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Emission of .Styrene During the Hand Lay-Up 

Molding of Reinforced Polyester 

Arto J. Slimanen,* Ralmo I. Niemeia,6 Tuula K. Blomqvist,c and Eeva M. NIKander4 

Technical Research Centre of Finland, Safety Engineering Laboratory, P.O. Box 656, SF-33101 Tampere, 

Finland; "Institute of Occupational Health, Department of Industrial Hygiene and Toxicology, Laajaniityntie 1, 

SF-01620 Vantaa, Finland;

 cNeste Chemicals, Polyester, P.O. Box 320, SF-06101 Porvoo, Finland 

The emission rates of styrene monomer from standard and lowstyrene-eraission (LSE) resins were determined during the hand 

lay-up molding of reinforced polyester. The evaporation tests 

were carried our in controlled laboratory conditions by .__.ir_g 

0.16S m2 laminate. The emission rate was highest in the rolling 

phase, ranging from 59 to 79 mg/s/m*. The emission, rate of 

styrene with LSE resin wasj^|£ percent lower than thar of 

standard resin. T^f y*-» nf T.SF i-p^ln reduced the total evaporation 

of styrene 30-60 percent compared to standard resin. This Is due 

to the fact tb"at LSE resin has a lower evaporation rate in the 

period between the rolling and curing. The evaporarion rates 

obtained by the gravimetric evaporation test do not include che 

rolling period and should not be used to estimate the emission 

rate of sty-^nj i^ -—•-•i --»ni-_---f- opemtiom. saamimen, AJ.; 

Nlemeli. R.L; Biomqvist, T.K.; Nikander, LM - Emission of Siyrene 

During the Hand Lay-Up Molding of Reinforced Polyester. Appl. Occup, 

Environ. Hyg. 6:790-793; 1991. 

Introduction 

During the past 10 years, ihe hygienic limits for styrene 

monomer have been lowered in che Scandinavian countries. The present hygienic limit in Finland (20 ppm 8-hour 

time-weighted average (TWA|) indicates an increasing need 

for exposure control measures in the reinforced plastics 

industry. Both the U.S. Occupational Safety and Health 

Administration 8-hour standard and the American Conference of Governmental Industrial Hygienists threshold 

limit value for styrene monomer is an 8-hour TW\ of 50 

ppm. Ventilation seems to be one of the most important 

control methods of styrene vapors."-4) Local exhaust ventilation is to be preferred because vapors are captured at 

the source before dispersing into the laminator s breathing 

zone and into the general atmosphere ofthe working area. 

By contrast, exposure control by general ventilation is based 

on dilution of contaminants below the acceptable level by 

flushing the entire workroom with clean air. As the emission rate of styrene vapor and its time history in different 

phases of the lamination process is insufficiently known, 

however, the basis for the calculation of ventilation air 

flow's is often inadequate, resulting in high concentrations 

of styrene. Furthermore, dilution-ventilation may not be 

the most efficient control for hand lay-up molding because 

the operator has to work close to styrene-emialng surfaces. 

If the emission rate of siyrene vapor during differeru phases 

is known, it makes selection ofwhich ventilation principle 

to use to ensure adequate control much simpler. 

In order to reduce die employees' styrene exposure, socalled low-styrene-emission (LSE) resins have been introduced. The reduaion in emission has been achieved by 

adding suppressant additives to the resin. According to 

gravimetric evaporation tests, the use of these agents in 

the resin decreases styrene emission levels 50-90 percent.-^ In these tests, a weighed amount of catalyzed resin 

is poured Into a preweighed disc mold and the loss of 

weight is deteaed by a laboratory balance during curing. 

The use of LSE resins, however, has not succeeded in 

reducing the exposure in the workshops as effectively as 

assumed on the basis of the gravimetric evaporation tests. 

The overall reducdonof the styrene exposure in the workshops using LSE resin? has been -so-so percent or^'Weh 

lgss.Qj s-?) Therefore, the gravimetric test method, based 

on the determination of siyrene evaporation under static, 

laboratory conditions, does not ftve a correa estimate of 

the emission rate of styrene in actual molding operations.-

tne aim oi diis t>mdy ~ tu-deiWTminr rhp.rmi-wten nttcy 

of styrene monomer from two different polyester resins 

during hand lay-up molding. The emission rates were determined by measuring the flow rate and the concentration 

of styrene in the exhaust duo. The evaporation rates of 

styrene at different phases of the molding operation are 

reported. The results can be used as the criteria fbr designing ventilation and other engineering control measures. 

Materials and Methods 

The emission rates of styrene monomer were measured 

from two different polyester resins by determining the 

flow rate of styrene evaporated during the hand lay-up 

molding process. The commercially available resins used 

790 -M?-3aXttfS-79-|"BJ*0/« © 1»t AIH Apn. OCCUP. tNvmoN. HYB. eia) • SWEMBEI. IMI 
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.W , RUG 31 '95 11:43AM EPfi DURHRM 

TABLE I. Properties of Tested Resins 

Resin type 

Styww coniem. % 

Viscosity at 2CTC. mPas 

Cone and Plate 

Bfootfield. 10 min-' 

Curing at 20'C. 100 0 resin, 1 % MEK peroxide 

Gel time, min 

Peak -BOtherm, *C 

Gravimetric styrene evaporation g/m2 

Standard 

41.3 

218 

1200 

43.0 

107 

80 

LSE 

40.4 

205 

1480 

41.0 

103 

30 

in this study were preaccelerated, of the thixotropic and 

onhophtalic type, and intended for boat building and other 

similar open mold methods. The first resin was a lowstyrene-emission type, whereas the second was a conventional "standard" resin. The characteristics of the resins 

are given in Table I. 

The evaporation tests were carried out in controlled 

laboratory conditions by using 0.165 m2 laminates. Four 

or twelve layers of 450 j*/m*- emulsion-bound chopped 

strand mat were laid down at a resin-to-glass ratio of 2.33 

using a metal roller to wet out the glass. These two laminate 

thicknesses were selected because they are widely used 

in industry. The resin was catalyzed with 1 percent of 

methyl ethyl ketone peroxide. 

The tests were carried out in an enclosure (V => 0.60 

m by 0.45 m by 0.30 m) made of plastic film, which was 

ereaed inside the laboratory hood (Figure 1). The test 

plate was laminated inside the plastic enclosure. In the 

test, a weighed amount of resin and glass liber mat were 

laminated one layer at a time, and the laminate rolled after 

application of each layer. The rolling time was about 5 

minutes in the case of the 4-layer laminate and ranged 

from 11.5 to 13 minutes in the case of the 12-layer laminate. 

STYRENE CONCENTRATION 

EXHAUST AM PLOW RATE 

LABORATORY CUPBOARD 

PLASTIC ENCLOSURE 

AIR TEMPERATURE 

RELATIVE HUMIDITY 

AMVELOcrnr 

TEMPERATURE INSIDE LAMINATE 

ROME 1. Experimental setup tor the measurement ot styrene emission during hand lay-up molding of reinforced polyester. 

P. 3/5 

After rolling, the laminate was left inside the enclosure 

until it was cured Each laminate thickness and resin type 

was tested twice. The air was exhausted from the enclosure 

at the flow rate, Q, of 0.12 mVs. The time constant of the 

enclosure, V/Q, was 0.7 seconds, enabling rapid measurement of the styrene emission from the exhaust air. 

The concentration of siyrene was continuously measured in the exhaust dua during the active lamination and 

the subsequent exotherm with an infrared analyzer (Miran 

1 A, wavelength 11.05 nm, pathlength 20.25 m, slit 1 mm). 

The air flow rate in the exhaust dua (diameter 200 mm) 

was measured using a calibrated orifice flowmeter located 

at a distance of seven due-diameters from the junction of 

the hood The pressure drop across the orifice meter was 

deteaed by a micromanometer (Alnor 3KDS). The mass 

flow rate of styrene was obtained by multiplying the concentration of styrene and the air flow rate in the exhaust 

dua Another Miran 1A was used to detea possible leakage 

of styrene at the front of the enclosure. No leakage was 

observed however. Thermocouples wet£ used to measure 

the. temperature inside the laminate and of the air above 

the laminate. The accuracy of the styrene concentration 

measurement was estimated to be 5 percent and the accuracy of the air flow measurement was about 5 percent, 

giving one overall emission rate measurement accuracy of 

7 percent 

Air velocities, deteaed with a hot wire anemometer, 

varied from 0.15 to 0.25 m/s above the laminate and represented velocities normally found ln workshop air. The 

direaion of the air flow was parallel to the test plate. The 

air temperature during die tests was 22°C, and the relative 

humidity varied from 20 to 30 percent 

Results 

The emission rate of styrene varied strongly with time 

(Figure 2). The emission rate was highest during the phase 

of rolling. When the lamination was finished the emission 

rate decreased rapidly in the case of LSE resin, whereas 

widi standard resin, the evaporation continued intensively. 

In the curing phase of the LSE resin, a strong emission 

pulse accompanied the heat generation inside the laminate 

(Figure 2). Vith standard resin, the changes in the emission 

rate after rolling were notably less than with the LSE resin. 

The total amounts of styrene that evaporated during 

hand lay-up molding are given in Table II. The total evaporation of styrene with LSE resin was 30-60 percent lower 

than thai of standard resin. The average emission rates of 

styrene during die rolling ranged from 59 to 79 rcgfefai2. 

In the case of the 12-layer laminate, the emission rate of 

the standard resin was 79 mgferm2 and thai ofthe LSE resin 

76 mgft/m2. The corresponding values fbr the four-layer 

laminate were 68 mgft/m2 and 59 mg/s/m2, respeaively. 

Figure 3 shows the proportions of styrene evaporated at 

different phases of the laminadon process. The results 

indicate that both resin types released about the same 

amount of styrene during rolling- On the other hand, the 

evaporation of styrene during the time between the rolling 

APH. OCCUP. EHm0N.HY6.m • SEPTtMBEMSI 791 
AUG 31 '95 11:44AM EPR DURHAM 

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RGURE 2. The emission rate 

B: the 12-layer laminate. 

1

 CUMNCJ • 

TIME (min) 

o( styrene and me temperature Inside A: the 4-layer laminate 

P. 4/ 5 

and 

TABU II. The OveraU Styrene Has During Hand Lay-Up 

ot Test laminate 

Test 

No. 

1 

2 

3 

4 

S 

6 

7 

8 

Resin 

Type 

STO 

STD 

LSE 

LSE 

STO 

STD 

ISE 

LSE 

Umtnate 

Thickness 

4-layer 

4-ltyer 

4-ftyer 

4-layer 

12-tayer 

12-tayw 

12-layer 

12-layer 

Total Styrene 

Evaporation 

(fitafl 

116 

124 

SO 

55 

182 

1S3 

124 

111 

Styrene Loaa 

% of Resin 

Volatile Content 

6.9 

5.8 

23 

13 

14 

28 

24 

l\ 

STO - sandMt (_SE •* kj*«»rer__-tr_sslo*v 

-**•» 

and curing phases with the standard resin was four time 

greater than that with the LSE resin. 

Discussion 

The evaporation of styrene is greatest during the rollln 

process, as was shown by Pritchard and Swap_llai.<6> Ei 

pedally with the LSE resin, about 30-50 percent of th 

total evaporation occurred in the shon rolling phase. Heno 

the duradon of the rolling phase dominates the evapon 

don of srytene when LSE resin is used. In the case < 

standard resin, there was also considerable evapotado 

after the active lamination. Changes in the rolling time di 

not have as strong an effea on the toul styrene emtssic 

APPL OCCUP. O/VMOW. HYG. 6U) . SEPTEMBER 19 
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AUG 3 1 '9 5 11=44AM EPA DURHAM 

{____] CURING PHASE 

ESS PHASE BETWEEN ROLUNG AND CURING 

ROLLING PHASE 

1S0 

ex I 

I 

5 

Ul 

IOO 

60 

STD LSE STO LSE 

12-LAYER LAMINATE 4-LAYER LAMINATE 

FIGURE 3. The overall siyrene evaporation divided into subgroups according 

to lamination period. STO * standard resin; LSE - low-styrene-emisslon 

resin. 

as with the LSE resin. During the rolling, die emission rate 

of styrene was 4-14 percent lower widi LSE resin than 

widi standard resia The average emission tares observed 

in diis smdy are in agreement wiih earlier results.(6> Variations in styrene evaporation between replicated tests, 

•which were on the order of 6-16 percent, were also in 

accord with data given by Pritchard and SwapiUaL(*> 

Compared to die standard resin, die LSE resin has a 

P. 5/5 

lower evaporation rate during die period becween die 

rolling and curing. This 6 a explains the smaller total mass 

of styrene evaporated from the LSE resia The determination of styrene evaporation with the gravimetric test procedure does not Include the rolling phase. The test results 

obtained with the gravimetric test procedure, therefore, 

underestimate die emission of styrene in the actual molding operadon. 

Because die rate of styrene vapor generation is highest 

during die rolling phase, it is of crucial importance to keep 

diis period as short as possible. The rolling time can be 

minimized by using resins and mats with good wetout 

properties. The use of LSE resins notably reduces die total 

evaporation of styrene compared with standard resia "When 

LSE resins are used, die engineering control measures 

should focus on the rolling and curing phases. 

References 

1. KalUokodd, P.: Kolsdnen. T.; JUsketiinen, MJ Prevention of Styrene 

H-oards—Hygienic Approaches, tit Industrial Hazards of Mastla and 

Synthetic Elastomers, pp. 279-286. J. J__tvisak>, P. PflOU, and H. vunlo, 

B& Alan R. Uss lot. New Yo* (1984). 

2. fan inkn-d--, P.; SMmAnen, A; halo. L*. KokocL R: Eapotute to Styrene 

Can Be Controlled- Am. Ind. Hyg. Assoc J. 49-1 (1968). 

3. Sch\imicher,iU^Breys*^PA;C__riyCftW._U^ 

in die Fiberglass Fabrication Industry in Washington Sou. An. lad 

Hyg. Assoc J. 42:143 (1981). 

4 Todd, TO.; Shulman, SA.. Control of Scyrene Vapor in a Large Fiberglass Boat M-mufanurtpg Open-don. Am. Ind Hyg. Assoc J. 45-817 

(1»4). 

5. *fl"-al__-^L_;S*cdcwvS_tLow-Scyiene-E-iut'^ 

bin the Wortplxe. Mod Plast 62:78 (1985). 

6. Pritchard. G.; SwapillaL GJ.: Styrene Loss Dunng the Fabrication of 

Glass Reinforced Polyeaser Products. SAMPS J. 14:19 (1978). 

7. Duffy, MJ_> Reducing Stytene Emission from Unsaturated Polyester. 

Plas. Eng. 35-33 0979} 

Rmfcid M« h mfew MsiMi MO/90: ffiHslon 2/4/91; anp M 2/2S91 

APPL OCCUP. ENVtltON. HYG. Nt) • SEPTEMBER 1" ! 793