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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U.S.POSTAGE

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     Official Business
     Penalty for Private Use $300

     EPA/600/S2-89/063
                                           ISE"CI
            cmciso

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