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End-of-life Environmental Issues with PVC in Australia

Prepared by Dr. John Scheirs,
ExcelPlas Polymer Technology (EPT) for
Environment Australia, June 2003

2. Summary

In recent times there has been a shift in focus from PVC production and service life issues to end-of-life issues such as landfilling, incineration and recycling. In particular, there exists ongoing debate regarding the environmental and health effects arising from the use of phthalates (as plasticizers in flexible PVC) and heavy metals (as PVC stabilisers) once end-of-life PVC products are disposed of in landfills or by incineration.

2.1 Range, quantities and life expectancies of major PVC products and applications

PVC lies second only to polyethylene in terms of volume of thermoplastics consumed. This is a function of its wide range of flexible and rigid forms, its low cost, ease of processing combined with its good physical and chemical properties. PVC is also unique amongst commodity plastics in that it is more an inorganic plastic rather than an organic or hydrocarbon polymer on account of its high chlorine content (57% chlorine by weight).

Australian Vinyls is the sole producer of raw PVC resin (available in powder form) in Australia. This resin is compounded with stabilizers and in some cases with additives (typically fillers, plasticizers and pigments) depending on the application. Suspension PVC resin occupies some 95% of the PVC market while emulsion PVC (which accounts for < 5%) is no longer manufactured domestically. The total consumption of PVC resin in Australia for 2001 was some 194,500 t. In addition some 31,000 t of PVC was imported in the form of finished PVC products. This gave an overall PVC consumption figure of around 225,500 t. Other estimates put the total market at between 220-240 kt.

A major proportion of the PVC market comprises long-term applications (with life expectancies greater than 10 years and even 50 years or longer for PVC pipe). This is evident in the building and construction sector (approximately 80% of the PVC market) where it is used for diverse applications including sewerage pipe, cable trays, guttering, house siding, wire and cable insulation, flooring etc. It is worthwhile noting that more end-of-life PVC will become available in the next ten years as the building products installed in the 1960s and 1970s approach the end of their service life.

The availability factor is a key factor that influences the amount of accessible end-of-life PVC. It considers the likelihood of different end-of-life PVC products entering the post-consumer waste stream. For instance end-of-life PVC pipes are generally left in situ and are thus not available for recovery. Figures for Europe indicate that some 71% of PVC pipes are left in situ and the situation in Australia is predicted to be significantly higher as indicated by the pipe installers. Likewise the availability factor for PVC bottles indicates that only some 30% of PVC bottles consumed are placed out for kerbside collection.

PVC pipe is the dominant application (63% market share) for PVC resin in Australia accounting for approximately 142,000 tpa. Three main pipe manufacturers (Vinidex, Iplex and Key Plastics) supply 90% of this market. The market split for pressure pipe and non-pressure pipe is approximately equal at 35% each with the remainder being comprised of conduit. Non-pressure PVC pipe and conduit is formulated with lead stabilizers at levels of approximately 1.5% lead sulfide, lead stearate or tribasic lead sulphate. An estimated 1,400 tpa of lead stabilizer is consumed in PVC pipe production in Australia. Potable water pipe uses calcium/zinc (Ca/Zn) stabilizer systems. All major manufacturers of PVC pressure pipe have also opted to use Ca/Zn stabilization.

PVC cables (such as power cable, data cable and domestic cabling) are manufactured by Olex (National Cable) and Pirelli. The total consumption of PVC for cable insulation applications in Australia is approximately 22,000 tpa. However industry sources suggest the volume of locally-manufactured cable insulation accounts for about 12,000 tpa. Again tribasic lead sulphate (TBS) is the stabilizer of choice for PVC cables (~0.5 wt.%) and accounts for around 110 tpa of this additive.

Post-consumer PVC cable insulation is mechanically recycled in Australia each year at a level of approximately ~1500-2000 tpa. Given that at least 10,000 tpa of PVC cable scrap is available substantial quantities of PVC cable strippings are still being landfilled or exported. In much of this the current high level of residual copper content in the PVC strippings (sometimes > 5 wt.%) is too high for PVC recyclers to tolerate.

Packaging applications account for approximately 13,000 tpa of PVC with some 6000 tpa converted into bottles (e.g. fruit juice and cordial) with the rest used in flexible packaging (e.g. cling wrap and film) and rigid packaging (e.g. blisterpacks, thermoforming). About 90% of bottle applications are clear with some 3940 tpa being blow moulded domestically and approximately 2060 tpa being imported. Kerbside collection of PVC bottles is actually higher than the bottle recycling rate since the majority of recovered PVC bottles are exported.

PVC is also widely used for hoses (~13,000 tpa) such as industrial hose, suction hose, pneumatic hose, garden hose and fire hose. The major hose producers include Barfel, Eslan, RX and Premier. PVC hose is an established outlet for incorporating high loadings of PVC recyclate (it can contain up to 90% recycle-content). For instance some 80% of the PVC recyclate that one of the largest PVC recyclers (Cryogrind P/L) produces (about 2000 tpa) is used to make garden hose and industrial hose.

The automotive sector only uses about 3-4% of PVC resin (5,800-7,760 tpa) which is used in the production of vehicle components including instrument panels, seat covers, arm rests, door cladding, wire covering, sealers, and under-coating.

Other significant PVC sectors include stationary, medical products, flooring and geomembranes/liners which collectively account for approximately 5,000 tpa.

2.2 End of life environmental issues and impacts relating to PVC additives

PVC is never used as a virgin resin. Rather it relies on stabilizers and additives to impart desired characteristics. In flexible PVC products the plasticizer content frequently comprises about 30 wt.% of PVC end products but can be as high as 60 wt.%. The stabilizers and additives most often cited as creating environmental impacts are lead heat stabilizers, cadmium heat stabilizers, cadmium-based pigments, organotin heat stabilizers, phthalate plasticizers and bisphenol A-stabilized plasticizers

2.2.1 Lead and cadmium stabilizers

A range of lead-based stabilizers are used in PVC (such as tribasic lead sulphate, dibasic lead phosphite, dibasic lead phthalate and dibasic lead stearate). The toxic effects of lead compounds are well documented. The total usage of lead stabilizers for PVC in Australia is approx. 2000 tpa.

In the main, lead stabilizers are immobilized in the PVC matrix. This encapsulation ensures that leachability into the environment is extremely low. However under the circumstances of finely divided PVC waste products (such as cable fluff or granulated profiles) the increased surface area may facilitate extraction under specific conditions (e.g. acidic landfill leachates). Lead stabilizer replacement has occurred gradually with the advent of improved Ca/Zn stabilizers, especially in PVC pressure pipe applications.

Cadmium-based stabilizers (e.g. cadmium laurate or cadmium stearate) have been used traditionally in PVC products such as roofing material, rain gutters, window profiles, pools, and tarpaulins. The Australian PVC industry (in 2002) accounts for approximately 120 tpa of cadmium stabilizers with the majority of this manufactured locally. Imported PVC products can also still contain cadmium stabilizers and the mechanical recycling of end-of-life PVC containing cadmium will continue for some time into the future.

The nature of the cadmium species determines its human and environmental toxicity. Cadmium in the form of cadmium pigments is complexed and calcined and not available to enter into biochemical pathways. In contrast cadmium in cadmium stabilizers is more labile and could therefore be very toxic. The recent EU Green Paper found that a potential contamination of the environment by the use of lead or cadmium stabilizers in PVC can take place during the waste management phase. A study has shown a 10% release of lead stabilizer from one type of flexible PVC cable containing a mixture of plasticizers. It is possible that the same mechanism could apply to cadmium-based stabilizers.

Waste PVC contributes to the heavy metals content in the municipal solid waste (MSW). Disposal of PVC by incineration could be a potential source of diffuse spreading of lead and cadmium where there is incorrect disposal of bottom and fly ashes of the incinerators. Europe assigns a figure of approximately 10% to cadmium in MSW originating from PVC. This is a higher figure than in Australia due to the prevalence of PVC windows in Europe.

2.2.2 Organotin stabilizers

Organotin stabilizers are extensively used in clear PVC and ultimately degrade into inorganic tin by microbial activity. Due to low aqueous solubilities, a high affinity to soil and organic sediments as well as a rapid conversion to inorganic tin in water, the potential of mono- and dialkyl tin compounds for ecotoxic effects is low. The purported toxicity of mono- and dialkyl tin compounds however is sometimes confused with the known toxicity of tributyl tin compounds (not used in PVC products) to aquatic life.

2.2.3 Phthalates

The usage of phthalate plasticizers in flexible PVC applications is of the order of 12,000 tpa (based on 1999-00 data). The PVC cable industry consumes most of this volume since phthalates can constitute between 23-30% of the PVC cable formulation.

Diethylhexyl phthalate (DEHP) is the most prevalent plasticizer in PVC formulations and is also the dominant phthalate found in the environment with highest concentrations detected in sediment followed by sewage sludge. The detected levels of phthalates found in the environment are considered to be generally lower than the concentration required to induce any known toxic, reproductive or developmental effects on living organisms.

Phthalates can accumulate in environments that are anaerobic and poorly colonized by microbes. Similarly cold conditions slow down biodegradation of phthalates. DEHP could pose an environmental risk under conditions where local concentrations in excess of its aqueous solubilities can arise, such as with sediments close to point emission sources (e.g. sewage treatment plant outfall). Studies have also found that DEHP could leach out from automotive shredder residue containing plasticized PVC.

Although the toxic effects of DEHP have been well established in experimental animals, its ability to produce these effects in humans is still controversial. With regard to human health risks, the areas of most concern involve exposure of neonates and pregnant women. However, it is important to note that the EU Scientific Committee on Medicines and Medical Devices has found (as recently as 24 October, 2002) no reason to limit the use of DEHP-plasticised medical devices for any patient group, although it encourages continued study into potential adverse effects.

The three main types of non-phthalate plasticizers being suggested as replacements for problematic phthalates are adipates, citrates and cyclohexyl-based plasticizers. In Europe substitution of DEHP has occurred in the PVC sector, largely by replacement with DIDP and DINP. DEHP usage has fallen from 55% of phthalate use to 35% over the period 1999-2001.

2.3 End-of-life environmental issues and impacts relating to in situ PVC

Environmental risk posed by in situ disposal is considered to be low. Bulk PVC products are very resistant to biodegradation and the additives (apart from phthalate plasticizers) are generally encapsulated within a stable polymer matrix. In the long term however some thermal degradation of PVC could result in product embrittlement and porosity. The greater the physical breakdown the higher the corresponding rate of additive migration. Present knowledge suggests that rigid PVC articles will take of the order of 1000 years to break down.

2.4 End-of-life environmental issues and impacts relating to landfilling of PVC

Landfilling is the predominant form of waste disposal for PVC waste throughout the world. The relevant issues surrounding PVC in landfills include the stability of the PVC polymer matrix under landfill conditions, the fate of additives (particularly phthalates and heavy metal compounds) as well as the necessity to divert PVC waste streams from landfills (due to resource loss considerations), or to impose additional containment measures.

DEHP plasticizer may leach from automotive shredder residue containing plasticized PVC in a landfill. In another example, thin PVC packaging film has been found to have undergone degradation under specific landfill conditions. The conditions were at the extreme end of conditions found in average landfills - that is under aerobic conditions and at a temperature of 80C.

The EU Green Paper (2000) highlighted some concerns with landfilling of PVC. The conclusions have been challenged by the European PVC industry on the basis that the extreme temperature used to accelerate aging of materials in the study affected the outcome. Other independent studies simulating typical landfill conditions have concluded that PVC in landfill (including plasticized applications) is environmentally safe.

On the basis of the available research and evidence the landfilling of end-of-life PVC seems to be environmentally acceptable when mechanical recycling and thermal treatment processes are not possible. The overall conclusion of the most recent studies is that PVC products do not constitute a substantial impact on toxicity of landfill leachate and gas.

2.5 Major Impediments to PVC Recovery and Recycling

The primary impediments to PVC recycling are:

  1. the limited quantities of end-of-life PVC available for recycling at present and as a consequence the lack of available infrastructure for collection of long-life PVC products (which constitutes some 80% of PVC applications)
    • the fact that PVC rigid packaging (ie. bottles) are available in a wide range of styles and capacities. This diversity is partly the reason why PVC is not readily identifiable by the consumer as being associated with any single distinguishing bottle application (except cordial bottles).
    • the diverse and highly formulated nature of many PVC products
  2. the presence of various types of contamination (e.g. fibre-reinforcement, foam backing) and commingled (incompatible) polymers mixed with the PVC stream.
    • the relative thermal instability of PVC and the resulting potential machinery corrosion due to hydrochloric acid attack
    • the prevalent low cost of landfilling in Australia making this form of disposal an easy option for most waste streams
    • the lack of industry schemes and initiatives aimed at encouraging higher recovery and recycling rates for specific PVC product types
    • the lack of assurance of supply continuity in closed-loop recycling of PVC products
    • the unfavourable margins between the cost of recycling compared to the price of the final recyclate

The presence of sustainable end markets for PVC recyclate and the availability of sorting processes and recycling technologies for PVC wastes are not considered barriers to its greater recycling.

2.6 End of life environmental issues and impacts relating to mechanical recycling of PVC

The recent EU Green Paper supports the contention that there are no significant environmental impacts during mechanical recycling of PVC. PVC can be reprocessed several times due to its thermoplastic nature. Mechanical recycling makes ecological and economic sense wherever sufficient quantities of homogeneous, separated and sorted PVC waste streams are available. Conventional mechanical recycling processes generally involve separation, shredding, grinding, pulverization and melt extrusion. PVC products that lend themselves to mechanical recycling include profiles, pipes, cable insulation, rigid sheeting and window profiles. Recycled PVC applications include waste water pipes, hose, floor tiles and shoe soles.

The ratio of pre-consumer to post-consumer recycling of PVC in Australia is approximately 7 : 1. There is currently a very high demand for clear, rigid PVC (mainly pre-consumer) which is achieving very high levels of recovery and recycling. Furthermore approximately 50% of clear, rigid PVC packaging scrap is being exported.

Mechanical recycling is currently not an ecologically sound option for post-consumer PVC film and sheeting which is generally too contaminated, too thin and too dispersed spatially and geographically. For PVC waste that is more dispersed, commingled and contaminated, thermal processes may become more favourable.

Closed-loop recycling or recycling into the same family of products (e.g. rigid pipe into multilayer pipe) is clearly favoured for PVC compounds containing heavy-metal additives. This form of recycling minimizes the dispersion of such additives in the environment.

Solvent-based recycling technology developed in the past few years in Europe use solvents to selectively dissolve the PVC matrix. Potential applications exist for recycling mixed and composite PVC wastes. Solvent-based PVC recycling processes are well suited to recover pure PVC compound from PVC composite waste. This technology may not be viable in Australia due to low volumes of waste PVC available.

In the case of recycling of post-consumer PVC, accessibility, collection and sorting continue to be the major impediments. Beside PVC bottles, other types of PVC packaging are often too dispersed and commingled for economic recycling to be viable. This presents an opportunity for industry to explore options for dealing with stream of PVC.

2.7 End-of-life environmental issues and impacts relating to incineration and Waste-to-Energy processing of PVC

2.7.1 MSW Incineration with Energy Recovery

Waste-to-energy (WTE) processes utilize some form of thermal treatment step to extract heat content, combustible gases and/or hydrochloric acid from PVC waste. WTE processes may be viewed as legitimate forms of recycling. The main thermal treatment processes are:

PVC waste contributes some 38 to 66% of the chlorine content in MSW. The remainder comes mainly from putrescibles (approximately 17% : table salt), bleached paper (approximately 11%) and miscellaneous combustibles (approximately 30%).

The solid waste streams from MSW incinerators are the bottom ash, the fly ash and residues from neutralization of acidic gases. The most abundant waste stream is the bottom ash, which accounts for more than 90% of the total solid waste output. The fly ash and neutralization residues (collectively known as air pollution control residues - APC residues) account for the remaining 10%. Waste PVC contributes to some 10% of the APC residues, but negligible amounts to the bottom ash.

PVC together with sources of chloride salts such as food residues in MSW are known to affect the formation and partitioning of metal chlorides in the incineration discharges. Incineration trials in Germany show that the volatile heavy metals (particularly cadmium) show a significant transfer from the bottom ash into the fly ash with increasing chlorine load in the feedstream. Thus the greater the toxicity of the fly ash. The fly ash stream from MSW incinerators however is already classified as a prescribed waste with special disposal requirements. The upside is that the bottom ash is relatively free of heavy metals and thus has higher reuse potential.

The incineration of waste containing PVC leads to increased neutralization residues and hence higher costs for their disposal. In general, the incineration of PVC (whose concentration in MSW is 0.6 to 0.8 %) appears to increase the content of leachable salts (primarily chlorides of Ca, Na and K) by a factor of 2.

PVC is often cited as the main source of hydrochloric acid (HCl) in incinerator emissions. However HCl scrubbers are required even in the absence of PVC in the waste feed to control emissions from other chlorine sources in the waste stream. Using new technology, Germany currently has nine incineration plants that absorb the HCl from the flue gases and upgrade it to a commercial HCl grade.

Current knowledge indicates that incineration of PVC waste with energy recovery and with appropriately designed flue gases purification equipment is acceptable from an environmental viewpoint.

2.7.2 Medical Waste Incineration

Clinical waste containing PVC (e.g. blood bags, drips, IV solution and tubing) is generally incinerated or chemically treated. It has been shown that PVC influences the chlorine content of clinical waste more than in the case of MSW - 50 to 86% of the chlorine in clinical waste is contributed by PVC compared to 38 to 66% in MSW.

A number of studies have concluded that no statistically significant relationship exists between the composition or amount of polychlorinated dioxins and furans (PCDD/F) concentrations in the gases emitted from medical waste incinerators and the amount of chlorine in the waste feed. However other studies exist to contradict this view. It has been shown that the operating conditions (in particular, bed temperature, residence time and air turbulence) of a medical waste incinerator can have a greater effect on dioxin formation than the presence of PVC.

The load of dioxins produced by the incineration of clinical waste in Australia is estimated at 0.9-19 g/year teq but this figure is regarded as small compared with dioxin emissions from other sources (estimated to be 149-2080 g/yr teq). Medical incinerators rapidly quench the flue gases thus minimizing dioxin. This is because medical incinerators do not capture energy from the combustion process.

Alternative disposal technologies exist for the sterilisation of PVC-containing clinical waste which do not involve incineration. These include mechanical/chemical treatment (hammer mills followed by treatment with disinfectant solution), plasma torch, thermal deactivation, electro-thermal deactivation, autoclaving, microwaving and electron beam sterilisation.

2.7.3 Incineration in Cement Kilns

Co-incineration of wastes in cement kilns is a viable solution for waste disposal and energy recovery. Cement kilns can handle low -levels of PVC waste quite effectively. The very large quantity of lime present in the clinker process means that the cement kiln in effect acts as a huge scrubber. Because of the neutralisation of acids by the lime, no additional scrubber system is required. The cement process is not well adapted however to treat plastic wastes containing appreciable levels of PVC. Generally cement processes do not allow greater than 1% chlorine levels (preferably 0.1 to 0.5%) in order to meet the specification for chlorine content in the manufactured cement.

During the process of cement kiln incineration, heavy metals present in the waste plastics (the majority of which come from PVC) are fixed by the clinker into very stable silicate structure. Australia's leading cement manufacturers (Blue Circle Southern Cement and Queensland Cement) do not currently use alternative fuels containing waste PVC.

2.7.4 Gasification

Gasification is the conversion of organic waste into combustible gas (synthesis gas) via controlled heating in an oxygen-starved, reducing atmosphere.

A close-coupled gasifier has been installed by Visy at Coolaroo (VIC). This installation is still being optimized. The process has a chlorine limit of just 60 ppm. A steam gasifier has been installed as part of the SWERF in Woolongong (NSW) by Energy Developments Ltd. (Brightstar). Since the SWERF process has a water scrubber between the gasifier and the energy recovery step, it can handle large quantities of waste PVC in the incoming feed stream without adverse consequences. Energy Developments Ltd. are still to conduct a spiking trial under independent supervision in accordance with EPA recommendations.

2.7.5 Pyrolysis

Pyrolysis of waste plastics involves heating them under vacuum or inert atmosphere to temperatures in the range 350-450C to give shorter chained hydrocarbons resembling oils, diesel, kerosene and paraffins. These products can be used as fuels directly or as chemical feedstocks in the petrochemical industry. The presence of PVC waste is undesirable as HCl is evolved and chlorinated by-products can be formed.

Problems Associated with PVC in WTE Processes

Problems with PVC in waste-to-energy systems are related mainly to corrosion and the ensuing low steam parameters resulting in thermal efficiencies of the order of 20%. Evolved HCl leads to corrosion and pitting of construction metals. This process is accelerated with increasing temperature and pressures. Thus the presence of PVC necessitates the need to strike a balance between minimizing pitting and maximizing steam pressure and operation efficiency.

Dioxins emissions from the incineration of PVC continue to be a controversial topic. A clear distinction should be drawn between the incineration of MSW containing PVC and plastic-derived fuel (PDF) based on mixed waste plastics containing PVC. In the first category there appears to be little correlation between the percentage of PVC in the waste and dioxins produced (due to the presence of chlorine from other sources). In the second category there is clear evidence that the presence of PVC contributes directly to dioxin formation as there are no other sources of chlorine in waste commodity polymers.

PVC is also a strong chlorine source for the formation of copper chloride which is in turn a potent catalyst for the formation of dioxins. It has been shown that copper chloride contributes to dioxins formation by promoting chlorination via catalytic reactions of copper compounds and carbon. There are however a number of operating strategies to reduce dioxin formation during incineration of waste containing PVC.

2.7.6 Counter Measures to Deal With PVC in WTE Processes

Fortunately PVC behaves differently to most other commodity plastics in that it decomposes quantitatively to HCl at around 200-400C. The remaining carbonaceous residue can then be combusted, gasified or pyrolyzed like any other chlorine-free, solid waste-derived fuel.

Given that the chlorine content of PVC can be thermally removed, many waste-to-energy processes for waste plastics incorporate a pretreatment step whereby the PVC fraction is dehydrochlorinated by heat treatment above 300C. The other advantage with pretreatment is that the HCl that is evolved can be recovered and used commercially. Alternatively a separate dehydrochlorination stage based on calcium hydroxide (slaked lime) injection can be incorporated. This method is used by a number of pyrolysis processes since the fuel oil products need to be low in chlorine.

2.7.7 Uncontrolled Burning of PVC

There is a much clearer link between the presence of PVC and dioxin formation in the case of uncontrolled burning of domestic waste (so-called bin-burning or backyard burning). Backyard burning fortunately is not prevalent in Australia. Recent studies in this area have found that as the PVC level in the waste is increased from 0 to 1%, the dioxin emissions increase seven fold. PVC may have an indirect impact by lowering the burning temperature (due to its high chlorine content which is not combustible) and/or augmenting the residence time, thereby resulting in increased dioxin releases.

In particular, burning of waste which is wet, compacted and contains PVC will promote dioxin formation. These are generally the conditions experienced in backyard barrel burning and inadvertent fires. In the case of accidental fires of houses and warehouses however, incineration conditions in general are better (that is, higher temperatures, less compaction, less wetness/moisture) however dioxin formation can still be significant due to the large scale of such fires.

Polcyclic aromatic hydrocarbons (PAHs) are also produced in uncontrolled fires, whose toxicity and carcinogenic potential is many times higher than that of dioxins.

Where polymers are involved, HDPE gives a higher overall emission of PAHs than PVC, however PVC tends to give higher-ringed PAHs. In particular, DEHP-plasticized PVC gives higher levels of PAHs than EDOS-plasticized PVC. The mutagenicity of particulates from combustion of PVC is higher than those produced from the combustion of other commodity plastics such as PS, PET, and PE.