Method For Measuring The Emission Rate Of Hexabromocyclododecane(HBCD) From Polystyrene Foam

Hexabromocyclododecane(HBCD)is a widely used additive in expanded polystyrene foam(EPS),extruded polystyrene foam(XPS)and high impact polystyrene Production of ethylene(HIPS).Due to its high-volume production,high toxicity,environmental persistence,bioaccumulation and long range transport potential,HBCD,it has attracted great attention of the Environmental Science Society.On May 2013,HBCD was listed in Annex A of the Stockholm Convention on Persistent Organic Pollutants,which stipulated a worldwide restriction on the production and use of HBCD,but commercial exemption right to HBCD added to EPS and XPS was allowed.HBCD added to plastic materials can be continuously released to the surrounding environment during production,lifetime,and recycling processes,as HBCD is semivolatile and physically embedded in plastic materials.characterizing the emission mechanism,measuring the releasing rate and predicting the environmental release behavior are prerequisites for describing HBCD migration and conversion and environmental risks.In 2012,we investigated the release of HBCD from polystyrene foam during thermal cutting and found that the thermal cutting process resulted in about 0.2%release of HBCD from polystyrene foam at 150 ℃.However,at present,there is still no research on the emission mechanism of HBCDs from plastic materials at low or ambient temperature,and the actual releasing rate during daily use has not been reported ever.In order to determine the emission rate of small amount of HBCD in polystyrene foam at low temperature or ambient temperature,we have developed a new type of chamber.The chamber was designed to measure the emission rate of HBCD from EPS foam board with low HBCD addition at 60 ℃ and from XPS foam board at 35 ℃.Mathematic model for estimating emission rate has been established.The emission of HBCD from EPS and XPS had the same characteristics.No significant difference was found for the emission behavior of the three major HBCD isomers(a-HBCD,β-HBCD and y-HBCD).The concentration of HBCD in the gas phase increased gradually during the early stage,then the concentration tended to be stable.However,there is a simple linear model to describe the stainless steel surface-gas partition behavior of HBCD.The emission rate of HBCD from EPS at 60 ℃was 246.5 ng·m-2·d-1 and 210.96 ng m-2·d-1 from XPS at 35 ℃.The results of the mathematic model showed that the release of HBCD mainly depended on the material-gas partition coefficient K and convective mass transfer coefficient hm,which was not basically affected by the internal diffusion coefficient D.According to the measured HBCD emission rate under the condition of 35 ℃,HBCD cumulative emission for one year make up 0.0003%of the total amount of HBCD from XPS foam board.