Emission behaviour of brominated compounds in thermal treatment of printed
circuit board under inert and oxidative atmosphere
O. Terakado*, H. Takagi and M. Hirasawa
Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya University, Japane-mail: teramon@numse.nagoya-u.ac.jp; phone & fax: +81-52-789-3250

Abstract
In the view of the emission control in thermal treatment of wastes electrical and electronic equipment, thermal
degradation of a printed circuit board has been studied both in inert and oxidative atmosphere. The presence of oxygen inatmosphere reduces the yield of hydrogen bromide, a major brominated comopound in pyrolysis treatment, andenhances the formation of bromine as well as hypobromous acid. The presence of zinc oxide in sample results in theformation of zinc bromide. Moreover, the release of brominated compounds is promoted in comparison to the case ofpure PCB.

Keywords: Printed circuit board, Brominated flame retardant, Hydrogen bromide, Bromine, Emission control

1. Introduction
Waste electrical and electronic equipment, WEEE,
contains variety of valuable metals, so that thedevelopment of the metal recovery process is of greatimportance for the establishment of sustainable society.
Various processes have been proposed so far:conventional ones are based on the hydrometallurgicaltreatment after the combustion of WEEE. It should be
noted that many flame retardants are used in electricaland electronic equipments in order to ensure their fire
safety. In general, the share of brominated flame
retardant, BFR, reaches up to 40 % [1], so that special
attention should be paid in the thermal treatment ofWEEE.
In the course of our studies on the application of metaloxides to the halogen fixation in pyrolysis of halogencontaining polymer, we have found that bromine
originating from tetrabromobisphenol A, a typical BFR,
and a printed circuit board containing BFRs can be fixedin the form of stable metal halide or oxyhalide [2,3].
In the present work, we have carried out thermal
treatment of a printed circuit board, PCB, under inert andoxidative atmosphere in the presence of metal oxide. The
influence of atmosphere and oxides are compared anddiscussed.

2. Materials and Methods
Printed circuit boards, containing BRRs, were kindly
supplied from Hitachi Kasei Co., Ltd. They are FR-4 typesamples, where epoxy resin is reinforced by woven glassfibres. The copper plate was coated on the board, which
was removed by iron chloride aqueous solution in thepresent study. The copper-free PCB was crushed andground down to less than 250 µm. The powder wasmixed with metal oxide powder (Kanto Chem. Co., Ltd. or
Kishida Chem. Co., Ltd.). As an example, thecomposition of zinc oxide was 2.6 mass%, whichcorresponds to the stoichiometric ratio for the formationof ZnBr2.
Themogravimetric analysis, TGA, has been carried out
with TGA-2050 equipment (TA Instruments) at theheating rate of 10 °C/min under the atmosphere ofhelium-oxygen mixture. Thermal decomposition
experiments were carried out with a horizontal typereactor (700 mm in length and 26 mm in i.d.) under
helium and air atmosphere. The experimental set-up is
as same as that described elsewhere [2]. The hydrogen
bromide captured in a water trap was monitored throughthe amount of bromide ion, Br-, with an ion meter (IM-40S,TOA Electronics). The hypobromous acid, HBrO, in thetrap was determined by iodometry [4]. The bromine
adhered at the cold part of the reactor was collected withpure water, and converted to bromide ion by theirradiation of light into the solution, whose ion
concentration was then determined by the ion meter. The
char after thermal treatment was characterized by XRD(XRD-6100, Shimadzu) and FT-IR (FT-IR 230, JASCO)
analysis.

3. Results and Discussion
Fig. 1 shows the result of TGA of PCB specimen at
different oxygen partial pressure. The mass reduction
around 310-350 °C is due to the thermal decompositionof epoxy resin. Obviously, this decomposition stage isindependent of atmosphere, because the mass reduction
behaviour is essentially the same. However, the mass
after this stage is higher in the presence of oxygen,
which suggests the formation of oxygen-containing
functional groups in the char, as observed also in theoxidative treatment of ABS resin [4]. This is confirmed by
an FT-IR analysis of the char obtained from a sample

7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013

Fig. 1 Results of TGA of PCB at the heating rate of
10 °C/min under different atmosphere. The curveassignment follows the order of the arrow on the graph.

heated at 370 °C under 50%O2-He atmosphere, where
the increase in the peak intensity at 1750 cm-1, assigned
to the C=O stretching mode, was observed.
On the other hand, the second mass reduction stage
around 400-600 °C is strongly influenced by theatmosphere in the gas phase. The mass reduction rate
becomes higher with increasing oxygen partial pressure.
The result indicates that this mass reduction stage
involves the oxidation of char matrix formed at the firstmass reduction stage.

As known in literature [3,5], pyrolysis treatment of PCB
results in the formation of hydrogen bromide with byproducts of brominated organic compounds.
The presence of oxygen in the atmosphere gives rise to
the significant change in the distribution of brominatedcompounds, and the yield of bromine increases withincreasing oxygen concentration in the gas phase [6].
Fig. 2 shows the yield of hydrogen bromide, bromine andhypobromous acid evolved at different reaction time ofthermal treatment of pure PCB under inert and air
atmosphere and PCB-ZnO mixture under air atmosphere,respectively.
The gradual increase of HBr with increasing treatment
time of pure PCB under helium is in consistent with ourprevious observation [3]. It is noteworthy that bromine isalso formed in thermal treatment under inert atmosphere.
On the other hand, the yield of HBr is considerably low inthermal treatment of pure PCB under air atmosphere.
Obviously, the oxidation of Br- takes place in this case,since the yield of Br2 and HOBr is higher. Furthermore,
the amount of bromine in the reactor decreasesapparently with increasing reaction time. This is probably
due to the evaporation of volatile bromine.
The presence of zinc oxide leads to the formation of zincbromide. The release of brominated compounds
completes obviously at 150 sec in contrary to the sample
without oxide. It is therefore considered that the additionof the oxide enhances the decomposition of PCB. It
should be noted that high portion of bromine remains in
the reactor. Thus, attention should be paid in thermal
treatment waste PCBs.

4. Conclusions
In the present work, we studied the emission behaviourof brominated compounds in thermal treatment of printed
circuit board in inert and oxidative atmosphere. It was
found that the presence of oxygen leads to the oxidationof hydrogen bromide to bromine or hypobromous acid.
The bromine remains in the cold part of the furnace andgradually evaporates. The intentional addition of oxide,
such as ZnO, leads to the fixation of bromine, andapparently promotes the release of brominatedcompounds from PCB.

References[1] Web site of flame retardant chemicals association ofJapan: http://www.frcj.jp/[2] O. Terakado, R. Ohhashi and M. Hirasawa, J. Anal.
Appl. Pyrolysis, 91 (2011) 303-309.
[3] O. Terakado, R. Ohhashi and M. Hirasawa, J. Anal.
Appl. Pyrolysis, (2013) in press.
[4] W.R. Haag, Water Res., 15 (1981) 937-940.
[5] K. Marsanich, S. Zanelli, F. Barontini, V. Cozzani,
Thermochim. Acta, 421 (2004) 95-103.
[6] Y.-q. Jin, L. Tao, Y. Chi and J.-h. Yan, J. Hazard.
Mater., 186 (2011) 707-712.
Fig. 2 Yield of major brominated compounds at different
reaction time.

7th International Symposium on Feedstock Recycling of Polymeric Materials (7th ISFR 2013)
New Delhi, India, 23-26 October 2013