Document aB4zvLGrVkNxV7yYx0nNdeERy

BIO-MEDICAL RESEARCH DOCUMENT DESCRIPTION FORM Duplicate in all cards: 63 68 69 76 ll yo I 0M9324 year as-1961- File number [Right justify [Numeric only] Author(s), as Last Name FS (No Punctuation) and coden for journal as JAMA preceeded by one blank space 120 21 /' r.'] c. f\ ~ u _____ n^ 1 40 41 77 78 Sub-Index Code 60 61 62 11 12 13 Title of Report; end with space-hyphen-hyphen-space. Follow with Index Terms, separated from each other with comma-space. Avoid other punctuation; Brief Summary 12 10 SUMMARY: 61 62 61 62 63 64 R&S 111371 0000324 Vinyl Chloride Formation from the Thermal Degradation of Poly(Vinyl Chloride) I. B. WAKEMAN and H. R. JOHNSON Tenneco Chemicals, Inc. Corporate Research and Development Department Piscataway, New Jersey 08854 The volatile products from the thermal degradation of polvjvinyl chloride)(PVC) resins and compounds are shown to contain trace amounts of vinyl chloride. Data presented show the effect of temperature and resin type on the amount of vinyl chloride formed. At the maximum temperatures involved in PVC processing which may reach 21QC, vinyl chloride monomer (VCM) evolution amounts to less than 1 ppm (resin basis). A technique employing a thermogravimetric balance and charcoal adsorption of volatiles is described for studying thermal degradation of PVC. The volatiles are analyzed for vinyl chloride by gas chromatography. Peak identity was confirmed by mass spectrometry. INTRODUCTION Numerous studies and surveys have been published describing the thermal degradation and pyrolysis products of poly(vinyl chloride) (PVC). These studies have shown that at elevated temperatures essentially quantitative dehydrochlorination of PVC occurs, result ing in the formation ofa complex mixture ofaromatic and aliphatic hydrocarbons with benzene being the largest single component (1-8). Stromberg, et al. (1) studied the decomposition of PVC under vacuum at temperatures up to 400C and measured the variations in the decom position products as a function oftemperature. They did not indicate the formation of any vinyl chloride monomer (VCM) under these conditions. Boettner, et al. (2) investigated the thermal degradation of PVC in air up to 600C. Using infrared spectroscopy and gas chromatography-mass spectroscopy, they identified ap proximately 50 volatile degradation products and mea sured the rate of formation of the major products as a function of temperature. Their data indicate that up to 600 ppm ofVCM is formed from PVC homopolvmer and up to 3000 ppm from PVC compounds. Although no mention is made of residual VCM in the polymer, the bulk of the VCM was detected in the 2S0-430C range and it is inferred that VCM is produced during the thermal decomposition. Woolley (3) reported low levels of VCM in PVC pyrolysis products but did not measure residual VCM, and it is not clear whether any VCM was actually formed during the decomposition. Lewis (4) has recently reported degradation studies ofa hoinopolymer having a residual VCM content of < 0.5 ppm and found a maximum VCM formation of 35 ppm at 350C. The recent findings (9) of carcinogenicity on pro longed exposure of test animals to elevated conccn- trations of vinyl chloride in the air and of cases of an giosarcoma in vinyl chloride workers have caused seri ous concern about the effects on workers involved in all phases of PVC manufacture and fabrication. Although present day manufacturing processes have reduced the residual VCM content of PVC resins and compounds to very low levels (10), the possibility of forming VCM by degradation of the polymer during calendering, extru sion, and thermoforming operations is still a cause of concern. There is very little likelihood of VCM formation dur ing thermoforming of PVC for food packaging applica tion since this operation is carried out under mild conditions(90-120C for a few seconds). It has been demonstrated previously that no detectable VCM is formed in up to 1 h exposure at 130C, using an analyti cal method capable of detecting 1 part per billion of VCM (10). During calendering and extrusion operations, how ever, temperatures may reach the 175-210C range for brief time periods. We know of no published informa tion involving VCM formation under these conditions. Our present work involved the investigation of the thermal degradation of PVC over the 130-500C tem perature range with special emphasis on VCM formation at 210C, the upper limit used in PVC fabrication. EXPERIMENTAL Thermal degradation studies were carried out using a duPont Model 950 thermal balance which provided a convenient method for accurately controlling the tem perature and heating rates. Samples ofS0-100 mg were placed in a platinum foil boat suspended on the thermal balance sample holder. The furnace tube surrounding 404 POLYMER ENGINEERING AsO SCIENCE, APRIL, 1978, V0I. 18, No. 5 Vinyl Chloride Formation from the Thermal Degradation of Poly(Vinyl Chloride) the sample was s\vept with clean air at 60 ml/min. Prior to starting the thermal degradation run, the sample was held at 130aC for 30 min with air flowing in the furnace (tube. This procedure has been demonstrated to com pletely remove all residual VCM in the sample without causing any decomposition (10). After this conditioning period, the exit side of the furnace was fitted with a short glass U-tube immersed in a cracked ice bath. This served to cool the sweep gas prior to passing it through a standard NIOSH approved, charcoal personnel monitoring tube (SKC #226-01) to adsorb any VCM resulting from the degradation of the sample. At the completion of the run the contents of the charcoal tube were transferred to a vial capped with a Teflon lined septum (SKC 226-02-100). The vial was held in an acetone-dry ice bath and 1 ml of carbon disulfide injected through the septum. The vials were then allowed to stand at room temperature for 30 min to desorb the VCM. Gas Chromatography A Perkin Elmer Model 3920 gas chromatograph equipped with dual flame ionization detectors was used in this work. In view of the large number of products formed during the thermal degradation of PVC, and the additional degradation products formed from additives incorporated in PVC compounds, a variety of columns were screened to obtain optimum separation of the VCM peak. A combination column of a 10 ft x 1/8 in. Porapak P (Waters Associates) followed by a 10 in. x 1/8 in. Chromoso'rb 104 (Johns Manville) was finally selected for the separation. This column operated at 85C with a helium carrier gas flow of 25 ml/min gave good separation of the VCM peak (retention time--6 min). Initially, in order to definitely establish the identity of the "VCM" peak, exposed charcoal tubes were submit ted to a commercial laboratory (11). Using the same GC column, samples of the carbon disulfide solutions were injected into a gas chromatograph-mass spectrometer instrument. Mass spectrometer scans made at three points on the VCM peak (peak maximum and leading and trailing portions) identified the peak as being en tirely VCM. The VCM peak from the thermal degrada tion of certain PVC compounds prepared with sulfurcontaining stabilizers, however, showed the presence of sulfur dioxide. This interference was eliminated by plac ing a 2-in. tube packed with Mallcosorb (Mallinckrodt Chemical Works) immediately before the carbon ad sorption tube. The Mallcosorb tube was shown to have no effect on VCM recovery by passing known amounts of VCM through the tube and analyzing the effluent gas. Ten microliter aliquots of the carbon disulfide solu tion were injected into the gas chromatograph. Peak areas were determined using a Spectra-Physics Model 6300 digital integrator. The VCM produced was calcu lated by comparing the VCM peak area of the sample to the areas produced by injecting known gas standards (Alltech Associates). The minimum amount of VCM which could be detected was 0. L nanogram, equivalent to 0.1 ppm of VCM from the 100 mg resin sample. Thermal Degradation Initial studies involved thermal degradation of PVC over the 130 to 500C range using a heating rate of 103C/min. A variety of PTC resins from different pro ducers were tested for total VCM evolution over this temperature range to determine if resin txpe of man ufacturing source has any effect on the amount of VCM produced. A few commercial compounds were similarly tested to determine the effect of stabilizers and other additives on VCM evolution. Thermal Degradation at PVC Fabrication Temperatures In order to determine ifany exposure danger exists for workers involved in PVC fabrication operations, a series ofpolymers, compounds and PVC sheets were tested for VCM formation during 5 and 30 min heating periods at 210C the maximum temperature which would be em ployed in PVC processing. Effect of Temperature on VCM Formation VCM formation as a function of temperature was de termined on a homopolymer sample over the range of 200-450C at a heating rate of3/min. The charcoal tubes were changed at 25 intervals during the heating cycle and analyzed individually for VCM content. The corre sponding thermogravimetric analysis (TGA) curve was recorded at the same time to provide a comparison of weight loss with VCM formation. RESULTS V The total amounts of VCM evolved from the thermal decomposition of a variety of PVC homopolymers and PVC-PVAC copolymers are listed in Table l. Samples are included from six different producers. A consistently low level of VCM amounting to 15-30 ppm (based on Table 1. VCM Formation from Thermal Degradation of PVC (130-500C) Resin VCM, ppm (resin basis) Homopolymers Suspension low mol wt Suspension low mol wt Suspension medium mol wt Suspension high mol wt Suspension high mol wt Dispersion Dispersion Dispersion Dispersion Dispersion Dispersion Blending Blending Blending Solution Polym. 19 23 22 18 20 21 20 19 16 22 19 19 15 31 21 Copolymers Type 1 Type 2 Type 3 20 25 20 R&S 111372 POLYMER ENGINEERING AND SCIENCE, APRIL, 1973, VoI. 18, No. 5 405 I. B. Wakeman and H. R. Johnson resin) was found in the volatile decomposition products from all of the samples tested, regardless of resin type or manufacturing source. To insure against a possible catalytic effect from the platinum boat, two homopolvmer and one copolymer samples were run using a glass boat. The levels of VCM produced were identical to those obtained using the platinum boat. Results obtained from the degradation of typical PVC compounds containing the most commonly used com mercial stabilizers are shown in Table 2. Again, low levels ofVCM were found for all samples, indicating that the presence of stabilizers and other additives in the compounds does not inhibit the formation of VCM. The effect of temperature on VCM formation from homopolymer is shown in Table 3 and in Fig. 1. Pro gramming a 100 mg sample from 200 to 450C at 3/min resulted in the formation of a total of23.2 ppm of VCM, the major portion being generated in the 275-350 re gion. The corresponding weight loss curve shows that dehydrochlorination occurs most rapidly in the 250275C temperature interval. During this period only 2.3 ppm ofVCM is formed. Under the conditions employed in these studies, the major amount of VCM is formed after dehydrochlorination is essentially complete, leav ing a dark-colored residue. Programming the same homopolymer at 10/min and finishing with a 30 min hold at 450C, also resulted in the formation of 23 ppm of VCM. A primary objective of this study was the determina- r Table 2. Formation of VCM from Degradation of PVC : Compounds Heated from 130 to 500C at 10*C/mln Compound type Stabilizer type VCM, ppm (compound basis) Filled flexible Filled rigid Flexible Flexible Flexible Flexible Pb Pb Unknown Butyl tin Unknown Ba, Cd, Zn, P 27 13 40 27 27 52 Table 3. Effect of Temperature on VCM Formation from Homopolymer Temperature, `C Total VCM formed, ppm (resin basis) Weight loss, percent by weight 200 N.D. 225 N.0. 250 N.D. 275 2.3 300 8.6 325 15.4 350 19.4 375 21.4 400 22.4 425 23.2 450 23.2 Simple &<z * 1D0 mg. T*mp*fi(ur< progrimmlng * J'mln. NO. * nont' dcltciid, * 0.1 ppm. N.D. 0.5 5 46 57 60 62 63 64 66 72 Temperature C. Fig. 1. FVC degradation and VCM formation at a function of temperature. tion of the levels of VCM to be expected at PVC fabrica tion temperatures. This was carried out by holding samplesat210C, the upper limit ofthe fabrication tempera ture range, for periods of 5 and 30 min. As shown in Table 4, only traces of VCM are formed under these conditions amounting to a maximum of 0.5 ppm (resin basis) after 5 min exposure and a maximum of 1.2 ppm after 30 min exposure. This is particularly significant since it demonstrates that workers involved in PVC fabrication are not exposed to dangerous concentration^^ of VCM, and that VCM levels in fabrication areas well below the limits established by OSHA and EPA standards. Table 4. Vinyl Chloride Formation at PVC Fabrication Temperature (210C) Sample VCM, ppm (resin basis) 5 Minute 30 Minute heating heating Homopolymers Suspension Low Mol. Wt. Suspension Medium Mol, Wt. Suspension Medium Mol. Wt. Suspension High Mol. Wt. Blending Blending Dispersion N.D. N.D. N.D. N.D. N.D. 0.5 N.D. 0.3 0.4 0.4 0.3 0.5 1.2 0.2 Copolymers Type 1 Type 2 N.D. N.D, 0.1 0.3 Films Flexible Flexible Rigid Rigid Flexible N D. N.D. N.D. N.D. N D. N.D. N.D. N.0. N.D. N.D. Compounds Flexible Flexible Filled flexible Rigid N.O. nont dtleclrd. ' 0.1 ppm. N.D. 0.1 N.D. 0.1 N.D. N D. N.D. N.D. R& s 111373 406 POLYMER ENGINEERING AND SCIENCE, APRIL, 1978. V0/. 18, No. 5 Vinyl Chloride Formation from the Thermal Degradation of PolylVinyl Chloride) The amounts ofVCM detected during thermal degra dation of PVC resins and compounds in this study are in good agreement with those published by Lewis (3). A recent paper by Hoffman, et al. (12) describes the detection and determination of low nanogram levels of VCN1 in the smoke from tobacco. Their data suggest that the total inorganic chloride in tobacco is the determining factor for the amount ofVCM in the smoke, the neces sary organic radical being generated by the burning of the tobacco products. A similar mechanism may account for the low levels ofVCM observed in our work. ACKNOWLEDGMENTS The authors wish to acknowledge the assistance of M. Sidey, N. Conzo, and P. Heiney in carrying out much of the analytical work in support of this project. REFERENCES t. R. R. Stromberg, S. Strauss, and B. C. Achhammer.y. Polym. Sri,. 35. 335 (1959). 2. E. A. Boetnner. C. Ball, and B. Weiss,y. Appl- Palyrri. Sci., 13. 377 (1969). 3. \V. D. Woolley, Brit. Polym. J,. 3, 1S6(1971). 4. J. W. Lewis, Paper presented at meeting of American Soci-' ety for Mass Spectroscopy, Houston, Texas (May 197.5). 5. A. R. Berens, Polym. Eng. Set., 14, 318(1974). 6. E. P. Chang and R. Salovey,/. Polym, Sci., 12, 2927 (1974). 7. D. Braun, Pure Appl. Chem., 26, 173 (1971). 8. M. M. 0`Mara.y. Polym. Sci., 8, 1887 (1970). 9. OSHA Permanent Standard 39 Federal Register 3-5890. 10. I. B. Wakeman. M. Saggese, and F. Owens. Symposium Reprints, Chemical Marketing and Economics Division, A.C.S. Meeting New York (April, 1976). 11. Collob Analytical Service Corp. 12. D. Hoffmann, C. Patrianakos, K. D. Brunnemann, and C. B. Gone, Ann/. Chem., 48, 47 (1976). w .e m s h* POLYMER ENGINEERING AND SCIENCE, APRIL, 1978, VoI. 18, No. 5 407