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American Industrial Hygiene Association Journal ISSN: 0002-8894 (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/aiha20 The Toxicology of the Pyrolysis Products of Polychlorotrifluoroethylene H. A. Birnbaum , L. D. Scheel & W. E. Coleman To cite this article: H. A. Birnbaum , L. D. Scheel & W. E. Coleman (1968) The Toxicology of the Pyrolysis Products of Polychlorotrifluoroethylene, American Industrial Hygiene Association Journal, 29:1, 61-65, DOI: 10.1080/00028896809342982 To link to this article: https://doi.org/10.1080/00028896809342982 Published online: 27 Dec 2007. Submit your article to this journal Article views: 2 View related articles Citing articles: 2 View citing articles Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=uoeh20 The Toxicology of the Pyrolysis Products of Polychlorotrifluoroethylene H. A. BIRNBAUM,* L. D. SCHEEL, and W. E. COLEMAN Minnesota Mining and Manufacturing Company, St. Paul, Minnesota, and the Occupational Health Program, National Center for Urban and Industrial Health, Public Health Service, Cincinnati, Ohio @ The toxicity of the products of pyrolysis of polychlorotrifluoroethylene (CTFE) was studied by exposure of rats for one hour and three hours. The concentration of the exposure was controlled by the rate of pyrolysis. The three-hour LC, was 31.5 gm/hr for pyrolysis at 375C whereas it was 23.5 gm/hr at 400C. The greater toxicity of the products of pyrolysis at higher temperature was not accompanied by an increase in hydrolyzable fluoride (associated with COF2). It appears that the toxicity may be associated with the particulate products of pyrolysis. Introduction H E POLYMERIZATION of chlorotrifluoroethylene (CTFE) produced a lin- ear polymer with a density of 2.1-2.2, a tensile strength of 4500 to 6000 psi and heat resistance up to 350' to 390F (176' to 193OC). I t has a useful temperature range for applications of 423'F to 390F (-253' to 198'C) and can be molded in conventional thermoplastic molding equipment. Its very low water vapor transmission makes it an outstanding gas and liquid barrier. The high melt viscosity of the plastic at temperatures around 500'F to 600'F (350' to 385'C) requires great care to be taken during the molding process to prevent fracture lines and excessive degradation of the melt during molding operations. The CTFE polymerization reaction which produces long molecules of up to 2000 linked CTFE units is shown in Figure 1. In earlier studies on the pyrolysis of polyCTFE by Treon,l it was reported that the toxicity of the fumes formed during pyrolysis was highest for cats and guinea pigs, less effective in rats and mice and least toxic to rabbits. The cause of death after exposure, in their studies, was reported as acute pulmonary irritation (chemical pneumonitis) and diffuse degeneration of the brain, liver and kidney cells. Their data indicated, but they did not state, that the toxicity of the pyrolysis fumes increased as the temperature of pyrolysis increased above 392'F (200'C). Methods Additional studies on the pyrolysis products of poly-CTFE were conducted in cooperation with the Toxicology Section of the Occupational Health Program at the National Center for Urban and Industrial Health in Cincinnati, Ohio. I n these studies % inch poly-CTFE rod was continuously fed into a 1'/2 inch monel pipe heated to the desired temperature by an electric furnace. The airflow through the FF II F C1 n 1 to 2,000 'Minnesota Mining and Manufacturing Company. FIGURE1. CTFE polymerization. 61 62 January-February, 1966 .- I I I I I I EXPOSURE I 9 I I I I I I I I ,- -/--- , I 'RESSEO AIR INLET I lEXhAUSTl1 SAMPLING PL\ENUM @T FIGURE2. Diagram of the system used for the pyrolysis of CTFE and exposure of animals to the products. furnace was regulated at 4 liters per minute. This airflow produced a rate of flow around the pyrolyzing rod of 5.075 cmJsec. The hot zone in the furnace was 32 cm long and therefore the pyrolysis gases from the rod were present in the hot zone of the furnace for 6.31 seconds. Thus, ample time for gas phase or particle and gas phase interaction was available. The furnace and chamber diagram is shown in Figure 2. The products of pyrolysis contained in the furnace airstream were then delivered into a dilution airstream of 142 liters per minute in a stainless steel pipe connected to the chamber inlet. The chamber was an aluminum wall with Plexiglas window, 1240 liter TABLE I One Hour Exposure to CTFE Pyrolysis Products at a Furnace Temperature of 375OC CTFE Decomposed (Km/hr) Hydrolyzable Fluoride in Chamber (ppm) Mortality (14 days) 21.2 27.9 28.8 35.5 42.9 0 0/10 0 0/10 0 1/10 4.8 1/10 0 0/10 capacity unit. I t was operated as a continuous flow-dynamic system during the exposures. The exposures were accomplished by placing ten rats (five males and five females) in the airlock attached to the chamber and after allowing the chamber to come to equilibrium (30 minutes) the animals were rotated into the chamber exposure atmosphere. The animals were then exposed for the desired time and then removed to the airlock and immediately removed to room air from the airlock. The rats used in these studies were Greenacres, Controlled Flora, Wister strain rats, eight to ten weeks old, which are free of endemic respiratory disease. All exposure groups consisted of ten animals at each exposure concentration and an unexposed group of ten controls was used for each series of exposures. During each exposure four air samples of 2800 cc were collected in 0.5N NaOH for hydrolyzable fluoride determinations. One sample for mass spectrographic evaluation and one sample for infrared analysis were also taken from the chamber during each exposure. Anic ricnn Industrial Hjigiene Association Journal 63 Results During the exposure period of one hour at 375OC (See Table I for the results of this exposure) all of the animals showed minimal discomfort and survived for the total of 14 days, except for one animal lost a t the 28.8 gm/hr and one at the 35.5 .gm/hr concentration. During the exposure a heavy fog was formed by the decomposition particles making it difficult to see the animals. No hydrolyzable fluoride was found in the samples taken except during the 35.5 gm/hr exposure. At the end of the one-hour series a final run at 375OC was carried out. T h e furnace was operated at the maximum rate of pyrolvsis for a total of 31/4 hours. A total of 185.5 grams was decomposed. During exposure, these animals showed hyperactivity but other\vise appeared to be normal. However, shortly after removal from the chamber the animals showed respiratory difficulties, and within two hours two of the animals had died. At the end of 24 hours, three additional animals had died. All the rest died within 48 hours. These animals showed respiratory difficulty due to p u l m o n a r y edema, possibly froin the particles inhaled, In the second series of exposures, animals T V C T ~ exposed for three hours to quantities pyrolized ranging from 27.6 grams to 40.5 gm/hr. For the three-hour period this gave total quantities pyrolized during the exposure of 83 to 122 grams. During the exposure period a very heavy fog was produced in the chamber. These animals showed some hyperactivity but otherwise showed no ill effects during the time of exposure. As shown in Table 11, at the 27.6 gm/hr level: four out of ten animals died in 14 days. while at the 32.8 gm/hr level: seven out of ten animals died in 14 days, and a t the 40.5 gm/hr concentration ten out of ten died. At the 35.2 gm/hr concentration only one out of ten died. T h e calculated LC,, for this exposure is 31.5 gm/hr or 99 grams for the total exposure to CTFE. L'pon autopsy of the animals following a 3% hour exposure to the pyrolysis products from 185.5 <e;m of CTFE, all of the lungs cxhihitrd essentially similar findings. T h e gross appearance of the lungs exhibited hemorrhagic edema. T h e microscopic examination of these lungs revealed numerous small focal hemorrhages, congestion of alveolar walls, and peribronchiolar edema. I n addition, focal emphysema and alveolitis were observed. One animal exhibited focal alveolar cell hyperplasia and fibrin deposition within the alveoli. T h e livers exhibited prominent sinusoidal congestion. No hepatic necrosis was observed. T h e spleens of the animals exhibited prominent reticulum cells. The kidneys e x h i b i t e d severe congestive TABLE I1 Three Hour Exposure to CTFE Pyrolysis Products at a Furnace Temperature of 375% CTFE Decomposed (gm/hr) Total CTFE Burned (gm) Hydrolyzable Fluoride in Chamber (ppm) Mortality (14 days) 27.6 32.8 35.2 -_4 0_ . 5 _ 82.8 98.4 105.5 121.5 15 4/10 37 7/10 13 1/10 39 10/10 FIGURE3. This section of luna tissue shows pro- teinaceous exudative chemical pneumonitis following a 3-hour exposure to fume from the pyrolysis of CTFE. 64 0.1 I 2 5 10 20 40 60 80 90 95 9899 988 FIGURE4. Size distribution of particles in fume from pyrolysis of CTFE. TABLE I11 One Hour Exposure to CTFE Pyrolysis Products at a Furnace Temperature of 4OO0C CTFE Decompo s e d (gm/W Hydrolyzable Fluoride in Chamber (ppm) Mortality (14 days) 16.5 21.2 22.8 26.5 2.2 0/10 2.6 1/10 4.7 2/10 4.7 10/10 January-February, 1968 changes but no foci of necrosis were observed. No particles are seen in the lungs. It would appear that most of the inhaled materials are in the liquid phase (See Figure 3 ) . Figure 4 shows the particle size distribution obtained by electron microscopy from a Millipore@ filter sample obtained from the exposure chamber during a 28 gm/hr pyrolysis. This figure shows that the mean particle size is 0.5 micron with 8570 of the particles being less than 1 micron and 99% of the particles less than 2 microns. Thus the data indicates that all the particles found on the filter are of inhalable size. These results are similar to the size distribution reported in previous papers.2 Since the previous exposure for one hour to 375C had not produced sufficiently lethal results, it was decided to increase the temperature. A series of exposures was carried out using decomposition products at 40O0C, results of which are shown in Table 111. An approximate LC,, value of 23.5 grams of CTFE pyrolyzed per hour was obtained. Mortality at other levels is shown in the table. During this exposure the same fog n v 5 6 7 8 9 10 I I 12 13 W A V E L E N G T H , (JJ) FIGURE5. Infrared spectrum of decomposition products from CTFE pyrolyzed at 540O"C. American lndustrial Hygiene Association Journal 65 type conditions existed in the chamber. I t appears that the increase in temperature greatly increased the effect of the decomposition products of CTFE. Although there is an increase in the hydrolyzable fluoride correlating with the total grams burned, no extrapolation can be made for the amount of hydrolyzable fluoride giving a midway point, since 4.7 ppm in one case killed two out of ten animals and in another case killed all of the animals. During exposures, samples were taken for infrared spectra and one spectrum is shown in Figure 5. This particular one was for an exposure carried out at 54OoC which was the highest temperature used in our studies. The spectra at lower temperatures were quite similar, except that the intensities at the various peaks such as 5.18, 8, 11, etc. were lower. Examination of the spectra shows peaks which may be attributable to COF, or CClF and other peaks which may be due to the COCl groups, and COFCl. I t is postulated that the COCl absorption may come from CF,CICOcl. A typical scan on the mass spectrometer is shown in Table IV. Again, the amount of many of these components increases with the increase in temperature. In all of the analytical work carried out there was no evidence for phosgene. Some other preliminary conclusions appeared to be that the ratio of fluorine to chlorine seems to be similar to that found in the polymer. Presence of many of the ions may be due to the depolymerization of polytrifluorochloroethylene. Additional work is necessary to separate the various components and carry out the identification. The amount of hydrolyzable fluoride when converted to carbonyl fluoride does not seem to be present in sufficient quantities to account for the toxic effect. No other known compounds were found that could account for the lethal results. The action may be similar to polytetrafluoroethylene in that the "particulate" matter may account for the toxic action of the pyrolysis p r o d ~ c t s . ~ - ~ Mass # 47 50 66 69 81 85 93 101 116 131 147 TABLE IV Typical Scan Ion + COF+ or c c 1 + CF2+ COF2+ or CClF+ CF3t cz F3+ CF,Cl+ c3 F3+ CFCl,+ C F el+ C: F: + C,F,Cl+ Summary A series of exposures of rats to the pyrokysis products of polytrifluorochloroethylene has been carried out. In an exposure for one hour at 375C as much as 43 grams was pyrolyzed without attaining a lethal concentration. An approximate LC,, figure of 31% gm/hr or a total of 99 grams in the three hours, was obtained for the 3-hour exposure at 375OC. At a higher temperature of 4OO0C an LC,, of 23% gm/hr was obtained. During exposure large amounts of particles are formed having a size range from 0 to 2 microns. Mean particle size was 0.5 micron. Death may be due to inhalatior, of particles rather than toxic by-products. Analysis of the breakdown products shows a large number of different components present which may include small amounts of carbonyl fluoride, COFCl and COCl containing groups. References 1. TLARREsOoiNJR..F.bJ.. W. CAPPELF ATCHLEY a'nd . P. R. CLEVELANDE. T. DENHA;: T E. he Toxicit; of the Products 'Formed by the Thermal De- composition of Certain Organic Products. Amer. In$. H y g . Assoc. Q u m t . 16: 187 (1955). 2. COLEMANE, ., L. D . ScnEeL and C. GORSKI:The erticles Resulting from Polytetrafluoroethvlene PlrolySU. Amer. I n d . H y g . Assoc. J . 29: 19 (1968). 3. WiciAtyRIdR R. S., and Pyrolysis B. K . KWON:The Inhalation ToxProducts of Polytetrafluoroethylene Heated Below 500 Decrees Centigrade. Amer. Ind. H y g . Assoc. J . 29: 19 (1968). 4. Z*PP J. A. JR.: Toxic and Health Effects of Plastics and Resins. ' A M A Arch. of En&. Health 4: 335 (1962). 5. CLAYTONJ. W. JR.: The Toxicity of Fluorocarbons with SpAcial Reierence to Chemical Constitution. J Occup. M e d . 4: 262 (1962).