Nanotechnology is often touted as the biggest scientific breakthrough of the 21st century. The potential impacts of nanotechnology arise from the altered physicochemical properties of the materials at the nanoscale that enable a broad spectrum of novel applications. It is beyond doubt that the inherent properties of nanoscale materials do pose several new challenges. Some of these include identifying and characterizing new risks associated with the widespread use of nanomaterials, evaluation of economic and environmental trade-offs, and addressing the public and regulatory concerns about this new technology. Various researchers and agencies have identified the need for a holistic evaluation of nanotechnology using Life Cycle Assessment (LCA). However, LCA of nanotechnology has received very little attention due to several challenges. Firstly, the existing life cycle inventory databases are limited in scope and are useful for evaluating only common products and processes. Secondly, there is very little quantifiable data available on the human health and ecosystem impacts of products and byproducts of nanomanufacturing. Besides these, nanotechnology is still in its infancy and nanomanufacturing processes are evolving rapidly.

This paper presents the first most comprehensive Life Cycle Energy Analysis and LCA of Carbon Nanofiber (CNF) based Polymer Nanocomposites (PNCs). Carbon Nanofibers belong to a new class of materials that have captured the attention of scientific community because of their exceptional mechanical strength and electrical conductivity. One of the applications of CNFs is their use as the reinforcing phase in the manufacture of PNCs. Nanocomposites are a new class of composites that have a dispersed phase with atleast one ultrafine dimension, typically a few nanometers. PNCs can improve mechanical reinforcement, offer high temperature durability, enhanced barrier properties, and reduced flammability. Previous work by the authors [1] indicates significantly higher life cycle energy investment and higher environmental impact of CNFs as compared to traditional materials like aluminum and steel on a per kg basis. This is due to the enormous amount of energy input in creating huge surface area for CNFs that represent highly ordered form of matter. These results represent first important step towards LCA of nanotechnology, but specific CNF based products need to be studied to evaluate their environmental performance. This is especially important since quantity of use of these highly energy intensive CNFs is likely to influence whether products based on these engineered nanomaterials are greener than alternatives for specific applications.

In this study, a “cradle-to-gate” life cycle study of CNF based PNCs is carried out. Previous work on CNF life cycle by the authors served as a basis for this analysis. The boundaries of the CNF life cycle are expanded to include the production of PNC and the end product manufacture. A typical life cycle for nanocomposites consists of selection of raw material, selection of method of production, product manufacture, use, recycle, and disposal phases. Alternatives exist at each processing stage for the above mentioned production methods based on the choice of feedstock and the final product manufacture. For e.g., three synthetic routes are routinely used in the preparation of polymer nanocomposites: solution blending, melt compounding, and in-situ polymerization [2]. Life Cycle data is complied with information reported by the open literature and industrial collaborators. Polypropylene based CNF nanocomposites are considered as the first example. In the second example, a thermosetting epoxy polymer nanocomposites synthesis is studied. Once the CNFs are dispersed in the polymer, these reinforced materials can be either extruded or injection-molded to obtain a variety of end products. In this study, two such end product applications will be described. One is the use of these reinforced PNCs for automotive applications and another is their use as casting molds in industrial processes.

These materials are compared with traditional alternatives like aluminum, steel, and pristine polymers. The various steps in the life cycle along with the LCA results will be described. Steps in the life cycle with the maximum energy consumption and environmental burden will be highlighted. Different scenarios for the production and use phase of PNCs are also analyzed. Preliminary results show that the life cycle energy and environmental impact are sensitive to the loading ratios of the reinforcing phase. Current work is in progress to address the end of life issues relevant to PNCs. Proxy indicators are also being explored to get insight into the broader ecotoxicity of these engineered nanomaterials in the absence of detailed ecotoxicological studies.

References:

[1] Khanna, V., Bakshi, Bhavik R., Lee, L. James, 2007, Life Cycle Energy Analysis and Environmental Life Cycle Assessment of Carbon Nanofibers Production, IEEE International Symposium on Electronics and the Environment, 7-10 May, Orlando, Florida, USA.

[2] Vaia, R.A., Giannelis, E.A., Polymer Nanocomposites: Status and Opportunities, MRS Bulletin, May 2001, 394-401.