Recycling of PVC-U in windows and building products
There is much ill-informed criticism regarding the suitability of PVC for use in windows and other building products. The claims of certain environmental groups, particularly Greenpeace, are based largely on emotional arguments regarding PVC and chlorine - the "devil's element".
If you take chlorine (a toxic and deadly gas) and mix it with a highly reactive metal (sodium) the resulting compound is sodium chloride or NaCl. This product of two deadly chemical is that most harmless of all products - common table salt - and without salts in our bodies we would die very quickly. The wonder of chemistry is that the properties of a compound are not related to the properties of the individual elements that make up the compound! Greenpeace, however, have taken the simplistic view that anything which involves chlorine is "bad" and have targeted the PVC industry on this basis. This is despite some simple facts that all the blood bags used to transport human blood in Europe are manufactured from plasticised PVC, PVC is one of the most preferred and approved materials for the manufacture of medical tubing and PVC is involved in saving lives on a daily basis in current medical technology - if this is the material that is a danger to mankind then we certainly need a lot more materials like this.
The extrusion and general use of PVC in particular has come under attack from environmental groups such as Greenpeace because of the presence of chlorine in the material. The industry has replied strongly to the "technical" claims of the environmental groups but this has also been mainly at a technical level rather than at the emotional level of the main environmental argument. The arguments against PVC have varied between demanding a ban on the usage for certain applications to seeking substitution of PVC with other more "eco-friendly" materials. Since the growth in the application of extruded products has largely been at the expense of other materials by substitution (pipes and window profiles in particular) it is perhaps ironic that PVC is now seen by some as a candidate for substitution.
The general environmental arguments for and against PVC have been significantly and comprehensively discussed in many industry publications and particularly in the Chlorophiles Pages.
Eco-profiles for extrusion and materials
Ecological appraisals and life cycle assessments have been carried out for both the extrusion process and for the materials used in extrusion. These have been not only by the manufacturers and their trade associations but also by government and independent organisations throughout the world. The Association of Plastics Manufacturers in Europe (APME) has prepared an eco-balance methodology for commodity thermoplastics and a series of eco-profiles on both the processing methods and the various polymers. These eco-profiles use data derived from real plants to provide a complete analysis from production through to packing. As well as providing information for external analysis, this process of eco-profiling has also given manufacturers a clearer insight into the efficiency of plant operation.
Other Life Cycle Assessments (LCA) have been carried out for specific products to compare the relative impact of different materials when used for common applications. These have mainly been for short life cycle products, such as packaging but studies on long life cycle products have found that PVC is better than or equal to other materials considered. Significant results of the studies carried out have been:
LCA studies on iron, polyethylene and PVC pipes by van den Berg et al showed that in terms of a variety of environmental themes the plastic materials were equal to or better than other materials. The "cradle to grave" approach shows that extruded plastic pipes do not present a significantly different environmental impact to competing materials.
LCA studies on window profile materials by Novak and Ecker compared PVC, aluminium and wood as window frame construction materials and concluded that there was no basis for recommending any particular material on environmental impact grounds. Any firm conclusions on environmental impact required an analysis of the specific requirements of the application.
Some key points were :
- The environmental impact for products varies as much from plant to plant as it does from material to material.
- The environmental impact at production level for various materials is much smaller than the environmental impact of the product over its lifetime.
- The balance of evidence suggests that in long life cycle applications (such as building products) there is no alternative material to PVC that has less overall effect on the environment.
Overall, the environmental criticism of the use of PVC products in either short or long term applications appears to be the product of emotion rather than science.
This section focuses specifically on the recycling aspects of PVC-U, the current technologies and methods used to recycle PVC.
At the most basic level, the principles of reducing the impact of any process or product consists of avoiding waste, recovering waste and recycling waste. In the current competitive marketplace, every industry sector is aware of the need to avoid and recover waste where possible. The PVC-U industry is not alone in this but it is in front in terms of recycling waste to minimise environmental impact.
All thermoplastics (and PVC-U is a thermoplastic) are by their very nature recyclable and can be reprocessed in a variety of ways. The consumer waste area, notably packaging, is definitely the most visible area of plastics usage. However 88% of all PVC used has a service life span of over two years and the recycling of PVC must take this into account.
PVC is definitely recyclable and the logo for PVC that would appear on any consumer goods is shown below - This logo is part of a larger system for the identification of common plastics that can be recycled.
The recycling of any material can relate either to the raw material i.e. recycling the PVC back into the processing system) or to the chemical products (i.e. recycling the energy and the basic chemicals which make up PVC back into the chemical industry).
Any discussion of recycling must first define where the recycling occurs. A distinction needs to be drawn between the re-use or reclamation of scrap and head waste inside the extrusion factory and the true recycling operation which refers to post-application re-use of the material. The APME has produced an outline of the various routes to recycling and this is shown below:
The APME outline of recycling processes
The re-use of scrap or reclamation of scrap and head waste as a materials source for further products is well developed in most extrusion companies. This is a source of valuable material, which can be blended with virgin material to extend and sometimes improve the properties of the virgin blend. In this case. the material is free from contamination and is prepared from unused PVC profile that is below standard in dimensional terms or from the start-up of the run. It may also include off-cuts from quality testing or other areas. The material is reprocessed in the factory where it was originally produced and the material formulation can be precisely defined.
Where in-house re-use is not possible, the scrap is sold commercially for further treatment and resale. It is estimated that up to 95% of in-house scrap is re-used in this way. The effect of multiple extrusion cycles on polymers varies with the thermal sensitivity and history of the polymer but provided the addition is kept low, there is rarely any significant loss of performance. In some cases blends of up to 50% recycled material has been used successfully and have achieved optimum properties. Research carried out by the BPF Windows Group on a range of profiles and percentages of reprocessed materials shows that certain mechanical properties of the PVC-U are actually improved by adding defined amounts of reprocessed material. The current British Standard BS 7413 for PVC-U windows allows the use of reprocessed material in the production of Kitemarked PVC-U profiles.
Reprocessing is already carried out to a large degree by extrusion companies to conserve raw materials and reduce product costs. As a general rule the amount of material available for this operation is less than 7% of the total material used in the process.
Allied to in-house reprocessing is fabricator reprocessing. This involves the fabricator selling off-cuts and other waste PVC-U material generated in the factory. This material is classed in the draft European standards as "external reprocessable material" (ERM). The two possible types of ERM are: ERMa, only PVC-U window profile; ERMb, a mixture of window profile and other PVC-U products. Only ERMa may be used for the further production of PVC-U windows and then only as the core of a co-extruded profile.
This type of reprocessing is carried out by most fabricators who sell their off-cuts to recycling companies. In general the amount of PVC-U available and reprocessed in this manner is also less than 7% of the total material used in the process.
Currently only a small proportion of the PVC actually used in building products enters the solid waste stream and it forms only about 0.7% of all domestic and trade solid waste. This is because the majority of PVC is used for durable products in the pipe. window and general building industries and 64% of all PVC products have a service life of more than 15 years.
The long life span of most PVC-U products in the building industry and the life span of PVC-U windows in particular means that there is little experience of post consumer use recycling in the UK or indeed the rest of the world. The recent development of recycling systems in Germany by the PVC-U processing industry however shows that managing this aspect of the recycling chain is possible when the need eventually arises.
Specialist disposal firms are used in Germany to separate the PVC-U frames from other materials. Recent developments by companies such as VEKA show that it is possible to mechanise the PVC recycling process to improve efficiency. To date though, even in Germany, there is only a small quantity of PVC-U in the waste stream. This will increase with time and as products are replaced due to changing consumer preference. The systems will then be in place for efficient recycling of PVC-U.
A prerequisite for efficient recycling is the identification of large PVC-U components (such as window frames) before they enter the solid waste stream and become part of more general waste.
Sorting or collecting at source is always more effective than sorting afterwards and this requires care from all levels of the industry.
It is worth noting that the concept of materials recycling means returning the material for use in the original product. The subsequent reuse of material for other products with lower requirements. sometimes termed "downcycling" is not true recycling. By this definition, PVC-U can be truly recycled which means that it is better placed than many other building materials.
The need for recycling, at any level of extruded products, is not yet fully developed because of these long life cycles. For instance, in the UK the first PVC windows are only now approaching 25 years old and have not yet reached the end of their service life and are therefore not entering the post application waste stream. The Swedish National Environmental Protection Board found that the greatest potential for the re-use of PVC is to be found in the building and construction industries. This is because these products are easily identified and increasing quantities will become available in the future. Recycling technologies for extruded products are being developed and refined and the systems are being put into place to cope with the materials when they become available.
The UK experience with plastics recycling has had mixed success despite the best efforts of many participants from industry and government but trial projects and technology development continues in many areas.
Plastic products represent less than 8% by weight of the municipal solid waste stream in Western Europe but techniques are already being developed to recycle these materials rather than incinerate or use them for landfill.
Where the material to be recycled is a single plastic type the recycling process is easier and recycled materials have been used for a variety of end uses such as PVC supermarket trays recycled into the foamed layer for co-extruded cladding.
Where the material to be recycled is not of a single plastic type and sorting is not economical then the extrusion process is an essential component of the recycling technology. Mixed plastics waste (MPW) is recycled by first grinding or otherwise reducing the plastics particles to a manageable size. The granulated waste must be reasonably homogeneous and consistent in composition but the constituents can also be modified by additives or blending. Processing can then be by single or twin screw extruders to enable the production of pipes, profiles or sheet or compression moulded products. Examples of this technology are the production of noise reduction screens for motorway traffic and building profiles. The current technologies used are mainly mechanical in format and new technologies are being developed to improve the composition and quality of the basic feedstock.
In terms of basic raw material usage, PVC is a particularly efficient type of polymer. The raw material for the base resin are 57% chlorine (derived from salt and 43% ethylene (derived from either crude oil or coal). These products can be almost totally recovered by the correct incineration processes to give both energy and chemicals. This process also produces very little CO2 compared with the incineration of other materials.
PVC is responsible for about 50% of the HCI generated in incinerators and the rest comes from other salt and chlorine containing products (wood, paper etc.). It has proved possible in Germany to complete the "salt cycle" by purifying and neutralising the HCI with caustic soda to regenerate the salt that originally started the cycle to produce PVC. This process also removes 50% of the HCI that did not come from the PVC in the first place.
This salt cycle embodies the recycling ethic. The raw materials are used for a time but are eventually returned whence they came. The use of PVC-U for windows and other building applications gives us an opportunity to use a material that is recyclable at many levels and that truly has life after death.
The complete map for PVC-U recycling is shown below:
For more information on Chlorine in the environment and the Greenpeace campaign see the Chlorophiles Pages.
Last edited: 11/03/10
© Tangram Technology Ltd. 1999
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