United States Environmental Protection Agency Risk Reduction Engineering Laboratory Cincinnati OH 45268 Research and Development EPA/600/S2-89/063 Feb. 1990 Project Summary Exposure to Chemical Additives from Polyvinyl Chloride Polymer Extrusion Processing Cathy S. Lamb This report presents a model to predict worker inhalation exposure due to off-gassing of additives during polyvinyl chloride (PVC) extrusion processing. Data on off-gassing of additives were reviewed In the literature, the off-gassing at normal PVC processing temperatures was studied in the laboratory, process variables were estimated from an equipment manufacturer survey, and worker activities and possible exposure sources were observed in an industrial survey. The purpose of this study was to develop a theoretical model to predict worker inhalation exposure to additives used during PVC extrusion processing. A model to estimate the generation rate of the additive from the polymer extrudate was derived from the mass transport equations governing diffusion. The mass flow rate, initial additive volatile weight fraction, off-gassing time, dlffusivlty, and slab thickness are required to determine the generation rate from the model. This Protect Summary was developed by EPA's Risk Reduction Engineering Laboratory, Cincinnati, OH, to announce key findings of the research project that is fully documented in a separate report of the same title (see Project Report ordering Information at back). Introduction During polymer processing, heating polymer that is blended with additives may cause off-gassing of residual monomer, polymer degradation products, and some chemical additives into the workers' environment. PVC, the third largest volume extrusion resin, was selected for this study because PVC contains more types and amounts of additives than the two larger volume systems. The study focused on extrusion because most thermoplastics are extruded either in the compounding or fabrication stage. Before developing the model, the important variables affecting off-gassing were determined from a literature survey, a laboratory data study, an equipment manufacturer survey, and an industrial data survey. Literature Survey The literature survey was conducted to obtain existing information on worker exposure to off-gassed compounds during PVC extrusion and to correlate the worker exposure to types of additives, to worker activities, and to other processing variables. Nine articles documented worker exposure to phthalate plasticizers, lead stabilizers, and vinyl chloride monomer in different polymer processing operations. Although the literature lacked information on operating parameters, some important variables, such as PVC film thickness, additive vapor pressure, and ventilation controls, were identified. The off-gassing rate depends on film thickness; this indicates a diffusion- controlled mechanism. An additive with a lower vapor pressure causes a lower generation rate. Calendering and compounding had slightly higher exposure levels than did extrusion processing, but local exhaust ventilation ------- reduced these exposure levels for phthalate plasticizers. Laboratory Data Study The laboratory data study was conducted to determine whether any toxic gaseous compounds are off-gassed as a result of additives at normal PVC processing temperatures. Pyrolysis of five commercially supplied PVC samples was conducted with the use of a pyrolysis probe connected to a tandem gas chromatograph/mass spectrometer at temperatures of 150°C, 300eC, and 600°C. The analyzed samples included an engineering resin, two different wire jacketing compounds, a pipe extrusion resin, and a window profile resin. The additives included in the samples were stabilizers, plasticizers, fillers, lubricants, a copolymer, an impact modifier, and a pigment. The results of the laboratory data study were that little or no off-gassing occurred at the normal extrusion temperature of 150°C. Small weight losses of 6.7% to 6.9% for the pipe extrusion resin and window profile resin indicate the off- gassing of small amounts of the copolymer and the impact modifier. The weight loss was too small to identify or quantitate the off-gassed components. As the temperature was increased to 300°C, pyrolysis of the PVC samples resulted in significant weight losses of 32% to 57%. Most of this weight loss was due to the degradation of the PVC, but some off- gassed compounds were attributed to the presence of additives. Phthalate plasticizers off-gassed intact or degraded to form 1,2-benzenedicarboxylic acid. The copolymer in the pipe extrusion resin resulted in off-gassing of branched saturated hydrocarbons, benzoic acid, and an alkyl benzene. The impact modifier in the window profile resin resulted in off-gassing of unsaturated hydrocarbons and benzoic acid. At 600 °C, the weight losses ranged from 56% to 75%. The off-gassed compounds at 600" C were similar to the compounds observed at 300°C except for more aromatic compounds caused by the cyclization of the polyvinyl chloride. Equipment Manufacturer Survey The equipment manufacturer survey was conducted to obtain information about extrusion processing parameters and techniques. The survey involved contacting manufacturers and suppliers of extruders and downstream equipment and obtaining information on the different processing variables, such as operating temperatures, flow rates, and different cooling systems. The survey also included attending a laboratory workshop on extrusion processing where information on types of equipment, equipment configurations, and possible exposure sources was obtained. PVC is processed using either rigid or flexible formulations. Flexible formulations contain 20% to 60% plasticizer, which reduces the melt viscosity. Because of this lower viscosity, flexible compounds are processed at temperatures ranging from 150°C to 190°C whereas rigid compounds are processed at temperatures ranging from 180°C to 210°C. Rigid compounds require lower flow and shear rates and higher pressures because of the higher melt viscosity and greater possibility for thermal degradation. A typical extrusion line consists of a single or twin screw extruder, a profile die, a cooling device, a collection device, and a cutter or winder. There are very few sources of exposure within the extrusion line. The extruder is completely enclosed except for the hopper and the extruder die. Some volatiles may travel back through the solids conveying zone and exit through the hopper. This limited exposure could be controlled by negative pressure ventilation hoods situated over the hoppers. For extruders with devolatilization sections, removing volatiles while still in the extruder could significantly reduce worker exposure. Once the extrudate leaves the die, the worker would be exposed if an air cooling method was used. If a water trough or vacuum-forming device was used, the volatiles would be transferred to the water or collected in the vacuum system. With an air cooling system, the exposure would continue until the extrudate was solidified in the first section. Most air- cooled parts are rigid compounds that contain fewer additives than do plasticized or flexible compounds. Because most flexible compounds are handled by water cooling devices, the exposure is very limited. Industrial Data Survey The industrial data survey was conducted to obtain information about worker activities and exposure sources under normal processing conditions. During walk-through surveys at four polymer processing facilities, the number of workers required for safe operation, worker activities, possible exposure sources, ventilation controls, and coolin systems were recorded for each proces The different types of polyrru processing observed include compounding, calendering, extrusio injection molding, blow molding, ar compression molding. During the walk-through surveys, ti worker exposure was very limited. TI most noticeable source of exposu occurred during start-up of the extrusii operation when the worker wou manually support and guide the extrude into the cooling system. For norm operation, the worker was exposed to t hot extrudate in the small area (1 to 6 i between the die and the cooling syste For a water or vacuum cooling syste the worker exposure ended as t extrudate entered the cooling system. F air or forced-air cooling devices, t exposure continued until the prodt solidified. Of the extrusion process observed, air cooling was only used the case of sheet extrusion. Duri injection, compression, and bl molding, the worker was never expo; to the hot extrudate. Most compound processes occurred in enclose automated systems with ventilati controls to limit the exposure to worker. In all cases, ventilation conti could be used to reduce even the limi exposure that did exist. The worker scenarios for the differ extrusion processes were similar. At start-up of the procedure, the extruc was manually supported and guided the cooling device and puller. The woi would load the hopper; check the hop level, on-line gauging system, < extrusion temperature and pressi collect the product; and inspect product quality. Product quality cor involved monitoring an on-line gau( system for dimensions of the produc manually measuring the dimensions. surface quality of the product was examined for defects, such as die rm the sharkskin or chatter effect, ora peel appearance, or surface burn These problems could be solved proper adjustment of the extri operating conditions. The worker si most of his time either at the end ol extrusion line where the product examined or at the control panel or extruder observing operating paramel Worker Exposure Model Following these surveys and studii theoretical model was develope predict the worker exposure during extrusion processing. To represent ------- vorst case, the model for the chemical eneration rate was derived from the transport equations governing diffusion in a large, flat slab. To determine the generation rate from a table of DAtf/L2 and QwAom' values, the mass flow rate, 'nitial volatile weight fraction, off-gassing ime, diffusivity, and slab thickness must 36 estimated from the limited information ibout the additive and processing method supplied in the Premanufacture Notice system. In the full Project Report, equations to estimate the initial volatile mass concentration and diffusivity based on the chemical properties of the additive and extrusion operating variables are included. The mass flow rate and off- gassing time for different applications and formulations are presented in tabular form. A Gaussian plume dispersion model to estimate worker inhalation exposure from the generation rate is also included. The full report was submitted in fulfillment of Cooperative Agreement No. CR813355 by Southwest Research Institute under the partial sponsorship of the U.S. Environmental Protection Agency ------- Cathy S. Lamb is with Southwest Research Institute, San Antonio, TX 78228-0510. Dennis L Timberlake is the EPA Project Officer (see below). The complete report, entitled "Exposure to Chemical Additives from Potyvinyl Chloride Polymer Extrusion Processing," (Order No. PB 90-151 7701 AS; Cost: $23.00, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Risk Reduction Engineering Laboratory U.S. Environmental Protection Agency Cincinnati, OH 45268 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati OH 45268 UNOFFICIAL MAIi U.S.POSTAGE = 025: Official Business Penalty for Private Use $300 EPA/600/S2-89/063 ISE"CI cmciso ------- |