PVC and the Environment
The raw materials required for the manufacture of PVC are common salt and mineral oil or natural gas. Chlorine is obtained from common salt, and ethylene is obtained from mineral oil or natural gas. Chlorine is precipitated during the electrolysis of common salt in conjunction with sodium hydroxide solution. This gas is used to produce the polyvinyl chloride.
PVC is manufactured by polymerising, or joining together, molecules of vinyl chloride (VC). VC is toxic and it is often said that PVC must therefore also be hazardous to health. On the same basis common salt, which is made from sodium and chlorine (both hazardous chemicals), is a hazardous substance. However, processed PVC today has a VC content of less than 0.1 ppm (parts per million) and, in many cases, even less that 0.01 ppm. A VC content of 1 ppm conforms to the limit set for articles in contact with food so that the quantities in processed PVC are negligible.
The manufacture of PVC uses very little energy and energy balances show that the energy used is much less than that for the production of other materials. The manufacture of a given volume of PVC requires only 40% of that required for the manufacture of an equivalent volume of steel and 13% of that required for the manufacture of an equivalent volume of aluminium. PVC also uses less oil than other polymers due to the fact that common salt is used for 57% of the raw material. The oil contained in PVC products can also be used to generate energy in incineration plants.
PVC material not only conserves natural resources but it also contributes towards the conservation of tropical rain forests. If tropical hardwoods are used for the construction of windows they should come from managed sources otherwise they involve the continued exploitation of the tropical rain forests. Most softwoods come from managed forests which do not involve depletion of resources and there are more softwoods in growth today than for many years.
Wood requires repeated expenditure on upkeep and the constant use of paints and varnishes. Natural minerals are not necessarily `harmless' and this is demonstrated by the fact that beech and oak wood dust are proven as carcinogenic to man.
The full 'cradle to grave' analysis for window materials has been carried out in Austria and shows little difference between the various materials. Details of this report are given later in this Section.
Stabilisers are added to PVC to give the required long term stability when used outdoors. Lead stabilisers are by far the most common, followed by tin stabilisers, barium zinc stabilisers, cadmium stabilisers and calcium zinc stabilisers.
Lead, tin and zinc stabilisers are largely harmless, but cadmium soaps are suspect. They produce excellent stabilisation and are extensively used for PVC windows although active steps are being taken to remove them from PVC production altogether.
The stabiliser in PVC windows is insoluble in water and since the products do not rot the stabilisers remain permanently in the PVC. The stabilisers are also insoluble and non volatile and cannot escape into the air or ground.
When burnt in refuse incineration plants, the constituent heavy metals can be retained by electrofilters and a process has been developed to recover heavy metals from electrofilter dusts.
PVC is a thermoplastic material and is both reused inside the processing factory and recycled after use.
The disposal of PVC in refuse incineration plants is harmless to man and the environment and produces significant quantities of energy. Flue-gas collectors and electrofilters can retain resultant hydrogen chlorides and any heavy metals released during the incineration process.
Dumping of PVC is also harmless. PVC cannot rot and is insoluble in water. Constituent substances remain incorporated and these substances themselves are also insoluble and non-volatile.
PVC-U in landfill sites cannot be attacked by chemical processes and micro-organisms thus ruling out the possibility of any adverse effects on the environment as a result of heavy metals contained in rigid PVC. The dumping of plasticised PVC could lead to organic substances or heavy metals seeping into drainage water as a result of the microbial degradability of a number of additives (although this is an exceptionally long term process).
Incineration Of Waste PVC
Improvements to plant design and operation have made it possible to avoid the formation of dioxin resulting during incineration of refuse.
Numerous tests carried out provide no evidence that dioxin is formed when PVC is correctly incinerated.
The dioxin emission levels detected during refuse incineration, irrespective of their origin present no risks because they fall well below the recognised limits for tolerance concentrations.
PVC is often criticised for producing HCl when it is burnt during the incineration of domestic refuse. Only about one half of the HCI produced during incineration is due to PVC. The other half is from other plant materials which contain chlorine compounds. Even without any PVC in domestic refuse there is an output of HCl which must be dealt with by scrubbing technology.
It is claimed that, when burnt, PVC contributes to the formation of highly toxic dioxin. Dioxins are a group of 75 chemically related materials of widely varying toxicity. Very few people know that dioxins are also widely found in nature.
Dioxins will always be produced in fires where organic substances containing chlorine are involved, i.e.. in cigarette smoke, burning wood or burning PVC. Present methods of analysis can now detect dioxins in a concentration of one to a billion. The dioxin traces detected in the waste air from refuse incineration plant present no hazard to man and the environment since the concentration levels fall well below the internationally recognised limit values.
The claim that PVC contained in domestic refuse causes large quantities of dioxin in refuse incineration cannot be proven. Experiments performed both in refuse incineration plants as well as in the laboratory have categorically shown this. It has been shown that a 300% increase in the content of PVC in domestic refuse gave no increase in dioxin output from previous measurements. Tests performed in a closed system, in which dioxins were measured, are not comparable with conditions prevailing in house or residential fires. When burnt in the open, the chlorine contained in PVC escapes at temperatures as low as 200oC in the form of hydrogen chloride and is therefore no longer present to form dioxin. However, in the `cold' section of incineration plants e.g.. in the vicinity of the electrofilters, dioxin may be produced from unburned carbon if chlorine or chloride, metal salt traces, in particular copper chloride, and oxygen are present at the same time. If one of these components is absent, no dioxin will be produced or any dioxin produced will be destroyed. This is why flue-ash now undergoes after treatment in a new process at approx. 600oC where oxygen is excluded. Attempts are also being made to integrate this method of after treatment into the process of refuse incineration.
The following points should be noted:
- dioxins may be produced from the burning of any chlorine containing organic substance.
- the presence of PVC has no effect on the quantity of dioxin formed.
- the formation of dioxins can be virtually completely avoided by implementing appropriate precautionary measures at plant level.
In the discussion of dioxin, a number of substances, each exhibiting different properties, are frequently a subject of confusion. A clear distinction should be drawn between the following substances:
- TCDD (22.214.171.124 - tetrachloro-dibenzo-para-dioxin)
- TCP (2.4.5 - trichlorophenol)
- 2.4.5-T (2.4.5 - trichlorophenoxyacetic acid
- PCP (pentachlorophenol)
- PCB (polychlorinated biphenyls)
- PCDD (polychlorinated dibenzo dioxins)
- PCDF (polychlorinated dibenzo furans)
- TCSS (126.96.36.199-tetrachlorobenzo-para-odioxin)
These are all dioxins and dioxin is only the commonly used term for a group of 75 chemically related substances which differ widely in their degree of toxicity. This often results in misunderstandings. For instance, there are 22 different types of TCSS alone. Only one of these, 188.8.131.52-TCDD, is the highly toxic `Seveso dioxin' (referred to below as TCDD only). This mainly occurs in mixtures with other dioxins and, in chemical terms, can only be separated from them with difficulty. In the discussion surrounding dioxins, it is therefore important to specify exactly which dioxin is being discussed.
It has recently become clear that dioxins may also be produced in incomplete incineration processes involving organic substances and substances containing chlorine. This also includes, for example, natural substances such as wood.
Traces of TCDD have probably been present in man's environment since prehistoric times and have only been recently detected due to advances in the analysis methods available.
Disposal of TCDD
TCDD can be incinerated in appropriate plants at temperatures of above 1000oC after a sufficient period of incineration.
The American Environmental Protection Authority, EPA, has defined the daily intake of 1 billionth of a gramme of TCDD per kilogramme of body weight as harmless to man. The average person can only absorb TCDD through respiratory air or through food possibly containing dioxin.
In assessing risks, the German Federal Environmental Agency concluded that even under worst case conditions the level measured fell short of the EPA safety threshold many times over.
The German Federal Environmental Agency described the risk of dioxin toxification from refuse incineration plants as negligibly low. Even in the immediate vicinity of German incineration plants. inhabitants are subject to no measurable pollution of the respiratory air by traces of TCDD. In purely arithmetical terms, pollution was 10,000 times lower than the EPA safety threshold.
In fires, there has been concern that fumes resulting from burning PVC could contain dioxins. Soil and ash samples have been analyzed in various cases. No dioxins have been detected.
For more details of the 'Transparent Case for PVC-U windows' please download the BPF document on this
Last edited: 11/03/10
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