United States
Environmental Protection
Agency
National Risk Management
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/6QQ/SR-97/018 September 1997
of
to
Processes
Emery Kong, Mark Bahner, Robert Wright, and Andrew Clayton
This study evaluated several pollu-
tion prevention techniques that could
be used to reduce styrene emissions
from open molding processes in fiber-
glass-reinforced plastics/composites
(FRP/C) and fiberglass boat building
industries. Styrene emissions using
standard industry techniques, materi-
als, and equipment were evaluated in a
controlled environment and compared
to a baseline condition to determine
the effects of these pollution preven-
tion techniques on styrene emissions.
The study found that using controlled
spraying (i.e., reducing overspray), low-
sty rene and styrene-suppressed mate-
rials, and non-atomizing application
equipment can reduce styrene emis-
sions by from 11 to 52%. Facilities
should investigate the applicability and
feasibility of these pollution prevention
options to reduce their styrene emis-
sions. The calculated emission factors
were from 1.6 to 2.5 times the mid-
range AP-42 emission factors for the
corresponding gel coat and resin ap-
plication. These results indicate that
facilities using AP-42 emission factors
to estimate emissions in open molding
processes are likely to underestimate
actual emissions.
This Project Summary was developed
by EPA's Air Pollution Prevention and
Control Division of the National Risk
Management Research Laboratory, Re-
search Triangle Park, NC, 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
Gel coat and resin sprayup are com-
monly used in open molding processes in
the fiber-reinforced plastics/composites
(FRP/C) and boat building industries. How-
ever, styrene, a compound listed as a
hazardous air pollutant, is emitted during
the application and postapplication (roll-
out and curing) stages. These emissions
are coming under increasingly stringent
regulations as the maximum achievable
control technology (MACT) standards are
developed by the U.S. Environmental Pro-
tection Agency (EPA). The MACT regula-
tions are to be promulgated in November
1997 for the FRP/C industry and in No-
vember 2000 for the boat building indus-
try. To help industry meet future emission
requirements, pollution prevention options
such as new materials and equipment
have been developed by various vendors.
However, information is needed about the
percentage of reduction in emissions that
these options can achieve. To meet this
need, Research Triangle Institute (RTI),
working with the EPA's Air Pollution Pre-
vention and Control Division, evaluated
several of these pollution prevention op-
tions. Also, emission factors calculated
from the results of a prior EPA test in an
FRP facility indicated that they were higher
than those reported in the EPA AP-42
document. Since the AP-42 emission fac-
tors have been used by the facilities to
estimate their styrene emissions, a com-
parison of the emission factors calculated
from this test result with the existing AP-
42 emission factors for gel coat sprayup
and resin applications would verify the
accuracy of the existing AP-42 emission
factors.
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Background
During the gel coat and resin sprayup
operations, polyester resins are atomized
and projected onto a mold. Gel coat and
resin materials contain styrene, which
cross-links the resin molecules under the
effects of a promoter and an initiator to
form a solid polymer. An initiator such as
methyl ethyl ketone peroxide (MEKP) is
mixed with the resin material to initiate the
cross-linking process. The initiator is mixed
with resin material within the spray gun or
application equipment (internal mixing) or
just outside the spray tip (external mix-
ing). Wet resin material cures on the mold.
For resin lamination, a roll-out step fol-
lows the application step to remove air
bubbles entrained in the laminate. During
the application and postapplication (i.e.,
rolling-out and curing) stages, excess sty-
rene not cross-linked in polymerization is
emitted from atomized resin particles and
from wet laminate.
Testing Approaches
For the pollution prevention technique
evaluation, RTI quantified styrene emis-
sions from test runs using standard indus-
try techniques, materials, and equipment.
All the formulations and application equip-
ment tested are available commercially.
Cook Composites and Polymers (CCP)
supplied all gel coats. Reichhold Chemi-
cals provided the facility, all resins and
catalysts, and laboratory analyses for resin
properties. Catalyst ratios suggested by
CCP and Reichhold were used for the gel
coat and resin materials. Magnum Indus-
tries provided all application equipment
and an experienced operator. PPG Indus-
tries supplied all fiberglass materials.
Styrene emissions during the test runs
were measured and compared to a
baseline condition to examine reduction
achieved using various pollution preven-
tion options. The baseline test conditions
and the various options examined are sum-
marized in Table 1. Six factors were ex-
amined in three separate experiments to
determine their impact on styrene emis-
sions.
Pilot Experiment
Operator spraying technique - nor-
mal vs. controlled spraying
Linear air flow velocity in the spray
area - 12 vs. 30 m/min (40 vs. 100
ft/min)
Operator techniques affect the amount
of overspray and the associated excess
emissions. Spraying technique was ex-
pected to affect styrene emissions because
poor technique creates more overspray
(i.e., sprayed material that does not end
up on the mold but on the surrounding
area). More overspray means more mate-
rial is used and more surface area is cre-
ated for styrene emissions. Normal
spraying (i.e., spraying without consciously
controlling the spray pattern) was com-
pared with controlled spraying (i.e., spray-
ing in a manner that consciously reduces
overspray by projecting the spray pattern
more precisely on the mold and flange).
Air flow velocity in the spray area was
expected to influence styrene emissions
from a pure diffusion transfer point of view.
Styrene emission is expected to increase
with increasing air flow velocity; therefore,
tests at these two air flow velocities would
reveal their effects on styrene emission.
Based on the results of this experiment, a
low air flow velocity and a controlled spray-
ing technique were used for subsequent
gel coat and resin experiments.
Gel Coat Experiment
Gel coat formulation - regular vs.
low-VOC gel coats
Gel coat application equipment -
air-assisted airless (AAA) vs. high-
volume, low-pressure (HVLP) spray
guns
Styrene content in the gel coat formula-
tion affects styrene emissions. Typical gel
coat materials contain 35 to 50% of sty-
rene monomer; low-VOC gel coat mate-
rial contains less than 35% styrene. A
comparison between a regular gel coat
and a low-VOC gel coat would reveal the
effect of styrene content on emissions.
The low-VOC gel coat formulation was
first introduced by CCP in late 1994, and
its sprayup emission has not been com-
pared with that of a regular gel coat.
AAA and HVLP spray guns (either in-
ternal or external catalyst mixing) are com-
monly used for gel coat application. Certain
Table 1. Baseline Test Conditions and Pollution Prevention Options Evaluated
Factor
Base Conditions
Pollution Prevention Option
Spray technique
Air flow velocity in spraying area3
Gel coat formulation
Gel coat application equipment
Resin formulations
Resin application equipment
Experienced operator, normal technique (i.e.,
without consciously controlling overspray)
30 m/min (100 ft/min)
Regular, isophthalic acid-based gel coatb (styrene
content 38.7%)/initiated by 1.8% MEKP; 17 min
gel time;18 to 24 mil gel coat thickness
AAA spray (external catalyst mixing)
Regular (low-profile), dicyclopentadiene-based
resin (styrene content 38.3%); initiated by 1.5%
MEKP; 20 min gel time; 70 to 100 mil laminate
thickness
AAA spray (external catalyst mixing)
Experienced operator, controlled spraying technique (very
careful spraying to prevent significant overspray)
12 m/min (40 ft/min)
Low-VOC, isophthalic acid/neopentyl glycol-based
gel coat (styrene content 25.4%)/initiated by 1.8%
MEKP; 27 min gel time
1. HVLP spray gun (internal catalyst mixing)
2. HVLP spray gun (external catalyst mixing)
1. Low-styrene, dicyclopentadiene-based (styrene con-
tent 35.3%)/initiated by 1.4% MEKP; 30 min gel time
2. Styrene-suppressed, orthophthalic acid-based resin
(styrene content 43.5%)/initiated by 1.5% MEKP;
17 min gel time
3. Orthophthalic acid-based styrene-suppressed resin
plus 0.1 % wax/initiated by 1.5% MEKP; 17 min
gel time
1. Flow coater (internal catalyst mixing)
2. Pressure-fed roller (internal catalyst mixing)
aAir velocity in the spraying area was controlled by a baffle upwind of the spraying area.
bGel coats contained no methyl methacrylate to allow assumption that total emissions were styrene.
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spray gun designs were said to have a
more confined spray fan or improved cata-
lyst mixing, thereby reducing overspray
and styrene emissions. Three different
spray guns were evaluated to determine
the effects of spray gun designs and cata-
lyst mixing on styrene emissions.
Resin Experiment
Resin formulation - regular vs. low-
sty re ne and styrene-suppressed
resins
Resin application equipment - AAA
spray gun vs. flow coater and pres-
sure-fed roller
The effects of a low-styrene resin and a
styrene suppressant on resin sprayup
emissions were evaluated using the AAA
spray gun. A low-styrene resin contains
less than 35% of styrene by weight vs. a
regular resin containing 35 to 50% of sty-
rene. A styrene suppressant typically is a
paraffin or wax additive in the resin formu-
lation, which migrates outward to the sur-
face of the wet laminate during the curing
stage and forms a waxy layer that pre-
vents styrene from further evaporation. The
styrene suppressant is not expected to
have a significant effect on emissions dur-
ing the application and roll-out stages, be-
cause a stagnant condition is necessary
for the styrene suppressant to work.
Other resin application equipment (i.e.,
flow coater and pressure-fed roller) that
do not atomize resin materials were com-
pared with the AAA spray gun using a
regular low-profile resin. A spray gun at-
omizes resin material into small droplets
that create a large surface area for sty-
rene to evaporate. RTI evaluated a flow
coater and a pressure-fed roller to reveal
the effects of non-atomizing application
equipment and identify pollution preven-
tion options for resin application.
Test Setup
Gel coat sprayup or resin application
was conducted in an isolated spray booth
of dimensions typically used in FRP/C fa-
cilities. Emissions in the spray booth were
exhausted through a stack. Emissions re-
sulting from gel coat or resin application
and curing were quantified using EPA
methods. Styrene emission concentrations
were continuously monitored and recorded
every 2 seconds at the exhaust stack dur-
ing a test run. A test run started when gel
coat or resin was applied to the mold
surface and ended when the material was
completely cured and the monitored con-
centration returned to the baseline con-
centration. The exhaust flow rate was
monitored for each test run so that the
emission quantities could be calculated.
Environmental conditions (i.e., tempera-
ture and relative humidity) were maintained
at constant levels, and background con-
centrations of volatile organic compounds
(VOCs) were recorded before the test run.
Gel coat or resin materials were applied
onto a box-shaped, male FRP mold by an
experienced operator. The same operator
applied the materials during a 5-week pe-
riod to ensure that a consistent technique
was used and to reduce any possible vari-
ability in operation. The mold measures
0.61 m (2 ft) high, 0.76 m (2.5 ft) long,
and 0.61 m (2 ft) wide. A 5.1-cm (2-in.)
wide flange surrounds the bottom of the
mold. The amount of gel coat or resin
material used in each test run was mea-
sured using a high precision balance with
a 150,000-g (331-lb) capacity and 1-g
(0.002-lb) readability. Emissions from gel
coat sprayup test runs were compared
based on similar gel coat thicknesses of
18 to 24 mils. Emissions from resin appli-
cation test runs were compared based on
similar laminate thicknesses of 70 to 100
mils. Chopped strand mats were used for
the flow coater and pressure-fed roller,
and fiberglass roving was used for the
AAA spray gun.
Results and Conclusions
All tests were conducted in triplicate to
permit statistical analysis of the results.
Percent emission reductions in the follow-
ing discussions are based on total grams
of styrene emitted or grams of styrene
emitted per unit mold surface area. Per-
cent emission reductions are different
when emissions are expressed as a per-
centage of available styrene, because sty-
rene contents in the gel coat and resin
materials are different. Using the emis-
sion concentration profile and the duration
of the application stage, emissions from
the application and postapplication stages
could be determined separately. These
separate emission quantities aided the
analysis of emission characteristics result-
ing from different materials and equipment.
The pilot experiment (shown in Table 2)
indicated that:
Over the velocity range examined,
12 vs. 30 m/min (40 vs. 100ft/min),
linear air velocity had no significant
effect on styrene emissions.
Controlled gel coat spraying tech-
nique reduced total styrene emis-
sions by 24% compared to normal
spraying technique.
Controlled spraying on the male
mold reduced gel coat usage by
12% due to less overspray.
Under normal spraying, 48% of to-
tal emissions were emitted during
gel coat spraying; the remainder
were emitted during curing.
Under controlled spraying, 38% of
total emissions were emitted dur-
ing gel coat spraying; the remain-
der were emitted during curing.
The gel coat experiment (shown in Table
3) indicated that:
The low-VOC gel coat reduced to-
tal styrene emissions by 28% when
compared to the regular gel coat.
The low-VOC gel coat required a
higher air pressure and larger spray
tip to achieve the same spray fan
as the regular gel coat.
The AAA (external catalyst mixing)
and HVLP (internal and external
catalyst mixing) gel coat spray guns
made no difference in terms of to-
tal emissions.
Evaluation of resin formulations under
controlled spraying (shown in Table 4)
indicated that:
The low-styrene resin reduced total
emissions by 11% compared to the
regular low-profile resin.
The styrene-suppressed resin emit-
ted 36% less styrene than the regu-
lar low-profile resin and the majority
of the reduction was achieved dur-
ing the postapplication stage.
Table 2. Summary of Emissions Using Normal and Controlled Gel Coat Spraying
Spraying
technique
Normal
(6 runs)
Controlled
(6 runs)
Materials used
9
2,119
1,868
Reduc. (%)
BL
12
Total emissions
g Reduc. (%)
513 BL
391 24
Emission factor
%AS
62.5
54.1
Reduc. (%)
BL
13
Emission factor
g/g Reduc. (%)
0.242 BL
0.210 13
BL = Baseline condition for emission reduction calculation.
Note: Material usage and emission quantities are the averages of the number of test runs for that condition.
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Table 3. Summary of Emissions Using Regular and Low-VOC Gel Coats
Type of gel
coat
Regular gel coat
(9 runs)
Low-VOC gel
coat (9 runs)
Materials used
9
1,783
2,025
Total emissions
g Reduc. (%)
387 BL
278 28
Emission factor
%AS
56.0
54.2
Reduc. (%)
BL
3
Emission factor
g/g
0.217
0.137
Reduc. (%)
BL
37
BL = Baseline condition for emission reduction calculation.
Note: Material usage and emission quantities are the averages of the number of test runs for that material.
Table 4. Summary of Emissions Using Different Resin Formulations (Applied by Controlled
Spraying)
Type of resin
Regular, low-profile
(5 runs)
Low-styrene
(3 runs)
Styrene-suppressed
(3 runs)
Styrene-suppressed
+wax (3 runs)
Materials
used
g
6,670
6,472
6,258
5,912
Total
emissions
g
445
395
286
266
Reduc.
BL
11
36
40
Emission
factor
AS
17.5
17.3
10.6
10.6
Reduc.
BL
1
39
39
Emission
factor
g/g
0.067
0.061
0.046
0.046
Reduc.
BL
9
31
31
BL = Baseline condition for emission reduction calculation.
Note: Material usage and emission quantities are the averages of the number of test runs for that material.
The styrene-suppressed resin with
0.1% wax emitted 40% less sty-
rene than the regular low-profile
resin; however, the effect of addi-
tional wax on total emissions was
not significant.
For regular and low-styrene resins,
47 to 48% of total emissions oc-
curred during spraying; the remain-
der were emitted during
postapplication.
For the styrene-suppressed resin
with or without additional wax, 63%
of total emissions occurred during
spraying, which implies that styrene
suppressant was effective in reduc-
ing curing emissions in the
postapplication stage.
Evaluations of resin application tech-
niques and equipment (as shown in Table
5) indicated that:
Controlled resin sprayup emitted
30% less styrene than normal resin
sprayup.
Flow coating and pressure-fed roller
equipment resulted in 52 to 53%
lower emissions than normal spray-
ing.
Flow coating and pressure-fed roller
equipment resulted in 31 to 33%
lower emissions than controlled
spraying.
Comparison of Test Results
with Existing EPA AP-42
Emission Factors
Table 6 compares emission factors from
the EPA AP-42 document and from the
test results. Emission factors are ex-
pressed as a percentage of available sty-
rene. It is important to note that the styrene
emission factors calculated from the test
results were from 1.6 to 2.5 times greater
than the mid-range AP-42 emission fac-
tors for the corresponding gel coat and
resin application. The deviation of RTI's
measured emission factors from AP-42
emission factors is consistent with the find-
ings of the recent Open Molding Styrene
Emission Study conducted by the Com-
posites Fabricators Association at Dow
Chemical. These results indicate that fa-
cilities using current AP-42 emission fac-
tors to estimate gel coat and resin
application emissions in open molding pro-
cesses are likely to substantially underes-
timate actual styrene emissions.
Recommendations
The results of this study show that dif-
ferent materials, application equipment,
and techniques can reduce styrene emis-
sions to varying degrees. Each facility
should investigate the applicability and fea-
sibility of the available pollution preven-
tion options to reduce its styrene
emissions.
Based on the results of this study, RTI
recommends the following pollution pre-
vention options for open molding opera-
tions:
Use operator training to improve
application technique and reduce
overspray.
Use low-styrene or styrene-sup-
pressed materials, where feasible.
Use non-atomizing application
equipment, where feasible.
Emission factors and the percent of
emission reductions presented in this pa-
per were determined under specific study
conditions (e.g., gel coat and resin prop-
erties, equipment setup, environmental
conditions), which may not represent the
conditions in all facilities. Therefore, the
results presented in this paper provide
general trends, not absolute values, of the
effectiveness of various pollution preven-
tion options.
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Table 5. Summary of Emissions Using Different Resin Application Techniques and Equipment
Type of
equipment
AAA spray gun
(normal
spraying, 1 run)
AAA spray gun
(controlled
spraying, 5 runs)
Flow coater
(3 runs)
Pressure-fed
roller (3 runs)
Materials
used
9
6,133
6,670
5,619
5,096
Total emissions
g Reduc. (%)
634 BL —
445 30 BL
306 52 31
299 53 33
Emission factor
%AS Reduc. (%)
27.1 BL —
17.5 35 BL
1 4.2 48 1 9
15.3 44 13
Emission factor
g/g Reduc. (c
0.104 BL
0.067 36
0.055 47
0.059 43
*)
—
BL
18
12
BL = Baseline condition for emission reduction calculation.
Note: Material usage and emission quantities are the averages of the number of test runs for that equipment.
Table 6. Comparison of Emission Factors (in
Results
available styrene) from EPA AP-42 and Test
Type of material and
operation
Gel coat sprayup (NVS)
AP-42
emission
factor
range
26-35
AP-42
EF
midpoint
30.5
Emission factors from
test results
62.5 (normal spraying)
56 (controlled spraying)
54.2 (low-VOC gel coat,
Ratio
2.0
1.8
1.8
Resin sprayup (NVS)
controlled spraying)
9-13 11 17.5 (controlled spraying) 1.6
27.1 (normal spraying) 2.5
Resin sprayup (VS)
Resin hand layup (NVS)
3-9
5-10
6
7.5
10.6 (styrene-suppressed
resin, controlled spraying)
15.3 (pressure-fed roller)
1.8
2.0
NVS=non-vapor-suppressed.
VS=vapor-suppressed.
As shown in Tables 2 through 5, the
percentage of reduction varies when emis-
sion factors are expressed as a percent-
age of available styrene and the calculated
emission factors are substantially higher
than the current AP-42 emission factors;
therefore, facilities should not apply the
percentage reductions reported in this pa-
per to emission estimates calculated us-
ing current AP-42 factors. Doing so could
enormously underestimate actual emis-
sions. Facilities should check with the gov-
erning agencies or trade associations to
determine the appropriate procedures for
estimating their current emissions.
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E. Kong, M. Bahner, R. Wright, and A. Clayton are with Research Triangle
Institute, Research Triangle Park, NC 27709.
Geddes H. Ramsey is the EPA Project Officer (see below).
The complete report, entitled "Evaluation of Pollution Prevention Techniques to
Reduce Styrene Emissions from Open Contact Molding Processes," consists
of two volumes:
Volume 1 is the final report (Order No. PB97-181440; Cost: $21.50, subject to
change);
Volume 2 is the appendices (Order No. PB97-181457; Cost: $31.00, subject to
change). Both volumes 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
Air Pollution Prevention and Control Division
National Risk Management Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
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POSTAGE & FEES PAID
EPA
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EPA/6QQ/SR-97/018
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