PARTⅢ MECHANICAL RECYCLINGRESEARCH ON SEPARATING BROMINATED FLAME
RETARDANTS FROM WASTE TV HOUSING PLASTIC
Peng Shaohong1, Chen Lieqiang 2, Li Liubin2 , Xie Mingquan2, Huang Huajie2, Liu
Xiaodan212

College of Chemistry and Life Science, Maoming University, Maoming 52500, China;
The Key Laboratory of Enhanced Heat Transfer and Energy Conservation, Ministry ofEducation, South China University of Technology , Guangzhou 510640, China
E-mail: sh-peng@tom.com

Abstract: The thermal stability and degradation kinetic of TV housing plastic and brominatedflame retardants were studied by the means of thermogravimetry (TG) instruments, the effectsof treatment temperature on the removal rate of Br were investigated by a tube furance reactor
under isothermal and vacuum. The results show that the weight loss of TV housing plastic
was divided into two different stages, thermal degradation of brominated flame retardants
mainly occurred at 290℃~ 350℃, the HIPS resin mainly occurred at 350℃~ 455℃. Over
90% of Br can be released from the TV housing plastic if the treatment temperature exceeds
280℃.
Keywords: TV set housing; high impact polystyrene; Brominated flame retardants
1. Introduction
TV housing is generally manufactured from high impact polystyrene(HIPS) orpolystyrene(PS), styrene polymers is belong to flammable material type and easily cause afire accident, Brominated flame retardants (Br-FR) such as Decabromodiphenylether(Deca-BDE), tetrabromo bisphenol-A or polybrominated epoxy resins in combination
with Sb2O3 synergist are used in HIPS to prevent combustion during accidental fires[1,2]. In
recent years there has been a growing concern in environmental pollution from waste electricand electronic equipment (WEEE), recycling of plastics from WEEE is an important subject
not only from the point of waste treatment but also from the aspect of recovering valuableorganic materials, so far, TV housing plastic was mainly recycled by the physical process.
Unfortunately, the recycled plastics from waste TV have been banned to used for
manufacturing new electrical equipments against duo to the presence of polybrominted
diphenyl ether(PBDEs)[3], though the conversion of waste plastics into chemical fuel orfeedstock is a good alternate technique for physical process, but material recycling offlame-retarded plastic wastes may result in the formation of toxic or harmful organobromine- 165 -The 5th ISFR (October 11-14, 2009, Chengdu, China)
compounds[4,5], which will influenced the further utilization of pyrolytic product. therefore,
so it is very necessary to separate brominated flame retardants from TV housing plastic before
recycling.
In this paper, the thermal stability of waste TV housing plastic was investigated, and thefeasibility of separating Br from TV housing plastic under vacuum and isothermal is also
discussed.
2. Experimental
2.1 Materials
The waste TV housing palstic used in this work was supplied by GuangDong ShuYe
Environmental Technology Co.LTD, it was identified that housing plastic was manufactured
from flame retarded HIPS resin containing 6.15 wt% of PBDEs (4%Deca-BDE, 0.18%
nonabromodiphenyl ether, 1.97% octabromodiphenyl ether)and 2.05wt% of Sb2O3. The
plastic sample was necessary to be crumbed into <0.85mm powders before used for thepresent experiments. Deca-BDE, commercial grade, was bought from Sino-Brom Compounds
Co.,Ltd.
2.2 Apparatus and measurement procedure
Thermogravimetric(TG) experiments were carried out on a NETZSCH TG thermal
system TG/DSC 409 in nitrogen atmosphere under a gas flow of 50 cm3／min at a heating
rate of 10℃／min from 30 to 800℃．Isothermal Thermogravimetric experiments wereperformed on the same TG instruments, temperature program was as fallow: heat temperature
to 280 at 10℃／min and then held for 60 min with a N2 carrier gas flow 50 cm3/min.
Thermal treatment experiments under isothermal and vacuum condition were performed
in a quartz tube reactor, approximately 0.5g of the sample was used for each experiment andheated up to the set temperature at heating rate of 10℃/min, then held for 60 minutes. Thepressure of reaction system was kept lower 5 kPa by a vacuum pump. The thermal gradationof the samples was studied by IR spectrum, PBDEs in the samples was separated by soxhlet’s
extraction with the mixture of toluene and isopropanol, then PBDEs extracted wasdetermined by HPLC.
3. Results and discussion
3.1 Thermal stability of waste TV set housing plastic
The TG curve of waste TV housing plastic in nitrogen is shown in Fig.1,which is very
similar to the TG curves obtained by E.Jakab[6] and Nona[7] with the mixture samples
prepared from HIPS, Deca-BDE and Sb2O3. It could be seen in Fig.2 that the temperature
range of weight loss was divided into two obvious different stages. The first stage is from290℃ to 350℃, which the weight loss is about 25%,The second stage is from 350℃ to- 166 -PARTⅢ MECHANICAL RECYCLING
455℃, which the weight loss reached 65%. The weight loss of the sample mainly occurredin the second stage, and the weight loss rate in the second stage was also faster than the firststage. The TG experimental results indicates that the TV housing plastic may contain two
type of compounds with different thermal stability at least.

Fig. 1 TG and DTG curves of waste TV set housing material in N2(10℃/min)
TV housing used for this present work was manufactured from HIPS, which is generallycomposed of polybutadiene (PB phase) and polystyrene (PS phase), However, Fig.2 showsthat the TG curve of pure HIPS resin only display a single stage, this proved that two weightloss stages of TV housing plastic should not result from the different thermal stability of twophases of HIPS. The activation energies and reaction orders of the degradation reactions in thetwo stages can be calculated according to Friedman method by determining the TG curves
under different heating rates, the calculating results listed in Tab. 1.
Tab.1 Kinetic parameters of thermal degradation of TV housing plastic
Reactionorderntemperature /K

Linear equation

Average activationenergy E/(kJ·mol-1)

290～350y=-18.03x+26.29

149.870.11

350～455y=-26.45x+35.25219.98

1.2

The kinetic study results in Tab.1 show that the activation energy and reaction order in
two stages are different, this clearly indicates that the two weight loss stages are respectively
controlled by the different chemical reaction mechanism. The activation energy in the firststage is significantly smaller than the second stage, thus it is deduced that the activationenergy in the first stage may reflect the thermal degradation of lower thermostability
compounds, and activation energy in the second stage may reflect higher thermostability
compounds. It is known that C-C and C-H bond of HIPS are more stable than C-Br bond ofbrominated flame retardants, the experimental results from Nona[7] also showed thatDeca-BDE can start to decompose at about 300 ℃ with the presence of Sb2O3.Therefore, it- 167 -The 5th ISFR (October 11-14, 2009, Chengdu, China)
can be concluded that weight loss in the first stage is mainly related to the evaporation ofadditives and flame retardants, and the weight loss in the second stage is mainly related to thedegradation of more stable HIPS, the activation energy number of the later is also close to theactivation energy of HIPS degradation in literatures published[8].

Fig. 2 TG curves of Deca-BDE and HIPS in N2 (10℃/min)Fig. 2. shows the intial weight loss temperature of Deca-BDE is lower about 50℃ thanpure HIPS, but the initial weight loss temperature of pure HIPS is higher than 350℃, whereas
HIPS in the TV housing has started to degrade at below 350℃. there may be two reasons, thefirst is that the aging of HIPS reduced the thermal stability due to the long term service of TV
set; the second is that the thermal chemical reaction of flame retardants change thedegradation mechanism of HIPS and caused partly degrading of HIPS at a lower temperature.
This shows that the degradation behavior of waste TV housing plastic is very different frompure HIPS resin.
2.2 The weight loss under isothermal conditions
The TG analysis of waste TV housing indicated that the decomposition temperature ofDeca-BDE is lower than HIPS resin, if the thermal treatment temperature is controlled at
below the decomposed temperature of HIPS, it is possible to separate Br from the waste TVhousing plastic. The isothermal TG curves of pure HIPS, Deca-BDE and TV housing plastic
at 280℃ are shown in Fig.3. it could be seen from Fig.3 that the weight loss of the waste TV
housing plastic reached about 14wt%, which obviously exceed about 2.5wt% of weight lossof pure HIPS , and was more closed to weight loss of Deca-BDE . the experimental results
indicate Br-FR containing in TV housing can be prior to degrading of HIPS polymer matrix,
that is to say, under the suitable isothermal condition, Br-FR can be first released from TV
housing plastic, and it can be avoid severly degrading of HIPS at the same time.

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Fig.3 TG curves of virgin HIPS and waste TV housingmaterial under isothermal condition at 280℃
2.3 Separating bromine from TV housing plastic
Polybrominated diphenyl ethers have the characteristics of high boiling point and low
volatility, it is not easy to separate them from the polymer matrix by evaporating underatmospheric pressure, however, the evaporating of PBDEs can be accelerated in a vacuum
condition. The removal rates of PDBEs at different temperature were investigated by a tube
pyrolyzing furnace under vacuum, the experimental results are shown in Fig. 4.

Fig.4 Removal rate of PBDEs in the housing plastic
under isothermal condition and vacuum
The results show that both the releasing rate of PBDEs increased with elevating of thethermal treatment temperature, over 90wt% of PBDEs can be removed if the treatment
temperature exceeds 280℃, but the weight loss of the samples will obviously increased when
the thermal treatment temperature was higher than 300℃, Therefore the separatingtemperature should be controlled below 300℃ to reduce decomposition extent of HIPSmatrix.
3. Conclusion（1）TG curve of the TV housing plastic was divided into two obvious different stages,
the first stage(280℃~ 350℃) reflect the thermal degradation of of the flame retardants and- 169 -The 5th ISFR (October 11-14, 2009, Chengdu, China)
the small part of HIPS resin, which activation energy is about 150kJ/mol; the second stage(350℃~ 450℃) is associated with thermal degradation of HIPS , which activation energy isabout 210kJ/mol.
（2）Over 90% of decabromodiphenyl ether can be firstly released from the waste TV
housing plastic under isothermal (> 280℃) and vacuum(<5kPa), but HIPS matrix will suffer
significant degradation if thermal treatment temperature is beyond 300℃.
Acknowledgements
The project was supported by Guangdong-Hongkong Technology Cooperation Funding(Project No. 2007A010701007) and Science and Technology Reserch Project of Guangdong
province (Project No. 20062050188).
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