PRODUCT EXAMPLE: PVC (Pipes) Introduction 4. 1 Of the large number of studies collected for this project, most of them dealing with products, all of them showed that PVC products have specific impacts (as do all products made of any materials) which cannot be described with generalizations. Nevertheless, the life cycle can be structured in different phases in order to describe the PVC life cycle from a top-down’ view in a simplified way (see Figure 4. 1). A general PVC life cycle does not exist, because the specific variations in the compound account for specific life cycle segments.
Figure 4. : Life cycle stages of PVC products 4. 2 PVC Production Stage Pure PVC is a hard, brittle material which degrades at around 1000C and is sensitive to deterioration under the influence of light and heat. Pure PVC is therefore supplemented with additives which improve its service life properties and allow it to be processed. With the right combination of additives, it is possible to tailor the material for various applications. There are many types of additives. Examples include: (RANDA EIJ.
OIO) plasticisers (especially phthalic acid esters or phthalates) pigments (titanium white, lead chromates)11 eat and light stabilisers (usually organic compounds based on lead, tin, zinc, barium, a number of organic antioxidants and co-stabilisers, cadmium)12 lubricants (wax, fatty alcohols, fatty acid esters) fillers (chalk, china clay, talcum, magnesium oxide) flame retardants (antimony trioxide, aluminium hydroxide, magnesium oxide, chloroparaffns), these are rarely used since PVC itself is relatively flame retardant impact modifiers; and fibres used as reinforcing materials (rarely used for PVC) Table 4. contains the typical composition of various PVC products. In terms of eight, plasticisers are the most significant additives for soft PVC. The plasticiser content of so-called “flexible PVC” normally accounts for 20 to 40% of the weight of the PVC product, but there are also plasticized PVC formulas which consist of more than 60%. Table 4. 1 : Typical composition of PVC compounds (RANDA EIJ. 03) Component Share (weight – %) PVC polymer Plasticiser Stabiliser Filler Others Rigid PVC applications Pipes 1-2 Window profiles (lead stabilised) 85 3 4 8 Other profiles 6 Rigid films 95 -13 5 Flexible PVC applications Cable insulation 42 2 Flooring (Calendar) 15 41 Flooring (paste, upper layer) 5 32 Flooring (paste, inside material) 35 25 Synthetic leather 53 From a chemical viewpoint, PVC is a thermoplastic polymer based on chlorinated hydrocarbons. Figure 4. 2 provides an overview of the production processes leading from raw materials to finished products (RANDA EIJ. 03). PVC is produced from two primary raw materials, ethylene and chlorine. These react to form ethylene dichloride (EDC) which, upon cracking, yields vinyl chloride monomer (VCM). Free radical polymerisation is used to produce the PVC polymer itself. The two most important polymerisation techniques are suspension polymerisation nd emulsion polymerisation, leading to the production of S-PVC and E-PVC, respectively. These two types of PVC polymer have different properties and are used for distinct applications.
The SPVC process yields granules of polymer of 100 to 200 microns in diameter, which are used in processes such as injection moulding; extrusion and PVC film manufacture (RANDA EIJ. 003). Here, S-PVC is analysed in more detail, as it is more commonly used. The difference between S- and E-PVC is rather small, as the type of polymerisation has a low impact on the overall performance of the PVC over its life cycle. Figure 4. : Overview of PVC product manufacture (RANDA EU. 003). 4. 3 PVC processing Once PVC (granules or powder) has been mixed with the required additives, some form of heating is usually required.
This binds the PVC particles together and helps of PVC become freed and become entangled. Upon cooling, these recrystallise to form a three-dimensional structure, a process known as gelation or fusion. (RANDA EIJ. 003) Numerous techniques are used to process the various PVC compounds into the wide range of final products: Extrusion Injection moulding Calendaring Blow moulding Rotational moulding Dip moulding Coating process to produce PVC plastisols Environmental Impact: Emission of plasticisers to the external environment from PVC processing is estimated by Cadogan et. al. (1994) to be 0. 02 – 0. 7% of the total mass of plasticiser used, and is highest from the calendaring process (IPIJ. OOI 7). During manufacturing it is estimated that 91% of plasticiser emissions are released to air, and 7% directly to water. Evaporation, followed by air transport, and wet and dry deposition, are said to be the major routes for emissions to the environment. It is possible that this transport is global, as DEHP has been found in traces in Antarctic sediments. (IPIJ. OOI 7) Energy consumption for different processing methods is shown in table 4. 5. (IPU. 0017) Table 4. 2: Energy consumption for different processing methods (T?¶tsch, Gaensslen, 1992.
Based on Kindler, Nikles, 1980). Processing method Energy consumption (MJ/kg) Film extrusion 3-6 Film calendering Pipe extrusion 3-5 5-15 In this section, as mentioned previously, only the most prevalent product groups are discussed. Window frames In 1996, the materials used in window frames in Germany were (IKP-C)-6): PVC 49% wood Aluminium 20% Wood-aluminium 3% This confirms the importance of PVC in this market. Average composition: The verage composition of a PVC Window frame is shown in Table 4. 6. Table 4. 3: Average composition of a PVC-Window frame IKP-D-6 PVC 59. 3% 78. % – lead phosphate and stearate 1. 8% – ca,zn 5. 5% 5. 1% – powdered limestone 3. 65% Pigment – titanium dioxide 2. 54% 3. 4% 19. 76% 3. 49% Acrylate rubber 4. 38% 6. 8% Nitrile or PVC 4. 01% Petroleum wax and fatty acid ester 1. 12% 1. 1% Production process: The manufacturing of the window frames involves the following steps: (IKP-D-6) Extrusion of PVC granulate to form a window-frame profile Mitre off the profile Adding vents for drainage and for the attachment of fittings Welding of nooks and emoval of weld seams Assembly of fittings, glazing and seals Assembly of window frame and casement.
Environmental impact: The amount of primary energy required for the production and recycling of a PVC window frame is considerably larger than that for a wooden window frame. However, when taking into account the Global Warming Potential of each, it becomes clear that the difference is not that big because part of the required energy is embedded in the PVC material itself. (IKP-C)-6) The low value of the Photochemical Ozone Creation Potential for PVC is worth noting. PVC windows need no special surface treatment.
Additionally, the hydrocarbons emitted from the material during production are treated with exhaust air cleaning systems for workplace security and environmental reasons, and hence, do not reach the environment. (IKP-C)-6) The stabilisers based on CalZn compounds, considered in the IKP-D-6 study, are not toxic. But the production processes of the PVC material continue to dominate the ecological impact in this category. The production of the pigment titanium dioxide (Ti02) adds to the toxicity potential. Recycling is a crucial issue for the life cycle of PVC window frames.
A controlled losed-loop recycling scenario results in considerably lower environmental impacts. However, closed-loop recycling can only work in growing PVC markets, i. e. if the In addition, problems may arise in closed loop recycling because of the fast enhancement of stabiliser systems that may lead to non-compatible stabiliser systems appearing in the same recycling material. This problem, however, is not prevalent at the moment, as the most common stabilisers are compatible and can therefore be mixed together.
Co-extrusion with a cover layer of virgin material could solve this problem for non-compatible stabilizers. 4. 4 Manufacture of PVC Pipes According to IPlJ. 0019, in 1996 23% of sewer pipes in Sweden were made of PVC. In Germany, the use of PVC pipes in 1993 for various pipe applications was as follows (IKP DE-42): wastewater Pipes 45% Pipes for laying of cables 18% Freshwater pipes 18% Pipes for drainage 9% Other pipes 9% Average composition: Composition of pipes varies depending on the producer and the application. The following average compositions were provided in the studies collected: Table 4. : Average composition of sewer pipes in mass % (IPU. 0015) (IKP-NL-3) 92. 1 – tribasic lead sulphate 1. 4 – dibasic lead stearate 0. 5 – lead stearate 0. 2 1. 1 calcium stearate 0. 4 – lead stabiliser 3. 8 4. 70 Stearic acid 0. 1 Synthetic hard wax Paraffin (lubricant) 0. 7 – Carbon black 0. 02 – Titanium oxide The IPlJ. 0019 study provides a different composition. A share of 0. 75% lead-stabiliser or 0. 3 – 0. 4% tin-stabiliser is estimated. Further, 0. 1% synthetic hard wax is required, but no plasticiser is needed. The IPlJ. 0032 study lists 1. % stabiliser and 0. 15 – 0. 20% lead pigment content in red/brown pipes. PVC can consist of virgin and/or recycled material. A French study (RANDA FR. OOI) compares pipes made from virgin PVC and 9. 3% recycled PVC with pipes containing rimary zinc and 40% recycled zinc. Production process: Again, the production process varies by producer, application and composition of the pipe. For example, as described in the IKP CH-5 study, unplasticised PVC powder is mixed with additives in hot mixers prior to processing. Additives are contained in the PVC granules upon delivery.
Material is then converted Typical diameters and weights for water pipes are: (IKP-AT-5) 1 50 mm mpipe 250 mm = 6,59 kg/mpipe 400 mm = 16,81 kg/mpipe A scheme for the production of PVC pipes can be seen in Figure 4. 3. = 632 kV Figure 4. 3: Schematic flow diagram for the production of Pipe (IKP-AT-5) Environmental impact: The environmental impacts of pipes vary with composition and application. Some impacts included in the studies examined were: contribution to the greenhouse effect, photochemical ozone formation, acidification, eutrophication, air and water pollution, depletion of abiotic resources, aquatic eco- toxicity and human toxicity.
Pipes composed of virgin PVC or recycled PVC have lower impacts than those containing zinc or recycled zinc (RANDA FR. OOI). Primary zinc and mixed zinc coated steel pipes used 1. 6 times the amount of non-renewable resources than virgin and recycled PVC pipes. Furthermore, primary zinc pipes consumed 3. 4 times and recycled zinc almost double the amount of mineral material required by virgin PVC and recycled PVC pipes. However, zinc pipes consumed less than half the amount of water required by PVC pipes (RANDA FR. OOI).
Recycled zinc pipes for gutter and rainwater contribute twice the amount to the greenhouse effect than recycled or virgin PVC pipes contribute. Additionally, 40% recycled zinc pipes contribute more to ozone formation, acidification and eutrophication than PVC pipes do. For air and water emissions as a whole, recycled zinc pipes contribute almost 3 times more than recycled PVC pipes. Overall, PVC or recycled PVC pipes score higher in all categories than zinc pipes, with the exception of the water consumption category (RANDA FR. OOI).
For potable water and sewage disposal pipes, HDPE and unplasticised PVC systems contribute a greater amount to eutrophication and acidification than other materials (IKP-CH-5). Cast iron and stoneware systems contribute considerably to greenhouse potential. The same study also concludes that a preference for a particular material cannot be Justified on the basis of LCA results alone. Furthermore, the following results from the IKP-CH-5 study are worth noting: The results based on 1 metre lengths of pipe show stoneware, rather than PVC, to be an ecologically advantageous material over a large nominal width range.
However, if a complete wastewater line system in a factory is examined, PVC is among This is concluded despite the fact that the study determines PVC to be not scientifically durable as it is burdened by C02 emissions from an assumed decomposition of the material. Only if it is assumed that stoneware pipes will have a useful life twice as long as that of PVC pipes (which is hardly the case in reality), does the balance shift in favour of stoneware. For potable water and sewage systems, HDPE pipes required the greatest amount of energy for production, followed by PVC, and lastly by cast iron.
Greenhouse potential was highest for cast-iron pipes, followed by HDPE and PVC pipes. Acidification and eutrophication potential were higher for PVC pipes and lower for cast iron pipes for both sewage and potable water systems. The IKP CH-13 study compares pipe materials for drainage and sewage applications. The study compares vitrified clay, concrete, reinforced concrete, reinforced concrete with protection against corrosion, cast iron, HDPE and PVC. Vitrified clay required the least amount of energy for production, while cast iron required the most.
C02 emissions are lowest for PVC and HDPE production; however, these levels increase if decomposition is taken into account. Plastics as organic materials are eventually decomposed to C02, H20 and solid residual substances. This effect is only significant if extensive time frames are taken into consideration. Overall, the IKP CH-13 study concludes that for energy, the consumption level depends on the diameter and useful life of the pipe. This can also be verified in the IPlJ. 0032 study. Vitrified clay and plastics have lower energy consumption rates for small pipes.
Larger pipes require less energy when made from concrete, followed by vitrified clay, cast iron and plastics. However, when concrete pipes include corrosion protection, they fall to the level of plastics. C02 emissions are approximately analogous. If it is assumed that the pipes are not replaced during the use phase, vitrified clay becomes the preferred material (IKP-CH-13). Table 4. 5: Primary energy consumption during the life cycle of PVC sewer pipe in MJ/ m Pipe (IPU. 0032) Pipe prod. Laying Transport Total Diameter 110mm 69 20 74 1. 2 165