HBCDs

Suggested formulations for various polymers using hexabromocyclododecane (HBCD), a brominated aHphatic a chlorinated paraffin, ie, a chlorinated aHphatic and decabromodiphenyl oxide, a brominated aromatic, are shown in Tables 2—4. These suggested formulations may not be strictiy comparable because of differences in the nature of the base resins. However, the suggestions are specific to a given UL-94 rating. 

Acid scavenging stabilizeis aie typically recommended for use with HBCD in themioplastic appHcations. Stabilized grades are available from the manufacturers. 

Hexabromocyclododecane (HBCD) is prepared by the bromination of lZ,5E,9E-cyclododecatriene (CDT). The term "HBCD" will be used here to denote the commercial product containing various isomer compositions. Bromination of CDT leads to three isomers, HBCD-1 (y), HBCD-2 (P) and HBCD-3(a). All three isomers (Fig. 1) were isolated and fully identified (refs. 1,2). 

HBCD is a white free-flowing product containing about 74 weight percent (w/o) bromine and is recommended as a flame retardant for V-2 EPS, V-2 PP and V-2... 

HIPS in combination with stabilizers. Four basic types of HBCD are produced by all the HBCD producers, i.e. low melt, medium range, high melt and thermal stabilized HBCD. Analysis of the HBCD manufactured by several producers in given in Table 1 (ref. 3). The melting point of HBCD varies with changes in isomer ratio and composition of impurities. 

Table 1. Assay and isomer distribution of commercial samples of HBCD...

During experiments carried out at the Research and Development Division of the Dead Sea Bromine Group it was found that HBCD indeed decomposes at temperatures above 220 °C as reported in the literature (ref. 4) however it was also found that at temperatures below 2(X)°C thermal rearrangement takes place in a reaction not reported heretofore in the literature. 

Pure isomers were obtained from several crystallizations of HBCD from different sources. 

HBCD 2 Thermal rearrangement of commercial HBCD and crystallization. 

A sample of HBCD was weighed in a glass tube dipped in an oil bath with a temperature regulator of 1°C. During the experiment the sample was monitored for HBr formation. At different times the samples were taken out and cooled to room temperature, weighed and analyzed by quantitative HPLC. 

Table 3. Experimental results for thermal rearrangement of HBCD-1 at 190°C... 

Decomposition time was defined as the time taken for weight loss greater than 5 weight %. Results are presented in Table 6. No substantial differences between the three isomers can be discerned from the results. At temperatures up to 190 C isomers 2 and 2 are more resistance to thermal decomposition than isomer 1. Larsen (ref. 3) reported decomposition time to be 40-110 min. at 195°C for commercial HBCD (Table 1). 

Fig. 3. Comparison of processing heat stability at 230°C of HIPS/HBCD...

The application of FR-1206-HS ex Dead Sea Bromine Group provides longer residence time at 230°C without discoloration than the commercial heat-stabilized HBCD. The application of heat-stabilized FR-1206 was further developed by its use in fire retardant polypropylene (ref. 4). The new heat-stabilized HBCD, FR-1206/46, provides polypropylene with even better heat stability than FR-1206-HS (Table 4). 

It should be mentioned that fire retardant-polypropylene has higher impact energy than polypropylene without HBCD and this improved impact energy resulting from the addition of fire retardant is a rare phenomenon. Usually the addition (15-25%) of low molecular components decreases the high impact properties of plastics although we know that HIPS flame-retarded with decabromodiphenyl oxide (DECA), for example, has almost the same impact energy as non-retarded HIPS (Table 5). 

Dissolution (toluene)/precipitation (methanol) of EPS beads (atactic PS foams with ca. 2wt.% HBCD and BaSCL) with TLC separation and IR identification allowed detection of hexabromocyclododecane for quantification XRF analysis (Br) was used [629]. Disso-lution/precipitation of PS/lubricants with evaporation to dryness and redissolution was followed by FT1R analysis [106],... 

BFRs are one of the last classes of halogenated compounds that are still being produced worldwide and used in high quantities in many applications. In order to meet fire safety regulations, flame retardants (FRs) are applied to combustible materials such as polymers, plastics, wood, paper, and textiles. Approximately 25% of all FRs contain bromine as the active ingredient. More than 80 different aliphatic, cyclo-aliphatic, aromatic, and polymeric compounds are used as BFRs. BFRs, such as polybrominated biphenyls (PBBs), polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCD), and tetrabromobisphenol A (TBBPA), have been used in different consumer products in large quantities, and consequently they were detected in the environment, biota, and even in human samples [26, 27]. 

HBCD is a brominated aliphatic cyclic hydrocarbon used as a flame retardant in thermal insulation building materials, upholstery textiles, and electronics. In 2001, the world market demand for HBCD was 16,700 tons, from which 9,500 tons was sold in the EU. These figures make HBCD the second highest volume BFR used in Europe [29], HBCD may be used as an alternative for PBDEs in some applications. To date, there are no restrictions on the production or use of HBCD. As a result of their widespread use and their physical and chemical properties, HBCD are now ubiquitous contaminants in the environment and humans [30, 31]. 

---