Life cycle energy benefits of carbon nanotubes for electromagnetic interference (EMI) shielding applications

Journal of Cleaner Production 142 (2017) 1971e1978

Contents lists available at ScienceDirect

Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro

Life cycle energy benefits of carbon nanotubes for electromagnetic interference (EMI) shielding applications Leila Pourzahedi a, Pei Zhai a, b, Jacqueline A. Isaacs b, Matthew J. Eckelman a, * a b

Civil and Environmental Engineering, Northeastern University, Boston, MA, USA Mechanical and Industrial Engineering, Northeastern University, Boston, MA, USA

a r t i c l e i n f o

a b s t r a c t

Article history: Received 6 March 2016 Received in revised form 14 October 2016 Accepted 15 November 2016 Available online 16 November 2016

Carbon nanotube (CNT) composites have been developed for use as electromagnetic interference (EMI) shielding in satellites as well as other land-based applications. While CNT composites are costly and energy-intensive to produce relative to existing EMI shielding materials, they may offer both economic and energy benefits when considered on a life cycle basis. CNTs’ unique characteristics and enhanced physical and chemical properties have made them preferable as alternatives to conventional material. In comparing nano-enabled products with existing technologies, it is imperative to account for differences not just in production but also in performance and delivery. In this study, we considered CNT polymer composites as a replacement for aluminum (the current dominant EMI shielding material) on the basis of shielding effectiveness (in dB). Results demonstrate that CNT-enabled composites offer opportunities for more than 50% reduction in the mass of EMI shielding, while maintaining performance levels within ±10 dB of the shielding effectiveness of aluminum. Reduction in the mass of the EMI component of the satellite subsequently affects the total fuel required to launch it into orbit, reducing it by 6% when using CNT composites. Results show nearly 30% reduction of life cycle cumulative energy demand for the CNT polymer composite shielding compared to aluminum, with concomitant environmental benefits. © 2016 Elsevier Ltd. All rights reserved.

Keywords: Carbon nanotubes Life cycle assessment Nanomaterial benefits EMI shielding Satellite launch energy Cumulative energy demand

1. Introduction Concerns regarding the safety and potential environmental impacts of nanoparticles have been increasing with the rapid growth in the nanotechnology market (Miseljic and Olsen, 2014; Som et al., 2010). Such concerns can be addressed through prospective assessments of ecological and human health risks, as well as consideration of occupational hazards and environmental sustainability (Bauer et al., 2008). A holistic perspective on benefits, risks, and potential impacts of engineered nanomaterials (ENMs) to health and environment can also guide technology development, and many have suggested the use of life cycle assessment (LCA) for these purposes (Gavankar et al., 2012; Hischier and Walser, 2012; Miseljic and Olsen, 2014; Som et al., 2010). The LCA framework is more expansive than traditional risk analysis as it considers both direct emissions of nanomaterials as well as (non-nano) emissions of substances that result as a consequence of ENM production, use, and eventual disposal (Walker et al., 2015). LCA quantifies both

* Corresponding author. E-mail address: [email protected] (M.J. Eckelman). http://dx.doi.org/10.1016/j.jclepro.2016.11.087 0959-6526/© 2016 Elsevier Ltd. All rights reserved.

positive and negative effects, and so considers environmental benefits of ENM incorporation in products against resource- or emissions-intensive processes in the ENM life cycle that could potentially offset or negate those benefits. Therefore, LCA is an ideal method when the assessment goal is to evaluate unintended consequences and potential trade-offs between benefits and impacts to the environment and public health.

1.1. LCA studies for carbon nanotubes Due to their high electrical and thermal conductivity and superior mechanical properties (Zhirnov et al., 1999), CNTs have found various applications in electronics, sensors, and especially composites for use in consumer products, automotive, and aerospace industries (Keller et al., 2013; Li et al., 2006). Tests on CNT composites have shown an increase in the overall material properties, such as modulus, strength and conductivity (both thermal and electrical), compared to the original polymer matrix due to the high aspect ratio of the filler CNTs (Rawal et al., 2013). However, LCA studies of CNT manufacturing have revealed significant environmental burdens primarily due to energy-intensive manufacturing

1972

L. Pourzahedi et al. / Journal of Cleaner Production 142 (2017) 1971e1978

processes, emissions of impurities, and purification requirements (Dahlben et al., 2013; Eckelman et al., 2008; Healy et al., 2008;
n, 2008; Plata et al., 2009). Isaacs et al., 2006; Kushnir and Sande Life cycle-based evaluations of nano-enabled products should ideally quantify the functional benefits of nano-enabled products € hler et al., 2008), while accounting for environduring use (Ko mental and health implications of emissions and resource requirements of manufacturing and nanoparticle release at end-oflife (Eckelman et al., 2008; Som et al., 2010) But despite calls acknowledging the critical importance of including the functional benefits of nanotechnology in LCA (Gavankar et al., 2012; Gilbertson et al., 2015; Hischier and Walser, 2012; Upadhyayula et al., 2012; Wender and Seager, 2011), numerous studies have not accounted for the technological advantages from superior nanomaterial properties that could not otherwise be achieved by using conventional materials. Assessment of nano-enabled product benefits is highly dependent on the specific product application, the concentration of ENMs in the product, and the technological function that the ENMs convey. Life cycle benefits might be in terms of reduced energy use, environmental impacts, or health damages, depending on the product in question. Examples of such benefits for carbonaceous nanomaterials from the LCA literature include: fuel savings due to reduced weights of carbon nanofiber (CNF) composites or CNTenabled batteries in vehicles (Khanna and Bakshi, 2009; Zhai et al., 2016); electricity savings from a CNT-based electrical switch (Dahlben et al., 2013) or memory device (Zhai et al., 2016); enhanced sensitivity of chemical gas sensors and subsequent health benefits (Gilbertson et al., 2014); greater material strength in CNT-amended concrete (Zhai et al., 2016) thus requiring less material; and material savings from use of CNFs in turbine blades (Merugula et al., 2010); each compared against current materials or technologies. 1.2. CNTs for electromagnetic interference shielding One of the primary applications of ENMs has been in electronics (Keller and Lazareva, 2013). Electromagnetic interference (EMI) of radio frequency radiation with electronic appliances is a major concern that has grown with our increasing dependence on electronics and telecommunications (Chung, 2000; Huang et al., 2007; Li et al., 2006; Thomassin et al., 2008). EMI shielding refers to the protection of electronic compartments against electromagnetic radiation (Chung, 2000; Turer and Aydin, 2015). Shielding against EMI is critical in highly sensitive applications such as aerospace control and communication systems (Gaier and Terry, 1995; Turer and Aydin, 2015). For instance, significant EMI shielding is required for satellites at launch and during orbit (Turer and Aydin, 2015). Satellites in low earth orbits (LEO) are far more likely to encounter EMI due to solar winds and high-energy cosmic rays in space environments, as well as from accumulation of charged particles on the probe's surface (Macdonald and Badescu, 2014; Uhlig et al., 2014). Metallic plates are most commonly used as EMI shields (Chung, 2000; Li et al., 2006; Yang et al., 2005a; 2005b). Their shielding mechanism is mainly by reflection of the electromagnetic radiation rather than absorption (Chung, 2000). Metals typically used for shielding include aluminum, nickel, stainless steel, brass, and a highly permeable mu-metal (a nickel-iron alloy) (Geetha et al., 2009). Metallic shields have the disadvantage of being heavy, prone to corrosion, with low mechanical flexibility (Thomassin et al., 2008). To compete with the high density of sheet metals, at times metal-polymer composites with steel fibers or nickel coated carbon fibers have been used for shielding (Al-Saleh and Sundararaj, 2009; Gaier and Terry, 1995). For satellite

applications, if polymer composites could yield technical performance with reduced mass, then significant fuel savings could result (Gaier and Terry, 1995). In a recent roadmap, NASA gave high priority to research on structural and material weight reduction (Steering Committee for NASA Technology Roadmaps, 2012). Additionally, the application of ENMs were explored, recognizing their influence on material performance, and prioritizing the development of lightweight structures by ENM incorporation. Processing advantages, flexibility, corrosion resistance, and reduced mass are the main reasons for using conductive polymer composites for shielding applications (Chung, 2000; Huang et al., 2007; Li et al., 2006; Thomassin et al., 2008; Yang et al., 2005a; 2005b). CNTs are favorable as a filler material for composites as they possess high electrical conductivity, high aspect ratios, and exceptional mechanical properties (Huang et al., 2007; Li et al., 2006; Thomassin et al., 2008; Yang et al., 2005a; 2005b). Numerous studies have looked into the shielding effectiveness (SE) of CNT polymer composites, showing promising results, some comparable to the SE of metals. SE is a function of the rate of the incoming wave to the transmitted wave by the shield, measured in decibel (dB) units (Al-Saleh and Sundararaj, 2009). Table 1 summarizes the SEs for CNT composites, where for the same type of nanocomposite, higher CNT loadings results in higher levels of SE. Only the composites developed by Rawal et al. (2013) perform at the same SE levels of conventional shielding materials such as aluminum with SE of ~70e80 dB (Rawal et al., 2013), and pass the minimum SE requirements of NASA, which is 40 dB, as well (Ryschkewitsch, 2011). Considering the benefits of using CNT-enabled polymer composites for satellite applications, namely reduction of shielding mass and the subsequent fuel efficiency, we seek to compare these composites to the conventional metallic sheets on a mass and net primary energy demand basis. Assuming communication satellites launched to LEO, savings and benefits are to be quantified on the basis of EMI shielding function for this specific application, i.e., effectively shielding the satellite from interference in X-band frequencies (8.2e12.4 GHz). 2. Methodology Here we quantify the reduction in EMI shielding mass by using CNT polymer composites compared to conventional EMI shields in satellites, the fuel used for each scenario during launch, and the savings in total primary energy use upstream. This analysis focuses on the net energy savings of incorporating CNTs in satellites in the context of their function as EMI shields. Other environmental impacts associated with CNT manufacturing are not quantified in this analysis, but they can be found in previous LCA studies (Dahlben and Isaacs, 2009; Healy et al., 2008; Isaacs et al., 2006). LCA studies of nano-enabled products should include ENM releases where relevant. In this case, there are no direct CNT emissions during the use phase that would affect the terrestrial environment. Additionally, product disposal is not relevant for satellites as during their de-orbiting, they either burn at re-entry, or are sent to a ‘graveyard orbit’ at a higher altitude (Cornara et al., 1999). So, endof-life considerations such as recycling or ENM releases during waste treatment are not applicable here. This simplifies the scope of our analysis to comparing the primary energy used for the EMI shields and how their masses affect respective fuel requirements, assuming no change in other components of the satellite. The analysis breaks down into three parts: 1) calculating the mass of conventional and CNT composite EMI shield for satellites, 2) calculating the fuel that is required for launch, and 3) determining the primary energy used for each shielding scenario (Fig. 1). In order to calculate the mass of EMI shield on a satellite, a

L. Pourzahedi et al. / Journal of Cleaner Production 142 (2017) 1971e1978

1973

Table 1 Current CNT polymer composites technologies and their SE. Reference

CNT Type

Polymer type

Thickness (mm) CNT loading%

Al-Saleh and Sundararaj, 2009 MWCNT

Polypropylene

Yang et al., 2005a; 2005b Huang et al., 2007

Polystyrene Epoxy

0.34 1 2.8 1.45 2

Zhang et al., 2007

MWCNT Long SWCNT Short SWCNT Annealed SWCNT PES-MWCNT CNT sandwich panel CNT co-cured sheet MWCNT

Thomassin et al., 2008

MWCNT

Wang et al., 2012 Rawal et al., 2013

a

Polyether ether ketone M55J/Cyanate Ester

2 0.08e0.125 0.02e0.03 Polyurethane shape memory polymer 0.5 3 Polycaprolactone foamed 8 Polycaprolactone solid 8

1e7.5 vol% 1e7.5 vol% 1e7.5 vol% 0.5e7 wt% 0.01e15 wt% 0.01e15 wt% 0.01e15 wt% 3 - 12 wt% NA

SE average range (dB) Frequency rangea

0.9e22.3 2e34.8 4.6 - >24 2.84e18.56 2e25 1e16.5 1e21 28e50 82 75 1.7e6.7 wt% 4e16 1.7e6.7 wt% 5e35 0.049e0.249 vol% 30e70 0.16e0.48 vol% 13e28

X-band

X-band X-band

X-band X-band K-band Microwave

X-band (8.2e12.4 GHz), K-band (18e26.5 GHz), Microwave (25e40 GHz).

Fig. 1. Product system and system boundary of study.

breakdown of satellite components by mass is required. Tsiolkovsky's rocket equation can be used to determine the required fuel for launch, and finally, having the mass of the shields and the fuel, the total primary energy demand of these components can be calculated and compared for various shielding scenarios. These steps are explained in detail in Sections 3.1 through 3.3. For satellite EMI shielding components, the cumulative energy demand (CED, or primary energy) over the life cycle of the satellite was modeled using the CED 1.08 model as implemented in SimaPro 8.1 software
Consultants, Amersfoort, the Netherlands) and the primary (PRe embodied energy of materials modeled in CES EduPack 2015 (Granta Design Limited, Cambridge, United Kingdom). The energy use of components was linked to the respective unit processes in the US-EI life cycle inventory database (Earthshift, Huntington, VT), the ecoinvent database adjusted for U.S. energy grid inputs. Uncertainty analysis for all of the inputs to the model was performed using Monte-Carlo simulation over 10,000 iterations in SimaPro 8.1, using the default log-normal distribution for the US-EI database unit processes. Monte-Carlo simulation was also used to assess the uncertainty associated with the effect of change in satellite mass to the final results, utilizing the @Risk software (Palisdale Corporation, Ithaca, NY). Section 3.4 shows the results of the uncertainty analysis.

3. Analysis results 3.1. EMI mass calculation For the purpose of this study, communication satellites launched to lower earth altitudes were considered. It has been reported that typically 20% of the mass of the communication and electrical systems of satellites can be made up of EMI shielding (Gaier and Terry, 1995). Based on available data for satellite component breakdown by mass, for communication satellites an average of 23% of the satellite's mass is dedicated to the communication systems, and nearly 27% consists of the electrical and power systems (Lutz et al., 2012; Pritchard, 1984). To assess the wide span in the range of mass for satellites, two satellite sizes were assumed. First, an extremely light sample from the ORBCOMM network of satellites was chosen, with a launch mass of 45 kg, from an existing database (UCS Satellite Database, 2016) On the high end of the range, the Iridium NEXT satellite launched by Orbital ATK Inc. was considered, weighing 860 kg at launch (Orbital ATK, 2015) The launch mass of a satellite is the dry mass of the satellite, which includes the propulsion systems, a total of 93% of the launch mass, and the propellant required for orbit transfer and insertion (Lutz et al., 2012). By calculation, 4.9 kg and 93 kg of EMI mass out of

1974

L. Pourzahedi et al. / Journal of Cleaner Production 142 (2017) 1971e1978

the total launch mass of the satellite is assumed for low and high satellite scenarios, respectively. The conventional method of shielding requires an aluminum sheet with a thickness of 2 mm (Gaier and Terry, 1995). With the total mass of the shield, its thickness, and the density of aluminum (2.643 g/cm3), the area covered by the EMI shielding was calculated to be 17.6 m2 and 0.92 m2 for the high and low cases, respectively. When replacing the sheet of aluminum with a lighter composite, the technological performance must be maintained at the same level as aluminum for shielding. The performance of EMI shields can be quantified in terms of SE (with units of dB). For an aluminum sheet thicker than its skin depth (the depth at which the amplitude of the wave has diminished to approximately e
1 of its initial value (Al-Saleh and Sundararaj, 2009)), the primary mechanism of shielding is by reflection. The skin depth is defined as:

d¼


pffiffiffiffiffiffiffiffiffiffiffi
1 pf ms

(1)

where d is the skin depth (m), f is the frequency of the wave (Hz), m is defined as the magnetic permeability (H/m), and s is the electrical conductivity (S/n) of the shield. These parameters are intrinsic to the material. For an aluminum sheet at the X-band frequency (8e12 GHz), the average skin depth is calculated to be 0.8 mm (m¼1.257  10
6 (H/m), s ¼ 3.5  107 (S/m)). At the current 2 mm thickness of the aluminum sheet, it is safe to assume that the only mode of shielding is by reflection. A simplified formulation for calculating the SE by reflection is as (Al-Saleh and Sundararaj, 2009):

s SER ¼ 39:5 þ 10 log : 2pf m

Dv ¼ ve ln

m0 m1

(3)

where n v is the maximum change in velocity (km/s), ve is the effective exhaust velocity (km/s) and can also be calculated as ve ¼ g: Isp (Isp is the specific impulse of the fuel used and g the acceleration by gravity), m0 is the initial total mass at launch, and m1 is the mass without propellant (m0
Mfuel ). Communication satellites are typically launched to LEO altitudes, and occasionally to geosynchronous earth orbits (GEO) or geostationary transfer orbits (GTO). For the satellites modeled here, launch to LEO levels were assumed. To launch satellites to LEO altitudes, an approximate n v of 9.1 km s is required (Ward, 2010). The most common and most reliable fuel type (for its handling ease for satellite launch to LEO) is liquid fuel, a specific liquid oxygen (LOX)-kerosene mixture (Chartrand, 2004; Pelton et al., 2004). The LOX-kerosene liquid bipropellant has an Isp of 289 s (Ward, 2010), resulting in a ve of 2.83 km/s. Accounting only for the mass of the EMI shields, the amount of fuel that is required for their launch was calculated using the rocket equation, with values shown in Table 2. The mass of the liquid fuel components can be calculated by having the oxidizer to fuel ratio. This value was found to be 2.58 for LOX-kerosene propellants (Burkhardt et al., 2002), therefore the mass of LOX and kerosene for each scenario were subsequently determined. Compared to their conventional aluminum based counterparts, the CNT polymer composites require less propellant for launch as a result of lower mass. 3.3. Total CED for EMI shielding options

(2)

For aluminum in X-band frequencies, the average SE was calculated to be 66 dB. Minimum requirements of SE in space is set to 40 dB (Ryschkewitsch, 2011). Thus the composite chosen to replace aluminum should at least meet the minimum requirements. The CNT composite that was selected for substitution was developed by Lockheed Martin (Rawal et al., 2013). This composite consisted of a 25 mm thick multi-walled nanotube (MWCNT) sheet (areal density of 15 g/m2) co-cured as an outer ply on a 1e1.5 mm thick M55J/CE (cyanate ester, composite density ~1.6 g/ cm3) polymer in an autoclave, with an average SE of 75 dB. For comparison, an aluminum composite by the same company (Lockheed Martin) was also modeled (Rawal et al., 2013). This composite was composed of a thin aluminum foil co-cured on a M55J/CE substrate of the same thickness. An average value of 0.8 mm was assumed based on the available literature on similar technologies (Ryschkewitsch, 2011; Turer and Aydin, 2015). Using the high and low values for area covered by the EMI shields, masses of composite components (CNT, aluminum foil, and polymer) can be calculated, as shown in Table 2. Compared to solid aluminum, the CNT composites have lower mass in total and also meet the required mechanical properties as laminates with 0.05 cm thickness were successfully used in the launch of Juno spacecraft (Rawal et al., 2013). Fig. 2 shows the CNT composites used in various components of the Juno spacecraft.

3.2. Fuel consumption analysis The next step is to calculate how much fuel is actually being used to launch these components into space. We can use Tsiolkovsky's rocket equation to calculate that value:

Analysis of primary energy consumption for the scenarios mentioned was also carried out as part of this study. A representation of this rate is the CED of the processes, in units of MJ. CED accounts for both the direct and indirect energy use - fossil based, nuclear, hydro, and renewables e from raw material extraction to the end-of-life of a product or process (Huijbregts et al., 2010, 2006; Patel, 2003) The primary energy consumption for the various shielding options can be determined by summing the CED of EMI shielding components and the embodied energy of their respective fuel consumption. The CEDs were modeled using the SimaPro software. For the liquid fuel, the embodied energy for kerosene and LOX were modeled based on the unit processes available in the USEI LCI database, “Kerosene, at regional storage” and “Oxygen, liquid, at plant”, and were 54 and 9.72 MJ/kg respectively. The composites consist of the shielding element and the polymeric component. The M55J/CE is a carbon-cyanate ester composite with typical resin content of approximately 30% (DoD, 2002) Cyanate ester was modeled using batch scale production data reported in literature (Lakshmi and Reddy, 2002). This resin is synthesized by the reaction of cyanogen bromide and bisphenol A in the presence of trimethylamine as the catalyst (Lakshmi and Reddy, 2002). Bisphenol A unit process already exists in the US-EI database as “Bisphenol A, powder, at plant”, but cyanogen bromide and triethylamine required further modeling and addition to the database. Triethylamine was modeled using the stoichiometric reaction of ammonia and ethanol (NH3 þ 3 C2H5OH / N(C2H5)3 þ 3 H2O) (Eller et al., 2000). Cyanogen bromide was also modeled using stoichiometric proportions, relying on the reaction of sodium cyanide and bromine (NaCN þ Br2 / BrCN þ NaBr) (Morris et al., 2001). Bromine was modeled as part of this process using lab scale production based on stoichiometry (2 NaBr þ 3 H2SO4 / Br2 þ SO2 þ 2 NaHSO4 þ 2 H2O) (Gannon, 2005). Average heating, electricity and infrastructure use for cyanate ester synthesis were based on ecoinvent reports on life cycle inventory of chemicals

L. Pourzahedi et al. / Journal of Cleaner Production 142 (2017) 1971e1978

1975

Table 2 Various EMI options, mass of each component, the fuel required and cumulative energy demand (CED) for each scenario. EMI options

CNT M55J/CE laminate

Aluminum M55J/CE laminate

Aluminum sheet

Components

CNT sheet Polymer Carbon fiber Cyanate ester Propellant LOX Kerosene Autoclave curing Aluminum foil Polymer Carbon fiber Cyanate ester Propellant LOX Kerosene Autoclave curing Sheet rolling Aluminum sheet Propellant LOX Kerosene Sheet rolling

Mass (kg)

Total CED (GJ)

CV%

Iridium

ORBCOMM

CED (GJ) Iridium

ORBCOMM

Iridium

ORBCOMM

Iridium

ORBCOMM

0.264 42.2 29.5 12.7 1015 730 285 e 37.2 42.2 29.5 12.7 1897 1364 533 e e 92.9 2221 1597 624 e

0.0138 2.21 1.54 0.662 53.1 38.2 14.9 e 1.94 2.21 1.54 0.662 99.3 71.4 27.9 e e 4.86 116 83.6 32.7 e

0.274 23.2 20.5 2.68 22.5 7.09 15.4 3.26 743 23.2 20.5 2.68 42.0 13.3 28.8 6.08 0.457 18.6 49.2 15.5 33.7 0.875

0.0143 1.22 1.08 0.140 1.18 0.371 0.806 0.170 0.389 1.22 1.08 0.140 2.20 0.694 1.51 0.315 0.0234 0.972 2.58 0.812 1.76 0.0602

49.3

2.58

37.4

36.9

79.2

4.14

37.5

32.5

68.7

3.61

25.8

25.2

Fig. 2. (a) Tubular struts, and (b) engine cover components of the Juno spacecraft, both constructed using the CNT M55J/CE laminate. Image courtesy NASA/JPL-Caltech.

(Althaus et al., 2007). Additionally, a recycling rate of 90%, consistent with most LCI datasets for chemicals, was assumed for triethylamine. These modeling assumptions resulted in a CED of 212 MJ/kg of cyanate ester resin. To determine the primary energy required for 1 kg of carbon fiber, its manufacture was broken down into two processes: 1) the production of polyacrylonitrile (PAN) precursor fibers, and 2) PAN conversion to carbon fiber (Das, 2011). Based on the available literature, per 1 kg of PAN fibers 233 MJ in the form of heating by natural gas and 2.78 MJ of electricity is required (Das, 2011). Converting PAN to carbon fibers is done through a series of oxidation and etching processes. The total energy for this step per kg carbon fiber in the form of heating by natural gas was reported to be 97.8 MJ, in addition to 72.4 MJ electricity used (Das, 2011). Modeling these components in SimaPro resulted in a total embodied energy of 696 MJ per kg carbon fiber. Aluminum that is used for EMI shielding is typically a 6061 alloy (Cain and Croisant, 1996), with an embodied energy ranging from 190 to 210 MJ/kg according to the CES EduPack. An average value of 200 MJ/kg was used to represent

the CED of aluminum. A study on energy requirements for CNT manufacturing at industrial scale reported the thermal and electrical energy consumptions per kg MWCNTs as 295 and 187 MJ
n, 2008). These values resulted in a respectively (Kushnir and Sande total CED of 1040 MJ per kg MWCNT. The raw materials require further processing prior to their use as EMI shields. For raw aluminum sheet and foil, sheet rolling to the required thickness was modeled using the respective unit process in SimaPro, resulting in an energy demand of 12.3 MJ per kg aluminum. Co-cured composites, both with CNT sheet and aluminum foil, require processing in autoclave to further cure the polymer. Based on the available data in the literature, this process has an energy intensity of 21.9 MJ per kg of composite (Song et al., 2009). With information on all of the embodied energy per kg of material and the mass of all the components, the CED for each shielding scenario was calculated as shown in Table 2, illustrating the saving in primary energy consumption with the use of nanocomposites. The aluminum composite resulted in higher CEDs, despite weighing less than pure aluminum sheet (13.6 and 0.7 kg less for high and low scenarios

1976

L. Pourzahedi et al. / Journal of Cleaner Production 142 (2017) 1971e1978

respectively), due to the combined effect of considerable aluminum use and high embodied energy of the polymer. 3.4. Uncertainty analysis Uncertainty analysis for the cumulative energy results was carried out using the Monte-Carlo simulation in SimaPro. For all inputs and background processes, the default log-normal distribution set in the US-EI database was used. For any foreground processes, the probability distribution was determined using the pedigree matrix method, found in Table S1 of the Supplemental Information (SI) document. Uncertainty was highest among the CNT composites, with highest coefficients of variation (CVs), followed by the aluminum composites, as shown in the last two columns of Table 2. This largely stems from the high uncertainties of the MWCNT, carbon fiber and cyanate ester production processes. The CV for the aluminum sheet was the lowest among the various EMI shields as all the modeling components in this shielding option were previously established processes and required no further modeling of new technology. As mentioned earlier, a wide range of launch mass for LEO communication satellites exists, consisting of very small ’nanosatellites’ weighing as little as 10 kg, to satellites weighing almost a ton. This variability in mass can cause dramatic changes in the amount of fuel required to launch the equipment into orbit. MonteCarlo simulation was used to explore the effect of this uncertain parameter (satellite launch mass), on fuel consumption for the three shielding scenarios. Based on a database published by the Union of Concerned Scientists (gathered from a collective of publicly accessible academic articles, and governmental and nongovernmental sources), the distribution of mass for satellites launched to LEO by the U.S. was plotted, shown in Fig. 3a (UCS Satellite Database, 2016). Fig. 3b illustrates the probability density of fuel use under the three shielding materials (aluminum sheet, CNT M55J/CE laminate and aluminum M55J/CE laminate), emphasizing the possibility of lower consumption rates by adopting the lighter CNT-enabled polymer composite EMI shields. Fig. 3c is the graphical representation of total calculated CEDs, with error bars illustrating the 95% confidence intervals derived from Monte-Carlo simulation on all input parameters. 4. Discussion A comparison of current technologies in CNT-based EMI shielding with conventional aluminum sheets shows that use of CNT-based shields would allow for more savings in satellite mass and fuel use, while performing at the same level of SE. In addition, the use of CNT sheets as the outer ply of the laminate reduces the cost, time, and labor intensity of surface preparation, as these materials do not require any surface abrasion steps (Rawal et al., 2013). The composites also satisfy the mechanical requirements of spacecraft design based on the results of flexural tests comparing them with the solid polymeric sheet (Rawal et al., 2013). These properties favor the use of nanocomposites for future developments in space applications. Several specific process parameters are worth noting. First, while the CED value of 1040 MJ/kg for MWCNTs reflects industrialscale production, it is based on process modeling, and thus has associated uncertainty (discussed in section 3.4). Primary data from industrial producers would be useful in reducing this uncertainty. Another issue that introduces a level of uncertainty to the analysis is the method of resin curing. Resins can be cured through a variety of methods including thermal curing with autoclaves at different durations and temperatures (room temperature to 200  C) (Chaowasakoo and Sombatsompop, 2007; Chatterjee and Gillespie,

2010; Pillai et al., 1994; Strong, 2008), microwave curing (Lee and Springer, 1984; Tanrattanakul and Jaroendee, 2006), electron beam (Berejka and Eberle, 2002; Drobny, 2012; Janke et al., 1997), ultraviolet- and X-rays (Drobny, 2012; Janke et al., 1997). The curing method used is highly dependent on the manufacturer and application of the composite. Energy consumption of these methods differ greatly; as an example, electron beam curing has been reported to use only 10% of the energy used by thermal curing (Drobny, 2012). Ecoinvent's report on life cycle inventory of chemicals also acknowledges the variety in resin curing agents in addition to the different curing routes, where it is assumed that the data on the resin in many cases will provide a sensible approximation (Althaus et al., 2007). Also, the energy required for cutting and shaping the shields were not included as part of this study and were assumed to be similar between the shielding options. Based on the rocket equation (3), the fuel requirements for launch can increase exponentially with respect to the velocity ratios. Thus the analysis results can change by using a fuel with higher specific impulses such as LOX-hydrazine or solid rocket propellants. With regard to the CED of aluminum based technologies, the final outcomes can be affected by the thickness of the shielding device. The values used in this study were based on available literature, but with technological advancements, the thickness could be reduced further, resulting in lower CED levels. We have shown results for two satellite cases with launch to LEO, but as mentioned, there are various mass classes for satellites, for example, satellites launched to GTO can weigh as much as 5400 kg. Thus depending on the satellite's primary application and the final orbital altitude, the mass and ultimately the amount of propellant used could be influenced. Prior LCA studies on CNTs have often quantified their environmental implications without considering the potential energy and environmental benefits of their use. In this study we have attempted to capture the increased performance of the current technology by quantifying the benefits gained with respect to the substituted material. For many other cases, where there are societal and health gains in using nanotechnology, these benefits are not so easily quantifiable, such as determining quality of life or ethical concerns. Hence, it is important to develop quantitative methods to assess life cycle trade-offs of products. A recent study uses disability-adjusted life years (DALYs) as a measure for potential human health benefits of a CNT-enabled chemical gas sensor, defining impact-benefit ratios to assess the feasibility of the product (Gilbertson et al., 2014). Another study investigated the net energy benefit of using CNTs for several CNT applications (CNTincorporated reinforced cement, flash memory switches and lithium-ion batteries) (Zhai et al., 2016). Their results demonstrated that life cycle net energy benefits from CNT-enabled products are dependent on the application, in particular use phase and lifetime considerations. CNTs in cell phone flash memory devices, cement reinforcement and MWCNT for cathode of batteries showed positive net energy benefits, while for batteries with SWCNT anodes, net energy benefits were negative. These results illustrate the importance of evaluating life cycle ecological impacts and energy use of a technology prior to its adoption. Net energy benefits of nano-enabled products will likely increase with increased efficiencies from technological developments, but LCA concepts can still help to identify potential opportunities for improvement. 5. Conclusion CNT use is projected to increase for an array of technologies. Thorough analysis of potential environmental, human health impacts and benefits is required to assess the tradeoff of using nanoenabled products as opposed to conventional products. Here the

L. Pourzahedi et al. / Journal of Cleaner Production 142 (2017) 1971e1978

1977

Fig. 3. (a) Mass distribution of LEO satellites, (b) distribution of fuel consumption for launching the EMI shielding under various shielding scenarios, (c) total CED for Iridium NEXT and ORBCOMM satellites under various shielding scenarios with error bars representing 95% confidence interval from Monte-Carlo simulation on input parameters (CV values can be found in Table 2).

net energy benefits of using CNT-enabled composites for use as EMI shielding in satellites were quantified and compared to conventional aluminum sheets and composites. Results showed promising savings in terms of EMI mass and fuel use, with reduction in the primary energy demand, when using CNT based composites. Acknowledgements We acknowledge NSF award SNM-1120329 as well as the George J. Kostas Nanoscale Technology and Manufacturing Research Center at Northeastern University. We also thank S. Rawal for helpful discussions. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jclepro.2016.11.087. References Al-Saleh, M.H., Sundararaj, U., 2009. Electromagnetic interference shielding mechanisms of CNT/polymer composites. Carbon 47, 1738e1746. Althaus, H.J., Chudacoff, M., Hischier, R., Jungbluth, N., Osses, M., Primas, A., 2007. Life Cycle Inventories of Chemicals. Ecoinvent Report No. 8, v2.0 (No. 8). Swiss Centre for Life Cycle Inventories. EMPA Dubendorf. Bauer, C., Buchgeister, J., Hischier, R., Poganietz, W.R., Schebek, L., Warsen, J., 2008. Towards a framework for life cycle thinking in the assessment of nanotechnology. J. Clean. Prod. 16, 910e926. Berejka, A.J., Eberle, C., 2002. Electron beam curing of composites in North America.

Radiat. Phys. Chem. 63, 551e556. Burkhardt, H., Sippel, M., Herbertz, A., Klevanski, J., 2002. Comparative study of kerosene and methane propellant engines for reusable liquid booster stages. In: 4th Conference (International) on Launcher Technology¤ Space Launcher Liquid Propulsion.¥ Liege. Cain, B.L., Croisant, W.J., 1996. Electrical contact resistance of titanium nitride coatings for electromagnetic shielding applications. Surf. Coat. Technol. 82, 83e89. Chaowasakoo, T., Sombatsompop, N., 2007. Mechanical and morphological properties of fly ash/epoxy composites using conventional thermal and microwave curing methods. Compos. Sci. Technol. 67, 2282e2291. Chartrand, M.R., 2004. Satellite Communications for the Nonspecialist. SPIE Press. Chatterjee, A., Gillespie, J.W., 2010. Room temperature-curable VARTM epoxy resins: promising alternative to vinyl ester resins. J. Appl. Polym. Sci. 115, 665e673. http://dx.doi.org/10.1002/app.30740. Chung, D.D.L., 2000. Materials for electromagnetic interference shielding. J. Mater. Eng. Perform. 9, 350e354.
-Mora, M., Martinez de Aragon, A., 1999. Satellite Cornara, S., Beech, T., Bello Constellation Launch, Deployment, Replacement and End-of-life Strategies. Dahlben, L., Isaacs, J.A., 2009. Environmental assessment of manufacturing with carbon nanotubes. In: IEEE International Symposium on Sustainable Systems and Technology. Institute of Electrical and Electronics Engineers Inc. Dahlben, L.J., Eckelman, M.J., Hakimian, A., Somu, S., Isaacs, J., 2013. Environmental life cycle assessment of a carbon nanotube-enabled semiconductor device. Environ. Sci. Technol. 47 (15), 8471e8478. Das, S., 2011. Life cycle assessment of carbon fiber-reinforced polymer composites. Int. J. Life Cycle Assess. 16, 268e282. DoD, 2002. MIL-HDBK-17e2F: Composite Materials Handbook. Dep. Def. Handb. U. S. 17. Drobny, J.G., 2012. Ionizing Radiation and Polymers: Principles, Technology, and Applications. William Andrew. Eckelman, M.J., Zimmerman, J.B., Anastas, P.T., 2008. Toward green nano. J. Ind. Ecol. 12, 316e328. €ke, H., 2000. Amines, aliphatic. In: Ullmann's Eller, K., Henkes, E., Rossbacher, R., Ho Encyclopedia of Industrial Chemistry. Wiley-VCH Verlag GmbH & Co. KGaA.

1978

L. Pourzahedi et al. / Journal of Cleaner Production 142 (2017) 1971e1978

Gaier, J.R., Terry, J., 1995. Emi Shields Made from Intercalated Graphite Composites. National Aeronautics and Space Administration. Gannon, P., 2005. Revise AS Chemistry for AQA. Heinemann. Gavankar, S., Suh, S., Keller, A.F., 2012. Life cycle assessment at nanoscale: review and recommendations. Int. J. Life Cycle Assess. 17, 295e303. http://dx.doi.org/ 10.1007/s11367-011-0368-5. Geetha, S., Satheesh Kumar, K.K., Rao, C.R., Vijayan, M., Trivedi, D.C., 2009. EMI shielding: methods and materialsda review. J. Appl. Polym. Sci. 112, 2073e2086. Gilbertson, L.M., Busnaina, A.A., Isaacs, J.A., Zimmerman, J.B., Eckelman, M.J., 2014. Life cycle impacts and benefits of a carbon nanotube-enabled chemical gas sensor. Environ. Sci. Technol. 48, 11360e11368. http://dx.doi.org/10.1021/ es5006576. Gilbertson, L.M., Wender, B.A., Zimmerman, J.B., Eckelman, M.J., 2015. Coordinating modeling and experimental research of engineered nanomaterials to improve life cycle assessment studies. Environ. Sci. Nano 2, 669e682. http://dx.doi.org/ 10.1039/C5EN00097A. Healy, M., Dahlben, L., Isaacs, J., 2008. Environmental assessment of single walled carbon nanotube processes. J. Ind. Ecol. 12, 376e393. Hischier, R., Walser, T., 2012. Life cycle assessment of engineered nanomaterials: state of the art and strategies to overcome existing gaps. Sci. Total Environ. 425, 271e282. Huang, Y., Li, N., Ma, Y., Du, F., Li, F., He, X., Lin, X., Gao, H., Chen, Y., 2007. The influence of single-walled carbon nanotube structure on the electromagnetic interference shielding efficiency of its epoxy composites. Carbon 45, 1614e1621. Huijbregts, M.A., Hellweg, S., Frischknecht, R., Hendriks, H.W., Hungerbuhler, K., Hendriks, A.J., 2010. Cumulative energy demand as predictor for the environmental burden of commodity production. Environ. Sci. Technol. 44, 2189e2196. Huijbregts, M.A., Rombouts, L.J., Hellweg, S., Frischknecht, R., Hendriks, A.J., van de Meent, D., Ragas, A.M., Reijnders, L., Struijs, J., 2006. Is cumulative fossil energy demand a useful indicator for the environmental performance of products? Environ. Sci. Technol. 40, 641e648. Isaacs, J.A., Tanwani, A., Healy, M.L., 2006. Environmental assessment of SWNT production. In: Electronics and the Environment, 2006. Proceedings of the 2006 IEEE International Symposium on. IEEE, pp. 38e41. Janke, C.J., Norris, R.E., Yarborough, K., Havens, S.J., Lopata, V.J., 1997. Critical Parameters for Electron Beam Curing of Cationic Epoxies and Property Comparison of Electron Beam Cured Cationic Epoxies versus Thermal Cured Resins and Composites. Oak Ridge National Lab, TN (United States). Keller, A.A., Lazareva, A., 2013. Predicted releases of engineered nanomaterials: from global to regional to local. Environ. Sci. Technol. Lett. 1 (1), 65e70. Keller, A.A., McFerran, S., Lazareva, A., Suh, S., 2013. Global life cycle releases of engineered nanomaterials. J. Nanoparticle Res. 15, 1e17. Khanna, V., Bakshi, B.R., 2009. Carbon nanofiber polymer composites: evaluation of life cycle energy use. Environ. Sci. Technol. 43, 2078e2084. €hler, A.R., Som, C., Helland, A., Gottschalk, F., 2008. Studying the potential release Ko of carbon nanotubes throughout the application life cycle. J. Clean. Prod. 16, 927e937.
n, B.A., 2008. Energy requirements of carbon nanoparticle proKushnir, D., Sande duction. J. Ind. Ecol. 12, 360e375. http://dx.doi.org/10.1111/j.15309290.2008.00057.x. Lakshmi, M.S., Reddy, B.S.R., 2002. Synthesis and characterization of new epoxy and cyanate ester resins. Eur. Polym. J. 38, 795e801. Lee, W.I., Springer, G.S., 1984. Microwave curing of composites. J. Compos. Mater 18, 387e409. http://dx.doi.org/10.1177/002199838401800405. Li, N., Huang, Y., Du, F., He, X., Lin, X., Gao, H., Ma, Y., Li, F., Chen, Y., Eklund, P.C., 2006. Electromagnetic interference (EMI) shielding of single-walled carbon nanotube epoxy composites. Nano Lett. 6, 1141e1145. Lutz, E., Werner, M., Jahn, A., 2012. Satellite Systems for Personal and Broadband Communications. Springer Science & Business Media. Macdonald, M., Badescu, V., 2014. The International Handbook of Space Technology. Springer. Merugula, L., Khanna, V., Bakshi, B.R., others, 2010. Comparative Life Cycle Assessment: reinforcing wind turbine blades with carbon nanofibers. In: Sustainable Systems and Technology (ISSST), 2010 IEEE International Symposium on. IEEE, pp. 1e6. Miseljic, M., Olsen, S.I., 2014. Life-cycle assessment of engineered nanomaterials: a literature review of assessment status. J. Nanoparticle Res. 16, 1e33. Morris, J., Kov
acs, L., Ohe, K., 2001. Cyanogen bromide. In: Encyclopedia of Reagents for Organic Synthesis. John Wiley & Sons, Ltd. Orbital ATK, 2015. Iridium NEXT the Next-generation Satellite Constellation of

Iridium Communications Inc [WWW Document]. URL. http://www.orbitalatk. com/space-systems/commercial-satellites/communications-satellites/docs/ FS002_11_OA_3862%20IridiumNEXT.pdf. Patel, M., 2003. Cumulative energy demand (CED) and cumulative CO 2 emissions for products of the organic chemical industry. Energy 28, 721e740. Pelton, J.N., Oslund, R.J., Marshall, P., 2004. Communications Satellites. Global Change Agents. Routledge. Pillai, V.K., Beris, A.N., Dhurjati, P.S., 1994. Implementation of model-based optimal temperature profiles for autoclave curing of composites using a knowledgebased system. Ind. Eng. Chem. Res. 33, 2443e2452. Plata, D.L., Hart, A.J., Reddy, C.M., Gschwend, P.M., 2009. Early evaluation of potential environmental impacts of carbon nanotube synthesis by chemical vapor deposition. Environ. Sci. Technol. 43, 8367e8373. http://dx.doi.org/10.1021/ es901626p. Pritchard, W.L., 1984. Estimating the mass and power of communications satellites. Int. J. Satell. Commun. 2, 107e112. Rawal, S., Brantley, J., Karabudak, N., 2013. Development of carbon nanotube-based composite for spacecraft components. In: Recent Advances in Space Technologies (RAST), 2013 6th International Conference on. IEEE, pp. 13e19. Ryschkewitsch, M.G., 2011. Mitigating in Space Charging Effectsda Guideline. Natl. Aeronaut. Space Adm. Tech. Handb. NASA-HDBK-4002A. Som, C., Berges, M., Chaudhry, Q., Dusinska, M., Fernandes, T.F., Olsen, S.I., Nowack, B., 2010. The importance of life cycle concepts for the development of safe nanoproducts. Toxicology 269, 160e169. Song, Y.S., Youn, J.R., Gutowski, T.G., 2009. Life Cycle Energy Analysis of Fiberreinforced Composites. Compos. Part Appl. Sci. Manuf., Special Issue: 15th French National Conference on Composites, vol. 40. JNC15, pp. 1257e1265. http://dx.doi.org/10.1016/j.compositesa.2009.05.020. Steering Committee for NASA Technology Roadmaps, 2012. NASA Space Technology Roadmaps and Priorities: Restoring NASA's Technological Edge and Paving the Way for a New Era in Space. National Academies Press. Strong, A.B., 2008. Fundamentals of Composites Manufacturing, second ed. Materials, Methods and Applications. Society of Manufacturing Engineers. Tanrattanakul, V., Jaroendee, D., 2006. Comparison between microwave and thermal curing of glass fibereepoxy composites: effect of microwave-heating cycle on mechanical properties. J. Appl. Polym. Sci. 102, 1059e1070. http://dx.doi.org/ 10.1002/app.24245. Thomassin, J.-M., Pagnoulle, C., Bednarz, L., Huynen, I., Jerome, R., Detrembleur, C., 2008. Foams of polycaprolactone/MWNT nanocomposites for efficient EMI reduction. J. Mater. Chem. 18, 792e796. Turer, I., Aydin, K., 2015. Electromagnetic shielding properties of satellites. In: Recent Advances in Space Technologies (RAST), 2015 7th International Conference on. IEEE, pp. 401e404. UCS Satellite Database, 2016. [WWW Document]. Union Concerned Sci. URL. http:// www.ucsusa.org/nuclear-weapons/space-weapons/satellite-database.html (Accessed December.16.15). Uhlig, T., Sellmaier, F., Schmidhuber, M., 2014. Spacecraft Operations. Springer. Upadhyayula, V.K.K., Meyer, D.E., Curran, M.A., Gonzalez, M.A., 2012. Life cycle assessment as a tool to enhance the environmental performance of carbon nanotube products: a review. J. Clean. Prod. 26, 37e47. Walker, W.C., Bosso, C.J., Eckelman, M., Isaacs, J.A., Pourzahedi, L., 2015. Integrating life cycle assessment into managing potential EHS risks of engineered nanomaterials: reviewing progress to date. J. Nanoparticle Res. 17, 1e16. Wang, H., Wang, G., Li, W., Wang, Q., Wei, W., Jiang, Z., Zhang, S., 2012. J. Mater. Chem. 22 (39), 21232. Ward, T.A., 2010. Aerospace Propulsion Systems. John Wiley & Sons. Wender, B.A., Seager, T.P., 2011. Towards prospective life cycle assessment: single wall carbon nanotubes for lithium-ion batteries. In: Sustainable Systems and Technology (ISSST), 2011 IEEE International Symposium on, pp. 1e4. Yang, S., Lozano, K., Lomeli, A., Foltz, H.D., Jones, R., 2005a. Electromagnetic interference shielding effectiveness of carbon nanofiber/LCP composites. Compos. Part Appl. Sci. Manuf. 36, 691e697. Yang, Y., Gupta, M.C., Dudley, K.L., Lawrence, R.W., 2005b. Novel carbon nanotubepolystyrene foam composites for electromagnetic interference shielding. Nano Lett. 5, 2131e2134. Zhai, P., Isaacs, J.A., Eckelman, M.J., 2016. Net energy benefits of carbon nanotube applications. Appl. Energy 173, 624e634. Zhang, C.-S., Ni, Q.-Q., Fu, S.-Y., Kurashiki, K., 2007. Compos. Sci. Technol. 67 (14), 2973e2980. Zhirnov, V., Herr, D., Meyyappan, M., 1999. Electronic applications of carbon nanotubes become closer to reality. J. Nanoparticle Res. 1, 151e152.