R. Luijk

Thermal Degradation Characteristics of High Impact Polystyrene/Decabromodiphenylether/Antimony Oxide Studied by Derivative Thermogravimetry and Temperature Resolved Pyrolysis-Mass Spectrometry. Formation of Polybrominated Dibenzofurans, Antimony (oxy) Bromides and Brominated Styrene Oligomers

Abstract The thermal stability and the thermal degradation products of high impact polystyrene / decabromodiphenylether / antimony oxide (HIPS FR) have been studied in situ with derivative thermogravimetry (DTG), temperature resolved pyrolysis—mass spectrometry (Py-MS) and pyrolysis—gas chromatography / mass spectrometry (Py-GC /MS). With in-source temperature resolved Py-MS (negative ions) the thermal degradation processes of HIPS FR have been studied dynamically and antimony (oxy)bromides and brominated higher styrene oligomers upto n = 15 have been detected. During degradation of the HIPS FR polymer matrix several processes take place, such as debromination of the flame retardant decabromodiphenylether to form less brominated diphenylethers, bromination of polystyrene and formation of antimony bromides and antimony oxybromides. The formation of toxic polybrominated dibenzofurans (PBDFs) has been shown to occur in the temperature range in which the HIPS FR polymer matrix degrades (350–400°C). This is explained by debromination of decabromodiphenylether to form less brominated diphenylethers which are much more reactive towards formation of PBDFs.

The formation of polybrominated dibenzo-p-dioxins (PBDDs) and dibenzofurans (PBDFs) during pyrolysis of polymer blends containing brominated flame retardants

Abstract The formation of polybrominated dibenzo-p-dioxins and -dibenzofurans (PBDDs and PBDFs) during pyrolysis of two polymer blends containing decabromobiphenyl and tetrabromobisphenol-A, was investigated at different temperatures and carrier gas compositions. During pyrolysis of a polybutylene terephthalate/decabromobiphenyl blend PBDFs are formed at a ppm level. Even when there is oxygen available in the carrier gas, PBDDs are formed at a much lower level than PBDFs. In the presence of 10% oxygen the maximum yield of tetra- to octabromodibenzofurans is 70 ppm at 600°C. The contribution of 2,3,7,8-tetrabromodibenzofuran and 1,2,3,7,8-pentabromodibenzofuran is less than 4.5 ppm. During pyrolysis of acrylonitrile/butadiene/styrene with tetrabromobisphenol-A mono- to pentabrominated dibenzofurans were formed at a ppb level. The optimum temperature of formation of PBDDs and PBDFs was 600°C. The thermal degradation processes of these two polymer blends were investigated in a thermogravimetric analysis. Both flame retardants do not exert an influence on the elementary chemical degradation processes of the polymer blends. The flame retardant activity of decabromobiphenyl and tetrabromobisphenol-A consists of the emission of brominated species into the gas phase which scavenge the propagation radicals and reduce inflammability. The mechanism of formation of PBDDs and PBDFs from decabromobiphenyl in polybutyleneterephthalate consists of a combination of a condensed phase and a gas phase mechanism. In the case of tetrabromobisphenol-A only a gas phase mechanism of formation of PBDDs and PBDFs was observed.

The influence of the polymer matrix on the formation of polybrominated dibenzo-p-dioxins (PBDDs) and polybrominated dibenzofurans (PBDFs)

Abstract During micro-pyrolysis of polybrominated diphenylethers (PBDPOs), which are used as flame retardants in synthetic polymer blends, PBDDs and PBDFs are formed. The yield decreases from Br 5 DPO→Br 8 DPO→Br 10 DPO due to the energetically favourable elimination of HBr. The influence of the high impact polystyrene (HIPS) polymer matrix on the formation consists of a selectivity towards formation of PBDFs, a shift in the optimal PBDF formation temperature from T =600°C to the HIPS depolymerisation temperature T=350–400°C and an enhancement of the total yield of PBDFs with a factor 7. The key towards understanding of the low PBDF formation temperature lies in the fact that PBDPOs are incorporated in a polymer matrix. During radical depolymerisation of the HIPS polymer matrix PBDFs are formed by the exchange of hydrogen and bromine which is followed by a ring closure reaction. The thermal degradation processes of HIPS Br 10 DPO Sb 2 O 3 were studied dynamically with in-source temperature resolved Py-MS (negative ions). Several processes taking place during degradation of the HIPS Br 10 DPO Sb 2 O 3 polymer matrix, like debromination of the flame retardant Br 10 DPO to form less brominated diphenylethers, formation of PBDFs, bromination of polystyrene and formation of antimony (oxy)bromides, were elucidated with this technique.

The role of bromine in the de novo synthesis in a model fly ash system

Abstract The role of bromine in the de novo synthesis in a model fly ash system has been evaluated. A silica-alumina carrier was impregnated with a CuX2 catalyst system X=Cl, 0.5 wt%; X=Br, 0.8 wt%). A flow of air with 5 vol. % HX (X=Cl or Br) was passed over a fixed bed at 300°C. Several processes have been investigated concerning the role of bromine and chlorine in the formation of polyhalogenated dibenzo-p-dioxins and -dibenzofurans in municipal waste incinerator fly ash under conditions observed in an electrostatic precipitator: 1. (i) The exchange of bromine and chlorine in 2,3,7,8-tetrabromodibenzo-p-dioxin; 2. (ii) The reactivity and selectivity of bromine and chlorine in the halogenation of the parent structures dibenzo-p-dioxin and dibenzofuran; 3. (iii) The competition of bromine and chlorine in the de novo synthesis.

Determination of the liquid vapour pressure of low-volatility compounds from the Kovats retention index.

The isothermal gas-liquid chromatographic Kovats retention index and an infinite dilution equilibrium fugacity model are combined to arrive at an expression relating the Kovats indices and the McReynolds numbers of a series of compounds to their isothermal pure liquid vapour pressures. This novel expression is the basis for ultra-low vapour pressure determination at environmentally relevant temperatures of pure organic (sub-cooled) liquids by routine gas-liquid chromatography on a non-polar stationary phase. Examples of the potential of the method are given for chlorobenzenes and chlorophenols.

Calculation of heat of vaporization, molar volume and solubility parameter of polychlorodibenzo-p-dioxins

Abstract The heat of vaporization and molar volume of aromatic liquid CClHO compounds were modelled as sums of contributions of the parent molecule, Cl substituents, ClCl interactions and ClO interactions. Parameters belonging to these contributions were derived, enabling the calculation of the heat of vaporization, molar volume and solubility parameter of polychlorinated dibenzo-p-dioxins.

The formation of PCDDs and PCDFs in the catalysed combustion of carbon : implications for coal combustion

Abstract Experiments on combustion of an activated carbon (Norit RX Extra) catalysed by CuCl2 (0.5 wt%) were carried out in an air flow containing 5 vol.% HCl and 20 vol.% H2O at 300 °C. After partial combustion (2 h), the samples were analysed for polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). The total yield of these compounds amounted to 3–4 μg g−1 carbon, with a PCDD/PCDF ratio of 10. The major constituents were the hexa- and heptachlorinated dibenzo-p-dioxins (50 and 20 wt% respectively). The isomer distribution was characteristic of that of a typical fly ash from incineration of waste. The copper-catalysed combustion of the polyaromatic structure of activated carbon in the presence of HCl gives rise to partial chlorination of the carbon surface and local stabilization of the carbon burnoff. The isolated chlorinated aromatic fragments are assumed to be intermediates in the formation of PCDDs and PCDFs.

Descriptors for isomer resolution of (bio-) distribution of chlorinated aromatic compounds

Both Solubility Parameter (SOLPAR) and Linear Solvation Energy Relationship (LSER) theory utilize molar volume and energies as descriptors for distribution phenomena. They provide powerful methods for the prediction of the GLC retention indices of chlorobenzenes (CBzs) and tetrachlorodibenzo[p]dioxins (TCDDs). Almost complete isomer resolution is obtained with correlation coefficients (r) of greater than or equal to 0.9984 (CBzs) and greater than or equal to 0.9839 (TCDDs). The n-octanol/water partition coefficient (log Kow) of CBzs can be calculated with a standard error of regression of 0.04, which compares favourably with standard deviations of 0.03-0.26 in mean values based on four different experimental methods. The HPLC capacity factor of TCDDs on C18 columns can be predicted by SOLPAR with moderate accuracy (r = 0.9470), allowing for a preliminary calculation of log Kow. A simplified LSER method fails.