Ternary Reactions among Polymer Substrates, Organohalogens, and

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Chapter 9

Ternary Reactions among Polymer Substrates, Organohalogens, and Metal Oxides in the Condensed Phase under Pyrolytic Conditions M. J. Drews, C. W. Jarvis, and G. C. Lickfield School of Textiles, Clemson University, Clemson, SC 29634

The results reported here represent part of an extensive and continuing investigation concerning the antimony oxide/organohalogen synergism in flame retardant chemistry and in particular into the mechanisms of volatile antimony species formation during pyrolytic degradation and combustion, and the role of the polymer substrate in these reactions. Mixtures of decabromodiphenyl oxide (DBDPO) with antimony oxide, inert f i l l e r s , a variety of active metal powders and two different polymer substrates (high density polyethylene and polypropylene) were pyrolyzed isothermally in the TGA and the volatile DBDPO pyrolysis products characterized by capillary gas chromatography (CGC) and CGC/MS. Based on the results of these and other supporting experiments, mechanisms are proposed to account for the observed product distributions. The antimony oxide/organohalogen synergism i n flame retardant additives h a s been t h e s u b j e c t o f c o n s i d e r a b l e r e s e a r c h and d i s c u s s i o n o v e r t h e p a s t t w e n t y - f i v e y e a r s (1-17). In a d d i t i o n t o antimony o x i d e , a v a r i e t y o f b i s m u t h compounds and molybdenum o x i d e have been t h e s u b j e c t o f s i m i l a r s t u d i e s (18-20) . Despite this i n t e n s i v e i n v e s t i g a t i o n , r e l a t i v e l y l i t t l e has been c o n c l u s i v e l y e s t a b l i s h e d about t h e s o l i d s t a t e c h e m i c a l mechanisms o f t h e m e t a l component volatilization, except i n those cases where t h e organohalogen component i s capable of undergoing extensive intramolecular dehydrohalogenation. In t h e e a r l i e r l i t e r a t u r e , s e v e r a l d i f f e r e n t mechanisms have been p r o p o s e d t o a c c o u n t f o r t h e a n t i m o n y v o l a t i l i z a t i o n which o c c u r s d u r i n g t h e combustion o f polymer s u b s t r a t e s i n t h e p r e s e n c e of antimony o x i d e and an o r g a n o h a l o g e n .

0097-6156/90/0425-O109$06.25/0 © 1990 American Chemical Society

Nelson; Fire and Polymers ACS Symposium Series; American Chemical Society: Washington, DC, 1990.

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These r e a c t i o n sequences can be s e p a r a t e d i n t o two c a t e g o r i e s a c c o r d i n g t o whether o r n o t t h e o r g a n o h a l o g e n component can undergo intramolecular dehydrohalogenation. For those organohalogen compounds which can undergo i n t r a m o l e c u l a r d e h y d r o h a l o g e n a t i o n , r e a c t i o n sequence [1] has been proposed as t h e p r i n c i p a l r o u t e t o t h e g e n e r a t i o n o f v o l a t i l e antimony c o n t a i n i n g s p e c i e s (3, 5, 7, 18, 2 0 ) . R-CH CHX-R 6 HX + S b 0 2

R-CH=CH-R + HX t

*

2

•

3

2 SbX

+ 3 H0 T

3

2

Examples o f a d d i t i v e s and polymer s u b s t r a t e s which c o u l d r e a c t v i a [1] would be c h l o r i n a t e d p a r a f f i n waxes, hexabromocyclododecane (HBCD) and p o l y ( v i n y l c h l o r i d e ) o r p o l y ( v i n y l b r o m i d e ) . F o r t h o s e o r g a n o h a l o g e n compounds which cannot r e a d i l y undergo intramolecular dehydrohalogenation, two a l t e r n a t i v e reaction sequences, [2] and [ 3 ] , f o r t h e g e n e r a t i o n o f v o l a t i l e a n t i m o n y c o n t a i n i n g s p e c i e s have been p r o p o s e d (9, 21, 2 2 ) . R-CH CH -R 2

•

2

2 R-CH 2

R-CH - + R'-X

•

2

R-CH -R

f

2

+ X[2]

X- + R-CH CH -R 2

6 HX + S b 0 2

Sb 0 2

3

•

2

•

3

+ R-X

•

HX + R-CH CH-R 2

2 SbX

t

3

+ 3 H0 2

t

{SbO---X---R}* [3]

n {SbO---X---R}*

•

SbX

3

t

+ {R2O}*

Examples o f a d d i t i v e s t o which e i t h e r o r both o f t h e s e r e a c t i o n sequences could apply a r e decabromodipheny1 oxide (DBDPO), tetrabromobisphenol-A (TBBPA) and t h e c h l o r i n a t e d c y c l o p e n t a d i e n e adducts. There i s s u b s t a n t i a l d a t a t o s u p p o r t r e a c t i o n sequence [2] and some d a t a s u g g e s t i n g sequence [3] (21, 22) may o c c u r under c e r t a i n p y r o l y s i s c o n d i t i o n s , but no e v i d e n c e has been p u b l i s h e d f o r [3] i n t h e absence o f a l a r g e e x c e s s o f polymer s u b s t r a t e . In t h e c a s e o f [2] and [3] i t has been s u g g e s t e d t h a t t h e s e r e a c t i o n s would be dependent on t h e c a r b o n - h a l o g e n bond s t r e n g t h i n t h e o r g a n o h a l o g e n component ( 9 ) . Presumably o t h e r m e t a l o x i d e compounds, s u c h as b i s m u t h o r molybdenum o x i d e , c o u l d undergo similar reactions under t h e appropriate conditions. More r e c e n t l y , b a s e d on t h e r e s u l t s o f an e x t e n s i v e s e r i e s o f small scale degradation studies, two a d d i t i o n a l mechanisms f o r t h e v o l a t i l i z a t i o n o f antimony from antimony o x i d e / o r g a n o h a l o g e n flame r e t a r d a n t systems have been p r o p o s e d (23,24). Of t h e s e two p r o p o s e d mechanisms, [4] and [ 5 ] , [4] does n o t i n v o l v e HX f o r m a t i o n a t a l l and [5] s u g g e s t s an i m p o r t a n t r o l e f o r t h e d i r e c t i n t e r a c t i o n o f t h e polymer s u b s t r a t e w i t h t h e m e t a l o x i d e p r i o r t o i t s r e a c t i o n w i t h the h a l o g e n compound.


9.

DREWS ET AL.

Ternary Reactions under Pyrolytic Conditions

Sb 0 2

+ Polymer

3

•

111

Sb° + [Polymer-O-] [4]

Sb° + R-X

Sb 0 2

+ Polymer

3

•

[SbX O R ] + [R] n

•

y

z

[Sb 0 -Polymer] * 2

3

[5] [ S b 0 - P o l y m e r ] * + R-X 2

3

—

•

[SbX O Polymer] + [R* ] * n

y

Mechanism [4] was b a s e d on s t u d i e s i n v o l v i n g t h e d i r e c t r e a c t i o n of antimony m e t a l w i t h DBDPO i n t h e absence o f a hydrogen s o u r c e . The d a t a from t h e s e e x p e r i m e n t s c l e a r l y show t h a t i f t h e o x i d e i s r e d u c e d t o t h e m e t a l , d i r e c t i n t e r a c t i o n w i t h DBDPO would o c c u r , and t h a t t h i s i s a s p e c i f i c and h i g h l y e x o t h e r m i c r e a c t i o n . However, no d i r e c t e v i d e n c e f o r t h e p r e s e n c e o f m e t a l l i c antimony i n m i x t u r e s c o n t a i n i n g antimony o x i d e , a polymer s u b s t r a t e and an o r g a n o h a l o g e n compound was o b t a i n e d . Mechanism [5] was b a s e d on t h e r e s u l t s o b t a i n e d from m u l t i - s t e p s e q u e n t i a l p y r o l y s i s e x p e r i m e n t s i n an i n e r t atmosphere (23) . T h i s mechanism [5] d i f f e r s from [ 3 ] , p r i m a r i l y i n t h a t [5] was p r o p o s e d to be s u r f a c e c a t a l y t i c i n n a t u r e , and t h a t t h e r e a c t i o n between t h e o x i d e p a r t i c l e s u r f a c e and t h e organohalogen was c o n s i d e r e d o n l y as the f i r s t step, i n i t i a t i n g the process l e a d i n g to the eventual f o r m a t i o n o f v o l a t i l e antimony s p e c i e s . The r e s u l t s r e p o r t e d h e r e r e p r e s e n t o n l y a s m a l l p a r t o f an e x t e n s i v e and c o n t i n u i n g i n v e s t i g a t i o n d e s i g n e d t o e l u c i d a t e , i n more d e t a i l t h a n had p r e v i o u s l y been e s t a b l i s h e d , t h e mechanisms o f v o l a t i l e a n t i m o n y and o t h e r m e t a l s p e c i e s f o r m a t i o n d u r i n g t h e p y r o l y t i c d e g r a d a t i o n and combustion and t h e r o l e s o f t h e p o l y m e r s u b s t r a t e and o r g a n i c h a l o g e n s o u r c e s i n t h e s e r e a c t i o n s . Because of i t s commercial and p o t e n t i a l m e c h a n i s t i c ( s i n c e i t c o n t a i n s no CH bonds) s i g n i f i c a n c e , much o f t h e emphasis o f t h i s work has been f o c u s e d on t h e s o l i d s t a t e c h e m i s t r y which o c c u r s w i t h DBDPO as t h e halogen source. Experimental The t h e r m a l a n a l y s i s , tube f u r n a c e , and o t h e r a p p a r a t u s p r e v i o u s l y employed i n t h i s work, as w e l l as t h e p r o c e d u r e s f o r m e a s u r i n g t h e antimony volatilization gravimetrically have been described e l s e w h e r e (23-25). F o r t h e c o l l e c t i o n o f t h e v o l a t i l e o r g a n i c s from t h e p y r o l y s i s e x p e r i m e n t s , t h e use o f v a r i o u s t r a p d e s i g n s and a v a r i e t y o f s o l v e n t s was i n v e s t i g a t e d . For the majority of the c a p i l l a r y gas c h r o m a t o g r a p h i c (CGC) and CGC/MS a n a l y s i s p r o c e d u r e s , an Ace G l a s s Works g l a s s m i c r o i m p i n g e r c o n t a i n i n g 20.0 ml o f s o l v e n t (benzene, x y l e n e o r t o l u e n e ) c o n n e c t e d by a b a l l j o i n t t o t h e purge o u t l e t of the p y r o l y s i s apparatus (DuPont I n s t r u m e n t s 951 TGA module) was used. The CGC a n a l y s i s o f t h e v o l a t i l e d e g r a d a t i o n p r o d u c t s were performed using a Perkin-Elmer Sigma 2000 capillary gas chromatograph. The column u s e d was e i t h e r a f u s e d s i l i c a 0.25 m i c r o n , bonded m e t h y l s i l i c o n e (10 m, 0.25 mm I.D.) o r a m e t h y l / 5 % p h e n y l s i l i c o n e (15 m 0.25 mm I.D.) bonded p h a s e . The c a r r i e r gas was h e l i u m and t h e c a p i l l a r y column head p r e s s u r e was m a i n t a i n e d a t 20 p s i . The make-up gas f o r t h e p u l s e d e l e c t r o n c a p t u r e d e t e c t o r (ECD) was 95% Ar/5% methane s u p p l i e d a t a f l o w r a t e o f 60 ml/min.


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FIRE AND POLYMERS

A l l o f t h e i n j e c t i o n s were 1 m i c r o l i t e r and t h e c a p i l l a r y column s p l i t r a t i o was n o m i n a l l y s e t a t 200:1. Column and program t i m e s and t e m p e r a t u r e s were v a r i e d d e p e n d i n g on t h e v o l a t i l e p r o d u c t s being analyzed. All of the i n i t i a l CGC o r g a n o b r o m i n e d e g r a d a t i o n p r o d u c t s assignments were b a s e d on t h e use o f r e l a t i v e retention time standards. The relative retention times f o r the partially b r o m i n a t e d d e g r a d a t i o n p r o d u c t s were e s t a b l i s h e d e i t h e r by t h e s y n t h e s i s o f t h e e x p e c t e d d e g r a d a t i o n p r o d u c t s o r by t h e use o f s e l e c t i v e debromination r e a c t i o n s . In t h e l a t t e r s t a g e s o f t h i s i n v e s t i g a t i o n , CGC/MS was employed to c o n f i r m t h e assignments of t h e r e l a t i v e r e t e n t i o n time s t a n d a r d s . The i n s t r u m e n t a t i o n used i n the m a j o r i t y of t h e s e experiments c o n s i s t e d o f a H e w l e t t - P a c k a r d 5890A c a p l i l l a r y gas c h r o m a t o g r a p h i n t e r f a c e d d i r e c t l y t o a HP-5970B mass s e l e c t i v e d e t e c t o r (MSD). A l l o f t h e d a t a a c q u i s i t i o n and a n a l y s i s were done u s i n g a HP-59970C Chemstation and s o f t w a r e . A limited number of additional e x p e r i m e n t s were c a r r i e d out u s i n g a HP-5988A CGC/MS system. The c a p i l l a r y column employed f o r t h e mass s p e c t r o m e t r y s t u d i e s was a HP, 25m, m e t h y l / 5 % p h e n y l s i l i c o n e bonded phase, 0.25 mm ID f u s e d silica w i t h a f i l m t h i c k n e s s o f 0.33|Xm. The chromatographic c o n d i t i o n used f o r these experiments were as s i m i l a r t o t h o s e employed f o r t h e p r i o r CGC a n a l y s i s as t h e i n s t r u m e n t a t i o n would permit. For t h e decabromodiphenyl o x i d e (DBDPO) p y r o l y s i s r e a c t i o n s , two different procedures were u s e d to s y n t h e s i z e the s e r i e s of brominated d i p h e n y l o x i d e s a n d d i b e n o z o f u r a n s e m p l o y e d as t h e r e l a t i v e r e t e n t i o n time s t a n d a r d s : A l B r 3 / B r 2 i n ethylene dibromide and F e ° ( m e t a l ) / B r 2 i n t e t r a c h l o r o e t h y l e n e . The r a t e o f t h e i n i t i a l b r o m i n a t i o n s t e p s i n t h e former r e a c t i o n was so r a p i d t h a t o n l y t h e h i g h e r degree o f b r o m i n a t i o n adducts c o u l d be i s o l a t e d . The r a t e o f t h e Fe°/Br2 r e a c t i o n was found t o be much s l o w e r , e s p e c i a l l y d u r i n g t h e i n i t i a l s t a g e s , and t h e s e r e a c t i o n s y i e l d e d a b r o a d e r range o f r e l a t i v e r e t e n t i o n time r e f e r e n c e peaks. In a t y p i c a l b r o m i n a t i o n experiment 1.0 g o f d i p h e n y l e t h e r (or d i b e n z o f u r a n ) , 1.0 g o f F e ° powder and 15 ml o f Br2 were added t o a p p r o x i m a t e l y 250 ml o f t e t r a c h l o r o e t h y l e n e . The m i x t u r e was g e n t l y h e a t e d w i t h s t i r r i n g f o r a p e r i o d o f up t o two weeks. At i n t e r v a l s , a p p r o x i m a t e l y 20 U l o f t h e r e a c t i o n m i x t u r e was withdrawn, d i l u t e d to 3 ml with benzene and t h e r e s u l t a n t solution analyzed chromatographically. The assignment o f d e g r e e s o f b r o m i n a t i o n t o s p e c i f i c r e t e n t i o n t i m e s was b a s e d on f o l l o w i n g t h e p r o g r e s s i o n o f the v e r y slow r e a c t i o n , and t h e assumption t h a t t h e l o n g e s t o b s e r v e d r e t e n t i o n times correspond t o the f u l l y brominated s p e c i e s . This a s s u m p t i o n c o u l d be c o n f i r m e d f o r t h e DBDPO b u t not a b s o l u t e l y f o r the octabromodibenzofuran (OBDBF), s i n c e no pure OBDBF s t a n d a r d was available. An a n a l o g o u s s e r i e s o f d i b e n z o d i o x i n r e l a t i v e r e t e n t i o n t i m e s t a n d a r d s were p r e p a r e d from d i b e n z o d i o x i n (DBD) u s i n g Fe°/Br2 and t h e same p r o c e d u r e used t o b r o m i n a t e t h e e t h e r and t h e f u r a n . The DBD i t s e l f was p r e p a r e d by r e f l u x i n g o r t h o - c h l o r o p h e n o l w i t h NaOH. The r e l a t i v e r e t e n t i o n t i m e s employed i n t h e s t u d y o f t h e HBCD p y r o l y s i s r e a c t i o n s were o b t a i n e d by t h e use o f s e l e c t i v e c h e m i c a l debromination. The HBCD was s e l e c t i v e l y d e b r o m i n a t e d u s i n g Zn° (metal) powder i n a r e f l u x i n g e t h e r s o l u t i o n . A s m a l l amount o f a c e t i c a c i d was used as t h e c a t a l y s t .


9.

DREWS ETAL.


113

All of the organohalogen compounds s t u d i e d were c o m m e r c i a l p r o d u c t s o b t a i n e d from v a r i o u s m a n u f a c t u r e r s and u s e d as r e c e i v e d . Only t h e DBDPO was p u r i f i e d f u r t h e r by r e c r y s t a l l i z a t i o n f o r some o f t h e c h r o m a t o g r a p h y and t h e r m a l a n a l y s i s e x p e r i m e n t s . Samples o f a n t i m o n y t r i o x i d e and antimony p e n t o x i d e were a l s o o b t a i n e d from commercial sources. The u l t r a p u r e a n t i m o n y t r i o x i d e , bismuth t r i o x i d e , b i s m u t h m e t a l , antimony m e t a l , d i b e n z o f u r a n and d i p h e n y l e t h e r were a l l o b t a i n e d from A l d r i c h C h e m i c a l s . The p o l y ( p r o p y l e n e ) (PP) resin was 0.7 m f i , f o o d grade from Novamont and t h e p o l y ( e t h y l e n e ) was u n s t a b i l i z e d , h i g h m o l e c u l a r weight, HDPE from American H o e c h s t . R e s u l t s and D i s c u s s i o n On t h e b a s i s o f t h e d a t a o b t a i n e d from t h e e a r l y t h e r m a l a n a l y s i s and tube f u r n a c e p y r o l y s i s e x p e r i m e n t s p e r f o r m e d d u r i n g t h e i n i t i a l p h a s e s o f t h i s i n v e s t i g a t i o n , i t became a p p a r e n t t h a t i n o r d e r t o e s t a b l i s h t h e p r i n c i p a l r e a c t i o n pathways t o t h e g e n e r a t i o n o f v o l a t i l e antimony s p e c i e s , t h e v o l a t i l e d e g r a d a t i o n p r o d u c t s o f t h e DBDPO i t s e l f would need t o be c h a r a c t e r i z e d (24, 2 5 ) . To a c c o m p l i s h t h i s o b j e c t i v e a c a p i l l a r y gas c h r o m a t o g r a p h was u s e d a n d an a n a l y t i c a l p r o t o c o l f o r t h e a n a l y s i s o f t h e v o l a t i l e d e g r a d a t i o n p r o d u c t s o f DBDPO d e v e l o p e d . While t h e r e has r e c e n t l y been c o n s i d e r a b l e a c t i v i t y w i t h r e s p e c t t o t h e c h a r a c t e r i z a t i o n o f the t h e r m a l d e g r a d a t i o n p r o d u c t s o f c h l o r i n a t e d and brominated aromaties (26-30), i n c l u d i n g DBDPO (29,30), a t t h e t i m e t h i s work was f i r s t u n d e r t a k e n d u r i n g l a t e 1984, n e i t h e r an a n a l y t i c a l method nor a n a l y t i c a l s t a n d a r d s were a v a i l a b l e f o r t h e s t u d y o f t h e t h e r m a l d e g r a d a t i o n p r o d u c t s o f DBDPO. Therefore, several sets of r e l a t i v e retention time standards were p r e p a r e d corresponding to the a n t i c i p a t e d p a r t i a l l y b r o m i n a t e d d e g r a d a t i o n p r o d u c t s o f DBDPO ( 2 4 ) . These r e l a t i v e r e t e n t i o n time standards i n c l u d e d a s e r i e s of p a r t i a l l y brominated r e a c t i o n p r o d u c t s b a s e d on d i p h e n y l o x i d e , d i b e n z o f u r a n and d i b e n z o d i o x i n . In o r d e r t o c o n f i r m t h e r e l a t i v e r e t e n t i o n t i m e s e s t a b l i s h e d f o r DBDPO u s i n g o n l y CGC, a d d i t i o n a l s e t s o f p a r t i a l l y brominated d i p h e n y l o x i d e s and d i b e n z o f u r a n s were s y n t h e s i z e d u s i n g t h e F e ° / Br2 p r o c e d u r e . The c o u r s e o f t h e s e r e a c t i o n s was f o l l o w e d by b o t h CGC a n d CGC/MS. As a r e s u l t , i t was p o s s i b l e t o s i m u l t a n e o u s l y c o n f i r m t h e p r e v i o u s r e l a t i v e r e t e n t i o n time peak a s s i g n m e n t s as well as t o c o r r e l a t e the retention times between t h e two instruments. Some o f t h e p e r t i n e n t c o m p a r a t i v e r e t e n t i o n t i m e d a t a o b t a i n e d from t h e s e e x p e r i m e n t s i s summarized i n T a b l e I . Upon completion of the i n d i v i d u a l r e a c t i o n s , a c o c k t a i l c o n t a i n i n g both p a r t i a l l y b r o m i n a t e d f u r a n s and d i p h e n y l o x i d e s was mixed. A t y p i c a l CGC c h r o m a t o g r a m and a CGC/MS t o t a l i o n c h r o m a t o g r a m f o r t h i s c o c k t a i l a r e shown i n F i g u r e s 1 and 2, r e s p e c t i v e l y . On t h e b a s i s o f t h e r e s u l t s o b t a i n e d from t h e s e combined CGC and CGC/MS e x p e r i m e n t s i t was p o s s i b l e t o p o s i t i v e l y c o n f i r m a l l o f t h e r e l a t i v e r e t e n t i o n t i m e s a s s i g n m e n t s which had p r e v i o u s l y been made u s i n g CGC a n a l y s i s a l o n e . All o f t h e DBDPO a n d HBCD t h e r m a l d e g r a d a t i o n experiments r e p o r t e d here were c a r r i e d out i s o t h e r m a l l y w i t h a n i t r o g e n purge i n a t h e r m a l g r a v i m e t r i c a n a l y z e r (TGA) a t t e m p e r a t u r e s between 390 and 410° C f o r DBDPO and 240° C f o r HBCD, r e s p e c t i v e l y .


114

FIRE A N D POLYMERS

Table

I.

Comparison o f t h e Isomer R e t e n t i o n Ranges O b t a i n e d from CGC and CGC/MS A n a l y s i s o f t h e R e l a t i v e R e t e n t i o n Time S t a n d a r d s

R e n t e n t i o n Time Range, min D i p h e n y l Oxides

Bromine# 3 4

CGC

( 1 )

CGC/MS

DJbenzQfurans

(2)

CGC

( 1 )

CGC/MS

(2)

11

19

13-15

22-23

23-24 27-27

19-20 23-24

27-28

5

15 19-21

6 7

22-24 25-27

31-34

40-44

37-40

27-28 33-34

8

29-30

45-51

44-45

98-100

9

35-36

70-75

10

48-50

112-115

32-35 60

P e r k i n - E l m e r Sigma 2000,15m,methyl/5% p h e n y l s i l i c o n e column HP-5980-A,25m, m e t h y l / 5 % p h e n y l s i l i c o n e column.


9.

DREWS E T A L .


115

The samples p y r o l y z e d i n c l u d e d t h e pure o r g a n o h a l o g e n compound, simple mixtures of the organohalogen and a second component representative of a p o s s i b l e a d d i t i v e or r e a c t i o n product present during the thermal d e g r a d a t i o n o f a flame retarded polymeric m a t e r i a l , such as Sb203 o r a polymer s u b s t r a t e , and t e r n a r y m i x t u r e s containing a l l three components. After some p r e l i m i n a r y experimentation with a variety of mixing techniques, i t was concluded t h a t t h e most r e p r o d u c i b l e r e s u l t s were o b t a i n e d by p r e p a r i n g t h e sample m i x t u r e s d i r e c t l y i n t h e q u a r t z sample pans f o r t h e TGA p y r o l y s i s e x p e r i m e n t s . The r a t i o n a l e f o r t h e c h o i c e o f temperature ranges and e x p e r i m e n t a l c o n d i t i o n s employed have been d e s c r i b e d i n d e t a i l elsewhere (24,25). When p u r e DBDPO was p y r o l y z e d a t 3 9 0 ° C a n d t h e v o l a t i l e p r o d u c t s a n a l y z e d by CGC, 98% was r e c o v e r e d . The o n l y r e a c t i o n o f note a p p e a r e d t o be t h e d e g r a d a t i o n o f t h e n o n a b r o m o d i p h e n y l o x i d e w h i c h had been d e t e c t e d as an i m p u r i t y p r e s e n t i n t h e s t a r t i n g sample. These r e s u l t s a r e q u i t e d i f f e r e n t from o t h e r s which have been r e p o r t e d i n the l i t e r a t u r e concerning the high temperature (>600° C) t h e r m a l and t h e r m a l o x i d a t i v e d e g r a d a t i o n o f DBDPO, i n which >90% d e g r a d a t i o n was r e p o r t e d (28) . We c o n f i r m e d t h a t t e m p e r a t u r e was t h e p r i n c i p a l cause f o r t h e s e d i f f e r e n t o b s e r v a t i o n s , by r e p r o d u c i n g t h e 600° C i s o t h e r m a l p y r o l y s i s o f DBDPO i n which l e s s t h a n 10% u n r e a c t i v e DBDPO was r e c o v e r e d . As t h i s work p r o g r e s s e d , i t became c o n v e n i e n t f o r c o m p a r a t i v e purposes t o express the p y r o l y s i s r e s u l t s f o r a s p e c i f i c p y r o l y s i s experiment i n terms o f t h e e x t e n t o f t h e o b s e r v e d r e a c t i o n o f t h e initial organohalogen component content recovered chromatographically. The e x t e n t o f r e a c t i o n d a t a as d e t e r m i n e d by t h e CGC a n a l y s i s o f t h e v o l a t i l e r e a c t i o n p r o d u c t s f o r t h e p y r o l y s i s of some r e p r e s e n t a t i v e s i m p l e m i x t u r e s o f DBDPO a r e summarized i n Table I I . As i l l u s t r a t e d by t h e s e d a t a , t h e r e s u l t s o b t a i n e d f o r t h e DBDPO/Sb203 m i x t u r e s u g g e s t t h a t , i n t h e a b s e n c e o f a polymer s u b s t r a t e , Sb203 e x h i b i t s t h e same e x t e n t o f r e a c t i o n as o b s e r v e d f o r o t h e r i n e r t f i l l e r s such as g l a s s beads o r a l u m i n a . P r e v i o u s t h e r m a l a n a l y s i s s t u d i e s had i n d i c a t e d t h a t w h i l e Sb203 d i d not r e a c t d i r e c t l y w i t h DBDPO, t h e r e was some e v i d e n c e t h a t t h e r e a c t i o n o f a polymer s u b s t r a t e w i t h t h e Sb203 g e n e r a t e d a s p e c i e s which was v e r y r e a c t i v e (23) , and t h a t t h i s p r o d u c t was antimony metal (Sb°) . T h e r e f o r e , s i m p l e m i x t u r e s o f DBDPO w i t h powdered antimony, b i s m u t h and z i n c m e t a l s (mole r a t i o o f bromine t o m e t a l o f 3:1) were p y r o l y z e d and t h e e x t e n t o f r e a c t i o n d e t e r m i n e d by CGC. As shown by t h e d a t a f o r t h e s e m i x t u r e s a l s o p r e s e n t e d i n T a b l e I I . , under t h e c o n d i t i o n s employed here, a l l o f t h e s e m e t a l s r e a c t e d d i r e c t l y w i t h DBDPO. From a m e c h a n i s t i c p e r s p e c t i v e , t h a t f o r a l l t h r e e m e t a l s t h e p r i n c i p a l DBDPO v o l a t i l e r e a c t i o n p r o d u c t was o b s e r v e d t o be t h e o c t a b r o m o d i b e n z o f u r a n (OBDBF) was c o n s i d e r e d t o be t h e most i m p o r t a n t r e s u l t o f t h e s e e x p e r i m e n t s . The o b s e r v e d r e a c t i v i t y o f t h e m e t a l towards t h e DBDPO d e c r e a s e d i n t h e o r d e r Zn° > Sb° > Bi° . Of t h e s e d a t a , o n l y t h e r a t h e r l a r g e observed d i f f e r e n c e i n t h e r e l a t i v e r e a c t i v i t i e s o f Sb° (-38% OBDBF) and B i ° (-9% OBDBF) was u n e x p e c t e d b a s e d upon t h e thermodynamics f o r t h e formation of t h e i r respective halides. While s e v e r a l a d d i t i o n a l experiments i n d i c a t e d t h a t t h e low m e l t i n g p o i n t o f B i ° (271° C) may have e f f e c t e d t h e o b s e r v e d e x t e n t of r e a c t i o n , o t h e r f a c t o r s such as s i g n i f i c a n t d i f f e r e n c e s i n t h e s u r f a c e a r e a s o f t h e powdered m e t a l s cannot be r u l e d o u t .



u Retention Time, minutes

F i g u r e 1. CGC Chromatogram o f D i p h e n y l Oxide and D i b e n z o f u r a n Bromination Reaction Product's C o c k t a i l

u


F i g u r e 2. Bromination

CGC/MS TIC o f D i p h e n y l Oxide and Reaction Product's C o c k t a i l

Dibenzofuran

118

FIRE AND POLYMERS

By a n a l o g y t o t h e u t i l i z a t i o n of Zn° i n t h e W u r t z - F i t t i g r e a c t i o n (31), Scheme [6] i l l u s t r a t e d f o r Zn° i s p r o p o s e d t o account f o r t h e o b s e r v e d r e a c t i o n between DBDPO and any o t h e r a c t i v e m e t a l s such as Sb° o r B i ° .

Zn [6]

Z n

ZnBr

2

The two polymer s u b s t r a t e s i n v e s t i g a t e d as p a r t o f t h e s t u d y o f DBDPO m i x t u r e s were p o l y p r o p y l e n e (PP) and l i n e a r h i g h d e n s i t y p o l y e t h y l e n e (HDPE). While b o t h PP and HDPE decompose by s i m i l a r random c h a i n s c i s s i o n , r a d i c a l mechanisms, c h a i n t r a n s f e r o c c u r s much more r e a d i l y d u r i n g t h e p y r o l y s i s o f PP because o f t h e p r e s e n c e of t h e t e r t i a r y hydrogens. In a d d i t i o n , o n l y p r i m a r y c h a i n e n d r a d i c a l s a r e formed when t h e HDPE c h a i n c l e a v e s h o m o l y t i c a l l y . T h e r e f o r e , a comparison o f t h e PP/DBDPO and t h e HDPE/DBDPO m i x t u r e s ' v o l a t i l e p r o d u c t d i s t r i b u t i o n s was u n d e r t a k e n . In comparing t h e r e s u l t s o f t h e s e e x p e r i m e n t s as summarized i n T a b l e s I I I and IV, i t was f o u n d t h a t t h e e x t e n t o f r e a c t i o n was much g r e a t e r f o r t h e HDPE/DBDPO m i x t u r e s ( o n l y -8% undegraded DBDPO) t h a n f o r t h e c o r r e s p o n d i n g PP/DBDPO samples (-64% undegraded DBDPO). In a d d i t i o n , t h e peak a r e a f r a c t i o n f o r t h e o c t a - e t h e r was almost an o r d e r o f magnitude g r e a t e r , t h e f u r a n s ' a r e a s t h r e e t i m e s and t h e u n a s s i g n e d peaks' a r e a f r a c t i o n more t h a n f i v e t i m e s t h a t measured f o r t h e PP/DBDPO m i x t u r e s (=20% as compared t o =3%). One p o s s i b l e m e c h a n i s m w h i c h w o u l d be c o n s i s t e n t with the observed data, e s p e c i a l l y c o n s i d e r i n g the magnitude o f t h e d i f f e r e n c e i n t h e o b s e r v e d e x t e n t o f d e g r a d a t i o n between HDPE and PP, i s t h e c h a i n t r a n s f e r r e a c t i o n shown i n Scheme [ 7 ] . H H I I R-C-C-R' I I H CH

H I R-CI H

3

H I •C-R' I CH 3

[7]

H

H

R-C- • B r - ( ^ 5

H

O S

[g]-Br

5

-A*.

R

-c-Br • ^ - ( ^ " [ g j - B r , ] H

F u r t h e r e v i d e n c e t h a t t h e p r i n c i p a l d e g r a d a t i o n pathway i n v o l v e s c h a i n r a d i c a l a t t a c k on t h e DBDPO as shown i n [7] and n o t h a l o g e n r a d i c a l a t t a c k as would o c c u r i n [2] i n c l u d e s t h e r e l a t i v e l y s m a l l q u a n t i t y o f HBr formed (23,25) as w e l l as t h e l a r g e number o f


DREWS ETAL.


Table I I .

Mixtures

Summary o f V o l a t i l e P r o d u c t CGC A n a l y s i s f o r the E x t e n t R e a c t i o n o f Simple M i x t u r e P y r o l y z e d a t 390°C i n t h e TGA

DPO^io

DBDPO/Sb203 94 .7 DBDPO/AL2O3 92 .8

1

DP0 9

1.6 3.3

f

8

1

DP0 7 6 /

1

2

DP0 5 4

DBF 8,,7 D B F

/

0.7

3

91.8

3.1

0.1

81.6

5.3

8.7

DBDPO/Zn°

52.5

2.8

DBDPO/Sb°

58.3

3.0

DBDPO/GB

0.4

6-4

0.1

1.6 0.6

DBDPO/Bi°

2

14.1

10.1 38.4

Brominated d i p h e n y l oxides Brominated dibenzofurans G l a s s Beads

Table

III.

Summary o f t h e V o l a t i l e

P r o d u c t GC

Analysis for

t h e DBDPO/PP M i x t u r e P y r o l y z e d a t 390°C i n t h e

Component Peak Area, Br

#

3 4 5 6 7 8 9 10

DPCT

DBF

PHENOLS

TGA

% BENZENES

0.3 0.2 0.4 2.9 23.6 64.3

0.3 2.8 2.5

0.3

Brominated D i p h e n y l Oxides Brominated Dibenzofurans


120

FIRE AND POLYMERS

brominated a l k y l CGC a n a l y s i s .

fragments

d e t e c t e d by t h e ECD d e t e c t o r d u r i n g t h e

From a m e c h a n i s t i c p e r s p e c t i v e , one o f t h e most important aspects of the r e s u l t s of these experiments i s the further c o n f i r m a t i o n o f t h e f o r m a t i o n o f v o l a t i l e m e t a l h a l i d e s p e c i e s by a r e a c t i o n pathway, as i l l u s t r a t e d by Scheme [ 6 ] , t h a t does n o t i n c l u d e t h e f o r m a t i o n o f HX. In t h i s r e g a r d , i t s h o u l d be n o t e d a t t h i s p o i n t t h a t one o f t h e p r o d u c t s i d e n t i f i e d by CGC/MS from t h e s e p y r o l y s i s r e a c t i o n s was SbBr3. Furthermore, t h e d a t a p r e s e n t e d c o n c e r n i n g t h e importance o f t h e p o l y m e r s u b s t r a t e i n t h e d e g r a d a t i o n o f t h e DBDPO a n d t h e p r o p o s e d c h a i n r a d i c a l t r a n s f e r mechanism [7] would suggest t h a t t h e c o n d e n s e d phase c h e m i s t r y c o u l d be much more i m p o r t a n t i n antimony o x i d e / o r g a n o h a l o g e n flame r e t a r d a n t systems than had been p r e v i o u s l y thought. S e v e r a l s e r i e s o f t e r n a r y m i x t u r e s c o n t a i n i n g DBDPO w i t h PP and a v a r i e t y o f m e t a l s , m e t a l o x i d e s and o t h e r t h i r d components have been p y r o l y z e d i n t h e TGA a t 390° C and t h e i r v o l a t i l e s a n a l y z e d by CGC. The CGC d a t a from t h e s e e x p e r i m e n t s were f o u n d t o f a l l i n t o three d i s t i n c t c a t e g o r i e s with respect to the observed extent o f reaction. In t h e f i r s t c l a s s , C l a s s I , t h e e x t e n t o f r e a c t i o n was f o u n d t o be n o t s i g n i f i c a n t l y g r e a t e r t h a n t h a t measured f o r t h e PP/DBDPO m i x t u r e a l o n e . The d a t a f o r t h e C l a s s I components (Fe°, 100 m e s h - s i z e g l a s s beads and c h r o m a t o g r a p h i c grade aluminum o x i d e ) a r e summarized and compared t o t h a t from t h e s i m p l e PP/DBDPO m i x t u r e d a t a i n T a b l e V. As i l l u s t r a t e d by t h e d a t a i n T a b l e V, i n t h i s c l a s s , =50% o f t h e t o t a l v o l a t i l e peak a r e a c o r r e s p o n d e d t o u n d e g r a d e d DBDPO and t h e p r i n c i p a l d e g r a d a t i o n p r o d u c t was f o u n d t o be t h e nonabromo e t h e r (=33%). Of t h e s e r e s u l t s , o n l y t h e F e ° (metal) d a t a was s u r p r i s i n g s i n c e i t i m p l i e d t h a t F e ° was a c t i n g o n l y as an i n e r t f i l l e r and n o t forming significant quantities of iron halides under these experimental conditions. During the review o f t h i s manuscript i t was s u g g e s t e d t h a t t h e F e ° may have been s u r f a c e o x i d i z e d , w h i l e t h e TGA was c a r e f u l l y p u r g e d and a l l o f t h e m e t a l samples were r e a g e n t g r a d e o r u l t r a p u r e , s u r f a c e o x i d a t i o n c a n n o t be r u l e d o u t as an e x p l a n a t i o n f o r t h e o b s e r v e d l a c k o f r e a c t i v i t y f o r t h e F e ° samples. The second class, C l a s s I I , was r e p r e s e n t e d b y Z n ° a n d molybdenum (III) oxide (M0O3). These d a t a a r e summarized a n d compared t o t h e r e s u l t s f o r t h e s i m p l e PP/DBDPO m i x t u r e i n T a b l e V I . As shown by t h e d a t a i n T a b l e V I , o n l y -20% o f t h e t o t a l p r o d u c t peak a r e a was a c c o u n t e d f o r by t h e undegraded DBDPO i n t h i s c l a s s . In a d d i t i o n , =20% o f t h e p r o d u c t peak a r e a was a s s i g n e d t o f u r a n f o r m a t i o n as compared t o =10% f o r C l a s s I . Perhaps, t h e most s i g n i f i c a n t r e s u l t s from t h i s c l a s s a r e t h o s e f o r t h e M0O3 m i x t u r e s i n c e these data represent a c l e a r i n d i c a t i o n that t h i s metal oxide can undergo c h e m i s t r y s i m i l a r t o t h a t o b s e r v e d f o r Sb203 as has been s u g g e s t e d but seldom s u p p o r t e d i n t h e p a s t l i t e r a t u r e . The t h i r d c l a s s , C l a s s I I I , c o n t a i n e d t h o s e m i x t u r e s e x h i b i t i n g the g r e a t e s t e x t e n t o f r e a c t i o n . I n c l u d e d i n t h i s c l a s s were Sb203, Sb°(metal), Bi°(metal), bismuth trioxide (Bi203) and antimony t r i s u l f i d e (Sb2S3). These d a t a a r e summarized and compared t o t h o s e from t h e s i m p l e PP/DBDPO m i x t u r e i n T a b l e V I I . In t h e s e t e r n a r y m i x t u r e e x p e r i m e n t s , u n r e a c t e d DBDPO a c c o u n t e d f o r =4% o r l e s s o f t h e t o t a l v o l a t i l e peak p r o d u c t a r e a s .


DREWS ET AL.

Table


IV.

Summary o f t h e V o l a t i l e

Product

CGC A n a l y s i s

f o r t h e DBDPO/PE M i x t u r e P y r o l y z e d a t 390° i n t h e TGA

Peak Area, % Bromine

#

D i p h e n y l Oxides

5 6 7 8 9 10

Dibenzofurans

— 1.7 5.4 25.8 21.9 7.5

T a b l e V.

0.8 6.5 8.1 1.1

Summary o f t h e V o l a t i l e P r o d u c t CGC A n a l y s i s f o r the Class I Extent of Reaction Ternary M i x t u r e s a t 390°C

Component Peak A r e a s , Mixtures

1

DPO ^

1

DP0 9 8 f

1

DP0 7 6 /

1

% 2

2

D P 0 5 4 DBF g,7 D B F g_4 f

PP/DBDPO/Fe° 56.4 30..6 PP/DBDPO/Glass beads 49.6 35..8 PP/DBDPO/AL 03

.1

.1

8..1

0..5

.1

.1

8..4

0..2

2

49.5

36..2

.1

.1

9..8

1..1

64.3

26..5

0.6

.1

5..3

0..3

PP/DBDPO

Brominated d i p h e n y l o x i d e s Brominated dibenzofurans


122

FIRE AND POLYMERS

T a b l e V I . Summary o f t h e V o l a t i l e P r o d u c t CGC A n a l y s i s f o r the C l a s s I I Extent o f R e a c t i o n T e r n a r y M i x t u r e s a t 390°C

Component Mixtures

1

DP0 IQ

1

Peak A r e a s , %

1

DP0 g 8

1

DP0 7 g

/

DP0 5 4

/

/

2

DBF 8,7

2

DBF g_4

PP/DBDPO/Zn° 26.4 PP/DBDPO/M0O3

43.6

1.0

0.1

12.3

5.7

15.2

36.4

4.2

0.7

8.6

13.7

64.3

26.5

0.6

0.1

5.3

0.3

PP/DBDPO

Brominated d i p h e n y l oxides Brominated dibenzofurans

T a b l e V I I . Summary o f t h e V o l a t i l e P r o d u c t CGC A n a l y s i s f o r the C l a s s I I I E x t e n t o f R e a c t i o n T e r n a r y M i x t u r e s a t 390°C

Component Mixtures

1

DP0 IQ

PP/DBDP0/Sb203 3.3 PP/DBDPO/Bi203 1.4 PP/DBDPO/Sb° 2.0 PP/DBDPO/Bi° 0.8 PP/DBDP0/Sb2S3 3.2 PP/DBDPO 64.3

1

DP0 9 8 /

1

DP0 7 6 f

Peak A r e a s , % D p

1

2

0 5 , 4 DBF 8,7 D B F

2

5.4

29..3

8.0

1,.4

9..0

22,.4

8..7

9.2

7 .5 .

2.,9

16,.3

16,.7

28.8

0,.1

9..3

12,.2

4. .4

11.3

8,.0

2..8

22,.7

19,.0

6.7

5,.7

4..2

18,.2

26,.5

0.6

0,.1

5,.3

0,.3

Brominated d i p h e n y l oxides Brominated dibenzofurans


9.

DREWS ETAL.

123


The most s i g n i f i c a n t c h a r a c t e r i s t i c o f t h e s e d a t a , as compared t o t h a t from C l a s s I and I I , was t h e o v e r a l l i n c r e a s e i n component peak a r e a s f o r t h e l o w e r d e g r e e o f b r o m i n a t i o n f u r a n s (4 t o 6 bromines a c c o u n t i n g f o r 12-20% as compared t o =2% f o r C l a s s I and a maximum o f 14% f o r C l a s s I I ) and e t h e r s (6 and 7 bromines a c c o u t i n g f o r 7-29% as compared t o =1% f o r C l a s s I and a maximum f o r 4% f o r Class I I ) . In a d d i t i o n , f o r t h e C l a s s I I I components, a t l e a s t =30% and as much as =60% o f t h e peak a r e a s c o u l d n o t be a s s i g n e d t o known r e l a t i v e r e t e n t i o n times. In comparing t h e r e s u l t s o b t a i n e d w i t h i n this class, t h e g r e a t e s t o v e r a l l e x t e n t o f DBDPO r e a c t i o n was observed f o r the mixture c o n t a i n i n g PP/DBDPO/Bi°. A l s o , somewhat s u r p r i s i n g l y , t h e r e was e s s e n t i a l l y no d i f f e r e n c e o b s e r v e d between the extent of reactions f o r t h e DBDPO/PP/Sb203 and t h e DBDPO/PP/Sb2S3 m i x t u r e s . These r e s u l t s would s u g g e s t t h a t Sb2S3 s h o u l d be a t l e a s t as e f f e c t i v e an a d d i t i v e i n DBDPO/oxide f l a m e r e t a r d a n t f o r m u l a t i o n s as Sb203 In a d d i t i o n , i f t h e s u l p h u r i t s e l f was vapor phase a c t i v e , Sb2S3 c o u l d be more e f f e c t i v e t h a n Sb203. m

The extent of reaction data f o r the ternary mixtures PP/DBDP0/Sb203 and PE/DBDPO/Sb203 a r e summarized and compared t o t h e i r r e s p e c t i v e polymer/DBDPO s i m p l e m i x t u r e s i n T a b l e V I I I . As was o b s e r v e d e a r l i e r , a g r e a t e r e x t e n t o f r e a c t i o n was f o u n d f o r t h e PE t e r n a r y m i x t u r e t h a n f o r t h e PP t e r n a r y m i x t u r e , and b o t h o f t h e t e r n a r y m i x t u r e s showed s i g n i f i c a n t l y g r e a t e r e x t e n t o f r e a c t i o n than the r e s p e c t i v e simple mixtures. I f t h e d a t a summarized i n T a b l e V I I I a r e compared t o t h o s e i n T a b l e s I I I and IV, i t would a p p e a r as i f t h e p r e s e n c e o f t h e Sb203 t e n d e d t o reduce t h e d i f f e r e n c e s o b s e r v e d between t h e two p o l y m e r s y s t e m s . However, s i n c e t h e e x t e n t o f r e a c t i o n f o r t h e PE t e r n a r y m i x t u r e was so g r e a t t h a t o n l y =50% o f t h e peak a r e a s c o u l d be a s s i g n e d i t i s d i f f i c u l t to d i s c e r n with c e r t a i n t y t h a t t h i s i s t r u l y t h e case. In any case, i t i s c l e a r t h a t t h e s e two s i m i l a r p o l y m e r s e x h i b i t significant d i f f e r e n c e s i n t h e e x t e n t o f t h e DBDPO r e a c t i o n and t h e s e r e s u l t s emphasize the importance of t h e polymer s u b s t r a t e d e g r a d a t i o n chemistry with respect t o the formation of the v o l a t i l e metal species. Several experiments considered as pertinent to the i n t e r p r e t a t i o n o f t h e t e r n a r y mix d a t a w i t h r e s p e c t t o t h e p o s s i b l e r o l e o f p o t e n t i a l s p e c i e s formed i n - s i t u , such as S b B r 3 were c a r r i e d out w i t h HBCD and HBCD m i x t u r e s . The o r g a n o h a l o g e n HBCD i s p r e p a r e d by t h e b r o m i n a t i o n o f c y c l o d o d e c a t r i e n e a n d n o m i n a l l y c o n t a i n s b r o m i n e s a t t h e 1, 2, 5, 6, 9 and 10 p o s i t i o n s on t h e aliphatic ring. In the study of the p y r o l y s i s o f HBCD u s i n g b r o m i n e i o n s e l e c t i v e e l e c t r o d e s , i t was found t h a t an average o f t h r e e bromines per molecules was l o s t on h e a t i n g above the decomposition temperature (25). These d a t a , and t h e o r g a n i c l i t e r a t u r e , s u g g e s t e d that one p r o d u c t of t h i s elimination reaction should be a cyclododecatriene ring containing three v i n y l l i c b r o m i n e s which would be r e l a t i v e l y d i f f i c u l t t o remove, i f t h e p r o p o s e d e l i m i n a t i o n mechanism was c o r r e c t . When t h i s same r e a c t i o n was a n a l y z e d by t h e use o f CGC, i t was f o u n d t h a t t h e p y r o l y s i s o f HBCD by i t s e l f a t 240° C y i e l d s a v a r i e t y of products with d i f f e r e n t degrees o f b r o m i n a t i o n (13% -Brg, 7% - B r s , 17% -Br4, 31% -Br3, 19% -Br2 and 2% - B r i ) and not o n l y t h e p r o p o s e d t r i e n e . f


124

FIRE AND POLYMERS

Of t h e s e d i f f e r e n t p r o d u c t s t h e t r i e n e was f o u n d t o be t h e p r i n c i p a l p r o d u c t and t h e a v e r a g e l o s s o f b r o m i n e was i n f a c t o b s e r v e d t o be 3. However, c l e a r l y a l a r g e p e r c e n t a g e o f t h e debromination d i d n o t o c c u r s o l e l y by t h e p r o p o s e d concerted elmination (25) . However, GC/MS a n a l y s i s o f t h e d e g r a d a t i o n p r o d u c t s i d e n t i f i e d SbBr3 as one o f t h e p r i n c i p a l p r o d u c t s from a s i m p l e m i x t u r e o f HBCD and Sb203. To e v a l u a t e t h e e f f e c t s of s p e c i e s such a s SbBr3 on t h e d e g r a d a t i o n o f HBCD a d d i t i o n a l e x p e r i m e n t s were p e r f o r m e d which compared t h e CGC v o l a t i l e p r o d u c t d i s t r i b u t i o n s , t h e t i m e t o 50% weight l o s s ( i s o t h e r m a l TGA) and t h e t e m p e r a t u r e a t 50% weight l o s s (dynamic TGA) f o r m i x t u r e s o f HBCD w i t h Sb°, Sb203, g l a s s beads and SbBr3. Of t h e s e m i x t u r e s , as shown by t h e d a t a i n T a b l e s IX and X, t h e HBCD/SbBr3 was t h e most r e a c t i v e m i x t u r e as e v i d e n c e d by t h e s h o r t e s t time t o 50% weight l o s s and t h e g r e a t e s t e x t e n t o f r e a c t i o n b a s e d on t h e t o t a l CGC a r e a c o u n t s . In a second e x p e r i m e n t , Bi203 was

p y r o l y z e d a t 280°C w i t h HBCD. B a s e d on t h e GC/MS r e s u l t s o b t a i n e d from t h e HBCD/Sb203 m i x t u r e , i t was assumed t h a t one o f t h e p r o d u c t s formed under t h e s e c o n d i t i o n s w i t h Bi203 would be B i B r 3 , v i a t h e d i r e c t r e a c t i o n o f t h e B i 2 0 3 w i t h t h e HBr formed from t h e decomposing HBCD. Both t h e TGA weight l o s s and r e s i d u e d a t a were c o n s i s t e n t w i t h t h e f o r m a t i o n o f a significant q u a n t i t y o f B i B r 3 under t h e c o n d i t i o n s employed. C o n f i r m a t i o n o f t h e f o r m a t i o n o f B i B r 3 by GC/MS was u n s u c c e s s f u l . The B i B r 3 formed " i n - s i t u " was t h e n s u b s e q u e n t l y p y r o l y z e d a t 390° w i t h a m i x t u r e o f PP/DBDPO. T h i s t e r n a r y m i x t u r e was found t o y i e l d t h e most complete e x t e n t o f r e a c t i o n d a t a f o r any system which had been s t u d i e d as o n l y 0.3% o f t h e t o t a l v o l a t i l e p r o d u c t peak a r e a was f o u n d t o be u n d e g r a d e d DBDPO. However, t h e n a t u r e o f t h e s e e x p e r i m e n t s makes i t d i f f i c u l t t o t r u l y a s s e s s t h e s i g n i f i c a n c e o f t h e s e d a t a and any f u t u r e work w i t h t h i s system would have t o be c a r r i e d out w i t h w e l l c h a r a c t e r i z e d B i B r 3 . The o v e r a l l r e s u l t s o b t a i n e d from t h e HBCD m i x t u r e experiments were i n t e r p r e t e d i n terms o f a c a t a l y t i c e f f e c t o f s t r o n g Lewis a c i d s such as SbBr3 o r B i B r 3 on t h e d e g r a d a t i o n o f t h e HBCD by facilitating the loss of halogen. In t h e p o l y m e r / o x i d e / D B D P O ternary mixtures the i n - s i t u formation of these species should produce a s i m i l a r e f f e c t on t h e h a l o g e n l o s s from t h e system. In a d d i t i o n , s i n c e B i B r 3 i s s i g n i f i c a n t l y l e s s v o l a t i l e t h a n SbBr3 (bp. 441°C v s . 288°C), i n a t e r n a r y mix r e a c t i o n a t 390°C, t h e B i B r 3 would be e x p e c t e d t o remain i n t h e r e a c t i o n m i x t u r e f o r l o n g e r p e r i o d s o f time than t h e SbBr3. C o n s e q u e n t l y , i t c o u l d appear t o be a more e f f e c t i v e c a t a l y s t t h a n SbBr3 u n d e r t h e s e experimental c o n d i t i o n s and t h e r e f o r e , y i e l d a h i g h e r o v e r a l l e x t e n t o f r e a c t i o n . These d a t a suggest t h a t t h e f o r m a t i o n o f s p e c i e s such as SbX3 may n o t o n l y be i m p o r t a n t b e c a u s e o f t h e i r v o l a t i l i t y a n d f l a m e i n h i b i t i o n , but a l s o f o r t h e r o l e they p l a y i n t h e s o l i d s t a t e degradation chemistry. Summary From t h e r e s u l t s o f t h e s m a l l s c a l e t h e r m a l a n a l y s i s experiments p r e v i o u s l y r e p o r t e d (23,25), i t was c o n c l u d e d t h a t t h e a n t i m o n y v o l a t i l i z a t i o n and bromide r e l e a s e o b s e r v e d f o r t e r n a r y m i x t u r e s containing organobromine compounds, which d i d not undergo intermolecular dehydrohalogenation, c o u l d n o t be a c c o u n t e d f o r s o l e l y on t h e b a s i s o f HBr f o r m a t i o n d u r i n g d e g r a d a t i o n .


DREWS E T A L .


Table V I I I .

Summary o f V o l a t i l e P r o d u c t CGC A n a l y s i s f o r t h e E x t e n t o f R e a c t i o n o f PP and PE T e r n a r y M i x t u r e s P y r o l y z e d a t 390°C i n t h e TGA

Component Peak A r e a s , % Mixtures

1

DP0 IQ

1

DP0 9 8 /

1

DPO ?^

d p q 1

5,4

d b f 2

8,7

d b f

6-4

DBDPO/PP/Sb203 3.3 DBDPO/PE/Sb203 0.6

29.3

8.0

1.4

9.0

22.4

16.2

8.5

6.7

2.2

15.5

1 Brominated d i p h e n y l o x i d e s Brominated d i b e n z o f u r a n s

2

T a b l e IX. Summary o f t h e V o l a t i l e Product CGC A n a l y s i s f o r t h e HBCD M i x t u r e s P y r o l y z e d I s o t h e r m a l l y i n t h e TGA a t 240°

M i x t u r e Peak Area, % Bromine #

1 2 3 4 5 6

Neat

2.3 19.3 31.1 17.3 7 .1 12 .7

Count

( 1 )

4.5

Sb°

Sb2C>3

21.8 15.2 51.4

4. 3 9. 7 36. 8 •-

11.8 0.3

SbBr3

28.4 18.6 2.2

3.2 41.5 45.5

46. 9 0. 4

0.1

T o t a l i n t e g r a t o r counts f o r the e n t i r e by ( 1 0 ~ ) .

multiplied

G l a s s Beads

2.5

chromatogram

6


126

FIRE AND POLYMERS

T a b l e X. for

Summary o f t h e Time t o 50% Weight Loss Data t h e HBCD M i x t u r e s P y r o l y z e d I s o t h e r m a l l y i n the TGA a t 240°

Sample

Time t o 50% Weight Loss, min.

HBCD HBCD/Sb° HBCD/Sb 03 HBCD/SbBr3 HBCD/Glass Beads 2

11.5 2.6 6.8 2.3 11.4

From t h e CGC and CGC/MS a n a l y s i s o f t h e t h e r m a l l y i n i t i a t e d reactions o f HDPE a n d PP w i t h DBDPO a n d a v a r i e t y of other components r e p o r t e d here, i t has been shown t h a t a t t a c k o f p o l y m e r c h a i n r a d i c a l s on t h e DBDPO i s t h e most p r o b a b l e f i r s t m e c h a n i s t i c s t e p i n t h e t e r n a r y m i x t u r e p y r o l y t i c d e g r a d a t i o n o f DBDPO. E x p e r i m e n t s w i t h antimony m e t a l and DBDPO c l e a r l y d e m o n s t r a t e d f o r t h e f i r s t time t h a t antimony v o l a t i l i z a t i o n was p o s s i b l e i n t h e c o m p l e t e a b s e n c e o f any s o u r c e o f h y d r o g e n a t p o l y m e r p y r o l y s i s temperatures. On t h e b a s i s o f t h e r e s u l t s o b t a i n e d from a d d i t i o n a l e x p e r i m e n t s w i t h o t h e r m e t a l s i t was c o n c l u d e d t h a t i n t h e p r e s e n c e o f a c t i v e m e t a l such as S b ° o r B i ° o r Zn° d i r e c t a t t a c k on t h e DBDPO would r e a d i l y occur. However, a l l attempts t o d i r e c t l y measure t h e e x t e n t of Sb° formation from Sb203 d u r i n g polymer degradation were unsuccessful. From t h e s i n g l e component, s i m p l e m i x t u r e and t e r n a r y m i x t u r e e x t e n t o f r e a c t i o n d a t a p r e s e n t e d , i t was c o n c l u d e d t h a t t h e e x t e n t of DBDPO r e a c t i o n i n the ternary mixtures s t u d i e d , w h i c h was m e a s u r e d by CGC and CGC/MS a n a l y s i s , was g r e a t e r t h a n c o u l d be accounted f o r on t h e b a s i s o f t h e r e a c t i v i t y o f t h e i n d i v i d u a l components i n i t i a l l y p r e s e n t . Taken t o g e t h e r t h e s e d a t a suggest that a r e a c t i o n intermediate or product was f o r m e d d u r i n g t h e d e g r a d a t i o n o f t h e t e r n a r y m i x t u r e s which was e i t h e r : (a) more r e a c t i v e towards DBDPO i t s e l f o r (b) a p o w e r f u l c a t a l y s t f o r t h e subsequent d e h a l o g e n a t i o n o f t h e DBDPO. Data o b t a i n e d from s t u d i e s on t h e d e h y d r o h a l o g e n a t i o n o f HBCD w i t h m e t a l o x i d e s and m e t a l h a l i d e s c l e a r l y show t h e c a t a l y t i c e f f e c t o f s t r o n g L e w i s a c i d s on t h i s r e a c t i o n . These results s u g g e s t t h a t any s i m i l a r m e t a l h a l i d e o r o x y h a l i d e s c o u l d e x e r t a similar effect on t h e d e h y d r o h a l o g e n a t i o n of other halogenated o r g a n i c s formed d u r i n g t h e c o u r s e o f t h e s o l i d s t a t e d e g r a d a t i o n i n c l u d i n g the o r i g i n a l halogen source i t s e l f . Finally, the r e s u l t s r e p o r t e d here c l e a r l y demonstrate t h e u t i l i t y o f u t i l i z i n g t h e f l a m e r e t a r d a n t a d d i t i v e s as s e n s i t i v e p r o b e s i n t o s t u d y i n g t h e c o u r s e o f t h e s o l i d s t a t e c h e m i s t r y which occurs during p y r o l y s i s .


9. DREWS E T A L .


127

Acknowledgment The a u t h o r s would l i k e t o g r a t e f u l l y acknowledge t h e C e n t e r f o r F i r e Research o f t h e N a t i o n a l I n s t i t u t e o f Standards and Technology f o r t h e i r s u p p o r t o f t h i s work t h r o u g h G r a n t s NB79NADA0011, NB80NADA1042 and 60 NANB4D0033.

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