Decomposition of two types of electric wires considering the effect of the metal in the production of pollutants
Highlights
► Haloge-free and PVC wires are studied at different decomposition conditions. ► Runs are performed in the presence and in the absence of the metal conductor. ► Analysis of the pollutants emitted is done. ► Important differences were found at the different experimental conditions. ► Metal enhances chlorinated compounds emission while decreases aromatics.
Introduction
The wire and cable industry manufactures a wide range of products that support a multitude of applications. Some of the major markets are communication cables, power and cable wire, automotive wiring, control and signal cables, and building wiring. Generally wires differ in conducting and isolation materials. The classic conductor material has been copper but aluminum is also used frequently today.
Many wire insulation and covering compositions contain materials, such as lead, halogenated compounds, and other compounds, that impart electrical insulation and fire performance properties. Specifically, fire retardants are used to avoid the propagation of fire. One of the most frequently used types of fire retardant, Halogenated Flame Retardants (HFRs), have been proven to be a hazard to human life and environment, which has led to regulations on their use with the ultimate goal of removing from the market.
Recently, The European Parliament has considerate to review the Restriction of Hazardous Substances (RoHS) Directive to include compounds not previously covered by the legislation such as PVC and some HFRs in electronic equipment. The former directive is closely related to the directive on Waste Electrical and Electronic Equipment also known as WEEE directive (2003). WEEE directive promotes the reuse, recycling, and recovery of these wastes as well as the collection of electrical and electronic wastes as a separate waste stream, which enhances the prospects for economic recycling. In this sense, End-Of-Life (EOL) communications and low-voltage cables are valuable because these consist of approximately 50% copper by weight. The high price of copper ensures that an estimated 95% of EOL cable and wire is recycled.
In traditional metal recycling, physical techniques are used to separate metals and plastics. The result of this operation is a waste formed by a single mixed fraction of different polymers (PVC, PE, LLDPE, HDPE, PP, etc.). Until now plastic fractions of EOL cables have been landfilled because it was considered as a waste product with low value; however, today it is known that this waste has a great value and it is suitable for recycling, by material, chemical or energy recovery. In all cases previous polymer separation is advisable. Material recovery is an attractive option for PVC; whereas either material or energy recovery are equally attractive for polyolefin waste (Hagstrom et al., 2006).
Thermal treatment of PVC wastes it is a problematic way of recovery. Besides hydrogen chloride, chlorinated aromatic compounds are evolved during pyrolysis or combustion of PVC, such as chlorobenzenes (CBzs), chlorophenols (CPhs), chlorobiphenyls (PCBs) and, polychlorodibenzo-p-dioxins and polychlorodibenzofurans (PCDD/Fs) (Aracil et al., 2005). This could be especially alarming when the process is uncontrolled. Illegal recycling, open burning at landfills or accidental fires involves a serious damage to health and to environment. Moreover, when copper is present during combustion process, a catalytic formation of chlorinated compounds and dioxins, both in gas and solid phases, from phenols have been observed (Stanmore, 2004, Ryu et al., 2005, Ryu, 2008, Altarawneh et al., 2009).
Behavior of cables and wires considering their heat release has been previously studied (Hirschler, 1994), showing that cables with excellent fire performance can be made by using a variety of materials, so that it would seem to follow that it is important to specify fire performance and leave material choice to manufacturers.
There is not extensive information of the emissions from thermal degradation processes of electric wires in oxidative atmosphere, and less in the presence of conductive metal (Chaala et al., 1997, Thibert and Gautier, 1999, Gullett et al., 2007, Kantarelis et al., 2009). The present work aims to extend the information in this issue providing the basis for the analysis of environment impact and development of new products, taking special interest on the effect of the metal on the decomposition and the previsible differences between PVC and halogen-free wires.
Section snippets
Electrical wires
Supplied by General Cable, Co., two kinds of commercial cables have been employed in this work. The first one is a common wire (designed as P), with PVC cover and reticulated polyethylene as insulation. The second one is a special fire-resistant and halogen-free wire (designed as H). Fig. 1 shows the scheme of electrical wire, the composition of the two materials used and the weight percentage of each part. As we can see in Fig. 1, the material used in the cover (or jacket) of the halogen free
Results and discussion
Table 1 shows the results on the emission of PAHs for the four runs done in the laboratory reactor. Note that these results are expressed in mg/(kg of consumed material), i.e., considering only the plastic fractions in the basis; if the whole weight is considered in the weight base, emission of runs P1 + P2 + P3 and H1 + H2 + H3 will be approximately halved (composition is shown in Fig. 1). In the first column (Table 1) we can see the results for the combustion of the halogen free wire with no metal,
Conclusions
Combustion runs of two different wires, one of them halogen-free and another PVC based, have been performed in order to study the pollutant production in different conditions. PAHs, CBs, CPhs, mono to octa-chlorinated dioxins and furans and PCBs where determined for each run.
PAHs emission decreases in the presence of the metal conductor, whereas the emission of chlorinated species dramatically increases, by using both kinds of wires.
PVC wire presents very much higher emissions than halogen-free
Acknowledgments
Support for this work was provided by the Generalitat Valenciana (Spain) with Projects PROMETEO/2009/043/FEDER, and by the Spanish MCT CTQ2008-05520.
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