A LIFE CYCLE ASSESSMENT-BASED COMPARISON OF ENGINEERING THERMOSET AND ALUMINUM IN AN AUTOMOTIVE UNDER-THE-HOOD APPLICATION David P. Evers, Sigrid ter Heide, Tanis J. Marquette Hexion Inc. 180 E. Broad Street Columbus OH 43215 USA ABSTRACT The automotive industry is looking for options to reduce weight and increase engine efficiency to comply with new CO2 emission and fuel economy regulations. Substituting lighter weight materials may involve important trade-offs such as those to the environment. Life Cycle Assessment (LCA) is a holistic approach to evaluating the potential environmental impacts of a product or process. An LCA incorporates all of the product manufacturing steps starting with raw material in-the-ground, on-the-hoof, or on-the-stalk, through the ultimate management of the product and its residuals at the end of their life. This paper will discuss a comparative LCA on an automotive water pump housing manufactured of a thermoset composite resin relative to an alternative water pump housing manufactured from aluminum. The LCA results appear to support the conclusion that the lighter weight thermoset composite water pump housing has environmental benefits relative to the alternative aluminum water pump housing. LCA results can provide engineers and designers a (more) rational basis for comparing alternatives when used in conjunction with life cycle cost and product performance data. INTRODUCTION Life Cycle Assessment (LCA) is a structured process for assessing the potential environmental impacts of a product or process from cradle to grave. The process is established in two ISO standards: 14040 (2) and 14044 (3). Further, to help users create and interpret an LCA, many organizations (4, 5, 6) have produced guidance documents providing background discussion and examples. To help reduce the effort required producing an LCA, there are several commercial software packages available which help create an LCA, and most also provide data on generic processes, such as the generation of electricity or production of fuels. Hexion Inc. (Hexion) manufactures a variety of resin materials which are suitable for compounding with strengthening materials and fillers to form thermally stable, lightweight composite parts. This paper discusses the process of producing, and the results for an LCA for a thermoset composite water pump housing for the automotive market. This part is one-third lighter than the aluminum water pump housing it is designed to replace. The light weight should lead to better fuel economy, but there are still questions about the energy intensity of production of the resin and water pump housing, and what happens at the end-of-life for the water pump. When completed, an LCA can help to answer these questions, can identify areas where data gaps exist, and can be used to identify areas for further research to improve a product.
Functional Unit and System Definition The basis of analysis, or functional unit, for this LCA was defined as a thermoset composite water pump housing designed as a substitute for aluminum pump housing on a mid-size, gasoline-powered automobile. This pump has a service life of 200,000 km, at which point it is removed and managed through the normal, expected end-of-life management options potentially including reuse, recycling of the aluminum water pump, and energy recovery for the thermoset composite water pump. The system defined included the activities required to process the raw materials, create the resin or aluminum, create the water pump housing, and manage the water pump at its end-oflife. This also includes the auxiliary materials required where these differed between the two water pumps (seals, lubricants, etc.), conditions of resin, composite and pump housing manufacture, reuse and recycling opportunities, and disposal. Assumptions One difficulty encountered was defining the end-of-life of the composite water pump. The focus of this LCA effort was on the European market where the End-of-Life Vehicle Directive 2000/53/EC sets goals to European member states for the re-use, recycling and recovery rates. These targets can only be met if additional material recycling and recovery takes place on fractions from post shredder technology plants. European countries that have a landfill ban or high landfill taxes have invested in post shredder technology capacity and with the implementation of the End-of-Life Vehicle Directive additional capacity is added all over Europe. After the car reaches its end of life it is dismantled and goes through a shredder to recover scrap metals. The remaining automotive shredder residue (ASR) is supplied to a post shredder technology plant where the material is sorted into plastic granules, fibers and sand fractions depending on particle size and density. The plastic granules are further separated into 3 density fractions: the high density fraction contains chlorine due to the presence of PVC and is incinerated, the medium density fraction goes to a blast furnace and the low density fraction can be separated into the original polymers for recycling. While the engineering thermoset composite contains no chlorine, its material properties cause it to sort into the high density plastic granules fraction. Therefore incineration with energy recovery was included in the LCA model. The dismantler depollutes the end-of-life car, removes good quality parts that can be reused and delivers the car clean to the shredder. For the aftermarket there is basically no difference between metal or plastic parts, a second hand composite water pump could replace a damaged aluminum one after a car accident and vice versa. As no detailed collective re-used part data is available it is assumed in the LCA model that re-use of engineering thermoset composite and aluminum parts is similar and equal to the general 23.8% re-use after end-of-life reported by Automotive Recycling Netherlands (ARN) (1).
The last questions to be addressed in defining the system to be modeled were around the use phase. This phase included the automobile assembly operation and the driving cycle. Since there were not expected to be any differences between the current water pump and the composite pump during automobile assembly, this process has been omitted from the model. While the weight differential between the aluminum and thermoset composite pumps is expected to be small, on the order of 100 grams, including the expected changes in fuel consumption during the driving cycle was desirable to better understand the importance of the light weighting of the water pump. The typical approach in an LCA model would be to allocate the overall fuel consumption of a vehicle in proportion to the mass associated with the water pump. While the fuel consumption during the use phase is a potentially significant driver of environmental performance of both water pump systems, preliminarily calculated as part of this LCA as being approximately 90 percent of the energy consumed across the life cycle, with a proportionate share of Global Warming Potential emissions, as examples, differences in fuel consumption and the resultant potential environmental impacts could be seen. However, the mathematical allocation of the vehicle fuel consumption to a water pump is not significant overall with respect to the vehicle mass (corrected for fuel consumption to overcome air resistance). The water pump comprises between one and three hundredths of a percent or 1 to 3 parts in ten thousand (0.0001 to 0.0003, or the fourth decimal place), while the fuel economy is typically accurately measured only to three significant digits. From the perspective of the vehicle, the change in fuel consumption due to using either the aluminum or thermoset composite water pump is within the measurement error or the noise in the analysis. For this reason the driving cycle fuel consumption was not included in the LCA model. If the thermoset composite was used in a larger application on a high volume vehicle the mass savings and the total environmental impact would be significant. Taking into account these assumptions and the choice of processes to include or exclude, the systems to be analyzed were constructed as shown in Figures 1 and 2 for the thermoset composite and aluminum water pumps, respectively. Excluded processes were included on the diagrams for the sake of being complete, but are delineated in red. Included processes are delineated in gray. Figure 1. Thermoset Composite Water Pump System Boundaries
Life Cycle Assessment Modeling Figure 2. Aluminum Water Pump System Boundaries EXPERIMENTATION Data for background processes have been taken from the GaBi 6.108 (2014 update) database prepared by PE International. Modeling of the systems was performed using GaBi 6.4. Background data are denoted by the use of italics in Table 1 where inclusions or exclusions are shown. Specific GaBi data module names and geographies are included for background data also. Processes in regular typeface are those for which data was collected as part of preparing this LCA. These modules were assembled into the life cycle system as shown in Figures 1 and 2 above. Results were taken from GaBi, either the Balance or from the ILCD recommendations for potential environmental impacts, which is more appropriate for the European market.
Table 1. Study Components Included and Excluded Included Aluminium die-cast part [DE] Secondary Aluminium (Clean Scrap Remelting & Casting) [NA] Aluminium ingot mix [DE] Electricity grid mix [DE] Thermal energy from natural gas [DE] Diesel, at refinery Truck-trailer [GLO] EoL, Water Pump, Aluminum Scrapping, Water Pump, Aluminum Electricity grid mix [BE] Phenol [DE] Formaldehyde [US] Process steam from natural gas 85% [DE] Glass fibres [DE] Aluminium Scrap Credit (Open Loop) [Nation] Aluminium Recycling (2010) [EU-27] Phenol-Formaldehyde Resin 7045 Production [DE] PF 6510 Compound [BE] Injection Molding, Water Pump, Thermoset Resin [BE] EoL, Water Pump, Thermoset [RER] Waste incineration of plastics (unspecified0 fraction in municipal solid waste (MSW) [EU-27] Tap Water [EU-27] Landfill of Plastic Waste [EU-27] Landfill (Municipal household waste; AT, DE, IT, LU, NL, SE, CH) [EU-27] Landfill (Commercial waster for municipal disposal; AT, DE, IT, LU, NL, SE, CH) [EU-27] RESULTS Excluded Use Phase (Driving Cycle) Sealants Packaging Automobile Manufacture Reconditioning An LCA is an iterative process: as preliminary results are generated, the importance or significance of processes is better understood in the overall results. From this, the need to have better information can be defined leading to more data collection, modeling, and assessment. Further, for comparative LCAs, iteration often is driven by subtle, but important differences between systems, and the need to have comparable system boundaries, and levels of detail within the modeled system. Thus, the model presented here is currently still being refined as the modeling, assessment and interpretation of the results continues, as Sensitivity Analysis is completed, and as the Critical Review provides feedback. Please consider the results presented here as preliminary, but generally indicative of directional trends.
Table 2. Select LCA Results Units Aluminum Water Pump Thermoset Composite Water Pump Relative Change of Thermoset Composite Water Pump relative to Aluminum Water Pump Resource Consumption Energy, Net Calorific Value, Nonrenewable MJ 40.4 12.4-69.3% Energy, Net Calorific Value, Renewable MJ 12.1 0.806-93.3% Energy, Net Calorific Value, Total MJ 52.5 13.2-74.8% Water Withdrawals m 3 27.7 0.381-98.6% Potential Impacts for Emissions Global Warming Potential kg CO 2- equiv. 2.97 0.64-78.4% Ozone Depletion Potential kg R11- equiv. -3.24E-10-1.91E-9 490% Human Toxicity (Cancer) CTUh 5.87E-9 2.82E-8 380% Human Toxicity (Non-Cancer) CTUh 1.36E-7 1.50E-8-89.0% PM 2.5- Particulate Matter equiv. 8.12E-4 6.54E-6-99.2% kg Photochemical Ozone Creation NMVOC Potential -equiv. 6.63E-3 8.21E-4-87.6% mol H + - Acidification Potential equiv. 1.52E-2 4.12E-3-72.5% mol N- Eutrophication Potential, Terrestrial equiv. 2.49E-2 1.56E-2-37.3% kg P- Eutrophication Potential, Aquatic equiv. 1.58E-6 7.07E-6 347% Ecotoxicity CTUe 1.36E-1 5.57E-2-59.0% Resource Depletion, Water kg 2.74 1.66-39.4% Resource Depletion (Mineral and kg Sbequiv. Fossil) 3.74E-5 1.74E-5-10.6% Summary Comparative LCA Results Table 2 shows select LCA results for the systems. When examined in greater detail (not shown here), one can see that aluminum production: either as primary or secondary (recycled) drives many of the results for the aluminum water pump. However, for the thermoset composite water pump, drivers for many of the impacts are not the production of resin, but the fillers and reinforcements added. The one exception to this is seen for Eutrophication to Water, where phosphate emissions from fertilizers in cotton growth for the cellulose in the compounded resin drive the results. With this knowledge in hand, Hexion is currently investigating replacements to further reduce the potential environmental impacts.
Increasing the Recycled Aluminum Content The easiest scenario to justify would be to decrease the content of primary aluminum in the aluminum water pump, replacing it with recycled aluminum. A 30 percent value for recycled aluminum content was chosen based on http://www.alcoa.com/ingot/en/info_page/recycling.asp, which states Alcoa has a goal of reaching 50 percent recycled content for its ingots, implying the current standard is less than 50 percent. In table 3 energy consumption figures are presented for the base case, 30 and 50% recycled content. Table 3 [1]: Summary of Life Cycle Impacts with Alternative Recycled Content Fraction, per water pump 1. Impact Criterion 2. Units Aluminum Water Pump, base case Aluminum Water Pump, 30% recycled Aluminum Water Pump, 50% Recycled Thermoset Composite Water Pump Energy, Net Calorific Value, Nonrenewable MJ 40.4 29.9 22.8 12.4 Energy, Net Calorific Value, Renewable MJ 12.1 8.67 6.41 0.806 Energy, Net Calorific Value, Total MJ 52.5 38.6 29.2 13.2 CONCLUSIONS In pursuit of ever-increasing fuel economy, either to meet more stringent regulations or as a means of competitive differentiation, automobile manufacturers are looking at the use of lighter weight parts to reduce vehicle mass. These parts tend to be produced from aluminum, as a light weight metal alternative to steel; and increasingly from composites, using thermoplastic or thermoset resin as a base. The composite materials often offer significant weight advantages, but with the negative public perception that they are less environmentally friendly due to any of a number of actors such as the much lower ability to recycle these materials, or the use of petroleum products in their manufacture. This LCA effort was undertaken to demonstrate that the lighter weight thermoset composite water pump can be used without significant environmental disadvantages relative to the alternative aluminum water pump. While the LCA was unable to quantify any fuel economy benefits, if the thermoset composite water pump cannot provide at least as good an environmental performance as the aluminum water pump, the increase in fuel economy by itself may be insufficient to merit use of the thermoset composite. As shown in Table 2 above, the thermoset composite resin water pump would appear to perform at least as well as the aluminum water pump from an environmental impact perspective. Using engineering thermoset the energy consumption and global warming potential is significantly reduced and there is a larger credit for Ozone Depletion Potential thanks to energy recovery from manufacturing and end-of-life waste. The two indicators where the thermoset composite water pump has a larger impact are:
Human Toxicity (Carcinogenity). Though a firm conclusion is hard to make with the large margin of error in the toxicity results due to the many compounds in the matrix. Eutrophication to Water. The thermoset system result is driven by cotton-derived cellulose production. It will be investigated if this can be lowered by seeking out substitutes. If there is no significant fuel consumption attributable to either of the systems and especially no significant increase in fuel consumption attributable to the thermoset composite water pump--then these results would appear to support the conclusion the thermoset water pump does offer environmental advantages over the aluminum water pump. 1. ARN Sustainability Report 2013 REFERENCES 2. International Organization for Standardization. 2006. ISO 14040:2006 Environmental management -- Life cycle assessment -- Principles and framework. 3. International Organization for Standardization. 2006. ISO 14044:2006 Environmental management -- Life cycle assessment -- Requirements and guidelines. 4. UNEP-SETAC. 2005. Life Cycle Approaches - The road from analysis to practice. 5. UNEP-SETAC. 2007. Life Cycle Management: A business guide to sustainability. 6. UNEP-SETAC. 2011. Global Guidance Principles for Life Cycle Assessment Databases: A Basis for Greener Processes and Products.