Fire and Polymers II - American Chemical Society

Chapter 25

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 6, 2017 | http://pubs.acs.org Publication Date: July 21, 1995 | doi: 10.1021/bk-1995-0599.ch025

Formation of Polybrominated Dibenzodioxins and Dibenzofurans in Laboratory Combustion Processes of Brominated Flame Retardants Dieter Lenoir and Kathrin Kampke-Thiel Institute of Ecological Chemistry, GSF Research Center for Environment and Health, 85758 Oberschleissheim, Germany

Oxidative thermal degradation of a collection of polymers with 10 different kinds of brominated flame retardants has been studied under standardized laboratory conditions using varying parameters including temperature and air flow. Polybrominated diphenyl ethers like the deca-, octa-, and pentabromo compounds yield a mixture of brominated dibenzofurans while burning in polymeric matrices. Besides cyclization, debromination/hydrogenation is observed. Influence of matrix effects, presence of various metals, and burning conditions on product pattern have been studied, the relevant mechanisms have been proposed and the toxicological relevance is discussed.

Hazards identification and prevention in oxidative thermal degradation of polymers has become an important issue in the research of European countries (1) and in the US (1, 2). Great concern is given to the problem of acute toxicity of gaseous hazards like carbon monoxide, hydrogen cyanide and hydrogen halides during various kinds of accidental fires (3). Somewhat less concern is given to long-term toxic effects on humans caused by other pollutants emitted by fires like polycyclic aromatic hydrocarbons (4). Therefore, we have studied the formation of polybrominated dibenzodioxins and -furans (PBDD/F) from various types of brominated flame retardants under laboratory conditions. Some related results of PBDD/F formation during accidental burning of these materials in tunnels and in houses will be discussed. Experimental The following 10 bromine compounds were investigated, in general within their polymeric matrices (see Scheme 1): 0097-6156/95/0599-0377$12.00/0 © 1995 American Chemical Society Nelson; Fire and Polymers II ACS Symposium Series; American Chemical Society: Washington, DC, 1995.

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decabromobiphenyl ether (1) octabromobiphenyl ether (2) pentabromobiphenyl ether Q) 1,2-Bis (2,4,6,tribromphenbxy) ethane (4) tetrabromobisphenol A (5)

tetrabromophthalic anhydride (£) dibromopropyldian (2) 1,2-Bis (tetrabromophthalimide) (4) polybrominated styrene (2) hexabromocyclododecane (1Û)

I'

l i x + y = 10 2: x + y = 8 3; x + y= 5

lfl

Scheme 1. Structure of investigated Brominated Flame Retardants.

Nelson; Fire and Polymers II ACS Symposium Series; American Chemical Society: Washington, DC, 1995.

25.

LENOIR & KAMPKE-THIEL

Polybrominated Dibenzodioxins and -furans

decabromobiphenyl ether (1) octabromobiphenyl ether (2) tetrabromobisphenol A (£) tetrabromophthalic anhydride (6) dibromopropyldian (2)

379

pentabromobiphenyl ether (2) 1,2-Bis (2,4,6,tribromphenoxy) ethane (4) 1,2-Bis (tetrabromophthalimide) (&) polybrominated styrene (2) hexabromocyclododecane QQ)

The following polymeric materials (commercial products) were investigated: a) polystyrene with 10 % of 1 and 4 % Sb 0 b) polystyrene with 12,5 % of 1 and 4 % Sb 0 c) ABS with 14 % of 2 and 6 % Sb 0 d) polyurethane with 15,4 % of 2; e) ABS with 18 % of 4 and 7 % Sb 0 f) epoxilaminate with i; g) epoxilaminate with ί (other product) h) epoxilaminate copper-laminated with 5;


2

3

2

2

3

2

3

3

j) polycarbonate with 12 % of 5; k) polyurethane with 33 % of 6; 1) polyurethane with 6,4 % of 6; m)polyester with 2; n) polyester with 2 (other sample); o) polypropylene with 5,9 % of &; p) ABS with 11% of 2: q) polystyrene with 3 % of 1Q;

Laboratory combustion processes were performed with the three different furnaces: The German VCI-Apparatus and the German BIS-oven (BIS: fiayer, ICI, Shell) are shown in Figures 1 and 2. Besides these furnaces the German DIN-oven was also used, details can be found in the literature (5, 6, 7). These furnaces are designed to model the situation of a fire under laboratory conditions. Therefore we prefer the term „oxidative thermal degradation" compared to the term „pyrolysis", since the term „pyrolysis" is generally used for thermolysis without oxygen. By variation of temperature and air flow rate burning conditions rangingfroma smolderingfireto an open fire can be modeled. Details can be found in the literature (5, 6, 7). The furnaces are complementary to each other. In general, similar results are obtained. Special clean-up procedures have been developed for PBDD/F in the thermal degradation products formed by either furnace. One of these clean-up procedures is outlined below (see Scheme 2); details will be found in the literature (7, 8). For the relevant structures of PBDD/F, see formula below:

χ + y = 1 to 8 (135 Isomers)

χ + y = 1 to 8 (75 Isomers)

Identification and quantification of PBDD/F was performed by GC/MS techniques (5-9). This was done for all brominated PBDD and PBDF from mono-



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wool

Figure 1. VCI-Apparatus (Furnace of Verband der Chemischen Industrie; German Chemical Industry Association).




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Pyrolysate on Adsorbent

Extraction with 100 ml hexane/dichloromethane (1:1), 2 hrs

Crude Chromatographic Cleaning (in sequence) on 6 g sodium sulfate/sand 3 g IN NaOH on silica 12 g Fluorisil in 50 ml CH C1 2

2

Fractionation on 15 g alumina Β (Woelm) with: 1) 100 ml benzene 2) 50 ml hexane/dichloromethane (9:1) 3) 150 ml hexane/dichloromethane (1:1) 4) 50 ml dichloromethane

PBDD/F are in the 3rd fraction Evaporation GC/MS Scheme 2. Clean-up Procedure for PBDD/F in Pyrolysate of the VCI-Furnace.


25.

Polybrominated Dibenzodioxins and -furans 383

LENOIR & K A M P K E - T H I E L


through octabromo compounds using external standards which were either prepared or purchased. A total of 210 brominated compounds of PBDD/F exists. Since not all isomers are available a complete isomer-speciflc determination could not be performed. For further experimental details see also (9). Results and Discussion. The following results have been obtained in laboratory combustion studies. Polymers containing bromine compounds 4 and ί yield PBDD/F in the ppm range. Oxidative thermal degradation of compound ί gives PBDD isomers but no toxic isomers. Polymers containing brominated diphenyl ethers 1-2 however, yield PBDF in very high yields (6-10); depending on the applied conditions the conversion can be nearly quantitative. Therefore, this class of compounds has been investigated more thoroughly by different groups (8, 10-12). Compounds 6-IQ do not yield any detectable amounts of PBDD/F even in the ppm range. First, thermal behaviour of decabromobiphenyl ether 1 will be described. The thermal reactivity of this compound depends on the applied conditions; the pure compound reacts completely different in comparison to its reaction in polymeric matrices. Thermolysis of the pure compound gives a good yield (60 %) of hexabromobenzene. The main products obtained by laboratory combustion in the DIN-oven at three temperatures for pure 1 and 1 within a polypropylene matrix are shown in Table 1 and Figures 3 and 4. Table 1 : Main Products obtained by Oxidative Thermal Degradation of Decabromobiphenyl Ether 1 at three different Temperatures; Yields are in Percent by Weight 800°C Product 600°C 400°C 1 Hexabromobenzene

22,3 ; nd

b

12,3*; nd

b

PBDD/F

0,08" ; 253" 4,5* ; 3,

Fire and Polymers II - American Chemical Society

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