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Styrene emission during the moulding operation
S
PECIAL FEATURE
m
Styrene emission during the moulding operation Awareness of the importance of a c l e a n w o r k p l a c e e n v i r o n m e n t is g r o w i n g w o r l d w i d e . In t h e reinforced p l a s t i c s i n d u s t r y considera b l e e f f o r t s have b e e n m a d e to m i n i m i z e styrene e m i s s i o n s during l a m i n a t i o n w i t h u n s a t u r a t e d polyesters. Neste Polyester has been w o r k i n g w i t h LSE r e s i n s s i n c e t h e late 1970s. Magnus J o h a n s s o n says that t h e m o u l d i n g o p e r a t i o n and t h e styrene e m i s s i o n s o u r c e s can be b e t t e r u n d e r s t o o d by dividing the moulding operation into five phases: spraying, rolling, setting, g e l l i n g and curing.
FIGURE 1: Comparison of styrene emission from a LSE resin (using styrene suppressing additives) and a high solids resin (using low styrene content, 35% by weight).
efore emissions during various stages of t he moulding operation can be c o n s i d e r e d t h e m e t h o d u s e d to m e a s ur e the styrene m ust be decided upon.
B
0.3
I,,,,,,.
0.2
0.1
0 0
TIME (m/n)
I:
REINFORCED PLASTICS OCTOBER 1991
According to different gravimetric evaporation tests the use of low styrene emission (LSE) resins decreases e m i s s i o n levels by 70-90%. However, t h e s e figures a re too optimistic and do not correlate to m e a su re d styrene levels in a real moulding operation. In its m e a s u r e m e n t s Neste detected th e flow rate in the e x h a u s t duct and m e a su re d the styrene content in the duct using infrared spectroscopy. The moulding operation was done in a fume cupboard and in a closed application laboratory (5 x 3 x 2 m).
Different phases in moulding S Spraying Spraying still represents the most common fabricating procedure. In this t e c h n i q u e styrene will be atomized and because of t h a t easily evaporates. In addition, overspraying results in a loss of both resin and fibre. Parameters influencing styrene emission during this phase are: type of spray gun (airless, air atomized, etc.), nozzle type (size and angle), spraying p r e s s u r e , spraying distance, t e m p e r a t u r e and, of course, spraying operator. The advantage of using a LSE resin (which h e r e m e a n s a resin with suppressing additives to decrease styrene emission during the moulding operation) or high solids resin during t he spraying p h a se is minimal. A low styrene content in combination with low viscosity would give lower styrene levels. However, viscosity in so called 'high solids resins' -- using only 35% of styrene -- is normally high. The contribution of the styrene emission during the spraying phase to the overall emission can vary a lot. Neste has m easured figures between 40-60% of the total styrene emission. This n u m b e r seems quite high but can, to some extent, be c o m p e n s a t e d for by faster rolling in the n e x t phase.
0034-3617/91/$3.50 © 1991, Elsevier Science P u b l i s h e r s Ltd.
S gel-time and long green stage makes it • Rolling When using the h an d lay-up technique the possible to build up even a big laminate rolling p has e is the :first to emit styrene to with thickness of 10-15 m m wet on wet. After t h e a t m o s p h e r e . During this p h a s e t h e lamination edges can easily be trimmed. advantage of using a LSE resin can already Sawing, which causes lots of dust, is not be seen to some extent. Both LSE resins and necessaI:¢. high solids (low styrene content) resins give lower emissions during rolling. The drawback • Curing when using high solids resin is the bad Styrene emission during curing can be seen workability which in the test series gave in all types of resins. Factors influencing this much longer rolling times (Figure 1). This of e m i s s i o n are resi n e x o t h e r m , l a m i n a t e course results in higher styrene emission. It thickness, etc. The contribution to the overcan clearly be seen from the figure t h a t the all emission is small. If there is an emission two ways of decreasing the emission during during curing it will increase t he total rolling are changing the m o n o m e r to one styrene level if the p r o d u c t is left for curing with lower v a p o u r pressure a n d / o r giving the in a non-ventilated area. resin the best wettability properties possible, which means fast rolling. Use of LSE resin The contribution of the styrene emission during t h e rolling p h a s e to t he overall emission d ep en d s on the technique used. If The use of LSE resins is most advantageous spraying is used the contribution is smaller in the following situations: because of the high emission during spraying - - i n spraying and h a n d lay-up of large but in the h an d lay-up procedure, especially surfaces, where a small part of the surface when using a LSE resin, most of the styrene is t reat ed at a time and the rest of the is emitted during rolling. laminate sets. The LSE resin causes no styrene emission on setting; • Setting - - w h e n working within an enclosed space This is where LSE resins show their real inside a mould panel (tank, hull or deck of advantages over ottmr resins. Immediately a boat, etc.), regardless of the significant after rolling is finished the s u p p r e s s i n g reduction in styrene concentrations yieladditives in the resin prevent styrene from ded by LSE resin, additional ventilation or evaporating. respirator masks are still required; In this p h as e s t a n d a r d resins emit as - - i n spraying and hand lay-up of several much styrene as during the whole rolling small parts in the moulding shop. After phase (Figure 2). [[]ais is why LSE resins spraying and rolling in a spray booth the decrease the workshop styrene level by 50%. p r o d u c t and the mould can be moved to High solids resins also emit less styrene the w o r k s h o p w i t h o u t i ncreasi ng t h e (luring the setting phase, but the longer styrene concentration in the atmosphere; rolling time required increases the total styrene emission (Figure 1). The contribution of the styrene emission during t h e setting p h a s e to t h e overall 0.4 e m i s s i o n ag ain d e p e n d s on r e s i n a n d technique used. k
0.3
PECIAL FEATURE
FIGURE 2: Comparison of styrene emission from a LSE resin (using suppressing additives) and a standard resin with the same viscosity and gel-time. The emission during different phases of lamination is shown in the picture.
~/
• Gelling The difference in styrene emission between different resins in the gelling p h a s e is minimal. LSE r es in s us i ng s u p p r e s s i n g additives emit almost no styrene while the o th e r resins emit only small amounts. The resin gel-times used in open moulds vars~ a lot. Some fabricators prefer short geltimes (10-30 minutes) while others prefer long gel-times (40-70 minutes). When using s t a n d a r d resins a s h o r t e r gel-time gives a slightly lower overall styrene emission. On the o t h e r h an d a LSE resin with a long
i ~3TANDARDRESIN
~ 0.2 ~ o.li
°
ROLLING
sk'rlTNG •
0
10
GELLING 1
2O
CURING . . . . . . . . . .
TIME(min)
i ]
30
REINFORCED PLASTICS OCTOBER 1991
40
L:
50
S
PECIAL FEATURE
--
if styrene emission to outside air needs to be r educed the use of LSE resin is t he most economical way of decreasing styrene concent r a t i on outside the workshop.
Interlaminar
adhesion
The low styrene emission properties of Neste Polyester LSE resins have been achieved by a com bi na t i on of different additives. These additives pr e ve nt styrene from evaporating immediately after the rolling phase of the laminate. Because of the sensitive mechanism between additives and styrene in the laminate and on the surface, we regularly check i n t e r l a m i n a r adhesion of LSE resins. A 2 mm thick laminate with 2% catalyst is made. This is allowed to cure for t hree days at room t e m per a t ur e. A secondary laminate is built on top of the first and allowed to cure for one day. Then the pri m ary laminate is t or n off the secondary and the adhesion per c e nt a ge is evaluated as a ratio between b o u n d e d surface and glossy surface. We are developing a m e t h o d which will measure the force needed to t ear the laminate apart. If a LSE resin is not working properly a delay between lamination of only a couple of hour s can cause d e l a m i n a t i o n problems. However, if t he LSE has been p r o d u c e d and adjusted correctly good adhesion can be seen even after several days of delay between lamination, although Neste r e c o m m e n d s not delaying lamination for more t han 24 hours. This is also usually the rule when working with polydicyclopetadiene (DCPD) resins, w h i c h a r e k n o w n f o r good ai r dryi ng properties.
ROLLING
SETTING & .GELING
In Scandinavia most of the boat building industry has been using LSE resins successfully for m any years.
New monomers We can see from Figures 1 and 2 t h a t the concept of using suppressing additives to decrease styrene emission has been optimized. From here we can only progress by d e c r e a s i n g t h e c o n t e n t of sty re n e ( b u t keeping the same viscosity) or replacing it by a m o n o m e r having a lower v a p o u r pressure, like paramethylstyrene (PMS) or vinyltoluene (VT). We have also tested these mo n o m e rs and have seen t h a t t h e y b e h a v e e x a c t l y as expect ed because of lower v a p o u r pressure (Figure 3). The emission during spraying and rolling is significantly lower th a n when using styrene. The big question marks are price, availability and toxity of these compensating monomers. The prices are 50-100% higher t han the price of styrene, which is of course not attractive; at present the p ro d u c tio n level, because of the low d e m a n d at present, is low; and the toxicity of these compensating m onom ers has not been evaluated in the same way as toxicity of styrene. It seems t h a t the LSE resins of today t o g e t h e r with p r o p e r ventilation, correct working methods and personal protective e q u i p m e n t will continue to serve the reinforced plastics industry during the 1990s. m
CURING
W - % OF U S E D A M O U N T R E S I N
3.34 2.98
2.03
2.06
1.66
0.76
GIO2TA
MIOSTA
PMS-ST
PMS
VT
REINFORCED PLASTICS OCTOBER 1991
LSE-PMS
FIGURE 3: Comparison of styrene emission from different types of resins. GIO2TA (Neste standard resin), MIO5TA (Neste LSE resin), PMS-ST (standard resin, styrene - paramethylstyrene 2:1), PMS (standard resin, paramethylstyrene), VT (standard resin, vinyltoluene), LSE - - PMS (Neste LSE resin, paramethylstyrene).
PECIAL FEATURE
m
Styrene emission during the moulding operation Awareness of the importance of a c l e a n w o r k p l a c e e n v i r o n m e n t is g r o w i n g w o r l d w i d e . In t h e reinforced p l a s t i c s i n d u s t r y considera b l e e f f o r t s have b e e n m a d e to m i n i m i z e styrene e m i s s i o n s during l a m i n a t i o n w i t h u n s a t u r a t e d polyesters. Neste Polyester has been w o r k i n g w i t h LSE r e s i n s s i n c e t h e late 1970s. Magnus J o h a n s s o n says that t h e m o u l d i n g o p e r a t i o n and t h e styrene e m i s s i o n s o u r c e s can be b e t t e r u n d e r s t o o d by dividing the moulding operation into five phases: spraying, rolling, setting, g e l l i n g and curing.
FIGURE 1: Comparison of styrene emission from a LSE resin (using styrene suppressing additives) and a high solids resin (using low styrene content, 35% by weight).
efore emissions during various stages of t he moulding operation can be c o n s i d e r e d t h e m e t h o d u s e d to m e a s ur e the styrene m ust be decided upon.
B
0.3
I,,,,,,.
0.2
0.1
0 0
TIME (m/n)
I:
REINFORCED PLASTICS OCTOBER 1991
According to different gravimetric evaporation tests the use of low styrene emission (LSE) resins decreases e m i s s i o n levels by 70-90%. However, t h e s e figures a re too optimistic and do not correlate to m e a su re d styrene levels in a real moulding operation. In its m e a s u r e m e n t s Neste detected th e flow rate in the e x h a u s t duct and m e a su re d the styrene content in the duct using infrared spectroscopy. The moulding operation was done in a fume cupboard and in a closed application laboratory (5 x 3 x 2 m).
Different phases in moulding S Spraying Spraying still represents the most common fabricating procedure. In this t e c h n i q u e styrene will be atomized and because of t h a t easily evaporates. In addition, overspraying results in a loss of both resin and fibre. Parameters influencing styrene emission during this phase are: type of spray gun (airless, air atomized, etc.), nozzle type (size and angle), spraying p r e s s u r e , spraying distance, t e m p e r a t u r e and, of course, spraying operator. The advantage of using a LSE resin (which h e r e m e a n s a resin with suppressing additives to decrease styrene emission during the moulding operation) or high solids resin during t he spraying p h a se is minimal. A low styrene content in combination with low viscosity would give lower styrene levels. However, viscosity in so called 'high solids resins' -- using only 35% of styrene -- is normally high. The contribution of the styrene emission during the spraying phase to the overall emission can vary a lot. Neste has m easured figures between 40-60% of the total styrene emission. This n u m b e r seems quite high but can, to some extent, be c o m p e n s a t e d for by faster rolling in the n e x t phase.
0034-3617/91/$3.50 © 1991, Elsevier Science P u b l i s h e r s Ltd.
S gel-time and long green stage makes it • Rolling When using the h an d lay-up technique the possible to build up even a big laminate rolling p has e is the :first to emit styrene to with thickness of 10-15 m m wet on wet. After t h e a t m o s p h e r e . During this p h a s e t h e lamination edges can easily be trimmed. advantage of using a LSE resin can already Sawing, which causes lots of dust, is not be seen to some extent. Both LSE resins and necessaI:¢. high solids (low styrene content) resins give lower emissions during rolling. The drawback • Curing when using high solids resin is the bad Styrene emission during curing can be seen workability which in the test series gave in all types of resins. Factors influencing this much longer rolling times (Figure 1). This of e m i s s i o n are resi n e x o t h e r m , l a m i n a t e course results in higher styrene emission. It thickness, etc. The contribution to the overcan clearly be seen from the figure t h a t the all emission is small. If there is an emission two ways of decreasing the emission during during curing it will increase t he total rolling are changing the m o n o m e r to one styrene level if the p r o d u c t is left for curing with lower v a p o u r pressure a n d / o r giving the in a non-ventilated area. resin the best wettability properties possible, which means fast rolling. Use of LSE resin The contribution of the styrene emission during t h e rolling p h a s e to t he overall emission d ep en d s on the technique used. If The use of LSE resins is most advantageous spraying is used the contribution is smaller in the following situations: because of the high emission during spraying - - i n spraying and h a n d lay-up of large but in the h an d lay-up procedure, especially surfaces, where a small part of the surface when using a LSE resin, most of the styrene is t reat ed at a time and the rest of the is emitted during rolling. laminate sets. The LSE resin causes no styrene emission on setting; • Setting - - w h e n working within an enclosed space This is where LSE resins show their real inside a mould panel (tank, hull or deck of advantages over ottmr resins. Immediately a boat, etc.), regardless of the significant after rolling is finished the s u p p r e s s i n g reduction in styrene concentrations yieladditives in the resin prevent styrene from ded by LSE resin, additional ventilation or evaporating. respirator masks are still required; In this p h as e s t a n d a r d resins emit as - - i n spraying and hand lay-up of several much styrene as during the whole rolling small parts in the moulding shop. After phase (Figure 2). [[]ais is why LSE resins spraying and rolling in a spray booth the decrease the workshop styrene level by 50%. p r o d u c t and the mould can be moved to High solids resins also emit less styrene the w o r k s h o p w i t h o u t i ncreasi ng t h e (luring the setting phase, but the longer styrene concentration in the atmosphere; rolling time required increases the total styrene emission (Figure 1). The contribution of the styrene emission during t h e setting p h a s e to t h e overall 0.4 e m i s s i o n ag ain d e p e n d s on r e s i n a n d technique used. k
0.3
PECIAL FEATURE
FIGURE 2: Comparison of styrene emission from a LSE resin (using suppressing additives) and a standard resin with the same viscosity and gel-time. The emission during different phases of lamination is shown in the picture.
~/
• Gelling The difference in styrene emission between different resins in the gelling p h a s e is minimal. LSE r es in s us i ng s u p p r e s s i n g additives emit almost no styrene while the o th e r resins emit only small amounts. The resin gel-times used in open moulds vars~ a lot. Some fabricators prefer short geltimes (10-30 minutes) while others prefer long gel-times (40-70 minutes). When using s t a n d a r d resins a s h o r t e r gel-time gives a slightly lower overall styrene emission. On the o t h e r h an d a LSE resin with a long
i ~3TANDARDRESIN
~ 0.2 ~ o.li
°
ROLLING
sk'rlTNG •
0
10
GELLING 1
2O
CURING . . . . . . . . . .
TIME(min)
i ]
30
REINFORCED PLASTICS OCTOBER 1991
40
L:
50
S
PECIAL FEATURE
--
if styrene emission to outside air needs to be r educed the use of LSE resin is t he most economical way of decreasing styrene concent r a t i on outside the workshop.
Interlaminar
adhesion
The low styrene emission properties of Neste Polyester LSE resins have been achieved by a com bi na t i on of different additives. These additives pr e ve nt styrene from evaporating immediately after the rolling phase of the laminate. Because of the sensitive mechanism between additives and styrene in the laminate and on the surface, we regularly check i n t e r l a m i n a r adhesion of LSE resins. A 2 mm thick laminate with 2% catalyst is made. This is allowed to cure for t hree days at room t e m per a t ur e. A secondary laminate is built on top of the first and allowed to cure for one day. Then the pri m ary laminate is t or n off the secondary and the adhesion per c e nt a ge is evaluated as a ratio between b o u n d e d surface and glossy surface. We are developing a m e t h o d which will measure the force needed to t ear the laminate apart. If a LSE resin is not working properly a delay between lamination of only a couple of hour s can cause d e l a m i n a t i o n problems. However, if t he LSE has been p r o d u c e d and adjusted correctly good adhesion can be seen even after several days of delay between lamination, although Neste r e c o m m e n d s not delaying lamination for more t han 24 hours. This is also usually the rule when working with polydicyclopetadiene (DCPD) resins, w h i c h a r e k n o w n f o r good ai r dryi ng properties.
ROLLING
SETTING & .GELING
In Scandinavia most of the boat building industry has been using LSE resins successfully for m any years.
New monomers We can see from Figures 1 and 2 t h a t the concept of using suppressing additives to decrease styrene emission has been optimized. From here we can only progress by d e c r e a s i n g t h e c o n t e n t of sty re n e ( b u t keeping the same viscosity) or replacing it by a m o n o m e r having a lower v a p o u r pressure, like paramethylstyrene (PMS) or vinyltoluene (VT). We have also tested these mo n o m e rs and have seen t h a t t h e y b e h a v e e x a c t l y as expect ed because of lower v a p o u r pressure (Figure 3). The emission during spraying and rolling is significantly lower th a n when using styrene. The big question marks are price, availability and toxity of these compensating monomers. The prices are 50-100% higher t han the price of styrene, which is of course not attractive; at present the p ro d u c tio n level, because of the low d e m a n d at present, is low; and the toxicity of these compensating m onom ers has not been evaluated in the same way as toxicity of styrene. It seems t h a t the LSE resins of today t o g e t h e r with p r o p e r ventilation, correct working methods and personal protective e q u i p m e n t will continue to serve the reinforced plastics industry during the 1990s. m
CURING
W - % OF U S E D A M O U N T R E S I N
3.34 2.98
2.03
2.06
1.66
0.76
GIO2TA
MIOSTA
PMS-ST
PMS
VT
REINFORCED PLASTICS OCTOBER 1991
LSE-PMS
FIGURE 3: Comparison of styrene emission from different types of resins. GIO2TA (Neste standard resin), MIO5TA (Neste LSE resin), PMS-ST (standard resin, styrene - paramethylstyrene 2:1), PMS (standard resin, paramethylstyrene), VT (standard resin, vinyltoluene), LSE - - PMS (Neste LSE resin, paramethylstyrene).