Polymer Degradation and Stability 91 (2006) 3274e3280www.elsevier.com/locate/polydegstab

Studies of the effects of copper, copper(II) oxideand copper(II) chloride on the thermal

degradation of poly(vinyl chloride)

Susan M. Grimes a,*, Huma Lateef a, Ahmad J. Jafari b, Lina Mehta c,1

a Centre for Environmental Control and Waste Management, Imperial College, South Kensington Campus, London SW7 2AZ, UKb Centre for Environmental Research, Brunel University, Uxbridge, Middlesex UB8 3PH, UK

c Institute for the Environment, Brunel University, Uxbridge, Middlesex UB8 3PH, UK

Received 18 August 2004; received in revised form 12 June 2006; accepted 25 June 2006

Available online 9 October 2006

Abstract

Investigations of the pyrolysis of poly(vinyl chloride) (PVC) in the presence of copper metal (Cu), copper(II) oxide (CuO) and copper(II)chloride (CuCl2) are of potential importance because of the likelihood of the formation of these copper compounds during the thermal degra-dation of PVC-coated copper wires, a step in the recovery of copper from waste. The presence of Cu, CuO and CuCl2 (i) retards the thermaldegradation of PVC in air and in nitrogen and (ii) decreases the percentages of volatile products produced at both stages of the decomposition.These effects are greatest for PVCeCuO. The presence of copper, CuO or CuCl2 in PVC has a major effect on the nature of the gaseous emis-sions of the thermal decomposition in air and in nitrogen. The concentrations of total chlorine, aliphatic hydrocarbons, aromatic hydrocarbons,chlorinated hydrocarbons and soot particulates are all affected relative to an equivalent amount of PVC. These changes are greatest for thePVCeCuO system for which total chlorine emissions in air and nitrogen are reduced by 40% in air and 20% in nitrogen, benzene emissionsare reduced by greater than 90% in air and nitrogen, other aromatic and chloroaromatic emissions are reduced, and soot particulate emissionsare reduced by more than 50% as the concentrations of aliphatic compounds are increased. These changes are consistent with the presence ofcopper or its compounds permitting more efficient combustion of the carbon content of the PVC and particularly in the case of PVCeCuO withthe removal of chlorine during pyrolysis in the inorganic phase.� 2006 Elsevier Ltd. All rights reserved.

Keywords: PVC; PVCeCuO; PVCeCu; PVC-coated cable; PVC degradation; Soot reduction

1. Introduction

Incineration of municipal refuse has become an alternativeto the practice of disposing of refuse in landfill sites. Thereis some concern, however, that incineration of waste pro-duces pollutants, which may cause more harm to the envi-ronment than other forms of waste disposal. Combustionprocesses in general, and particularly uncontrolled

* Corresponding author. Tel.: þ44 20 7594 5966; fax: þ44 20 7594 1511.

E-mail address: s.grimes@imperial.ac.uk (S.M. Grimes).1 This author contributed partly to this work.

0141-3910/$ - see front matter � 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.polymdegradstab.2006.06.010

incineration of refuse, emit potentially hazardous substances,for example, soot particulates, benzene, dioxins, acidic gases,heavy metal containing particulates, and aliphatic and aro-matic compounds, all of which can cause damage to the en-vironment and health [1e7].

PVC has played a key role in the development of theplastics industry over the past 40 years and continues to bea polymer of major importance thus leading to the need forend-of-life disposal in industrial and municipal waste streams.In Western Europe, for example, the quantity of PVC enteringthe municipal waste stream has been estimated at about 2 mil-lion tonnes per year [8]. PVC dominates the chlorinated plas-tics in production and use with a major application in PVC

3275S.M. Grimes et al. / Polymer Degradation and Stability 91 (2006) 3274e3280

insulation of copper wires in electrical installations. Since in-cineration of PVC-coated cable is often used as a step in therecovery of copper, concern has been expressed about the na-ture of the emitted particulate, gaseous and volatile species.When PVC is incinerated it generates a considerable amountof smoke [9,10] as well as potentially harmful volatile organiccompounds.

The thermal degradation of PVC with the degradationproducts identified [10e12] and the effects on the kineticsor mechanism of the decomposition arising from the pres-ence of inorganic pyrolysis catalysts such as ZnCl2 [12],CdCl2 [13], TiO2 [14], Cu2O [15] and a mixture of Cu2Oand MoO3 [16] have been described. None of these publica-tions, however, contain information on the effects of the in-organic catalysts on the products of the thermal degradationexcept for particulates in the cases of Cu2O and the Cu2O/MoO3 mixture, which were studied as potential fireretardants.

The products of the thermal degradation of PVC in vac-uum at temperatures up to 500 �C and the material balanceshave been reported, for example by McNeill et al. [10].Hydrogen chloride is the major product of the decomposition(53% of the polymer) followed by a tar fraction (24%), a charfraction (9.5%), a liquid fraction (7%) and a gas fraction(6.6%). The authors also reported that about 10% of chlorineremained trapped in the polymer and was not removed untilhigher temperatures were reached. Quantitative analysisshowed that the liquid fraction contained benzene (80%), tol-uene (1.8%), o-xylene (1.3%), ethylbenzene (1%) and 1,2-methylethyl benzene (1%). Chloro hydrocarbons (mainlychlorinated alkenes and aromatics) that are of particular envi-ronmental concern account for only 1.75% of the liquidfraction.

PVC undergoes thermal degradation in two stages [10] ini-tially by dehydrochlorination. The dehydrochlorination pro-ceeds along the polymer chain resulting in the formation ofconjugated polyenes, which are responsible for the colour ofthe degraded polymer [17]. In the first stage, at 200e360 �C,hydrogen chloride is evolved and about 15% of the polyeneis converted to benzene. The formation of benzene in thistemperature range results from an intra-molecular processinvolving cyclisation of polyene segments [18], where intra-molecular condensation reactions lead to the production ofcyclohexene and cyclohexadiene both of which, at this stage,remain embedded in the aliphatic matrix. Alkyl, aromaticand condensed ring aromatic compounds (naphthalene,indene, indane, etc.) are formed in the second stage of the de-composition at 360e500 �C and very little hydrogen chlorideand benzene are formed in this temperature range. During thisstage, the polymeric network formed by polyene condensationbreaks down and permits aromatisation of cyclohexene andcyclohexadiene rings.

We now report on an investigation on the products of thethermal degradation of PVC in the presence of copper andsome of its compounds to determine the effects of the presenceof copper species on the nature and quantities of the individualproducts.

2. Experimental

2.1. Materials

PVC of d¼ 1.4 g/cm3 and inherent viscosity of 0.68 cp wassupplied by Aldrich Chemicals Co. Copper(II) chloride andcopper powder, and copper oxide of AR grade were obtainedfrom BDH Ltd. and Fisons Ltd., respectively.

The weight:weight ratio PVC:X (where X¼ Cu, CuCl2 orCuO) used throughout this work was 9:1. The experimentalweight losses ( y) from the mixtures were converted to the ex-trapolated value 10y/9 for comparison with the results ob-tained for the same weight of PVC alone.

2.2. Thermogravimetry

Thermal stability was determined by thermogravimetricanalysis using a Stanton Redcroft STA 780 simultaneous ther-mal analyser. The sample was heated in an aluminium cruciblein the micro-furnace with temperature programming from 20to 590 �C at a heating rate of 10 �C/min in air or nitrogen flow-ing at 35 ml/min.

2.3. Ion chromatography

A Dionex ion chromatograph model 2100 I with a conduc-tivity detector was used for the analysis of chloride ion (Cl�)and hydrogen chloride (HCl). A column HP1C-AS4A andguard AG4A were used with 0.025 N sulfuric acid as suppres-sor at a flow rate of 2.5 cm3/min. The eluent used was0.00075 M sodium bicarbonateþ 0.0022 M sodium carbonatesolution. Samples were placed as a thin layer in a silica com-bustion boat and fed to an electric furnace via a gate. The for-mation of chloride ion and hydrogen chloride during pyrolysisof the sample was studied under conditions similar to thoseused for thermogravimetry. The gases were trapped by draw-ing them through a bubbler containing 30 cm3 of the eluent so-lution, and then through a fritted bubbler that contained thesame solution. The flow rate was 0.75 l/min. All sampleswere filtered through acid-free filter paper to separate particu-lates and oily compounds. Care was taken to ensure that theanalyte samples did not contain interfering anions.

2.4. Gas chromatography

A 1 m packed column containing 60e80 mesh Chromosorb102 and flame ionisation detector at 200 �C was used in a PyeUnicam PU 4500 Gas Chromatograph. The temperature washeld for 4 min at 50 �C and then increased at the rate of16 �C/min to 200 �C, where the temperature was held for10 min. The carrier gas was nitrogen with a head pressure of0.55 kg/cm2. The sampling of short chain hydrocarbons wasachieved by passing the flue gas stream through a coolingtrap and a 37 mm fibre glass filter before collection in a Tedlarsampling bag using a small peristaltic pump. The samplingflow rate was constant at 30 cm3/min.

3276 S.M. Grimes et al. / Polymer Degradation and Stability 91 (2006) 3274e3280

2.5. Sampling and analysis of aromatic hydrocarbonsand chlorinated aromatics

A Supelco Carbotrap 300 with a gas flow rate of 35 cm3/min for 12 min was used in the determination of aromaticand chlorinated aromatic hydrocarbons. The multi-bed Carbo-trap contained the absorbents Carbotrap C, Carbotrap B andCarbosieve S-III. Each Carbotrap was conditioned beforeuse for 30 min at 350 �C with a helium flow rate of 3 cm3/min. The determination of 2,3,7,8-tetrachlorodibenzo-p-dioxin(TCDD) was achieved using a conditioned Supelco Carbotrap150 with a sampling flow rate of 50 cm3/min for 15 min. TheSupelco Carbotrap was linked to a high resolution gas chro-matograph coupled with a mass spectrometer (GCeMS) togive total analysis and a thermal desorption [19] direct recov-ery method to introduce analytes to the gas chromatograph(GC). Supelco fused silica capillary columns of30 m� 0.25 mm� 2.5 mm and 60 m� 0.25 mm� 0.2 mm, re-spectively, were used for the analysis of aromatic and chlori-nated aromatic hydrocarbons, and for TCDD respectively.The temperature programming of the GC for the analysis ofaromatic and chlorinated aromatic hydrocarbons was startedat 30 �C for 5 min, raised at the rate of 5 �C/min to 200 �Cand held there for 10 min. For TCDD analysis, the temperatureprogramming was 200 �C for 1 min rising to 260 �C at 8 �C/min and holding the temperature at 260 �C for 20 min. Themass spectrometer was used as the detector.

0

20

40

60

80

100

120

0 100 200 300 400 500 600 700Temperature (Degree Centigrade)

Weig

ht (%

)

PVCPVC+Copper(II)Oxide

Fig. 1. Thermogravimetric analysis in air of PVC and PVC in the presence of

CuO.

2.6. Control and analysis of particulate emission

A combustion chamber consisting of a furnace and a flaskmade of silica was placed in an oven equipped with an appro-priate thermocouple and a temperature control system. Thetemperature was preset to 600 �C or 800 �C. The samplewas placed in a porcelain crucible and introduced into the fur-nace. A 37 mm fibre glass filter or cellulose filter paper wasused for the collection of soot particulates drawn onto the filterat a flow rate of 1 l/min by a small vacuum pump. The filterpaper was left in an oven at 110 �C for 24 h before and aftercollection of particulates. The weight of particulate matterwas determined and optical density of the soot was measuredin a Dunedin photo-electric cell.

3. Results

A comparative study of the thermal stability of samples ofPVC alone and of PVC containing copper or the copper com-pounds, copper oxide (CuO) and copper chloride (CuCl2), inan atmosphere of air and nitrogen was made by thermogravi-metric analysis. All of the thermograms show a two-stageweight loss. The weight loss curves for PVC and PVCeCuOin air is shown in Fig. 1 and that for PVC and PVCeCuO innitrogen in Fig. 2. In both air and nitrogen atmosphere, decom-position of the PVC in the presence of copper and copper com-pounds occurs at higher temperatures for both stages of thethermal degradation. In an atmosphere of air, the loss ofweight for PVC, PVCeCu, PVCeCuO, and PVCeCuCl2 is59%, 55%, 39% and 53.5% in the first step and 37%, 24%,44% and 30% in the second step, respectively. The weight

0

20

40

60

80

100

120

0 100 200 300 400 500 600 700Temperature (Degree Centigrade)

Weig

ht (%

)

PVCPVC+Copper(II)Oxide

Fig. 2. Thermogravimetric analysis in nitrogen of PVC and PVC in the pres-

ence of CuO.

3277S.M. Grimes et al. / Polymer Degradation and Stability 91 (2006) 3274e3280

Table 1

Concentration of total chlorine as a percentage of the emissions found for PVC from the pyrolysis of PVC and PVC in the presence of copper and its derivatives in

air and nitrogen after 15 min at 600 �C

Atmosphere Chlorine concentration

in ppm (%)

PVC PVCeCu PVCeCuO PVCeCuCl2

Air 10 950 (100%) 8250 (75%) 6500 (59%) 11 825 (108%)

Nitrogen 10 600 (100%) 9045 (85%) 8500 (80%) 9900 (93%)

loss in an atmosphere of nitrogen is 58%, 53%, 52.5% and49.5% in the first step, and 27%, 14%, 14.5% and 14% inthe second step for PVC, PVCeCu, PVCeCuO and PVCeCuCl2, respectively. These results show that Cu, CuO andCuCl2 retard thermal degradation of PVC.

The effects of copper and the copper compounds on thegaseous emissions from the thermal degradation of PVChave been studied at temperatures up to 600 �C in both airand nitrogen. The total concentration of chlorine (HClþCl2as ppm Cl) in the gaseous emissions from the samples, ex-pressed as a percentage of the emissions found for PVC at600 �C, is given in Table 1.

The levels of chlorine in the gaseous emissions are alsofound to depend upon the PVC:Cu and PVCeCuO ratio.The total percentages of Cl emitted relative to PVC in thePVCeCuO system for w:w ratios 1:0.1, 1:1 and 1:3 are, forexample, found to be 59.4, 9.6 and 6.2%, respectively.

Analyses of the short chain linear hydrocarbons producedduring the pyrolysis of the samples in an atmosphere of airand nitrogen were carried out by gas chromatography, andthe results are shown in Figs. 3 and 4. The only chlorinated

0

5000

10000

15000

20000

25000

30000

PVC

PVC-Cu

PVC-CuO

PVC-CuCl2

Sample

Co

ncen

tratio

n (p

pm

)

MethaneEthylene

EthanePropylene

Propane1-Butene

Fig. 3. Concentration (ppm) of aliphatic hydrocarbons produced from the py-

rolysis of PVC and PVC in the presence of copper, copper oxide and copper

chloride in air.

aliphatic compound detected in the thermal degradation is tet-rachloroethane, which consists of 1 and 1.8 ppm of the gas-eous products for PVC in air and nitrogen, respectively.

The effect of different concentrations of copper oxide onthe evolution of the hydrocarbons during the pyrolysis ofPVCeCuO samples was studied, and the results are shownin Fig. 5.

The concentrations of aromatic hydrocarbons and chlori-nated aromatic compounds emitted during the thermolysis ofPVC and PVC containing copper or copper compound sam-ples in air and nitrogen at 300 and 600 �C were determinedby GCeMS, and the results are depicted in Tables 2e5.

The amount of aromatic compounds produced from the py-rolysis of PVC and PVCeCuO at different concentrations ofCuO was also determined, and the results are summarized inTable 6.

The amount of soot produced in the combustion of PVCand PVCeCuO at different concentrations of CuO, studied

0

5000

10000

15000

20000

25000

30000

PVC

PVC-Cu

PVC-CuO

PVC-CuCl2

Sample

Co

ncen

tratio

n (p

pm

)

MethaneEthylene

EthanePropylene

Propane1-Butene

Fig. 4. Concentration (ppm) of aliphatic hydrocarbons produced from the py-

rolysis of PVC and PVC in the presence of copper, copper oxide and copper

chloride in nitrogen.

3278 S.M. Grimes et al. / Polymer Degradation and Stability 91 (2006) 3274e3280

at 600 and 800 �C, was determined by optical density mea-surements, and the results are presented in Table 7.

4. Discussion

In the presence of copper oxide, the data in Figs. 1 and 2show that the thermal degradation of PVC is retarded in that

MethaneEthylene

EthanePropylene

Propane1-Butene

0

5000

10000

15000

20000

25000

30000

PVC

PVC-(2%)CuO

PVC-(5%)CuO

PVC-(10%)CuO

Sample

Co

ncen

tratio

n (p

pm

)

Fig. 5. Concentration (ppm) of short chain hydrocarbons from the pyrolysis of

PVC and PVCeCuO at different concentrations (wt%).

Table 2

Weight (mg) of aromatic compounds produced from the pyrolysis of PVC and

PVC in the presence of copper and its derivatives at 300 �C in air

Product Weight (mg)

PVC PVCeCu PVCeCuO PVCeCuCl2

Benzene 440 410 37 40

Toluene 11 4.1 2.1 3.2

o-Xylene 0 0 0 0

Naphthalene 0 0 0 0

Chlorobenzene 2 2.1 0.003 0.003

Ethylbenzene 1 0 0 0

p-Dichlorobenzene 0 0.008 0.001 0.001

o-Dichlorobenzene 0.07 0.012 0.0002 0.0002

1,2,4-Trichlorobenzene 0.09 0 0 0

1,2,4,5-Tetrachlorobenzene 0.03 0.045 0.0005 0.0005

Pentachlorobenzene 0.01 0.023 0 0

Hexachlorobenzene 0.03 0.08 0 0

2,3,7,8-Tetrachloro-

dibenzo-p-dioxin

15 ng 46 ng 32 ng 32 ng

it occurs at higher temperatures for both stages of PVC de-composition and produces smaller quantities of gaseousemissions.

The presence of copper and its compounds also has a majorinfluence on the nature of the products of the pyrolysis ofPVC. The concentrations of total chlorine, short chain ali-phatic hydrocarbons, aromatic hydrocarbons, chlorinated aro-matic compounds and soot particles in the decompositionproducts are affected in the thermal degradation of PVC inboth air and nitrogen. These changes are largest for thePVCeCuO system and for this system the nature of thechanges is also shown to be dependent on the PVC:CuOw:w ratio.

The total concentration of chlorine (mainly HCl) in the gas-eous emissions from the decomposition of PVC is reduced rel-ative to that from the same amount of PVC. The reduction inthe presence of copper metal is 25% in air, and 15% in nitro-gen, and in the presence of copper oxide is 40% in air, and20% in nitrogen. The reduction in the chlorine content ofthe gaseous products must result from the chlorine reacting

Table 3

Weight (mg) of aromatic compounds produced from the pyrolysis of PVC and

PVC in the presence of copper and its derivatives at 600 �C in air

Product Weight (mg)

PVC PVCeCu PVCeCuO PVCeCuCl2

Benzene 500 410 45 80

Toluene 68 54 2 33

o-Xylene 0.9 0.8 0.2 0.2

Naphthalene 3.65 2.9 0.255 0.42

Chlorobenzene 1.22 1.27 0.7 0.9

Ethylbenzene 4.05 4 2.8 3.1

p-Dichlorobenzene 0.35 0.5 0.08 0.12

o-Dichlorobenzene 8.56 9.1 1.8 2.3

1,2,4-Trichlorobenzene 5 6.1 2 2.5

1,2,4,5-Tetrachlorobenzene 6.2 7.8 2.2 3.1

Pentachlorobenzene 3.8 4.7 1.1 1.6

Hexachlorobenzene 4 5.3 1.4 1.9

2,3,7,8-Tetrachloro-

dibenzo-p-dioxin

8 ng 29 ng 16 ng 23 ng

Table 4

Weight (mg) of aromatic compounds produced from the pyrolysis of PVC and

PVC in the presence of copper and its derivatives at 300 �C in nitrogen

Product Weight (mg)

PVC PVCeCu PVCeCuO PVCeCuCl2

Benzene 480 445 40 44

Toluene 30 11 6 8.2

o-Xylene 0 0 0 0

Naphthalene 0 0 0 0

Chlorobenzene 3 3.3 0.007 0.01

Ethylbenzene 1.2 0 0 0

p-Dichlorobenzene 0 0.012 0.001 0.005

o-Dichlorobenzene 0.09 0.015 0.0003 0.0008

1,2,4-Trichlorobenzene 0.1 0 0 0

1,2,4,5-Tetrachlorobenzene 0.045 0.06 0.0008 0.001

Pentachlorobenzene 0.02 0.028 0 0

Hexachlorobenzene 0.04 0.1 0 0

2,3,7,8-Tetrachloro-

dibenzo-p-dioxin

0 0 0 0

3279S.M. Grimes et al. / Polymer Degradation and Stability 91 (2006) 3274e3280

with the inorganic phase. In the case of PVCeCuCl2 system,the copper chloride does not show a major effect because cop-per chloride would not be able to take up any extra chlorine bychemical reaction, and in air a slight increase in the chlorineemissions is found because of the extra chlorine available inthe CuCl2.

The amounts of simple aliphatic compounds (methane, eth-ylene, ethane, propylene, propane, 1-butene) produced in thethermal degradation of PVC are increased in the presence ofcopper and its compounds relative to those produced by anequivalent amount of PVC in air. This suggests a more effi-cient combustion of the carbon content of the PVC in the pres-ence of the additives. Similar results are obtained for thedecomposition in nitrogen except for the PVCeCu system,where only the levels of ethane, propane and 1-butene are in-creased. The only chlorinated aliphatic compound detected inthe thermal degradation is tetrachloroethane, which consists of1 and 1.8 ppm of the gaseous products for PVC in air and ni-trogen, respectively. This rose to 2 ppm for the PVCeCuO andPVCeCuCl2 systems in air and to 2.2, 3.8 and 3.8 ppm,

Table 5

Weight (mg) of aromatic compounds produced from the pyrolysis of PVC and

PVC in the presence of copper and its derivatives at 600 �C in nitrogen

Product Weight (mg)

PVC PVCeCu PVCeCuO PVCeCuCl2

Benzene 670 530 52 101

Toluene 158 121 3 75

o-Xylene 1.17 1.05 0.22 0.4

Naphthalene 4.7 3.75 0.3 0.53

Chlorobenzene 1.65 1.6 0.79 1.134

Ethylbenzene 5.3 5 3.1 3.9

p-Dichlorobenzene 0.45 0.5 0.085 0.15

o-Dichlorobenzene 11 11.7 1.95 2.8

1,2,4-Trichlorobenzene 6.5 7.6 2.15 3.1

1,2,4,5-Tetrachlorobenzene 8.2 7.5 2.35 3.15

Pentachlorobenzene 5 6.1 1.2 1.95

Hexachlorobenzene 5.25 6.6 1.57 2.39

2,3,7,8-Tetrachloro-

dibenzo-p-dioxin

0 0 5 ng 0

Table 6

Weight (mg) of aromatic compounds produced from the pyrolysis of PVC and

PVCeCuO at different concentrations (wt%) at 600 �C in nitrogen

Product Weight (mg)

PVC 5% CuO 10% CuO 20% CuO

Benzene 500 59 45 49

Toluene 68 24 20 18

o-Xylene 0.9 0.38 0.2 0.19

Naphthalene 3.65 0.36 2.55 0.25

Chlorobenzene 1.22 0.71 0.7 0.69

Ethylbenzene 4.05 2.8 2.8 2.8

p-Dichlorobenzene 0.35 0.1 0.08 0.08

o-Dichlorobenzene 8.56 1.9 1.8 1.7

1,2,4-Trichlorobenzene 5 2.7 2 1.97

1,2,4,5-Tetrachlorobenzene 6.2 2.35 2.2 2.1

Pentachlorobenzene 3.8 1.1 1.1 1.0

Hexachlorobenzene 4 1.5 1.4 1.25

2,3,7,8-Tetrachloro-

dibenzo-p-dioxin

8 ng 15.5 ng 16 ng 17 ng

respectively, for the PVCeCu, PVCeCuO and PVCeCuCl2system in nitrogen, at a pyrolysis temperature of 600 �C.

The presence of CuO and CuCl2 in PVC has a major effecton the concentration of the aromatic products in the thermaldegradation of PVC in air and nitrogen at both 300 �C and600 �C. The presence of CuO in particular reduces the amountof benzene to less than one-tenth of the concentration pro-duced by an equivalent amount of PVC. Large reductionsare also found in toluene, o-xylene and naphthalene emissionsin the PVCeCuO and PVCeCuCl2 systems. The presence ofcopper metal in PVC does reduce the amount of aromatic hy-drocarbons but to a lesser extent. In general, for the systemscontaining CuO and CuCl2 there is also reduction in the con-centration of chlorinated aromatics in the gaseous products,although there is evidence of an increase in the low levelsof 2,3,7,8-tetrachloro-dibenzo-p-dioxin formed particularlyin air.

The increase in concentration of aliphatic hydrocarbonscoupled with decrease in aromatic hydrocarbons found inthis work is mirrored by a decrease of >50% in the amountof soot produced in the combustion processes, particularly inPVCeCuO system. These results all suggest a more efficientcombustion of the carbon content of the PVC.

5. Conclusions

The results of this study show that the thermal degradationof PVC in the presence of copper or its compounds and partic-ularly of copper(II) oxide occurs at higher temperatures withmajor changes in the concentrations of the components ofthe gaseous products. These changes result from the abilityof copper compounds to cause cross linking of the polymerand copper oxide compounds produce a relatively higher de-gree of cross linking. Further, this cross linking is well knownto decrease the yields of aromatic hydrocarbons, such as ben-zene and to increase the yields of aliphatics at very high tem-peratures [20]. For the PVCeCuO system for example, totalchlorine emissions are reduced by 40% in air and 20% in ni-trogen, benzene emissions are reduced by greater than 90% inair and nitrogen, other aromatic and chloroaromatic emissionsare reduced, and soot particulate emissions are reduced bymore than 50% as the concentrations of aliphatic compoundsare increased. These changes are consistent with the presenceof copper or its compounds permitting more efficient combus-tion of the carbon content of the PVC and particularly in the

Table 7

Weight and optical density of soot produced from combustion of PVC and

PVCeCuO at 600 and 800 �C

Sample 600 �C 800 �C

Weight

(mg)

Optical

density

Weight

(mg)

Optical

density

PVC 16 3.7 7 1.2

PVCe(2%) CuO 5.3 1.6 3.3 0.5

PVCe(5%) CuO 5 1.6 3.2 0.5

PVCe(10%) CuO 5.1 1.5 3.2 0.5

3280 S.M. Grimes et al. / Polymer Degradation and Stability 91 (2006) 3274e3280

case of PVCeCuO with the removal of chlorine during pyrol-ysis in the inorganic phase.

Acknowledgements

A.J.J. is grateful to the Iranian Ministry of Health and Med-ical Education for a research support grant.

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