Brominated flame retardants (BFRs) have been used for more than four decades in electronic equipment and building materials such as circuit boards, capacitors, and textiles to increase their flame resistance [1
]. The addition of BFRs is one of the lowest cost ways to meet flammability regulatory requirements. The most intensively used BFRs are tetrabromobisphenol A (TBBPA), hexabromocyclododecane (HBCD), and three commercial mixtures of polybrominated diphenyl ethers (PBDEs), that is, decabromodiphenyl ether (BDE209), octabromodiphenyl ethers (octaBDEs), and pentabromodiphenyl ethers (pentaBDEs).
Recently, many environmental studies have focused on PBDEs, owing to their persistence and probable carcinogenic human health effects [2
]. The accumulation of PBDEs in sediment and biota of aquatic environments is regarded as a serious environmental problem around the world [3
]. European and North American countries banned the use of pentaBDEs and octaBDEs in 2004. Decabromodiphenyl ether, the mostly widely used in all markets, was banned on April 1, 2008 by the European Court of Justice. In the United States, Maine has banned the use of BDE209 (the only PBDE still on the market in North America) in mattresses and residential upholstered furniture produced and sold in that state [6
Hexabromocyclododecanes, as an alternative to BDE209, have been increasingly used in Europe and Asia in recent years, and studies have shown that the levels of α-HBCD, the most persistent of the HBCDs, are increasing in biota and humans [7
]. However, HBCDs are presently only banned in Norway [9
]. Tetrabromobisphenol A, which represents half of the usage of BFRs globally, has been detected in various environmental media and biota, such as water, air, soil, and sediments [10
]. Nevertheless, owing to its low potential for bioaccumulation [11
], no restrictions have currently been placed on the production of TBBPA [9
Vapor pressure data are important parameters for models that predict the fate and transport of such BFRs in the environment. However, few vapor pressure data have been reported for these BFRs, Because of their high molecular weight and their degradation at high temperatures [12
]. Therefore, it is desirable to employ techniques that can measure relatively low vapor pressures to study this property of these BFRs. Beyond the vapor pressures themselves, these data offer insights into other thermodynamic properties of these materials, such as cohesive energy in the condensed phase (related to the sublimation enthalpy).
The gas chromatography-retention time method has been employed to measure the hypothetical subcooled liquid state vapor pressure of 31 PBDEs [14
], but this method could not be used to measure the vapor pressures of octaBDEs and BDE209 Because of their strong affinity to the generally employed column. In addition, it should be noted that most BFRs are in a solid state, not a liquid state, at ambient temperature, so that the subcooled liquid state data need to be corrected to a real state, if they are to be used.
In the present study, the solid state vapor pressures of three BFRs, i.e. TBBPA, HBCD, and octaBDE, were measured using the Knudsen effusion method, which has been successfully used by our group to measure the vapor pressure of BDE209 [17
]. The enthalpies of phase change and melting temperature range of these BFRs were also determined by using a differential scanning calorimetry and melting point apparatus. The solid vapor pressures of these BFRs were also compared with those of BDE209.