Harmison, L. T. (1980). "Carbon/Graphite Fibers: Environmental Exposure and Potential Health Implications." US, DHHS, NIOSH, Cincinnati, OH.