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
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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
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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
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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
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Penalty for Private Use $300
EPA/600/S2-89/063
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