5-7 OCTOBERISFR2011

143

TOLEDO (SPAIN)

DEBROMINATION OF HIGH IMPACT POLYSTYRENE CONTAININGDECABROMODIPHENYL ETHANE
H. Tanaka, G. Grause, T. Kameda and T. Yoshioka
Graduate School of Environmental Studies, Tohoku University
e-mail: yoshioka@env.che.tohoku.ac.jp

Abstract
The debromination of high-impact polystyrene (HIPS), containing decabromodiphenyl ethane (DDE), was carried out in
NaOH/ethylene glycol (EG) solution, using a ball mill. The results were compared with those obtained by the reaction in aflask. The degree of debromination increased with increasing reaction temperature and was about 98% at 190 °C after 24hours. The maximum degree of the debromination was reached at 0.5 M NaOH. While the degree of debromination in a flask
was 43%, it was found that the ball mill was more effective for the debromination of HIPS/DDE. The debromination in a flask
followed an apparent first-order reaction and the debromination rate decreased during the reaction. It is considered that thedebromination progressed in a first step at the surface of the HIPS/DDE sample and after that the debromination progressedinside the samples. When a ball mill was used, the debromination process followed the modified shrinking-core model. The
debromination rate was constant during the reaction indicating that the reaction always proceeded at the surface of theHIPS/DDE sample due to the grinding by the ball mill.

Keywords: debromination, brominated flame retardant, high-impact polystyrene, ethylene glycol, shrinking core model

1. Introduction
In 2000, law for recycling of specified kinds of home
appliances took effect in Japan and similarly, the Waste
Electrical and Electronic Equipment Directive wasenforced in the EU. Since these laws require therecycling of home appliances, recycling of these plastics
is needed. However, these plastics contain brominatedflame retardants such as tetrabromobisphenol-A anddecabromodiphenyl ethane, releasing environmentally
harmful brominated compounds during decomposition.
Accordingly, debromination is necessary for the recyclingof these plastics as a pretreatment.
In this study, the debromination of HIPS containing
decabromodiphenyl ethane (DDE) in NaOH/EG solution
was proposed., The debromination was studied using aflask or ball mill reactor. We also studied the kinetics ofthe debromination applying the modified shrinking coremodel.

width 60 mm) containing 400 Y2O3̽ZrO2 balls 5 mm indiameter. The rotation speed of the reactor was 60 rpm
at 150̽190 °C in N2 atmosphere at a flow rate of 100 mL
min-1. The reaction time was 24 hours. In case of using aflask, the procedure was same as for the ball mill. Aftercooling the reactor with water, the solution was filtered,washed with deionized water and methanol, and dried atreduced pressure.
Vent

Evaporator

Sampling

Water
N2

Siliconeoil2. Materials and methods
2.1. Materials
HIPS containing DDE was used for the debromination
experiment. The sample was prepared for research
purposes by extrusion using HIPS raw material and DDE.
2.2. Debromination experiments and analyticalmethods
NaOH/EG solution was prepared by dissolving NaOH in
EG. In this study, a flask and a ball mill were used asreactors. In case of using the ball mill, 1 g of HIPS/DDE
powder was added to 50 mL of 0 ̽ 1.0 M NaOH/EGsolution in a 1 L ball mill reactor (inner diameter 150 mm;

interiores libro.indd 143

Ball millreactorHeaterFigure 1. Ball mill reactor

The Br- level in the filtrate were determined using aDionex DX-100 ion chromatograph. The degree ofdebromination was calculated as the amount of Br- in thefiltrate to the total amount of Br.

3. Results and discussion
3.1. Debromination behavior
Fig. 2 shows the debromination as a function oftemperature in 0.5 M NaOH/EG solution. The degree ofdebromination increased with increasing temperature.

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6th International Symposium on Feedstock Recycling of Polymeric Materials

When a flask was used, the debromination reached 43%,
when a ball mill was used, it exceeded 98% at 190 °C
after 24 hours. It was found that the ball mill was more
effective for the debromoination than the flask.

(ks: rate constant per unit area, S: surface area, c:proportional constant, r0: initial radius of the particle)
At last, considering the equations above and the massbalance of the solids, Eq. (4) is obtained.

㻝㻜㻜㻝㻥㻜㽅㻯㻝㻣㻜㽅㻯㻰㼑㼎㼞㼛㼙㼕㼚㼍㼠㼕㼛㼚㻌㼇㻑㼉㻤㻜㻝㻡㻜㽅㻯㻝㻥㻜㽅㻯㻌㻔㼒㼘㼍㼟㼗㻕㻢㻜㻠㻜㻞㻜㻜㻜㻢㻝㻞㼀㼕㼙㼑㻌㼇㼔㼉㻝㻤㻞㻠Figure 2. The ball mill assisted debromination as functionof temperature in 0.5 M NaOH/EG solution
Fig. 3 shows the debromination as a function of theNaOH concentration at 190 °C. The degree ofdebromination increased with increasing NaOH
concentration and the maximum debromination wasreached at 0.5 M NaOH independent from the reactor.
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㻰㼑㼎㼞㼛㼙㼕㼚㼍㼠㼕㼛㼚㻌㼇㻑㼉㻤㻜(4)
31(1 + cX)
ksCA)
ln= Kt (K =rȨ
1+c(1 – X)0(r: radius of the particle, U: density)
Fig. 4 shows the debromination rate as a function oftemperature in 0.5 M NaOH/EG solution. In case of using
the flask, the debromination followed an apparent firstorder reaction. However, the debromination rate
decreased after about 6 h. In opposite, the plot for theball mill increased linear with the temperature. It can beassumed that when a flask was used, in a first stepdebromination occurred at the surface of the sample by
the contact of DDE with the OH- in the solution. After theend of the reaction at the surface, OH- penetrated theparticle and reacted with deeper located DDE. As a result,the debromination rate decreased during the reaction.
When the ball mill was used, the debromination occurred
first at the surface. However, before the reaction at thesurface finished, unreacted surface area was created bygrinding. Accordingly, the reaction always proceeded at
the surface of the sample and the debromination rate
was constant during reaction.

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㻜

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Figure 3. The ball mill assisted debromination as afunction of NaOH concentration at 190 °C
3.2. Reaction kineticsThe reaction kinetics were analyzed, using theexperimental data shown in Figure 2. When a flask wasused, the experimental data shown in Fig. 2 were fitted toEq. (1).
-ln(1-X) = kt
(1)
(X: debromination, k: rate constant, t: time)
In case of using the ball mill, a modified shrinking-coremodel for debromination was assumed. The reaction rate
is proportional to the concentrations of Br in DDE anddissolved OH- as follows:(2)
v = kCBrCOH(v: debromination rate, C: concentration)
Assuming that the rise in the affected reaction surface
area of HIPS/DDE by ball milling is proportional to theincrease in the debromination rate, S is proportional to (1- X)(1 + cX) as follows:v = ksSCOH = 4πr02ks(1 –X)(1 + cX)COH(3)

interiores libro.indd 144

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㻜㻜㻢

㻝㻞㼀㼕㼙㼑㻌㼇㼔㼉㻝㻤㻞㻠

Figure 4. The ball mill assisted debromination rate as afunction of temperature in 0.5 M NaOH/EG solution

4. Conclusions
The debromination proceeded most efficiently in 0.5 M
NaOH/EG solution at 190 °C. When a flask was used
under these conditions, the degree of the debromination
was 43%. However when the ball mill was used, thedebromination reached 98%. The debromination in aflask followed an apparent first-order reaction and thedebromination rate decrease during the reaction
indicating that in a first step the debromination occurs at
the surface of the sample and aftrer that, the reaction
proceeded inside the sample at a lower speed. The
debromination by the ball mill was represented by amodified shrinking-core model and proceeded in one
stage, indicating that the reaction proceeded always at
the surface of the HIPS/DDE sample, since the ball
milling provided continuously new surface area.

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