M.A. Chappell, W-S Shih, J.K. Bledsoe, C. Cox, D. Janzen, S. Gibbons, R. Patel, A.J. Kennedy, J. Brame, M. Brondum, S.A. Diamond, J. Coleman, D. Edwards, J.A. Steevens
U.S. Army Engineer Research & Development Center,
Keywords: carbon nanotube sensors, environmental life cycle assessment
Summary:Here, we describe efforts to characterize the potential environmental impact associated with the manufacture of a newly developed printed electronic temperature sensor using environmental life cycle assessment (Eco-LCA). The sensor is composed of a specialized carbon nanotube (CNT) formulation, called CNTRENE® 1030 material, which was developed by Brewer Science. We created a gate-to-gate Eco-LCA model (Figure 1) with a functional unit representing 2400 sensors/day. The life cycle inventory was carefully constructed by sampling the actual manufacturing process for technosphere inputs (such as materials and power) and outputs or emissions during the manufacturing and waste-incineration processes. The total effects of the sensor manufacturing process cycle were represented computationally to include sub-processes associated with the manufacture of the CNTRENE® product and the conductive nanosilver ink, and the general encapsulation procedure for constructing the printed electronic temperature sensor. Total emissions for the gate-to-gate assessment were calculated from the mass balance of the inventory components (as represented through the Eco-Invent 2.0 database), and environmental impacts were assessed using commonly available impact assessment models. Given the very small quantities of materials used in constructing the sensor, as well as the fact that Brewer Science had completely sealed all systems (to eliminate occupational exposures) associated with handling the raw and formulated CNT products and wastes, the absolute environmental impacts calculated from the Eco-LCA model related to the sensor’s manufacture were remarkably low. Greenhouse gas emissions and natural resource depletions associated with the use of compressed gas and electrical power requirements for creating the temperature sensor represented the bulk of the relative environmental impacts, reflecting the inherent challenges in adapting conventional manufacturing processes to next-generation materials. Thus, the Eco-LCA approach emphasized the need to identify and improve energy and cost efficiencies for this particular process. Furthermore, we conducted an Eco-LCA to demonstrate the environmental impacts associated with optimizing the CNTRENE® material manufacturing process. While the Eco-LCA study was limited to the portions of CNTRENE® material product development directly under Brewer Science’s control, hypothetically including the manufacture of the raw CNT materials (a process controlled and performed by outside producers) produced a negligible difference in the outcome of the Eco-LCA due to the overall small quantity of CNTRENE® materials produced annually. Brewer Science improved the efficiency of manufacturing the CNTRENE® material formulation by reducing water usage, and consequently, waste generation by over 95%. Thus, Eco-LCA modeling showed optimizing CNTRENE® material production resulted in substantial absolute reductions in climate change and resource depletion-associated impacts, shifting the relative environmental burden from the energy consumption associated with hazardous waste incineration to electricity used in the manufacture of the CNTRENE® formulation. Overall, the case study’s conclusions can therefore be related to a much wider range of advanced materials’ manufacturing processes.