Chapter 14
Inorganic Tin Compounds as Flame, Smoke, and Carbon Monoxide Suppressants for Synthetic Polymers Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on June 15, 2016 | http://pubs.acs.org Publication Date: May 9, 1990 | doi: 10.1021/bk-1990-0425.ch014
1
2
P. A. Cusack and A. J. Killmeyer 1
International Tin Research Institute, Uxbridge, United Kingdom Tin Research Institute, Inc., Columbus, OH 43201 2
In view of the current demand for novel, non-toxic flame- and smoke-suppressant systems for synthetic polymers, certain inorganic tin compounds have been evaluated as fire retardants in a number of plastic and elastomeric substrates. The results obtained indicate that tin compound additives, in particular, zinc hydroxystannate and zinc stannate, exhibit beneficial properties both in halogenated and halogen-free formulations. The tin compounds appear to act predominantly in the condensed phase by a char -promoting mechanism, and this leads to a significant decrease in the amounts of smoke and toxic gases evolved during polymer combustion. The observed carbon monoxide-suppression is particularly interesting, since CO inhalation is now known to be the cause of death in the vast majority of fire fatalities.
The l a s t two decades have seen a major growth i n t h e use o f s y n t h e t i c polymers as m a t e r i a l s f o r c o n s t r u c t i o n , i n s u l a t i o n , p a c k a g i n g , u p h o l s t e r y and t r a n s p o r t a p p l i c a t i o n s (_1_). U n f o r t u n a t e l y , this p e r i o d has a l s o seen a d r a m a t i c i n c r e a s e i n t h e number o f s e r i o u s f i r e s , and t h e number o f deaths and i n j u r i e s i n f i r e s remains a p p a l l i n g l y high. F i r e deaths a r e n o r m a l l y v i o l e n t i n n a t u r e , and smoke i n h a l a t i o n and not f i r e i t s e l f i s t h e k i l l e r t h a t a c c o u n t s f o r over 80% o f f i r e deaths (2). T h e r e f o r e , r e c e n t advances i n f i r e t e s t i n g have p l a c e d g r e a t emphasis i n d e v e l o p i n g p r o d u c t s t h a t have low flame s p r e a d p r o p e r t i e s and a r e low smoke p r o d u c i n g . The use o f flame r e t a r d a n t s i n polymers has i n c r e a s e d d r a m a t i c a l l y i n r e c e n t y e a r s , i n p a r a l l e l t o t h e growth o f t h e p l a s t i c s i n d u s t r y (J_). Data f o r t h e U.S. consumption o f t h e s e c h e m i c a l s d u r i n g 1985 a r e p r e s e n t e d i n T a b l e I . Many o f t h e e x i s t i n g commercial a d d i t i v e s , however, have problems a s s o c i a t e d w i t h t h e i r use. In p a r t i c u l a r , c e r t a i n f l a m e - r e t a r d a n t systems a r e known t o cause an i n c r e a s e i n t h e amount o f smoke and t o x i c / c o r r o s i v e
0097-6156/90/0425-0189S06.50/0 © 1990 American Chemical Society
Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
190
FIRE A N D POLYMERS
gases g e n e r a t e d by p l a s t i c s i f they burn ( M . In a d d i t i o n , a number of the commercial f i r e r e t a r d a n t s have been found t o p o s s e s s u n d e s i r a b l e t o x i c o l o g i c a l p r o p e r t i e s themselves, ( 5 , 6 ) and t h e r e has been c o n s i d e r a b l e i n t e r e s t i n f i n d i n g new, s a f e r c h e m i c a l a d d i t i v e s f o r flammable m a t e r i a l s .
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Table I. Flame R e t a r d a n t s f o r P l a s t i c s (USA Consumption, 1 9 8 5 ) Metric
Chemical ADDITIVES: Alumina t r i h y d r a t e Antimony o x i d e s Boron compounds Bromine compounds C h l o r i n e compounds Phosphorus compounds Others REACTIVES TOTAL =
tonnes
93,900 16,000 5,000 17,000 13,000 28,000 8,100 8,900 189,900
SOURCE: Data from the Fire Retardant Chemicals Association. Reproduced with permission from ref. 3. Copyright 1985 Modern Plastics. As a r e s u l t , s e v e r a l i n o r g a n i c compounds have found a p p l i c a t i o n i n t h i s f i e l d , and alumina t r i h y d r a t e , A 1 ( 0 H ) i s now by f a r the h i g h e s t volume flame r e t a r d a n t (3). I t s use, however, i s l i m i t e d t o those polymers which can t o l e r a t e the e x c e p t i o n a l l y h i g h l o a d i n g s r e q u i r e d t o be e f f e c t i v e , w i t h o u t s e r i o u s l y a f f e c t i n g the m e c h a n i c a l p r o p e r t i e s o f the s u b s t r a t e (]_). At the p r e s e n t time, i n o r g a n i c t i n compounds f i n d a r e l a t i v e l y s m a l l use i n n a t u r a l polymers, p a r t i c u l a r l y as f l a m e - r e s i s t t r e a t ments f o r w o o l l e n rugs and s h e e p s k i n s ( 8 , 9 ) . Although c e r t a i n other metal d e r i v a t i v e s have r e c e i v e d more a t t e n t i o n , t h e r e has been much i n t e r e s t r e c e n t l y i n the p o t e n t i a l use o f t i n c h e m i c a l s as flame r e t a r d a n t s and smoke s u p p r e s s a n t s f o r s y n t h e t i c polymers ( 1 0 ) . The purpose o f t h i s paper i s t o b r i e f l y r e v i e w r e c e n t r e s e a r c h i n t o the e f f e c t i v e n e s s and mode o f a c t i o n o f t i n compounds as f i r e r e t a r d a n t s i n a number o f h a l o g e n a t e d and h a l o g e n - f r e e , p l a s t i c and elastomeric substrates. TIN
ADDITIVES
Anhydrous t i n ( I V ) o x i d e ( ' S u p e r l i t e ' g r a d e ) and B - s t a n n i c a c i d ('Metastannic a c i d ' ) were s u p p l i e d by K e e l i n g & Walker L t d . , S t o k e on-Trent. ' 3 - s t a n n i c a c i d p a s t e ' was p r e p a r e d a t C h i n g h a l l L t d . , M i l t o n Keynes, by d i s p e r s i n g K e e l i n g & Walker's M e t a s t a n n i c a c i d , a t a l e v e l of 7 3 % i n a phthalate p l a s t i c i s e r . ' C o l l o i d a l t i n oxide', a 2 5 % aqueous d i s p e r s i o n o f SnO^, was s u p p l i e d by N y a c o l P r o d u c t s I n c . , Ashland, Mass., U.S.A. Z i n c h y d r o x y s t a n n a t e and z i n c s t a n n a t e were s y n t h e s i s e d a t I.T.R.I, a c c o r d i n g t o p r e v i o u s l y r e p o r t e d p r o c e d u r e s : ( 1 1 , 1 2 )
Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
14.
CUSACK & KILLMEYER
Na Sn(OH) 2
ZnSn(OH), b
6
191
Inorganic Tin Compounds
+ ZnCl ^
H 2
2 ° ^ ZnSn(OH) | c
ZnSnO^ 3
+
+
2NaCl
3H 0 2 o
The i d e n t i t i e s of the p r o d u c t s were c o n f i r m e d by i n f r a r e d s p e c t r o s c o p y and x - r a y powder d i f f r a c t i o n p a t t e r n s . P h y s i c a l data on the i n o r g a n i c t i n a d d i t i v e s s t u d i e d a r e g i v e n i n T a b l e II.
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TEST METHODS Flammability. F l a m m a b i l i t y of the samples, i n the form o f t h i n s t r i p s o f approximate dimensions o f 120mm x 7mm x 3mm was determined by measurement o f t h e i r oxygen i n d i c e s ( 0 1 ' s ) a c c o r d i n g to ASTM D2863, u s i n g a S t a n t o n - R e d c r o f t FTA module. I t has been e s t a b l i s h e d t h a t the 01 v a l u e s o f polymers f a l l , :.n some c a s e s d r a m a t i c a l l y , when the s u r r o u n d i n g gas m i x t u r e i s heated (J_). C o n s e q u e n t l y , the 01 t e s t has been extended to m a t e r i a l s at e l e v a t e d t e m p e r a t u r e s , and the h i g h temperature 0 1 s o f polymer samples were determined u s i n g a S t a n t o n - R e d c r o f t HFTA i n s t r u m e n t . The temperature index (TI) o f a polymer i s d e f i n e d as the temperature at which the t e s t specimen j u s t s u p p o r t s combustion i n a i r . f
Smoke d e n s i t y . O p t i c a l d e n s i t y measurements on the smoke e v o l v e d from b u r n i n g p l a s t i c samples were c a r r i e d out u s i n g an NBS Smoke Chamber. The samples, which measured 75mm x 75mm, w i t h a t h i c k n e s s o f 0.6 - 4mm, were burned i n the ' f l a m i n g mode i n a c c o r d a n c e w i t h ASTM E662-79. S p e c i f i c smoke d e n s i t y (Ds) v a l u e s r e p o r t e d are the averages o f t h r e e independent d e t e r m i n a t i o n s . 1
Carbon Monoxide E v o l u t i o n . D e t e r m i n a t i o n of the carbon monoxide e v o l v e d d u r i n g combustion o f polymer samples i n NBS Chamber experiments was c a r r i e d out u s i n g a T e l e g a n CO Sensor (Type 3 F ) . Quoted v a l u e s are the n u m e r i c a l averages o f t h r e e independant determinations. HALOGEN-CONTAINING POLYMER SYSTEMS The f l a m e - r e t a r d a n t a c t i o n of c h l o r i n e and bromine compounds, e i t h e r as p h y s i c a l l y - i n c o r p o r a t e d a d d i t i v e s to an o r g a n i c polymer or as p a r t of the polymer s t r u c t u r e i t s e l f , i s w e l l e s t a b l i s h e d (J_). Indeed, h a l o g e n a t e d compounds f i n d e x t e n s i v e commercial use as flame r e t a r d a n t s , (3.) and these are o f t e n used i n c o n j u n c t i o n w i t h ' s y n e r g i s t s ' , such as antimony t r i o x i d e or phosphorus d e r i v a t i v e s (J_). However, h a l o g e n - c o n t a i n i n g polymers g e n e r a l l y e v o l v e l a r g e amounts of smoke and c o r r o s i v e gases d u r i n g combustion, and t h e r e i s a g r e a t demand f o r n o v e l smoke-suppressant formulations. Polyester resins. The f i r e - p e r f o r m a n c e c h a r a c t e r i s t i c s o f u n s a t u r a t e d p o l y e s t e r r e s i n s are o f utmost importance i n many a p p l i c a t i o n a r e a s , p a r t i c u l a r l y i n the c o n s t r u c t i o n , t r a n s p o r t a t i o n and e l e c t r o n i c s i n d u s t r i e s (J_3). C o n s e q u e n t l y , these p l a s t i c s r e p r e s e n t one o f the major growth a r e a s f o r f i r e r e t a r d a n t s i n r e c e n t y e a r s (J_4).
Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
oxide)
'paste'
8-stannic a c i d (hydrous t i n ( I V )
acid-
tin(IV)
3-stannic
Colloidal
stannate
Zinc
2
2
.xH 0 2
2
ZnSnO^
ZnSn(OH), 0
SnO
2
Sn0 .xH 0
2
Sn0 .xH 0
41.5*
51.1**
white powder
19.7
white powder
25% aqueous dispersion
51.3
70.3
white powder 73% d i s p e r s i o n in a phthalate plasticiser
78.8
white powder
(Reproduced with permission from Ref. 34, Copyright 1989 John Wiley & Sons Ltd.)
* Z i n c c o n t e n t = 22.8% * * Z i n c c o n t e n t = 28.2%
hydroxystannate
Zinc
oxide
Sn0
oxide
Anhydrous t i n ( I V )
2
Formula
Additive
Data on T i n A d d i t i v e s
Tin Content(%)
Physical
Physical State
Table I I .
3.9
3-3
1.3
-
5.2
6.9
Specific Gravity
2
ca. 1
ca. 1
0.03
ca.
ca.
2
Average Particle (Um) 0.3
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Size
14.
CUSACK & KILLMEYER
Inorganic Tin Compounds
193
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E a r l i e r s t u d i e s a t the ITRI have demonstrated the e f f e c t i v e n e s s o f t i n ( I V ) o x i d e , both i n i t s anhydrous and hydrous forms, as a f l a m e - and smoke-retardant a d d i t i v e f o r l a b o r a t o r y - p r e p a r e d p o l y e s t e r r e s i n f o r m u l a t i o n s (J_5). In a r e c e n t study, c a r r i e d out i n c o l l a b o r a t i o n w i t h a major U.K. company, a number o f i n o r g a n i c t i n a d d i t i v e s have been i n c o r p o r a t e d i n t o a commercial brominated polyester resin. A l t h o u g h t h i s r e s i n , which c o n t a i n s 28% by weight bromine, i s i n t r i n s i c a l l y f l a m e - r e t a r d a n t , g i v i n g samples w i t h an 01 o f c a . 41 and which meet the UL94-VO c l a s s i f i c a t i o n , f o r m u l a t i o n s w i t h improved flame and smoke p r o p e r t i e s a r e sought. Antimony t r i o x i d e , 3 - s t a n n i c a c i d (hydrous t i n ( I V ) o x i d e ) , z i n c h y d r o x y s t a n n a t e , and z i n c s t a n n a t e were i n c o r p o r a t e d i n t o the commercial brominated p o l y e s t e r r e s i n a t l e v e l s o f 1,2,5 and 10% by weight. No p r o c e s s i n g problems were e n c o u n t e r e d and the samples c u r e d s a t i s f a c t o r i l y t o g i v e r i g i d , opaque s t r i p s . The i n c o r p o r a t i o n o f Sb^O^ i n t o the p o l y e s t e r l e a d s t o an i n t e r e s t i n g f l a m m a b i l i t y e f f e c t : a p r o g r e s s i v e i n c r e a s e i n 01 i s o b s e r v e d up t o an a d d i t i v e l e v e l o f 2%, above which the 01 d e c r e a s e s d r a m a t i c a l l y ( F i g u r e 1). I t has p r e v i o u s l y been r e p o r t e d (16,17) t h a t the optimum atomic r a t i o o f h a l o g e n : antimony i n s y n e r g i s t i c f l a m e - r e t a r d a n t systems appears t o depend upon the n a t u r e o f the h o s t polymer, and may o f t e n be f a r g r e a t e r than the s t o i c h i o m e t r i c p r o p o r t i o n s ( v i z . 3*1). Indeed, the 01 o f p o l y p r o p y l e n e c o n t a i n i n g a c h l o r i n a t e d h y d r o c a r b o n p a s s e s t h r o u g h a v e r y s h a r p maximum, w i t h i n c r e a s i n g Sb 0 , a t a Cl:Sb r a t i o o f c a . 25:1 (J_8). In the brominated p o l y e s t e r , the Br:Sb atomic r a t i o f o r optimum flame r e t a r d a n c y a l s o appears t o be about 25:1. Of the t i n a d d i t i v e s s t u d i e d , the anhydrous and h y d r a t e d z i n c s t a n n a t e s , ZnSnO and ZnSn(OH), r e s p e c t i v e l y , a r e c o n s i d e r a b l y more e f f e c t i v e f l a m e - r e t a r d a n t s y n e r g i s t s w i t h the bromine p r e s e n t i n the p l a s t i c than 3 - s t a n n i c a c i d ( F i g u r e 1). In l i n e w i t h t h i s o b s e r v a t i o n , o x i d i c t i n - z i n c systems have p r e v i o u s l y been found to e x h i b i t s u p e r i o r f l a m e - r e t a r d a n t p r o p e r t i e s t o t i n o x i d e s a l o n e (1922). In a d d i t i o n , ZnSnO g i v e s h i g h e r v a l u e s o f 01 than S b 0 a t a l l i n c o r p o r a t i o n l e v e l s s t u a i e d , and, i n f a c t , the 1% ZnSnO - c o n t a i n i n g p l a s t i c s o u t p e r f o r m samples c o n t a i n i n g 2% S b 0 ~ . I t i s i n t e r e s t i n g to note t h a t 3 - s t a n n i c a c i d i s s i g n i f i c a n t l y more e f f e c t i v e as a flame r e t a r d a n t than anhydrous S n 0 a t low a d d i t i v e l e v e l s ( F i g u r e 2) as p r e v i o u s l y r e p o r t e d i n a number o f h a l o g e n - c o n t a i n i n g polymer systems (15,22,23). In t h i s c o n n e c t i o n , thermal a n a l y s i s s t u d i e s of ABS-decabromobiphenyl-tin(IV) oxide systems have shown t h a t v e r y l i t t l e t i n ( I V ) bromide or t i n ( I V ) oxybromide i s v o l a t i l i s e d when anhydrous S n 0 i s used, but, i f the t i n i s p r e s e n t as 3 - s t a n n i c a c i d , and i f the atomic r a t i o o f Br:Sn i s h i g h e r than s t o i c h i o m e t r i c ( v i z . 4:1), then s i g n i f i c a n t v o l a t i l i s a t i o n o c c u r s , g i v i n g r i s e t o a vapour-phase f l a m e - r e t a r d a n t a c t i o n (23). T h i s d i f f e r e n c e i n r e a c t i v i t y between the two forms o f t i n ( I V ) o x i d e may be due t o the d i f f e r e n c e i n the s u r f a c e a r e a s o f t h e s e m a t e r i a l s : d e s p i t e b e i n g a c o a r s e r powder i n terms o f i t s average p a r t i c l e s i z e ( T a b l e I I ) , hydrous SnO has a s u r f a c e a r e a o f a t l e a s t an o r d e r o f magnitude g r e a t e r than t h a t o f the anhydrous m a t e r i a l (24). The advantage o f u s i n g a p a s t e d i s p e r s i o n o f a f l a m e - r e t a r d a n t a d d i t i v e i n t h i s p o l y e s t e r r e s i n f o r m u l a t i o n i s e v i d e n t from the 2
2
2
2
Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
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FIRE AND POLYMERS
0.1.
40-1 0
1
1
2
1
1
1
4 Additive
1
1
6
1
8
1
r10
(%)
F i g u r e 1. R e l a t i o n s h i p between the f l a m m a b i l i t y and metal compound l e v e l o f brominated p o l y e s t e r r e s i n samples. (Reproduced w i t h p e r m i s s i o n from Ref.3 *, C o p y r i g h t 1989 John Wiley & Sons L t d . ) 1
Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
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14.
CUSACK & KILLMEYER
195
Inorganic Tin Compounds
m
°*
• 2%
(hyd)
(hyd) 'paste'
Sn0
2
F i g u r e 2. E f f e c t o f i n c o r p o r a t i o n l e v e l o f t i n o x i d e a d d i t i v e s on t h e f l a m m a b i l i t y o f brominated p o l y e s t e r r e s i n .
Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
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196
FIRE AND POLYMERS
d a t a shown i n F i g u r e 2. At i n c o r p o r a t i o n l e v e l s o f 2% and 5%, a d i s p e r s i o n o f 3 - s t a n n i c a c i d i n a p h t h a l a t e p l a s t i c i s e r ( s u p p l i e d by C h i n g h a l l L i m i t e d , M i l t o n Keynes, U.K.), g i v e s a s i g n i f i c a n t l y improved f l a m e - r e t a r d a n t performance over t h a t o f powdered 3 - s t a n n i c a c i d , presumably because o f i t s more u n i f o r m d i s t r i b u t i o n i n the polymer m a t r i x . A f u r t h e r improvement i n f l a m e - r e t a r d a n t e f f i c i e n c y i s observed when a c o l l o i d a l d i s p e r s i o n o f t i n ( I V ) o x i d e i s i n c o r p o r a t e d i n t o the p o l y e s t e r . At a 1.5% a d d i t i o n l e v e l , c o l l o i d a l SnO^ g i v e s an 01 v a l u e (49.0) which i s markedly h i g h e r than t h a t o b t a i n e d w i t h 5% l o a d i n g s o f e i t h e r anhydrous SnO (47.7) or 3 - s t a n n i c a c i d (47.9), as powdered a d d i t i v e s ( F i g u r e 2 ) . In a d d i t i o n t o i t s i n c r e a s e d f l a m e - r e t a r d a n t a b i l i t y , c o l l o i d a l S n 0 o f f e r s the f u r t h e r advantages o f t r a n s l u c e n c y i n the cured p l a s t i c , ease o f i n c o r p o r a t i o n and nons e t t l i n g i n the r e s i n p r i o r t o c u r e . E v a l u a t i o n o f the smoke g e n e r a t e d d u r i n g f l a m i n g combustion o f the brominated p o l y e s t e r r e s i n s has been c a r r i e d out i n an NBS Smoke Chamber. The d a t a o b t a i n e d , i l l u s t r a t e d g r a p h i c a l l y i n F i g u r e 3 and summarised i n T a b l e I I I , c l e a r l y i n d i c a t e t h a t both z i n c h y d r o x y s t a n n a t e and z i n c s t a n n a t e , when i n c o r p o r a t e d a t l e v e l s o f 2% or 5%, s i g n i f i c a n t l y reduce both the t o t a l amount and the r a t e o f p r o d u c t i o n , o f smoke e v o l v e d from the b u r n i n g brominated r e s i n . Although 3 - s t a n n i c a c i d and antimony t r i o x i d e have a s l i g h t b e n e f i c i a l e f f e c t on the r a t e o f smoke e m i s s i o n , n e i t h e r a d d i t i v e d e c r e a s e s the maximum o p t i c a l d e n s i t y o f the smoke, s a t u r a t i o n l e v e l s b e i n g reached i n each c a s e . Furthermore, ZnSn(OH). and ZnSnO are found t o be h i g h l y e f f e c t i v e as CO s u p p r e s s a n t s i n the r e s i n , when a s s e s s e d i n a n o v e l t e s t assembly c o m p r i s i n g the NBS Smoke Chamber i n c o n j u n c t i o n w i t h the c o n t i n u o u s CO monitor ( F i g u r e 4 and T a b l e I I I ) . S u b s t a n t i a l r e d u c t i o n s i n CO l e v e l s produced from z i n c s t a n n a t e - c o n t a i n i n g samples i n the NBS Smoke Chamber are e v i d e n t a t 3 minutes a f t e r i g n i t i o n and these e f f e c t s c o n t i n u e throughout the t e s t s , so t h a t maximum l e v e l s o f CO, a f t e r 10 minutes b u r n i n g , are a l s o much lower than f o r the base p l a s t i c . Antimony t r i o x i d e and B - s t a n n i c a c i d , a l t h o u g h showing some CO-suppressing a b i l i t y , a r e c o n s i d e r a b l y l e s s e f f e c t i v e i n t h i s r e s p e c t than e i t h e r ZnSn(OH)^ or ZnSnO (Table I I I ) . Hence, the z i n c s t a n n a t e s have been shown t o impart b e n e f i c i a l p r o p e r t i e s t o t h i s polymer system, i n terms o f f l a m m a b i l i t y and smoke/carbon monoxide e v o l u t i o n , and the improvements i n performance are c l e a r l y s u p e r i o r t o those e x h i b i t e d by the c o m m e r c i a l l y a v a i l a b l e antimony t r i o x i d e . 2
Other Halogenated Systems. I n o r g a n i c t i n compounds have been found t o e x h i b i t f l a m e - r e t a r d a n t and smoke-suppressant p r o p e r t i e s i n a number o f h a l o g e n - c o n t a i n i n g s y n t h e t i c polymer c o m p o s i t i o n s . In p a r t i c u l a r , T o u v a l (22) r e p o r t e d t h a t hydrous t i n ( I V ) o x i d e i s a t l e a s t as e f f e c t i v e as antimony t r i o x i d e when i n c o r p o r a t e d as a f l a m e - r e t a r d a n t s y n e r g i s t w i t h c h l o r i n e - c o n t a i n i n g compounds i n v a r i o u s t h e r m o p l a s t i c s i n c l u d i n g p o l y e t h y l e n e , p o l y p r o p y l e n e and a c r y l o n i t r i l e - b u t a d i e n e - s t y r e n e (ABS p l a s t i c ) . S i m i l a r l y , Fukatsu (25) demonstrated the f l a m e - r e t a r d a n t s u p e r i o r i t y o f hydrous S n 0 over S b 0 , a t l e v e l s o f 0.5% - 3%, i n a p o l y ( v i n y l a l c o h o l ) - p o l y ( v i n y l c h l o r i d e ) blended f a b r i c . Recent s t u d i e s a t I.T.R.I., c a r r i e d out i n c o l l a b o r a t i o n w i t h 2
2
Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
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CUSACK & K I L L M E Y E R
Inorganic Tin Compounds
D,
Time (min.) F i g u r e 3E f f e c t o f i n o r g a n i c a d d i t i v e s on the d e n s i t y o f the smoke e v o l v e d from brominated p o l y e s t e r r e s i n i n the NBS-type Smoke Chamber. (Reproduced w i t h p e r m i s s i o n from Ref.34, C o p y r i g h t 1989 John Wiley & Sons L t d . )
Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990. A d d i t i v e s on t h e F i r e P r o p e r t i e s o f Brominated P o l y e s t e r R e s i n
0%
1000
46.2
n
949
(Reproduced with permission from Ref. 34, Copyright 1989 John Wiley & Sons Ltd.)
a t end o f e x p e r i m e n t , i . e . 10 m i n u t e s a f t e r
61.1%
54.5%
24.0%
13.8%
i g n i t i o n o f sample.
866
1013
7.5
-
**Measurements r e c o r d e d
00
i g n i t i o n o f sample.
32.8%
672
56.1
1690
1917
37.5%
1390
2587
2813
4967
4783
56.5%
52.7%
16.5%
19.6%
38.7%
44.5%
3300 3645
8.2% 5463
18.0% 50.6%
-
1100
-
n
1825
3.5
3.0
-
4.0
3 minutes a f t e r
37.1%
629
56.0
CO
CO
881
850
GO
0 0
* Measurements r e c o r d e d
6
ZnSn0
"
3
ZnSn(OH)
"
2
S n 0 ( h y d ) 47.9
3
"
2
5% S b 0 10.1%
26.3%
737
54.2
899
29.8%
702
53.4
ZnSn0
"
6
ZnSn(0H)
"
3
12.1%
3
879
2
S n 0 ( h y d ) 45.1
"
2
51.2
-
41.2
Sb 0
2%
n
Smoke D e n s i t y
CO E v o l u t i o n (ppm) Red Time(min)to A c t u a l ( 3 m i n ) * R e d ( 3 m i n s ) Max.** (max). D (3min)* R e d * ( 3 m i n ) D_(max) D = s s CO 5950 2225 1000 3.0 00 4700 21.0% 1650 4.0 25.8% 851 14.9%
of Inorganic
None
Flammability 01
Effect
Additive
Table I I I .
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CUSACK & K I L L M E Y E R
[CO]
Inorganic Tin Compounds
p.p.m.
Time
(min.)
F i g u r e 4. E f f e c t o f i n o r g a n i c a d d i t i v e s on t h e e m i s s i o n o f carbon monoxide from brominated p o l y e s t e r r e s i n i n t h e NBS-type Smoke Chamber. (Reproduced w i t h p e r m i s s i o n from R e f . 3 4 , C o p y r i g h t 1 9 8 9 John Wiley & Sons L t d . )
Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
200
FIRE AND POLYMERS
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e x t e r n a l o r g a n i s a t i o n s , have shown t h a t c e r t a i n i n o r g a n i c t i n a d d i t i v e s , i n c l u d i n g SnO^, ZnSnCOH)^ and ZnSnO , are e f f e c t i v e f l a m e and s m o k e - r e t a r d a n t s i n a range o f c h l o r i n a t e d polymers, i n c l u d i n g r i g i d PVC, (26) f l e x i b l e PVC and neoprene. Hence, i t i s apparent t h a t c e r t a i n i n o r g a n i c t i n compounds are v e r y e f f e c t i v e flame r e t a r d a n t s and smoke s u p p r e s s a n t s f o r h a l o g e n a t e d polymer f o r m u l a t i o n s . S i n c e t h e s e a d d i t i v e s are g e n e r a l l y n o n - t o x i c , t h e i r p o t e n t i a l use as p a r t i a l or t o t a l r e p l a c e m e n t s f o r e x i s t i n g commercial flame r e t a r d a n t s , such as antimony t r i o x i d e , i s thought t o m e r i t s e r i o u s c o n s i d e r a t i o n . HALOGEN-FREE POLYMER SYSTEMS In r e c e n t y e a r s , t h e r e has been i n c r e a s i n g c o n c e r n about the t o x i c i t y and c o r r o s i v e n a t u r e o f the smoke and gases g e n e r a t e d d u r i n g the combustion o f h a l o g e n - c o n t a i n i n g polymers (27). Consequently, t h e r e i s a c o n s i d e r a b l e demand f o r p l a s t i c s which comply t o the s p e c i f i c a t i o n 'low smoke zero h a l o g e n (LSOH) flame r e t a r d a n c y , p a r t i c u l a r l y f o r use i n underground t r a n s p o r t , s h i p p i n g and power stations. As a r e s u l t , t h e r e has been much i n t e r e s t i n the use o f n o n - t o x i c i n o r g a n i c a d d i t i v e s and f i l l e r s , and the market f o r t h e s e compounds i s l i k e l y to c o n t i n u e i t s r a p i d growth i n the y e a r s ahead (28). 1
E t h y l e n e - a c r y l i c Rubber. The use o f PVC as a w i r e and c a b l e i n s u l a t i o n m a t e r i a l has d e c l i n e d i n r e c e n t y e a r s , and i t has been r e p l a c e d to a s i g n i f i c a n t e x t e n t by h a l o g e n - f r e e e l a s t o m e r i c compositions. At the p r e s e n t time, such f o r m u l a t i o n s a r e made f l a m e - r e t a r d a n t by the i n c o r p o r a t i o n o f a l u m i n a t r i h y d r a t e (ATH). A l t h o u g h ATH i s e s s e n t i a l l y n o n - t o x i c and r e l a t i v e l y inexpensive, h i g h a d d i t i o n l e v e l s are n e c e s s a r y f o r e f f e c t i v e n e s s , and t h i s o f t e n r e s u l t s i n a marked d e t e r i o r a t i o n i n the m e c h a n i c a l p r o p e r t i e s o f the polymer (29). While r e c e n t advances i n p r o d u c t i o n t e c h n o l o g y and s u r f a c e c o a t i n g have m i t i g a t e d some o f the problems a s s o c i a t e d w i t h h i g h f i l l e r l o a d i n g , (29) improved systems c o m p r i s i n g c o m b i n a t i o n s o f ATH w i t h o t h e r a d d i t i v e s are under i n v e s t i g a t i o n . A c o l l a b o r a t i o n has been u n d e r t a k e n w i t h the A d m i r a l t y Research Establishment, Poole, U.K., i n which the f i r e - r e t a r d a n t p r o p e r t i e s o f a number o f i n o r g a n i c t i n compounds i n a non-halogenated, ATHf i l l e d e t h y l e n e - a c r y l i c rubber f o r m u l a t i o n , are b e i n g a s s e s s e d . P r e l i m i n a r y r e s u l t s have i n d i c a t e d t h a t a marked flame-retardant s y n e r g i s m e x i s t s between c e r t a i n t i n compounds ( a t a 2.5% l e v e l ) and ATH (50% l o a d i n g ) , and an i n c r e a s e i n 01 from 27.5 ( f o r no t i n a d d i t i v e ) t o 33.0 was observed f o r the ZnSn(OH)^ c o n t a i n i n g formulations. I t has been r e p o r t e d (30_) t h a t an ATH l o a d i n g o f 60% i s n e c e s s a r y to r a i s e the 01 o f e t h y l e n e - a c r y l i c rubber t o a v a l u e o f 33, and t h a t such a f o r m u l a t i o n meets the MOD Naval S p e c i f i c a t i o n NES 518. Hence, i t appears t h a t lower t o t a l a d d i t i v e l e v e l s are r e q u i r e d f o r adequate performance when ATH - ZnSn(OH)^ c o m b i n a t i o n s are used than when ATH i s i n c o r p o r a t e d a l o n e . This s i g n i f i c a n t r e d u c t i o n i n the f i l l e r c o n t e n t may prove advantageous i n terms o f the m e c h a n i c a l p r o p e r t i e s o f the p o l y m e r i c s u b s t r a t e . E l e v a t e d temperature 01 d a t a ( F i g u r e 5) i n d i c a t e t h a t the t i n c o n t a i n i n g e l a s t o m e r s r e t a i n t h e i r f l a m e - r e t a r d a n t s u p e r i o r i t y up to a temperature o f 250°C above which the samples undergo e x t e n s i v e
Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
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14.
CUSACK & K I L L M E Y E R
201
Inorganic Tin Compounds
F i g u r e 5. E f f e c t o f temperature on the f l a m m a b i l i t y e t h y l e n e - a c r y l i c rubber samples.
Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
of
202
FIRE AND POLYMERS 1
t h e r m a l d e g r a d a t i o n and d e t e r m i n a t i o n o f 0 1 s becomes i m p r a c t i c a l . I t i s o f i n t e r e s t t o note t h a t the polymer c o n t a i n i n g ZnSn(OH)^ does not burn i n a i r even a t 250°C and, a c c o r d i n g l y , t h i s c o m p o s i t i o n has a temperature index o f a t l e a s t 50°C above t h a t o f the rubber c o n t a i n i n g ATH a l o n e . The 01 and h i g h temperature 01 d a t a t h e r e f o r e p r o v i d e s u b s t a n t i a l e v i d e n c e as t o the b e n e f i t o f u s i n g ZnSn(OH)^ as a f l a m e - r e t a r d a n t s y n e r g i s t w i t h alumina t r i h y d r a t e f i l l e r . Other Non-halogenated Systems. Although o x i d i c t i n compounds, i n c l u d i n g hydrous S n 0 and ZnSn(OH)., can impart a h i g h degree o f f l a m e - r e s i s t a n c e t o c e l l u l o s i c s u b s t r a t e s , such as c o t t o n f a b r i c (19) and paper, they are g e n e r a l l y i n e f f e c t i v e as flame r e t a r d a n t s i n h a l o g e n - f r e e s y n t h e t i c polymer f o r m u l a t i o n s , u n l e s s the c o m p o s i t i o n has a r e l a t i v e l y h i g h i n o r g a n i c f i l l e r c o n t e n t . However, t h e s e t i n a d d i t i v e s can e x h i b i t s i g n i f i c a n t smokes u p p r e s s a n t p r o p e r t i e s i n non-halogenated polymers. In a programme of s t u d i e s c a r r i e d out a t ITRI i n c o l l a b o r a t i o n w i t h Borax Research L i m i t e d , C h e s s i n g t o n , U.K., a s e r i e s o f d i v a l e n t metal h y d r o x y s t a n n a t e s and s t a n n a t e s were s c r e e n e d as smoke s u p p r e s s a n t s i n h a l o g e n - f r e e g l a s s - r e i n f o r c e d p o l y e s t e r (GRP) p a n e l s ( 3 1 ) . The b e s t r e s u l t o b t a i n e d was f o r a 2phr ( p a r t s per hundred o f r e s i n ) i n c o r p o r a t i o n l e v e l o f ZnSnO , which gave a 46% r e d u c t i o n i n smoke d e n s i t y compared to the c o n t r o l sample.
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2
Furthermore, H i r s c h l e r ( 3 2 ) has i n v e s t i g a t e d the smoke-reducing a b i l i t y o f a number o f metal h y d r o x i d e s and o x i d e s , a t i n c o r p o r a t i o n l e v e l s o f up t o 40 phr i n a c r y l o n i t r i l e - b u t a d i e n e - s t y r e n e (ABS) copolymer. At the lowest a d d i t i v e l e v e l s t u d i e d (10 p h r ) , SnO gave a h i g h e r degree o f smoke suppressancy ( v i z . 58%), than any o f the o t h e r compounds, and l o a d i n g s o f a t l e a s t 30 phr were found t o be n e c e s s a r y t o a c h i e v e comparable performance w i t h e i t h e r A1(0H) or Mg(0H) 5
Tne e f f e c t i v e n e s s o f i n o r g a n i c t i n compounds as flame and smoke r e t a r d a n t s , both a l o n e and i n c o m b i n a t i o n w i t h i n o r g a n i c f i l l e r s , i n s e v e r a l h a l o g e n - f r e e t h e r m o p l a s t i c , t h e r m o s e t t i n g and e l a s t o m e r i c s u b s t r a t e s , i s c u r r e n t l y under i n v e s t i g a t i o n a t the ITRI. MECHANISTIC STUDIES A l t h o u g h t h e r e have been many s t u d i e s on the mode o f a c t i o n o f f i r e r e t a r d a n t s g e n e r a l l y , (J_6) the m e c h a n i s t i c b e h a v i o u r o f t i n a d d i t i v e s i s l e s s c l e a r , and may depend on s e v e r a l f a c t o r s i n c l u d i n g the r a t i o of h a l o g e n : t i n i n the system. Thermal a n a l y s i s has been used e x t e n s i v e l y t o study i n d e t a i l the v a r i o u s i n d i v i d u a l s t a g e s o c c u r r i n g d u r i n g the breakdown o f polymers under the a c t i o n o f heat, and can p r o v i d e u s e f u l i n f o r m a t i o n r e g a r d i n g the mode o f a c t i o n and the e f f e c t i v e n e s s o f f l a m e - r e t a r d a n t additives. Simultaneous thermogravimetry (TG), d i f f e r e n t i a l thermogravimetry (DTG) and d i f f e r e n t i a l t h e r m a l a n a l y s i s (DTA), have been used a t the ITRI t o i n v e s t i g a t e the t h e r m a l breakdown o f v a r i o u s t i n - c o n t a i n i n g polymers and o f the a d d i t i v e s t h e m s e l v e s . Simultaneous TG/DTA s t u d i e s o f z i n c h y d r o x y s t a n n a t e ( F i g u r e 6 ) , i n d i c a t e t h a t d e h y d r a t i o n o f t h i s compound o c c u r s d u r i n g the temperature range 190°-285°C, w i t h a l o s s o f 19.1% o f i t s i n i t i a l weight, t h i s c o r r e s p o n d i n g t o the l o s s o f 3 moles o f water:
Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
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CUSACK & K I L L M E Y E R
Weight
1 0
Inorganic Tin Compounds
(%)
1
1 200
1
1 400
Temp.
1
1 600
1
1— 800
(°C)
F i g u r e 6. Simultaneous TG/DTA t r a c e s o f z i n c h y d r o x y s t a n n a t e in a i r . (Reproduced w i t h p e r m i s s i o n from R e f . 3 4 , C o p y r i g h t 1 9 8 9 John Wiley & Sons L t d . )
Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
204
FIRE AND POLYMERS ZnSn(OH). o
•
ZnSnCL 3
+
3H 0 2 o
T h i s t h e r m a l d e h y d r a t i o n i s accompanied by a l a r g e endotherm ( a b s o r p t i o n o f h e a t ) , as p r e v i o u s l y r e p o r t e d (J_2). A secondary p r o c e s s o c c u r s a t h i g h e r temperatures (ca_. 580°-800°C), accompanied by a broad exotherm, due t o a s o l i d s t a t e r e a c t i o n i n which no weight l o s s i s o b s e r v e d : (12)
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ZnSnO^
i
•
Zn SnO^ 2
+
J Sn0
2
E x t e n s i v e t h e r m o a n a l y t i c a l s t u d i e s have been c a r r i e d out on the brominated p o l y e s t e r r e s i n system. F i g u r e 7 shows the d i f f e r e n c e s i n the t h e r m a l breakdown b e h a v i o u r o f the 2% ZnSnO - c o n t a i n i n g p o l y e s t e r , when the atmosphere i s a i r as opposed t o argon. Although t h e r e a r e s l i g h t d i f f e r e n c e s i n the i n i t i a l d e c o m p o s i t i o n s t a g e s , the most s i g n i f i c a n t d i s s i m i l a r i t y o c c u r s a t h i g h e r temperature where, i n a i r , a t h i r d d i s t i n c t weight l o s s o c c u r s . T h i s l o s s i s accompanied by a l a r g e exotherm, i n d i c a t i v e o f an o x i d a t i v e 'burnoff of r e s i d u a l char. The r e a c t i o n s o f the polymer i n a i r a r e o b v i o u s l y more r e l e v a n t to i t s f l a m m a b i l i t y than those i n argon, and thermal a n a l y s i s d a t a f o r brominated p o l y e s t e r samples i n a i r , a r e p r e s e n t e d i n T a b l e IV. In the absence o f any i n o r g a n i c a d d i t i v e , the r e s i n l o s e s about 80% of i t s weight d u r i n g the i n i t i a l d e c o m p o s i t i o n s t a g e , t h i s c o r r e s p o n d i n g t o the l o s s o f s t y r e n e and HBr, (33) f o l l o w e d by char o x i d a t i o n (13-7% l o s s ) a t a DTG max (temperature o f maximum r a t e o f weight l o s s ) o f c a . 528°C. I n c o r p o r a t i o n o f a 2% l e v e l o f e i t h e r ZnSn(OH)^ or ZnSnO into the r e s i n , l e a d s t o marked d i f f e r e n c e s i n i t s t h e r m a l d e g r a d a t i o n profile. The i n i t i a l d e c o m p o s i t i o n comprises two d i s t i n c t s t a g e s , the major s t e p o c c u r r i n g a t a lower temperature than t h a t o f the u n t r e a t e d polymer, which may be i n d i c a t i v e o f promotion o f bromine v o l a t i l i s a t i o n by the z i n c s t a n n a t e s . Furthermore, the amount o f r e s i d u e b u r n t o f f i n the char o x i d a t i o n s t e p i s g r e a t l y i n c r e a s e d i n the t i n - c o n t a i n i n g samples, and the temperature a t which t h i s p r o c e s s o c c u r s i s s i g n i f i c a n t l y h i g h e r than i n the base r e s i n . Hence, the t i n a d d i t i v e s may a l s o be a c t i n g as condensed phase char promotors. In c o n t r a s t t o t h e s e o b s e r v a t i o n s , a 2% a d d i t i o n o f °3 the polymer r e s u l t s i n o n l y a s l i g h t change i n i t s t h e r m a l d e c o m p o s i t i o n , w i t h o n l y a modest i n c r e a s e i n char r e s i d u e , which i s , i n t u r n , b u r n t o f f a t a s l i g h t l y h i g h e r temperature than t h a t o f the c o r r e s p o n d i n g s t a g e i n the u n t r e a t e d r e s i n ( T a b l e I V ) . These findings indicate that S ^ ^ condensed phase f i r e r e t a r d a n t a c t i v i t y i n t h i s p o l y e s t e r system, and t h i s i s i n a g r e e ment w i t h the g e n e r a l l y a c c e p t e d o b s e r v a t i o n t h a t antimony a d d i t i v e s o p e r a t e p r i m a r i l y i n the vapour phase by i n t e r f e r i n g w i t h the f r e e r a d i c a l r e a c t i o n s a s s o c i a t e d w i t h combustion p r o c e s s e s ( 1 , 1 6 ) . Continuous m o n i t o r i n g o f the c a r b o n monoxide and carbon d i o x i d e e v o l v e d d u r i n g t h e r m a l d e c o m p o s i t i o n o f brominated p o l y e s t e r r e s i n samples, has been c a r r i e d out u s i n g a s i m u l t a n e o u s t h e r m a l a n a l y s i s mass s p e c t r o m e t r y t e c h n i q u e . In o r d e r t o a l l o w measurement o f the c a r b o n monoxide e v o l v e d , the atmosphere chosen f o r t h e s e runs was 21% oxygen i n argon, s i n c e the peak a t 28 atomic mass u n i t s (amu) S b
t
2
0
n
a
s
l
i
t
t
l
e
Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
o
14.
CUSACK & KILLMEYER
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Weight
205
Inorganic Tin Compounds
(%)
AIR
Temp. (°C) F i g u r e 7. Simultaneous TG/DTA t r a c e s o f brominated p o l y e s t e r r e s i n c o n t a i n i n g 2% ZnSnO i n a i r and i n a r g o n . (Reproduced w i t h p e r m i s s i o n from R e f . 3 4 , C o p y r i g h t 1989 John Wiley & Sons L t d . )
due t o n i t r o g e n (N^) i n a i r , would have o b s c u r e d the CO peak, a l s o a t 28 amu. CO^ was monitored a t 44 amu. The r e s u l t s o b t a i n e d ( T a b l e V) c l e a r l y show t h a t the p r e s e n c e o f 5% B - s t a n n i c a c i d i n the r e s i n s u b s t a n t i a l l y reduces both the t o t a l amounts o f , and the r a t e s o f e v o l u t i o n o f , CO and CO^, produced d u r i n g t h e r m a l d e g r a d a t i o n o f the p l a s t i c .
Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
78.5
50.5 13.9 372.3
337.3 406.2
: c a . 180-450°C
: c a . 450-650°C
++Temp. range
Atmosphere: a i r Flow r a t e : 20cm /min H e a t i n g r a t e : 10°C/min
+ Temp, range
* Experimental c o n d i t i o n s :
2% S b ^
J
414.3
15.7
2 % ZnSnO
332.1
48.4
361.6
Degradation* DTG max
2 % ZnSn(OH).
Initial Loss (%) (°C)
18.5
34.1
35.5
13-7
Weight
Data f o r Brominated P o l y e s t e r
80.7
Weight
Thermal A n a l y s i s
No a d d i t i v e
Sample
T a b l e IV.
Samples*
558.4
578.0
572.5
527.9
Char O x i d a t i o n * * Loss (%) DTG max
Resin
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(°C)
14. CUSACK & KILLMEYER
Inorganic Tin Compounds
207
T a b l e V. A n a l y s i s o f Gases E v o l v e d D u r i n g Thermal D e g r a d a t i o n o f Brominated P o l y e s t e r R e s i n Samples Sample -
No a d d i t i v e 5% S n 0 ( h y d )
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2
„ . ^. „ . ** S p e c i f i c Emission Carbon Monoxide Carbon D i o x i d e 1+ Total Total 1+ II++ II++ 146 211 78 65 375 453 262 18 232 88 70 30
ft Atmosphere : 21% oxygen i n a r g o n ; h e a t i n g r a t e = 2 0 ° C / m i n . *» I n t e g r a t e d gaseous p r o d u c t i o n , n o r m a l i s e d f o r i n i t i a l sample weight ( a r b i t r a r y u n i t s ) . F i r s t major d e c o m p o s i t i o n s t a g e ( c a . 3 5 0 - 3 7 0 ° C ) .
+
Second major d e c o m p o s i t i o n s t a g e
(ca.
540-560°C).
F u r t h e r i n s i g h t i n t o the mode o f a c t i o n o f the i n d i v i d u a l a d d i t i v e s i s p r o v i d e d by s i m p l e combustion e x p e r i m e n t s , c a r r i e d o u t in air. T a b l e VI shows t h a t the y i e l d o f i n v o l a t i l e carbonaceous c h a r , formed when brominated p o l y e s t e r i s burned t o c o m p l e t i o n , i s more than doubled when brominated p o l y e s t e r i s burned t o c o m p l e t i o n , i s more than doubled when 5% a d d i t i o n s o f e i t h e r 3 - s t a n n i c a c i d o r z i n c s t a n n a t e a r e made t o the p l a s t i c , t h i s o b s e r v a t i o n b e i n g c o n s i s t e n t w i t h condensed phase b e h a v i o u r . Elemental a n a l y s i s o f the r e s i d u e s s u g g e s t s t h a t , a l t h o u g h i n the case o f 3 - s t a n n i c a c i d , o n l y a s m a l l f r a c t i o n o f the t i n i s v o l a t i l i s e d , a v e r y s i g n i f i c a n t p r o p o r t i o n o f both the z i n c and the t i n i s v o l a t i l i s e d from the z i n c s t a n n a t e - c o n t a i n i n g polymer, which may be i n d i c a t i v e o f vapour phase action. I n t e r e s t i n g l y , the e x t e n t o f bromine l o s s i s s i g n i f i c a n t l y reduced f o r t i n - c o n t a i n i n g samples, p a r t i c u l a r l y those c o n t a i n i n g ZnSnO . Antimony t r i o x i d e , which undergoes almost complete v o l a t i l i s a t i o n i n the polymer, shows l i t t l e char e n c h a n c i n g b e h a v i o u r and o p e r a t e s p r i m a r i l y i n the gas phase. The a p p a r e n t a b i l i t y o f z i n c s t a n n a t e t o a c t i n both the condensed and vapour phases may account f o r i t s o v e r a l l f l a m e - r e t a r d a n t s u p e r i o r i t y t o the o t h e r inorganic additives studied.
CONCLUSIONS 1.
2.
Z i n c h y d r o x y s t a n n a t e and z i n c s t a n n a t e are v e r y e f f e c t i v e f l a m e r e t a r d a n t s y n e r g i s t s when i n c o r p o r a t e d a t l e v e l s o f 1-10% i n t o a brominated p o l y e s t e r r e s i n , and a r e , i n g e n e r a l , markedly superior to other inorganic a d d i t i v e s studied i n c l u d i n g , antimony t r i o x i d e , anhydrous t i n ( I V ) o x i d e , and 3 - s t a n n i c a c i d . The s u r f a c e a r e a and degree o f d i s p e r s i o n i n the polymer m a t r i x o f the f i r e - r e t a r d a n t a d d i t i v e has a pronounced e f f e c t on i t s efficiency. C o l l o i d a l t i n ( I V ) o x i d e i s s i g n i f i c a n t l y more e f f e c t i v e , i n terms o f i t s f l a m e - r e t a r d a n t a b i l i t y , than powdered t i n ( I V ) o x i d e o r 3 - s t a n n i c a c i d .
Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
element; bromine
itself
94.4
34.3
93.0
-
Sb
+
(1,16).
vapour
condensed vapour
condensed
-
Primary Phase of A c t i o n *
from Brominated
i n the vapour phase
(%)
a c t s almost e x c l u s i v e l y
-
42.9
18.4
-
Elemental V o l a t i l i s a t i o n Sn Zn
(Reproduced with permission from Ref. 34, Copyright 1989 John Wiley & Sons Ltd.)
*With r e g a r d t o m e t a l l i c
3
33.5
2
5%
Sb 0
52.8
5% ZnSnO^ 74.0
85.1
53.0
Sn0 (hyd)
5%
2
95.9
24.1
additive
Br
No
(%)
Char Y i e l d
R e s i d u a l Char Y i e l d s and E x t e n t s o f E l e m e n t a l V o l a t i l i s a t i o n P o l y e s t e r R e s i n Samples d u r i n g Combustion i n A i r
Sample
T a b l e VI.
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14. 3.
Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on June 15, 2016 | http://pubs.acs.org Publication Date: May 9, 1990 | doi: 10.1021/bk-1990-0425.ch014
4.
5.
6.
7.
CUSACK & KILLMEYER
Inorganic Tin Compounds
209
ZnSnCOH)^ and ZnSnO , a t l e v e l s o f 2% or 5%, s i g n i f i c a n t l y d e c r e a s e both the t o t a l amount and the r a t e o f p r o d u c t i o n , o f smoke and carbon monoxide g e n e r a t e d from brominated p o l y e s t e r r e s i n , when b u r n t under l i m i t i n g or f l a m i n g c o n d i t i o n s . Antimony t r i o x i d e and B - s t a n n i c a c i d o n l y e x h i b i t m a r g i n a l b e n e f i t s i n terms o f smoke and CO s u p p r e s s i o n i n t h i s polymer system. T h e r m o a n a l y t i c a l and r e l a t e d m e c h a n i s t i c s t u d i e s i n d i c a t e t h a t the t i n a d d i t i v e s a r e p r i m a r i l y condensed phase flame r e t a r d a n t s , and t h e s e can a l t e r the p y r o l y s i s o f h a l o g e n a t e d polymers by promoting the l o s s o f h a l o g e n and enhancing c r o s s - l i n k i n g , t o g i v e an i n c r e a s e i n the y i e l d o f t h e r m a l l y - s t a b l e carbonaceous c h a r , w i t h a concomitant d e c r e a s e i n the g e n e r a t i o n o f v o l a t i l e flammable p r o d u c t s . T h i s r e d u c t i o n i n the amount o f f u e l s u p p l i e d t o the flame l e a d s t o the o b s e r v e d s u p p r e s s i o n o f smoke and carbon monoxide. In a d d i t i o n , p a r t i a l v o l a t i l i s a t i o n of z i n c and t i n o c c u r s d u r i n g combustion o f brominated r e s i n s c o n t a i n i n g ZnSn(OH), or ZnSnO , and t h i s i n d i c a t e s t h a t t h e s e a d d i t i v e s may c o n t r i b u t e t o vapour phase flame r e t a r d a t i o n , which may account f o r t h e i r s u p e r i o r i t y t o t i n o x i d e i t s e l f , where the e x t e n t o f t i n v o l a t i l i s a t i o n i s v e r y low. Antimony t r i o x i d e has l i t t l e e f f e c t on the t h e r m a l breakdown o f the polymer and o p e r a t e s p r i m a r i l y i n the gas phase. C e r t a i n i n o r g a n i c t i n compounds a r e e f f e c t i v e f l a m e - r e t a r d a n t s y n e r g i s t s when i n c o r p o r a t e d a t a 2.5% l e v e l i n t o a 50% ATHf i l l e d e t h y l e n e - a c r y l i c rubber c o m p o s i t i o n . Tin-containing elastomer formulations r e t a i n t h e i r flame-retardant s u p e r i o r i t y at e n v i r o n m e n t a l temperatures up t o 250°C, and samples c o n t a i n i n g 2.5% ZnSn(OH)^ do not s u s t a i n combustion i n a i r a t t h i s temperature. In g e n e r a l , t i n compounds do not e x h i b i t f l a m e - r e t a r d a n t p r o p e r t i e s i n h a l o g e n - f r e e polymer systems, u n l e s s the composition contains a high inorganic f i l l e r loading. However, t i n a d d i t i v e s o f t e n a c t as smoke s u p p r e s s a n t s i n non-halogenated polymers. I n o r g a n i c t i n compounds, i n p a r t i c u l a r , z i n c h y d r o x y s t a n n a t e and z i n c s t a n n a t e , a r e e f f e c t i v e f i r e r e t a r d a n t s i n a number o f polymer systems. They appear t o have advantages over c e r t a i n e x i s t i n g commercial a d d i t i v e s , namely: (a) Non-toxicity (b) No d i s c o l o r a t i o n o f s u b s t r a t e (c) E f f e c t i v e a t low l e v e l s (d) L i t t l e apparent e f f e c t on m e c h a n i c a l p r o p e r t i e s (e) F l a m e - r e t a r d a n t s y n e r g i s m w i t h h a l o g e n s and/or alumina t r i h y d r a t e (f) Smoke s u p p r e s s i o n (g) Decrease i n c a r b o n monoxide p r o d u c t i o n (h) Wide range o f a p p l i c a b i l i t y
ACKNOWLEDGMENTS Messrs A.W.Monk and J.A.Pearce, and Miss S.J.Reynolds a r e g r a t e f u l l y acknowledged f o r e x p e r i m e n t a l a s s i s t a n c e . Miss J . R a t c l i f f e i s thanked f o r a s s i s t a n c e i n the d e s i g n o f F i g u r e s f o r t h i s paper.
Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990.
210
FIRE AND POLYMERS
LITERATURE CITED 1.
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2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31.
Cullis,C.F.; Hirschler,M.M. The Combustion of Organic Polymers; Oxford University Press, Oxford, U.K.,1981. Graham,R.A. Proc.Flame Retardants '87 1987, p 1/1. Anon. Mod.Plast.Int. 1985, 15, 63. Lindstrom,R.S.; Sidman,K.R.; Sheth,S.G.; Howarth,J.T. J.Fire Retard.Chem. 1974, 1, 152. Sanders,H.J. Chem.Eng.News 1978, Apr. 24, 22. Mischutin,V. Speciality Chemicals 1982, 2, 27. McAdam,B.W. Speciality Chemicals 1982, 2, 4. Ingham,P.E. Tin & Its Uses 1975, 105, 5. Benisek,L. Br.Patent 1 385 399, 1975. Blunden,S.J.; Cusack,P.A.; Hill,R. The Industrial Uses of Tin Chemicals; Royal Society of Chemistry: London, U.K., 1985. Dupuis,T.; Duval,C.; Lecomte,J. Compt.Rend. 1963, 257, 3080. Ramamurthy,P.; Secco,E.A. Can.J.Chem. 1971, 49, 2813. Stepniczka,H.E. J.Fire Retard.Chem. 1976, 3, 5. Nicholson,J.W.; Nolan,P.F. Fire & Mater. 1983, 7, 89. Cusack,P.A. Fire & Mater. 1986, 10, 41. Hirschler,M.M. Dev.Polym.Stab. 1982, 5, 107. Antia,F.K.; Baldry,P.J.; Hirschler,M.M. Eur.Polym.J. 1982, 18, 167. Hindersinn,R.R.; Witschard,G. In Flame Retardancy of Polymeric Materials; Kuryla,W.C.; Papa,A.J., Eds.; Marcel Dekker: New York, 1978; Vol.1, p 1. Cusack,P.A.; Hobbs,L.A.; Smith,P.J.; Brooks,J.S. International Tin Research Institute Publ. No. 641 1984. Busse,W.F. U.S. Patent 3 468 843, 1969. Toray Industries Inc. Br. Patent 1 382 659, 1975. Touval,I. J.Fire & Flammability 1972, 3, 130. Donaldson,J.D.; Donbavand,J.; Hirschler,M.M. Eur.Polym.J. 1983, 19, 33. Anon. Tin Oxide and Metastannic Acid. Keeling & Walker Ltd. Data Sheets, Stoke-on-Trent, U.K., 1987. Fukatsu,K. J.Fire Sciences 1986, 4, 204. Cusack,P.A.; Smith,P.J.; Kroenke,W.J. Polym.Degrad.Stab. 1986, 14, 307. Woolley,W.D.; Fardell.P.J. Fire Safety J . 1982, 5, 29. Anon. Plast. & Rubber Weekly 1987, Dec. 5, 9. Brown,S.C.; Evans,K.A.; Godfrey,E.A. Proc.Flame Retardants '87 1987, p 11/1. Anon. Martinal as a Flame-retardant Filler for Cables. Martinswerk GmbH Data Sheet No. 2/2, Bergheim, West Germany, 1986. Cusack,P.A.; Smith,P.J.; Arthur,L.T. J.Fire Retard.Chem. 1980, 7,
9.
32. Hirschler,M.M. Polymer 1984, 25, 405. 33. Haines,P.J.; Lever,T.J.; Skinner,G.A. Thermochimica Acta 1982, 59, 331. 34. Cusack,P.A.; Monk,A.W.; Pearce,J.A.; Reynolds,S.J. Fire & Mater. 1989, 14, 23. RECEIVED January 17, 1990
Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990.