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Waste Management & Research
2015, Vol. 33(7) 630 –643
© The Author(s) 2015
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DOI: 10.1177/0734242X15590651
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Scope
Polyvinylchloride (PVC) is widely used as a result of its low pro-
duction cost, wide workability, variety in use, and excellent elec-
tric and fire performance properties (Cullis and Hirschler, 1981;
Theuvenet et al., 1994). After polyethylene (PE) and polypropyl-
ene (PP) it is the third largest-selling commodity plastic and a
material of choice for construction, healthcare, transport, agricul-
ture, information technology (IT), and textiles (Buekens and Cen,
2011). Products made of PVC are varied and ubiquitous, such as
building materials, medical instruments, vehicle parts, plastic film,
cable sheathing and packaging. Yet, the potential formation of
dioxins has sometimes been regarded as the Achilles’ heel of PVC,
especially during combustion and fires (Costner et al., 1995).
PVC is used in two distinct forms. Unplasticised it is stiff and
hard (rigid PVC or PVC-U). Major applications are extruded
pipes and profiles for the building industry and clear bottles and
thin sheet used for packaging. When the polymer is combined
with liquid plasticiser, the material is softened and referred to as
flexible PVC or PVC-P. It is used in wire and cable insulation,
flexible sheets and films, flooring, roofing, toys, etc.
PVC resins are produced as a white powder, by emulsion or
suspension polymerisation of vinyl chloride monomer (VCM).
Only minor modifications in chemical structure can lead to sig-
nificant changes in its mechanical and electric characteristics.
Stabilisers as well as gliding agents are always added, since pure
PVC-U would thermally decompose at the temperatures used for
processing and moulding (Burgess, 1981). Stabilisers may contain
heavy metals, such as cadmium, lead, tin, or zinc. In the European
Union, following the Voluntary Commitment of Vinyl 2010, cad-
mium has been phased out from 2001, whereas lead will be com-
pletely phased out soon (2015). Presently there is increased focus
on the voluntary recycling of important flows of waste and closing
the PVC-cycle at sustainable cost (Vinyl 2010, 2001).
Additives embrace any substance added to a polymer to
improve its processing and use, including reinforcing materials
(such as glass fibre), carbon black, charges, e.g. precipitated lime-
stone, antistatic agents, and dyes and pigments, such as titanium
dioxide. Additives are added during compounding to achieve
desirable properties and they form a significant part of polymers at
large and of PVC in particular. Several books and documents pro-
vide a comprehensive view of all kind of additives, concentrating
Dioxins and polyvinylchloride in
combustion and fires
Mengmei Zhang, Alfons Buekens, Xuguang Jiang and Xiaodong Li
Abstract
This review on polyvinylchloride (PVC) and dioxins collects, collates, and compares data from selected sources on the formation of
polychlorinated dibenzofurans (PCDFs) and dibenzo-p-dioxins (PCDDs), or in brief dioxins, in combustion and fires. In professional
spheres, the incineration of PVC as part of municipal solid waste is seldom seen as a problem, since deep flue gas cleaning is required
anyhow. Conversely, with its high content of chlorine, PVC is frequently branded as a major chlorine donor and spitefully leads to
substantial formation of dioxins during poorly controlled or uncontrolled combustion and open fires. Numerous still ill-documented
and diverse factors of influence may affect the formation of dioxins during combustion: on the one hand PVC-compounds represent
an array of materials with widely different formulations; on the other hand these may all be exposed to fires of different nature and
consequences. Hence, attention should be paid to PVC with respect to the ignition and development of fires, as well as attenuating the
emission of objectionable compounds, such as carbon monoxide, hydrogen chloride, polycyclic aromatic hydrocarbons, and dioxins.
This review summarises available dioxin emissions data, gathers experimental and simulation studies of fires and combustion tests
involving PVC, and identifies and analyses the effects of several local factors of influence, affecting the formation of dioxins during
PVC combustion.
Keywords
Polyvinylchloride, PVC, uncontrolled combustion, dioxins, emissions, thermal decomposition, additives, flame retardation
State Key Laboratory of Clean Energy Utilization, Zhejiang University,
Zhejiang, China
Corresponding author:
Xiaodong Li, State Key Laboratory of Clean Energy Utilization,
Institute for Thermal Power Engineering, Zhejiang University,
Hangzhou 310027, China.
Email: lixd@zju.edu.cn
590651
WMR0010.1177/0734242X15590651
Waste Management & ResearchZhang et al.
research-article
2015
Review Article
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Zhang et al. 631
on their technical (chemistry/formulation, structure, function, main
applications) and commercial background (Babinsky, 2007; Blass,
1992; Green, 1996; Levchik and Weil, 2005). Additives consider-
ably change the characteristics of PVC, making it a very versatile
and widely used material. Conversely, since there is infinity of for-
mulations possible, it becomes very difficult to define in how far a
given sample of PVC is representative, or not: most additives
indeed influence upon thermal decomposition, charring, ignition
of volatile matter, and fire. Surprisingly few studies state these
essential features of the PVC-compounds tested, such as amount of
fixed carbon subsisting after proximate analysis of the PVC sam-
ples considered. Thermal intumescence, as well as HCl evolution,
is important in retarding PVC fires.
Despite the presence of stabilisers, the thermal decomposition
of PVC starts at a low temperature (<200 °C) and is proceeded by
two successive steps (López et al., 2011; Montaudo and Puglisi,
1991; Urabe and Imasaka, 2000). First dehydrochlorination takes
place all along the macromolecular chain by unzipping of HCl,
leaving a polyene structure formed by a linear sequence of
–CH=CH– units; as soon as hydrogen chloride starts being gen-
erated, also some benzene arises through the intermolecular
cyclisation of polyene radicals formed from direct scission of
these polyene chains. During the second step, the polyene chains
are believed to react through intermolecular reactions and these
cross-linked chains undergo further reactions, to form alkylaro-
matic hydrocarbons and charred residue. The latter acts specifi-
cally on the further formation of combustion by-products, so that
throughout this review the amount of fixed carbon is an impor-
tant, yet rarely available parameter.
Both organic and inorganic chlorine-containing materials,
when combusted incompletely, lead to the formation of dioxins, in
particular in the presence of fly ash or of transition metals as het-
erogeneous catalyst (Olie et al., 1998; Takasuga et al., 2000). PVC
accounts for a considerable proportion of the chlorine present in
solid waste, which might lead to a larger formation of dioxins dur-
ing incineration (Belliveau and Lester, 2004; Giugliano et al.,
1989; Katami et al., 2002). Indeed, burning PVC-enriched mate-
rial under adverse circumstances significantly increases dioxin
discharges, compared with burning chlorine-free material
(Costner, 2001; Giugliano et al., 1989; Katami et al., 2002).
Actually, modern incinerators are well equipped to cope with
such emissions, by both preventive and curative measures.
Adequate values of temperature, turbulence, and reaction time
(the three T’s) and of oxygen supply ensure that complete com-
bustion destroys any precursors, whether these are volatile (ben-
zene, toluene), semi-volatile (polycyclic aromatic hydrocarbons
(PAHs), chlorobenzenes (CBz), chlorophenols (CPh), polychlo-
rinated biphenyls (PCBs)), or residual carbonaceous sources
(soot, carbonised and charred organics). Curative countermeas-
ures comprise adsorption on activated carbon (AC) and separation
of AC by a filter, or adsorption and destructive oxidation on
DeNOx-catalysts (Buekens and Huang, 1998; McKay, 2002).
Most technical and professional sources in waste incineration do
not regard the presence of PVC in waste as seriously problematic.
Indeed, the presence or absence of PVC will not affect the need to
treat the flue gas and eliminate dioxins (Buekens and Cen, 2011;
Rigo et al., 1995; Vehlow, 2012).
However, uncontrolled combustion presents a much worse
case, in particular for waste containing PVC or other sources of
halogens such as salts (Takasuga et al., 2000): a much larger
amount of products of incomplete combustion (PICs) survives
and escapes from the fire and the presence of chlorine or bro-
mine sources enhances the formation of dioxins’ precursors
(Environmental Protection Agency, 2003a; Wong et al., 2007).
Thus, even though PVC diminishes the probability of fire
(William Coaker, 2003), its thermal decomposition and combus-
tion products could contribute significantly to the emission of
dioxins from a wide range of fires, including house fires, back-
yard burning of waste, landfill fires, thermal treatment of resi-
dues containing PVC (or brominated fire retardants), etc.
Given the widespread use of PVC products, their potentially
significant role in dioxins emissions, and the wide range of emis-
sion factors proposed, the purpose of this review is to summarise
available emissions data, gather experimental and simulation
studies of fires and standard combustion tests involving plastics,
and identify and analyse the effects of local factors of influence
(e.g. temperature, residence time, oxygen, metals, additives)
affecting the formation of dioxins during PVC combustion.
Dioxins from sources involving PVC
Survey
Dioxins first appeared in research laboratories more than a cen-
tury ago, signalling their presence by personnel affected by chlo-
racne (Leijs et al., 2014). CPhs condense at >160 °C to form
polychlorinated dibenzo-p-dioxins (PCDDs), as in the Seveso
disaster (1976). They also arise in trace amounts in agrochemi-
cals, herbicides (Agent Orange), or when bleaching paper pulp
with chlorine (Hites, 2010).
Dioxins later were shown to appear whenever any combination
of the elements carbon, hydrogen, oxygen, and chlorine were
reacted together at temperatures between 300 °C and 500 °C. Their
identification during municipal solid waste (MSW) incineration
(Olie et al., 1977) caused considerable consternation, given the
compelling character of these chemicals. Ever since, much research
has concentrated on their mechanisms of formation, largely lead-
ing to two distinct, yet complementary pathways: precursor forma-
tion from molecules with structures similar to those of dioxins
(CPh, CBz, PCBs, PAHs, etc.) and the de novo route, starting from
amorphous carbon and proceeding through catalytic chlorination,
followed by oxidation (Stieglitz et al., 1991). Demands rose to
abolish waste incineration, as well as PVC, as the most visible sup-
plier of the element chlorine in MSW.
During the 1980s and 1990s numerous new and unsuspected
sources of dioxins were identified, in particular in the iron and
steel industry and when melting metal scrap, as well as in CPh
and herbicide chemistry. Obviously, there was no link between
most of these processes, PVC, and dioxins. Still, it will be further
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632 Waste Management & Research 33(7)
investigated by which indirect pathways PVC could cause diox-
ins to be formed.
Vinyl polymers (polyvinylacetate, -chloride, -hydroxide, etc.)
are thermally unstable: at a low temperature they split off small
molecules (acetic acid, hydrogen chloride, water, etc.) leaving a
polyene backbone. Thermal decomposition of polymers has been
systematically reviewed, both in general and for individual poly-
mers, with respect to aspects important in fires, i.e. specific nature
of polymeric materials, of physical and chemical processes and
their interactions, experimental methods used, and their implica-
tions for fire performance (Beyler and Hirschler, 2002). Thermal
degradation and decomposition (pyrolysis), partial oxidation,
gasification, and combustion of plastics have given rise to a vast
literature related to markedly different issues, such as:
stabilisation of virgin and compounded PVC resins (Owen,
1984);
thermal behaviour for conditions of incipient and developing
decomposition and accompanying or subsequent fires (Urabe
and Imasaka, 2000);
gases and vapours emanating under such conditions, together
with their acute and long-term health effects, and the genera-
tion of minute amounts of highly objectionable compounds,
mainly PAHs and dioxins (Belliveau and Lester, 2004);
chemical, feedstock, and thermal recycling of specific and
mixed plastics (Braun, 2002; Buekens and Yang, 2014;
Buekens and Zhou, 2014).
Thermal decomposition of PVC gives a substantial rise to HCl
and benzene (<350 °C), as well as to other aromatics and tars
(McNeill et al., 1998). With respect to the potential formation of
dioxins, HCl has been identified as a rather mediocre chlorinat-
ing agent, when compared with chlorine gas (Addink and Olie,
1995). Routes forming PAHs and dioxins are based on further
transformation of secondary or even tertiary products and their
formation is likely to depend on both the formulation of PVC and
the precise conditions of thermal treatment. Obviously, neither of
these two factors is well documented, since formulations remain
proprietary and thermal conditions in fires stay unpredictable.
Dioxins formation from combustion and fires involving PVC
might be explained by several possible, yet distinct hypotheses:
the initial presence of dioxins in PVC (e.g. from absorption of
atmospheric dioxins) – these would be destroyed during com-
bustion at high temperature, but any dioxins desorbed would still
report to the pyrolysis products formed (Conesa et al., 2009);
any pyrolytic or oxidised compounds found during combus-
tion might act as a precursor and recombine to dioxins in the
low temperature zone following combustion (Rappe et al.,
1990; Wootthikanokkhan et al., 2003); and
the evolution of proven precursors of polychlorinated
dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) formation,
such as chlorinated benzenes and phenols (Aracil et al.,
2005b; Streibel et al., 2004) that could be generated from
PVC pyrolysis and incomplete combustion.
Depending on operating conditions, the amount and potency of
such precursors could vary over several orders of magnitude.
Virgin PVC – PVC production
The question has been raised in how far freshly produced virgin
PVC could already be contaminated with dioxins and also
whether the production chain chlorine/ethylene – VCM–PVC–
PVC transformation into products could be a source of dioxins.
Tiernan et al. (1995) found only octa-chlorinated dibenzo-
p-dioxin (OCDD) in virgin resins, in concentrations compara-
ble with blank analyses. Wagenaar et al. (1998) stated that the
dioxins load of virgin PVC is basically exempt of dioxins, a
conclusion conform to expectations. Since PVC is produced by
polymerisation of distillation-purified VCM, dispersed in
water, so that there is no route to convert VCM into dioxins’
molecules.
PVC readily dissolves dioxins in its mass, as any other poly-
mer, resin, or waxy material would. Similar dissolution occurs in
the polyester used to construct wet scrubbers, a property that
leads to cold memory effects in such units (Adams et al., 2000).
Forschungs-Zentrum Karlsruhe patented this opportunity pre-
sented by plastics to absorb dioxins from flue gas, scrubbing liq-
uors, etc. PP was selected as a reversible absorbing agent, with a
favourable absorption/desorption temperature cycle, and the
addition of AC renders it irreversible. Götaverken Miljö AB in
Sweden markets the process as ADIOX
®
(Andersson et al.,
2003).
In 1994, Evers et al. (1996) concluded that vinyl chloride pro-
duction was a significant source of dioxins in the sediments of the
River Rhine. Greenpeace published dioxins concentration values
for various VCMs manufacturing internal flows and effluents
(Stringer et al., 1995). Duh et al. (2007) assessed dioxins discharges
in wastewater from vinyl chloride manufacturing in Taiwan and
concluded to an annual emission of 3 mg Toxic Equivalence
Quantity (TEQ), clearly an irrelevant amount.
Dioxins can be generated during several steps of the PVC pro-
duction process (Evers, 1993; Thornton, 1997).
Brine electrolysis. Electrolysis cells and their associated pip-
ing consist of fairly compact, closed systems; sludge, long
ago arising from formerly used graphite electrodes, was
highly loaded.
Oxychlorination of ethylene to ethylenedichloride, using a
copper chloride catalyst.
Thermal oxidation of chlorinated production residues, i.e.
chlorinated tars. These are incinerated at appropriate condi-
tions that guarantee emissions well below 0.1 ng TEQ m
-3
.
Other important process steps, such as thermal cracking of ethyl-
ene dichloride to VCM, VCM purification, and VCM polymerisation,
do not generate dioxins. Principal potential emission points are the
oxychlorination reactor, the elimination of tars and the plant wastewa-
ter system. All sources are strictly controlled by The Convention for
the Protection of the marine Environment of the North-East Atlantic
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Zhang et al. 633
(OSPAR)/European Union regulations or requirements to use the best
available technique and the amount of dioxins emitted by the VCM/
PVC industry has been reduced significantly over the past 15 years.
The current contribution is less than 0.1% of the total emitted by
human activities, as can be derived by comparing the eco-profiles pro-
vided by Plastics Europe (2012) with those from the European
Pollutant Release and Transfer Register (2012).
PVC and fire
Fire hazard results from a combination of factors, including the
ignitability and flammability of the products from thermal
decomposition, the heat release and flame spread upon burning,
smoke obscuration and toxicity, as well as specific conditions of
the fire. The high chlorine content of PVC reduces its ignitability
and the heat it contributes to a fire. As the polymer resin is diluted
with additives, its fire performance changes: flammable organics,
such as plasticisers, increase flammability; addition of inorganic
charges, such as precipitated CaCO
3
, reduces it (Lyon and
Janssens, 2005).
Among general-purpose plastics, rigid PVC is inherently the
only fire-resistant resin, since it contains almost 57 wt.% chlo-
rine, prior to compounding. When PVC products are burned,
hydrogen chloride gas resulting from thermal cracking slows
down the combustion reactions in the flame and retards burning
by shielding off the PVC surface from air. PVC releases less
combustion heat than other plastics (although higher than wood
and paper); hence it contributes less to maintaining and spreading
fire and produces few flaming droplets or debris. Moreover,
burning PVC yields an expanding or intumescent carbonaceous
structure, forming a thermal barrier protecting underlying parts.
In some cases, such as pipes, PVC could even prevent fire spread-
ing by blocking orifices through walls or floors.
The Vinyl Institute (USA) presented data on 35 commercial
materials, of which a dozen are vinyl formulations. High ignition
temperature (ASTM D1929, 1996 or Setchkin test), time to igni-
tion or heat required to ignite the material (ASTM E1354 or cone
calorimeter test) result in safer resins. A widely used small-scale
test is the limited oxygen index (LOI) test (ASTM D2863), tell-
ing the lowest oxygen concentration in the atmosphere necessary
to sustain combustion. Only few common plastic materials have
a LOI higher than rigid PVC (Hilado, 1998).
The tendency of a material to spread flame can be measured
with a variety of tests widely used for specifications and building
code requirements. The sample sizes range from very small (UL 94,
the Standard for Flammability of Plastic Materials released by
Underwriters Laboratories of the USA) to quite large (ASTM E84,
Steiner tunnel). PVC materials tend to perform very well in both
tests: UL 94 V-0 and Steiner tunnel Class I (flame spread less than
25). A good indicator of performance for full-scale testing is the
radiant panel test, ASTM E162. Results from this test show that
PVC will not spread flame on its own. PVC formulations do not
drip when burning and develop an intumescent carbonaceous char
that inhibits the spreading of flames and the release of hydrogen
chloride inhibits combustion.
Toxic emissions from PVC fires
Upon combustion, all natural or synthetic organic materials give
rise to toxic gases and to smoke. The major gaseous products ema-
nating from PVC-fires are carbon monoxide, carbon dioxide,
hydrogen chloride, and water. Carbon monoxide (CO) is invisible,
odourless, and incapacitating, and thus the most lethal gas in case
of fire. Hydrogen chloride (HCl) presents two significant hazards
in fires: causing incapacitation through sensory irritancy (leading
to painful breathing, swelling of the airways, and ultimately death),
and inhibiting the conversion of carbon monoxide to CO
2
. The
LC
50
values calculated for a series of natural and synthetic materi-
als thermally decomposed according to the National Institute of
Standards and Technology (NBS) toxicity test method ranged from
0.045 to 57 mg l
-l
in the flaming mode and from 0.045 to >40 mg l
-l
in the non-flaming mode. The LC
50
results for a PVC resin decom-
posed under the same conditions were 17 mg l
-1
in the flaming
mode and 20 mg l
-1
in the non-flaming mode. Some sites represent
the hazards of fires involving PVC (Markowitz et al., 1989). The
toxic potential of combustion gases can be compared in terms of
their LD
50
values (Hirschler, 1987). Studies show that PVC fires
are not significantly more toxic than those from other common
building materials (Huggett and Levin, 1987). The presence of
hydrogen chloride in PVC fire gases causes irritation of the mucous
membranes already at concentrations much lower than those likely
to cause a threat. Thus HCl provides a warning of fire, in contrast
to carbon monoxide, a major constituent of all fire gases.
Smoke may obscure exit routes and induce disorientation in
fire victims. Under non-flaming conditions, PVC formulations
give similar smoke densities to those produced by wood. Under
flaming conditions PVC produces more smoke. Adapted addi-
tives may significantly reduce these emissions (Levchik and
Weil, 2005).
Conclusions
Virgin PVC is exempt of dioxins. Yet, it might absorb dioxins
from air, water, etc., and thus become a sink of dioxins, in par-
ticular of OCDD from the air. PVC is self-extinguishing
(LOI >> 21) and has excellent fire properties, since it evolves
HCl and develops intumescent carbon that thermally insulates
from heat developed by other sources. Since it evolves irritant
HCl, it signals incipient and developing fires. Smoke is problem-
atic with flaming fires. Specific additives are used to enhance fire
resistance and diminish fire hazards. Chlorinated PVC (Cl-PVC)
and polyvinylidene-chloride (PVDC) also show superior resist-
ance to ignition and fire.
PVC: Thermal treatment and fires
Laboratory studies
Numerous studies deal with thermal treatment, whether in inert
atmosphere, or more generally, with limited access of oxygen.
The thermal treatment of PVC has been studied at different
scales: in laboratory equipment, at pilot scale, or – rarely – at
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634 Waste Management & Research 33(7)
full-scale, e.g. as an a posteriori examination of environmental
damage caused by fire. Laboratory studies typically use methods
such as thermogravimetric analysis, differential thermogravime-
try, thermal volatilisation analysis, differential thermal analysis,
differential scanning calorimetry (DSC), pyrolysis gas chroma-
tography, and thermomechanical analysis, to study thermal
weight loss, heat effects, and the physical and mechanical proper-
ties of polymers during their heating. Evolving gaseous products
can be monitored by means of Fourier transformed infra-red or
mass spectrometric (MS) analysis, as well as using detectors,
such as thermistors, Flame Ionisation and Electron Capture
Detectors (FID, ECD). Standard tests were developed to investi-
gate the characteristics of combustible materials in a fire (cf. 2.3).
Dynamic measurements performed by combined thermogravim-
etry mass spectrometry, DSC, and isothermal measurements with
a closed-loop reactor led to new decomposition kinetics of PVC.
Benzene formation was identified as a second order reaction.
Dehydrochlorination at a moderate temperature can be distin-
guished in endothermal and exothermal parts (Bockhorn et al.,
1999). Although there is a vast literature on thermal decomposi-
tion under inert or oxidising conditions, very few studies pre-
sented clear conclusions as to potential pathways towards
formation and yield of dioxins.
Dioxins during thermal treatment
PVC shows two stages of degradation. During the first stage,
between 200 °C and 360 °C, mainly HCl and benzene with very
little alkylaromatic or PAHs are formed (Figure 1).
Thermal degradation of PVC has been monitored in vacuum
up to 500 °C by mass spectrometry of the main products (HCl,
aromatic and aliphatic hydrocarbons, CH
4
, H
2
). The major prod-
ucts were HCl (53 wt.% of the PVC sample), tar (24%), char
(9.5%), liquid (7%, largely benzene), and gas (6.6%). Some 10%
of the chlorine remained trapped until a high temperature gave
rise to chlorinated compounds (1.75% of the liquid fraction
and 0.14% of the polymer). Some 15% of the polyene generates
benzene, mainly accumulating in the polymer and active in inter-
molecular and intramolecular condensation reactions, forming
cyclohexene and cyclohexadiene embedded in an aliphatic
matrix. In the second stage of degradation, between 360 °C and
500 °C, alkylaromatic and PAHs are formed with very little HCl
and benzene. In this stage, the polymeric network formed by
polyene condensation breaks down, forming aromatics (McNeill
et al., 1995). Dioxins were analysed in tars obtained during three
tests (McNeill et al., 1998).
The generation of dioxins could commonly be observed dur-
ing PVC pyrolysis and oxidation (Conesa et al., 2009; Joung
et al., 2006; McNeill et al., 1998; Shibata et al., 2003).
Uncontrolled combustion and open fires
Without temperature controls, consistent oxygen supply, ade-
quate turbulence, and air pollution control equipment, large
amounts of PICs survive and escape from fires. In the presence of
catalysts (copper), the uncontrolled combustion of waste contain-
ing PVC as a chlorine donor significantly facilitates formation of
dioxins (UNEP, 2013).
House fires – structure fires. PVC is widely utilised in forms of
siding, pipes, wire insulation, window frames, upholstery, verti-
cal blinds, flooring, etc. In case of fire, plastics, PVC, as well as
any other flammable construction materials, inevitably will lead
to dioxins emissions. Since it is difficult to perform representa-
tive dioxins’ sampling during accidental fires, because of the
high temperature and the toxic combustion gases emitted, soot
samples collected after the fires have largely been used to
describe the formation of dioxins (Carroll, 1996; Wobst et al.,
1999). In addition, simulated house fires, considered as a practi-
cal and realistic modelling method, have been applied to estimate
dioxins emissions from real fires (Merk et al., 1995; Ruokojärvi
et al., 2000).
Carroll (1996) estimated the annual generation of dioxins in
the US as a result of PVC burning in house fires, using building
data and fire loss statistics as well as soot and ash samples obtained
from laboratory experiments and from building fires involving
PVC and other combustibles. Dioxins generation from PVC was
estimated to be 0.47 to 23 g TEQ y
−1
in house fires, a minuscule
fraction of the 20–50 kg TEQ annual deposition from the air esti-
mated by the US Environmental Protection Agency (1994).
However, studies addressing only soot or ash residues and neglect-
ing potential volatile emissions of dioxins may markedly underes-
timate the emissions from real house fires (Ruokojärvi et al.,
2000) since the partition of dioxins between the gas phase and
residue has been an unresolved question (Mätzing et al., 2001).
Merk et al. (1995) burned both wood and PVC (40 kg PVC and
400 kg wood) in a closed room and measured the levels of dioxins
in the gas and deposit samples, ending up with dioxins concentra-
tions of 5 ng TEQ m
-3
. Assuming that all the air in the room was
contaminated at the levels measured, an emission factor (to air) of
51 ng TEQ kg
-1
of the wood/PVC mixture was obtained.
Ruokojärvi et al. (2000) simulated house fires, using ordinary
furniture, chipboard, and PVC plastic, and measured the concentra-
tions of toxic chlorinated and polyaromatic hydrocarbons during
Figure 1. Thermal decomposition of some important
polymers (Bhaskar et al., 2006).
PET: polyethylene terephthalate; PVC: polyvinylchloride; PS: polysty-
rene; PP: polypropylene; PE: polyethylene.
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Zhang et al. 635
these fires. The amount of dioxins varied from 1.0 to >7.2 ng TEQ m
-3
in the combustion gas and from 0.8 to 7.7 ng TEQ m
-2
in deposited
soot. According to their results no clear relationship was found
between additionally added PVC (about 1 kg PVC plastic for each
sample) and an increase of dioxins concentrations, either in the
combustion gas samples or in soot. Presumably, the fire load itself
had contained enough chlorine and catalysing metals for the forma-
tion of dioxins. Obviously, the concentrations of dioxins released
from simulated house fires are relatively high, comparing with the
dioxins limit value for MSW incinerators of only 0.1 ng TEQ m
-3
(Blomqvist et al., 2007). Conversely, a Municipal Solid Waste
Incinerator (MSWI) plant treating 18.75 t h
-1
generates ca.
99,000 Nm
3
h
-1
(Chi et al., 2005) and a typical iron ore sintering
plant typically yields 1 to 3m Nm
3
h
-1
(Bernaert et al., 2001),
whereas house and structure fires occur erratically and infrequently
and produce relatively limited volumes of combustion gases.
Carroll (2001) collected published dioxins data for PVC (3–
6554 ng kg
-1
) from various sources (Ikeguchi and Tanaka, 1999;
Theisen et al., 1989; Vikelsoe and Johansen, 2000) and for wood
(0.01–173 ng kg
-1
) (Schatowitz et al., 1994) and worked out the
amounts of wood (21,000 kg) and PVC (180 kg) in a new house
in the US. Typically, PVC was tested at a small scale under rela-
tively poor combustion conditions and wood was tested at a large
scale under good combustion conditions. From the usage of PVC
and wood, and differences in emission factors, the overall dioxins
emissions from combustions of these two materials in house fires
were estimated, and it appears that the potential to generate diox-
ins in house fires is similar for PVC and wood. Numerous
American homes are prefabricated largely in wood.
Backyard burning. Backyard burning involves the burning of
household trash in a barrel, open fireplace or furnace, home-
made burn box, wood stove, outdoor boiler, or open pit; these
are mostly occurring in rural areas where there is no kerbside
trash pickup (Environmental Protection Agency, 2003a). Char-
acterised by low combustion temperatures, poor air distribution,
and the presence of chlorine, backyard burning inevitably gener-
ates toxic by-products, including dioxins (Wevers et al., 2004).
The largest contribution of chlorine in household trash comes
from PVC plastic and common salt (NaCl, KCl) (Kanters et al.,
1996; Riber et al., 2009). These emissions, released close to the
ground, pose a great public health threat (Belliveau and Lester,
2004).
Lemieux (1997) measured the emissions from simulated open
burning in barrels of two categories of household waste materials:
waste from avid recyclers, removing most recyclables from the
waste stream prior to combustion and waste from a non-recycler,
combusting the entire stream of household waste. Remarkably,
the avid recycling waste had a higher PVC mass fraction (4.5 wt.%)
as well as more copper than the other waste (0.2 wt. %). Thus,
emissions of HCl and chlorinated organics, particularly dioxins
and CBz, were times higher per mass burned basis.
Gullett et al. (2001) studied the uncontrolled combustion of
domestic waste at the Environmental Protection Agency’s Open
Burning Test Facility to determine the impact of waste composition
on combustion conditions and dioxins emissions from simulated
backyard burning tests. The chlorine content was changed by add-
ing organic (PVC) or inorganic (CaCl
2
) chlorine-sources. During
combustion, the average dioxins emissions from the tests with 0.0,
1.0, and 7.5 wt.% PVC were, respectively, 14,201, and
4916 ng TEQ kg
-1
of waste burned. The two tests with added inor-
ganic chlorine (7.0%) averaged 734 ng TEQ kg
-1
burned. The effect
of the two compositional variables (organic and inorganic) on diox-
ins’ TEQ values could be represented by a single parameter of total
chlorine concentration, so that the chlorine content of the fuel is
more significant for dioxins emissions during backyard burning,
rather than the form (i.e. PVC or CaCl
2
).
After a detailed and systematic study, two conclusions were
presented regarding PVC and dioxins emissions from open burn-
ing of domestic waste (Lemieux et al., 2003).
1. The effect of the chlorine-content of waste on dioxins emis-
sions is significant only at high levels of chlorine, atypical of
household trash. The same conclusion was reached at Umea
University (Wikström et al., 1996) on the basis of tests using
a pilot fluid bed test unit.
2. At these elevated chlorine concentrations, the impact of chlo-
rine on dioxins emissions was found to be independent of the
form of the chlorine (inorganic or organic).
Neurath (2004) re-analysed published data of the Environmental
Protection Agency on backyard burning emissions. When only
PVC was varied, a high correlation coefficient was found between
log (TEQ) and log (% Cl), also for tests with a PVC fraction of 1%
or less. His statistical analysis seems to contradict Environmental
Protection Agency’s conclusion (2 above) that there is no differ-
ence between organic and inorganic chlorine.
Landfill fires. The presence of plastics and PVC in landfills poses
significant long-term environmental threats, owing to the leaching
of toxic additives into groundwater, to toxic emissions in landfill
gases (Mersiowsky, 2002; Mersiowsky et al., 2001), mainly from
dioxin-forming landfill fires (Roots et al., 2004). There are two
major types of landfill fires: those above ground or surface fires,
and underground or subsurface fires (Bates, 2004). Typical tem-
peratures in landfill fires have been reported as 309 °C–406 °C for
surface fires against only 80 °C–230 °C for subsurface fires (Berg-
ström and Björner, 1992). These temperatures are much lower
than those found in MSW incinerators or any industrial or domes-
tic combustion process. Thus there is a much higher hazard of
products of pyrolysis and incomplete combustion, including diox-
ins, being formed. It is reported that four PVC products – pipes,
rigid foils, floorings, and cable wires – contribute about 40% to
the chlorine content in landfills (Mersiowsky et al., 1999), facili-
tating the formation of dioxins in the event of a fire. On top of the
low temperature and chlorine sources mentioned, the mixed com-
position, the heterogeneously compacted and poorly mixed mate-
rials, the lack of oxygen, and the presence of moisture present in
real landfill fires may seriously aggravate combustion conditions
and lead to abundant dioxins emissions (Blomqvist et al., 2007;
Ruokojärvi et al., 1995), even though their combined effect is
unpredictable and chlorine uncertain, to be rate-determining in the
absence of oxygen, necessary in de novo formation.
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636 Waste Management & Research 33(7)
Gullett et al. (2009) determined dioxins emissions from an
open burning residential waste dump. Concurrent measurements
of CO and CO
2
allowed determining of emission factors via the
carbon balance method. These ranged from 202 to
1700 ng TEQ kg
-1
C
burned
, with an average of 823 ng TEQ kg
-1
C
burned
, a value five times higher than those from backyard burn-
ing (Lemieux et al., 2003) and 2000 times higher than those
from modern municipal waste combustors (UNEP, 2001). Also,
more attention should be paid to the outcomes from smouldering
combustion, which shows greater propensity for formation of
dioxins than flaming combustion (Gullett et al., 2009).
Thermal treatment of residues. Typically, the chlorine content
of MSW is ca. 0.5 wt.%. This value is still unproblematic in
incineration, yet at the limit for co-firing in cement or limekilns,
or in coal- or lignite-fired power plant. This statement is relevant
for several high-volume waste streams, including automobile
shredder residue (ASR), the residue generated from car shred-
ding, waste sorting residues, and waste electric and electronic
equipment.
PVC plays an important role in vehicle manufacturing (Kanari
et al., 2003). End-of-life vehicles are dismantled to recover reus-
able parts and then sent to a shredding facility for steel and non-
ferrous recovery (Buekens and Zhou, 2014). An appropriate
method of disposing of ASR is thermal treatment (Kim et al.,
2004b). Simulated ASR, with 3.9 wt.% of PVC, was thermally
treated by controlled pyrolysis or gasification to observe the
yields of pyrolysis products (Joung et al., 2006). The emission of
dioxins and dioxin-like PCBs were studied at 600 °C, with and
without PVC, oxygen, and catalytic metals. When PVC was pre-
sent, dioxins and dioxin-like PCBs were produced in any operat-
ing condition. The presence of oxygen (air ratio = 0.5) and
catalytic metals (copper 3 wt.%, iron 3 wt.%) facilitated the for-
mation of dioxins and dioxin-like PCBs, suggesting that thermal
treatment of automobile shredder residue may lead to significant
dioxins and dioxin-like PCBs emissions.
Cable burning. It is still common practice in many parts of the
world to use open burning to remove the plastic coating around
cable so that the underlying copper wire can be reclaimed (Leung
et al., 2006; Li et al., 2007). PVC is a prevailing insulation mate-
rial of cable owing to its low price, high flame resistance, and
excellent electrical insulation (Wang et al., 2008). In cable burn-
ing, all ingredients to form dioxins are abundantly present: carbon
(sheath), chlorine (PVC), and a catalyst (copper) (UNEP, 2013).
Gullett et al. (2007) simulated practices associated with rudi-
mentary metal recovery operations of insulated wires and circuit
boards. The insulated wires were composed primarily of copper
(35 wt.%) and PVC-based insulation (65 wt.%), with an actual
chlorine content of 8.84 wt.%. The circuit boards had a large ash
component (66 wt.%), a much lower chlorine concentration
(0.2%), and a carbon content of 18 wt.%. The average dioxins
emissions were 11,900 ng TEQ kg
-1
and 92 ng TEQ kg
-1
for insu-
lated wires and circuit boards, respectively. The dioxins emission
factors for the circuit boards fall within the range of values
reported for tests of uncontrolled barrel burning of residential
waste (Gullett et al., 2001; Lemieux et al., 2003), whereas, the
value for insulated wires is about 100 times higher. These excep-
tionally high dioxins emissions from insulated wires burning
were likely exacerbated by the high concentration of chlorine-
containing insulation on the wires combined with the presence of
copper, as well as by other factors related to the uncontrolled
nature of the fire.
Conclusions
The thermal stability of PVC has been studied many times, often
in conjunction with the testing of heavy metal bearing stabilisers.
Thermal decomposition proceeds in two steps. In a first step HCl
unzips from the molecular chain and evolves, accompanied by
some benzene. This step strongly depends on the stabiliser sys-
tems added to virgin resin. Elimination of HCl leaves a polyene
structure that is further converted during the second step, gener-
ating alkylbenzenes, tar, and char. Each step is influenced by the
presence of additives, as well as by imperfections in the polymer
chain. Some studies in which thermal degradation was accompa-
nied by dioxins analyses were identified. One of these even pre-
sents a mass balance (McNeill et al., 1995).
At its end-of-life stage, PVC can preferably be recycled.
Mechanical recycling is common for production waste; post-con-
sumer waste should be clean and well identifiable before recy-
cling can be contemplated (Buekens, 1977). Another option is
chemical or feedstock recycling and thermal recycling. Polyolefins
score highest in this frame of feedstock recycling, yet they are still
hampered by unfavourable logistics and failing economy of scale.
PVC is a potential source of HCl, of fuel, and of char.
PVC is almost trouble-free in present-day MSW incineration.
Medical waste incineration is much more problematic, following
severe fluctuations in composition, including an unusually large
share of PVC disposables. Moreover, centralised treatment should
be preferred over elimination in small, batch-operated units.
Really problematic is open burning, for all plastics. These
require large amounts of combustion air that can readily be sup-
plied during MSW incineration, not however, under open fire
conditions. As a result there is evolution of large amounts of
PICs. Such problems are exacerbated by the presence of halogens
that are potential precursors of dioxins. House fires, backyard
burning, landfill fires, thermal treatment of PVC-rich streams,
burning cables, and electronic scrap are examples of fires illus-
trating accidents, arson, and also inappropriate forms of waste
management. For refuse rich in plastics and PVC waste, incinera-
tion seems the only technical and economic choice left, when
using dioxins as selection criterion. Backyard burning leads to
unacceptable emissions; landfill only defers this problem.
Factors of influence
In what follows, some of the factors responsible for the genera-
tion of dioxins are considered; in particular poor combustion,
often related to inadequate temperature, turbulence, and/or resi-
dence time. The chlorine of PVC, whether present massively or
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Zhang et al. 637
diluted in other waste, is almost totally eliminated before reach-
ing 360 °C (McNeill et al., 1995). The formation of dioxins in
turn depends on numerous specific parameters, including tem-
perature, residence time, availability of oxygen or of catalytic
metals, and inorganic versus organic chlorine; these are further
highlighted by specific studies. Still, most studies show only very
partial results in a specific domain of combustion conditions,
with high or low levels of PICs surviving, and referring to dis-
tinct chemical systems, varying with the PVC resin compound
and associated additives.
Effect of chlorine
When no chlorine is present, no dioxins are formed (Costner,
2001).
In the past decades, PVC, with its rather high chlorine con-
tent, has aroused extensive attention regarding prospective for-
mation of dioxins. Numerous experiments, estimates, and
analyses focused on possible relations among PVC, chlorine,
and dioxins. In 1997, the US Environmental Protection Agency
acknowledged several studies have identified strong correla-
tions between chlorine content and PCDD/Fs (dioxins) emis-
sions during combustion tests (Environmental Protection
Agency, 1997).
A review of experimental data from laboratory- and pilot-
scale studies clearly indicates an association between chlorine
content of feed/fuels and dioxins (Hasselriis, 1987; Hatanaka
et al., 2000; Wikström and Marklund, 2001; Yasuhara et al.,
2001). Rigo et al. (1995) argued that there is no such relationship
between chlorine input and dioxins output over a wide range of
industrial furnaces and incinerators, yet this statement was much
challenged. Moreover, PVC is frequently regarded as major chlo-
rine donor during open or uncontrolled combustion of waste
(Costner et al., 1995) with typical chlorine content ranging from
35% (flexible) to 55% (rigid) (Shibamoto et al., 2007). Yasuhara
et al. (2001) conducted combustion tests to investigate the effect
of chlorine-content on dioxins emissions and found a clear cor-
relation between dioxins formation and inorganic + organic chlo-
ride content (Table 1).
For small-scale and other combustion systems, increased
chlorine input (resulting from either PVC or other chlorine
sources) could lead to enhanced formation of dioxins. Several
studies (Carroll, 1996; Gullett et al., 2001, 2007, 2009; Joung
et al., 2006; Lemieux, 1997) analysed the effect of PVC as a chlo-
rine source on the formation of dioxins in this category of fires.
In other cases, such as MSW incineration, a chlorine supply is
no longer relevant in the generation of dioxins, since several
other factors (quality of combustion, catalytic effects of fly ash,
and oxygen content of flue gas) are much more significant
(Buekens and Cen, 2011; Vehlow, 2012).
Temperature
Temperature is one of the major operating parameters during
PVC combustion (Kim et al., 2003) and accordingly associated
with the formation (and destruction) of dioxins. The concentra-
tion of CO is one yardstick of quality of combustion (together
with total organic carbon in flue gas and carbon in ash). Generally,
a lower combustion temperature corresponds to higher CO
concentration.
Katami et al. (2002) conducted combustion experiments with
PVC in a firebrick combustion chamber for both low-CO (high
temperature) and high-CO (low temperature) conditions and ana-
lysed dioxins arising, resulting in amounts of dioxins found in the
exhaust gases of 824 ng g
-1
and 8920 ng g
-1
at low-CO conditions
and high-CO conditions, respectively.
Kim et al. (2004a) investigated the formation of several chlo-
rinated compound classes (CBz, CPh, dioxins, PCBs) and esti-
mated the effect of temperature on PVC combustion. The
temperature was adjusted to 300 °C, 600 °C, and 900 °C. This
temperature of 300 °C is still considered too low for pyrosynthe-
sis to occur vigorously. At 600 °C the dioxins’ concentrations
were high; above 900 °C their degradation was faster than forma-
tion, consistent with Hatanaka et al. (2001).
Residence time
The residence time of flue gas is a most important influencing fac-
tor in lab-scale experiments, affecting the completeness of com-
bustion. Kim et al. (2008) burned 0.5 g of PVC in a laboratory
furnace at 900 °C and adjusted airflow rates to three different val-
ues (0.5, 2, and 4 L min
-1
) to appraise the corresponding dioxins
concentration. After allowance for thermal expansion, the resi-
dence time was established as 11.5 s, 2.8 s, and 1.9 s, respectively.
The 0.5 L min
-1
test ranked as deficient air condition, 2 L min
-1
as
sufficient air + long residence time, and 4 L min
-1
as sufficient air
+ shorter residence time conditions. Finally, the dioxins concen-
tration resulting from PVC combustion was 2 L min
-1
<4 L min
-1
≦0.5 L min
-1
(see Table 2). In combustion facilities, an increase of
flue gas residence time generally decreases the concentration of
Table 1. Dioxins formation as a function of chlorine-content (Yasuhara et al., 2001).
Material News papers London plane
tree branches
Newspapers
impregnated with
sodium chloride
Idem + PVC Newspapers + PVC
Cl-content, wt.% Low Low 3.1 2.6 5.1
PCDD/Fs, ng g
-1
0.186 1.42 102 101 146
PCDD/Fs: polychlorinated dibenzo-p-dioxins and dibenzofurans; PVC: polyvinylchloride.
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638 Waste Management & Research 33(7)
dioxins, but for a flowrate of 0.5 L min
-1
, reduced availability of
oxygen was the reason offered for the excessive yield of dioxins.
Pyrolysis, gasification, and combustion
Pyrolysis, gasification, and combustion are all potential elimina-
tion methods of PVC waste. During these processes, the forma-
tion of dioxins is a significant element to be considered and
monitored.
Aracil et al. (2005a) conducted pyrolysis and combustion tests
on pure PVC powder to study the formation of dioxins under
those two thermal conditions. The dioxins obtained represented
(g
-1
sample): 4.72 ng or 0.215 ng TEQ for pyrolysis and 122 ng or
4.6 ng TEQ for combustion, respectively. The congener group
patterns obtained were surprisingly similar, suggesting that the
same mechanism was responsible for dioxins formation in both
cases. The fingerprint formed by the 17 2,3,7,8-substituted
PCDD/Fs, surprisingly, is virtually identical for pyrolysis and for
combustion (Figure 2).
Oudhuis et al. (1990) measured dioxins emissions from pyrol-
ysis (in N
2
) and oxidative degradation (in air) for two different
PVC samples. Dioxins emissions in air were 10 to 100 times
higher than those in inert surroundings; these results were con-
sistent with those of Aracil et al. (2005a).
Effect of additives
Additives are always blended into PVC products and signifi-
cantly alter their flammability and combustion, thus also affect-
ing any dioxins emissions. Some additives show suppressive
effects, while others seem to stimulate dioxins formation. Since
the pathways forming dioxins under particular conditions are still
unidentified, it is pure guesswork which additive will introduce
which effect. Additives that stimulate the formation of larger
residues of fixed carbon can be expected to stimulate smoulder-
ing combustion and thus longer generation and more dioxins.
Suppression can be expected from any sulphur- or nitrogen-con-
taining additives and from the addition of basic substances, such
as NaOH and Ca(OH)
2
(Stieglitz et al., 2003). Transition metals
catalyse the formation of dioxins. Conversely, they also acceler-
ate oxidation reactions so that their effect may turn from negative
towards more positive.
Phthalate plasticisers. The addition of plasticiser controls the
expected flexibility and hardness of the final PVC product. Kim
et al. (2006) incinerated PVC blended with dioctylphthalate
(DOP, a major plasticiser) at variable DOP content (0, 15,
50 wt.%) (Table 3). The concentration of dioxins and co-PCBs
slightly dropped for rising DOP content. These results obviously
contradict those from Oudhuis et al. (1990) who found higher
Table 2. Dioxins concentration at different airflow rate (Kim et al., 2008).
Airflow rate
(L min
-1
)
Dioxins Concentration
Total (ng g
-1
PVC) TEQ (ng TEQ g
-1
PVC)
1 2 3 4 1 2 3 4
0.5 1102 1108 2517 27.7 27.9 47.5
2 2.68 0.962 1.8 0.78 0.229 0.123 0.266 0.143
4 2.58 4.18 10.4 0.368 0.719 0.512
PVC: polyvinylchloride; TEQ: toxic equivalence quantity.
0
10
20
30
40
50
60
70
80
90
100
2378-TCDF
12378-PeCDF
23478-PeCDF
123478-HxCDF
123678-HxCDF
234678-HxCDF
123789-HxCDF
1234678-HpCDF
1234789-HpCDF
OCDF
Total PCDFs
2378-TCDD
12378-PeCDD
123478-HxCDD
123678-HxCDD
123789-HxCDD
1234678-HpCDD
OCDD
Total PCDDs
pyrolysis at 850°C
(weight unit)
combustion at
850°C(weight unit)
pyrolysis at 850°C
(TEQ unit)
combustion at
850°C(TEQ unit)
Figure 2. PCDD/F homologue fingerprint (wt. %) in pyrolysis and incineration (850 °C, PCDD/Fs = 100) (Aracil et al., 2005a).
CDF: chlorinated dibenzofuran; CDD: chlorinated dibenzo-p-dioxin; TEQ: toxic equivalence quantity.
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Zhang et al. 639
loads in the presence of diethylhexylphthalate, an almost identi-
cal additive. This contradiction once more suggests that the pre-
cise experimental conditions are more important than
composition. Correlation analysis shows good similarity between
the data sets for 0, 15, and 50 wt.%. The correlation between
dioxins and co-PCBs is unusually weak (r
2
= 0.809).
Charges. The addition of charges improves the wear resistance
of flooring. Finely milled or chemically precipitated CaCO
3
improves the durability of PP or PVC (Pan et al., 1991). Sun
et al. (2003) assessed the effect of CaCO
3
as well as TiO
2
on
dioxins generation from PVC incineration (Table 4). TiO
2
greatly promoted the generation of dioxins in both exhaust gas
and ash, possibly owing to its delaying effect on combustion of
PVC. However, the release of dioxins with exhaust gas was
greatly suppressed when CaCO
3
replaced half of the TiO
2
. The
rising amount of dioxins trapped in the ash may relate to the
adsorption capability of CaCO
3
for CPh and possibly to the gen-
eration of CaCl
2
.
Transition metal oxides and chlorides. Transition metal oxides
and (especially) chlorides are reputedly catalysing dioxins
formation.
Copper compounds, including CuCl
2
and CuO, have been
known to catalyse oxychlorination and dioxins formation, but they
also catalyse dechlorination and decomposition of dioxins, depend-
ing on their concentration (Luijk et al., 1994) and other reaction
conditions. Shibata et al. (2003) tested the effect of CuO on dioxins
emission from PVC pyrolysis at 300 °C, varying the molar ratio of
CuO:PVC (CuO:PVC = 1, 3, 5). Total amounts of dioxins
decreased with the increase of molar ratio of CuO:PVC (16,129,
1526, 98.7 ng g
-1
PVC for CuO:PVC = 1, 3, 5), as a result that sup-
plying more CuO-oxygen could promote the decomposition and
oxidation of dioxins. Though oxygen is necessary for chlorinating
organic compounds, oxygen may also promote the decomposition
and oxidation of the dioxins formed (Fiedler, 1998).
Yasuhara et al. (2005) scorched electric wire coated with PVC
and also pure PVC resin in a well-controlled oven, analysing gas
samples for PCDD/Fs and coplanar PCBs. In the presence of
copper wire, dioxins formation is reduced by 70% for PCDDs,
42% for PCDFs, and 45% for the total PCDD/Fs and coplanar
PCBs. Residual blue–green CuO material was collected from the
grate after the combustion test of electric wire coated with PVC.
These results are consistent with the previous study reporting that
net dioxins formation declined for rising CuO:PVC mol ratios
(Shibata et al., 2003).
Gupta and Viswanath (1998) focused on the role of metal oxides
in the thermal degradation of polyvinyl chloride. Dehydrochlorination
was delayed by oxides of vanadium, zirconium, chromium, iron,
molybdenum, and cerium, yet promoted by oxides of tin, titanium,
antimony, aluminum and both Cu
2
O and CuO.
Iron nanoparticles. Font et al. (2010) burned PVC as well as a
mixture of PVC and iron nanoparticles in two stages, with the
first stage proceeding in air at 375 °C; during the second stage,
the resulting char was first cooled down and subsequently burnt
at 850 °C. The presence of iron nanoparticles clearly causes a
large surge in the dioxins generation at 375 °C (Table 5), proba-
bly owing to the catalytic oxychlorination by iron chlorides of the
intermediate strongly unsaturated polymer chain, formed during
the dehydrochlorination of PVC. At 850 °C iron only occurs as
iron oxide and these particles act as oxidising catalysts, decreas-
ing the formation of chlorinated aromatic compounds, as
observed in literature (Shibata et al., 2001).
Fingerprints
In principle, dioxins fingerprints could yield a clue to the mechanism
of formation and the catalyst system involved. Wikström and
Marklund (2001) and Yasuhara et al. (2001) both conclude that there
are no significant modifications in fingerprint or in rate of formation
of dioxins when using organic (PVC) or inorganic chlorine sources.
Most tests directly involving PVC (pyrolysis, partial oxidation, com-
bustion) produce primarily high chlorinated congeners, such as
hepta- and octa- chlorinated dibenzo-p-dioxins and dibenzofurans
(H7CDD/F and OCDD/F), possibly because there is a large amount
of chlorine in PVC and thus of HCl in the carrier gas. A second
important feature is the high ratio of PCDFs to PCDDs formed. Thus
PVC tests yield a fingerprint distinct from MSW incineration.
Table 3. Concentration of dioxins and co-PCBs from PVC
combustion at various DOP contents (Kim et al., 2006).
DOP content in PVC, wt.%
0% 15% 50%
Dioxins Total (ng g
-1
) 1.556 0.968 0.472
TEQ (ng TEQ g
-1
) 0.190 0.148 0.050
Co-PCBs
Total (ng g
-1
) 3.523 3.658 1.526
TEQ (ng TEQ g
-1
) 0.046 0.039 0.007
DOP: dioctylphthalate; TEQ: toxic equivalence quantity; PCB: poly-
chlorinated biphenyl; PVC: polyvinylchloride;.
Table 4. Total amount of dioxins generated when 60 g PVC
was incinerated at 450 °C (Sun et al., 2003).
Sample Amounts of dioxins contained in
Exhaust gas (ng) Ash (ng)
PVC 580 1.4
PVC + TiO
2
(10%) 890 8.6
PVC + TiO
2
(5%) +
CaCO
3
(5%)
386 60.4
PVC: polyvinylchloride.
Table 5. Emissions of dioxins for four combustion runs (Font
et al., 2010).
PVC PVC + Fe
Dioxins 375 °C 850 °C 375 °C 850 °C
Total (ng g
-1
PVC) 25.1 14,100 758,000 403
TEQ (ng TEQ g
-1
PVC) 0.183 224 8217 6.44
PVC: polyvinylchloride; TEQ: toxic equivalence quantity.
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640 Waste Management & Research 33(7)
Wang et al. (2003) proposed a threshold value of 0.8–1.1 wt.%
chlorine content in fuels, using principal component analysis to
compare congener profiles of PCDD/Fs, in flue gases from vari-
ous emission sources. When the chlorine content in fuel remains
below 0.8–1.1 wt.%, the formation of PCDDs dominates; for
higher chlorine levels the formation rate of PCDFs increases
faster than for PCDDs. This could explain the leading share of
PCDFs in the congener profiles of PCDD/Fs from combustion
involving PVC-enriched materials.
Conclusions
PVC is a leading low-cost material, in particular in building and
in medical applications.
Conversely, once ignited, it may act as source of chlorine and
facilitate the formation of dioxins. PVC is not a problem in mod-
ern incinerators of MSW, since chlorine is extracted easily, either
as a solution of HCl or as neutralisation salts.
During uncontrolled combustion and in open fires (e.g. house
fires, backyard burning, landfill fires, etc.), however, plastics at
large, and in particular PVC materials, significantly contribute to
the emissions of dioxins, owing to poor combustion conditions, the
evolution of pyrolysis products and the formation of PICs, the pres-
ence of chlorides and HCl, the possible presence of catalysts (HCl
volatilises copper, lead, zinc, cadmium, etc., creating catalytic
activity upon de-sublimation of these salts), and the total absence of
flue gas cleaning facilities. The complexities of combustion visibly
interact with those of PVC compound formulations, the latter influ-
encing upon thermal decomposition, including the evolution of
volatiles and HCl and the amount and properties of char.
The formation of dioxins during PVC incineration or in fires
is strongly related to combustion conditions, yet in a way that still
defies scientific analysis. Additives mixed with PVC may signifi-
cantly change the characteristics of PVC during combustion and
affect its dioxins emissions by suppression (DOP, CaCO
3
, and
CuO) or facilitation at low temperature (iron nanoparticles). At
present, other articles are prepared on open burning and dioxins
in a more general context, as well as on the special case of landfill
fires, a rising threat in waste management.
Acknowledgements
The authors are grateful to Professor Dr Shengyong Lu, Dr Xujian
Zhou, and Dr Rixiao Zhao (Zhejiang University, China), who helped
improve this article with their constructive comments or by provid-
ing additional information.
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect
to the research, authorship, and/or publication of this article.
Funding
The author(s) disclosed receipt of the following financial support for
the research, authorship, and/or publication of this article: The
Program of Introducing Talents of Discipline to University [B08026]
and Program 111 financed this study.
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