Evaluation of specific application contexts

Building on this characterization of specific nanotechnologies and their manufacturing processes to date, the ongoing extrapolative assessment approach tracks the investigation of sustainability effects using specific application examples that are compared to existing products and processes. In this process, the focus was placed on environmental opportunities and risks.

As an assessment approach, the prepared environmental profiles are modeled on the life cycle assessment methodology. The life cycle assessment (LCA) is the most extensively developed and standardized methodology for assessing the environmental aspects and product-specific potential environmental impacts associated with the complete life cycle of a product. It has the advantage that by means of comparative assessments, an (extrapolative) analysis of eco-efficiency potential in comparison to existing applications is possible. With its method of extrapolation, however, this study goes far beyond the current state of the methodology. At the same time, the LCA methodology - as with all methodologies - has its characteristic deficits; there are impact categories for which generally accepted impact models and quantifiable assessments do not exist. This is particularly true in the relevant categories of human and environmental toxicity. And so, a consideration of the impact of fine dust particles (the PM-10 risk, for example, deals with the potential toxicity of particles smaller than 10 ^m) in assessments of nanotechnology applications is therefore already doomed to failure because of its reference to material flows expressed in weight. Furthermore, in LCA assessments the risks and the technological power (hazard) effectiveness of applications are not considered. A comprehensive methodology must provide for such analyses.

In the project an attempt was therefore made to compensate for these methodological shortcomings through the establishment of priorities in the selection of the specific application contexts. From the spectrum of all nanotechnology applications, four case studies were chosen in which, on the basis of a preliminary assessment and qualitative evaluation, particularly interesting eco-efficiency potentials could be expected. A further constraint in the selection of the case studies resulted from the requirement that only those examples be considered for which LCA data was (at a minimum) already available for the enlisted "conventional" technologies or products to be used in the comparison. The potential risks and hazards in those nanotechnology applications that were not considered were then analyzed and considered in a separate hazard analysis focusing specifically on nanoparticles.

Table 2. Overview of the case studies investigated

Application context

Goal

Eco-efficient nanocoat-ings

Nanotechnological process innovation styrene production in

Nanotechnological innovation in the video display field

Nano-applications in the lighting industry

Potential risks of nanotechnological applications involving nanoparticles

Presentation of the eco-efficiency potential of nano-coatings in the form of a comparative ecological profile

(Nanocoating based on sol-gel technology as compared with waterborne, solventborne, and powder coat industrial coatings)

Presentation of the eco-efficiency potential of nanotechnology in catalytic applications in the form of a comparative ecological profile (Nanotube catalyst as compared with iron oxide-based catalysts)

Assessment of eco-efficiency potential in video display development by means of a qualitative comparison

(Organic LED displays and nanotube field emitter displays as compared with CRT, liquid-crystal, and plasma screens)

Presentation of eco-efficiency potential of nano-applications in the lighting industry in the form of a comparative ecological profile (White LED and quantum dots as compared with incandescent lamps and compact fluorescents) Discussion of possible risks and harzards using titanium dioxide as an example; less a consideration of environmental impact

The results of the LCA comparisons make clear that nanotechnology applications neither intrinsically nor exclusively can be associated with the potential for a large degree of environmental relief. Nevertheless, for the majority of the application contexts - selected with these aspects in mind -significant eco-efficiency potentials could be ascertained using the chosen methods of comparative analysis of functionality.

The reliability of the ascertained numbers is, of course, dependant on the quality and accessibility of the material and energy data available for the individual applications. For those nanotechnological processes still in development, almost no quantitative evidence is available, although for the usage phase estimates (mostly in energy-savings potential) are possible. Likewise, when comparing established or mature technologies with those still in development, one must recognize that the new technology is at the beginning of its "learning curve," i.e., that it holds the potential for significantly greater increases in efficiency.

The case study "Eco-efficient Nanocoatings" makes impressively clear that in the field of surface coatings, with respect to all emissions and environmental considerations studied; there is great potential for a very high degree of eco-efficiency through the utilization of nanotechnology-based coatings. It was also possible to demonstrate the further advantages of a simplified pretreatment process (no chromating). The minimal coating thickness necessary to achieve the same level of functionality makes possible a five-fold increase in resource efficiency. Advantages in the use phase are particularly to be expected in the transport sector as the trend to lighter-weight fabrication continues. In addition to the automotive industry, the potential for greater efficiency will have an even greater effect on the airline and rail industries. A further potential for optimization can be found in the reduction of the proportion of solvents in nanocoating applications.

180 160 140 120 100 80 60 40 20

vzzz

B water

□ chromating

1K CC

2 K CC water CC powder CC nano-coat

Fig. 1. Coating and chromating quantities (g/m2 coated aluminum automobile surface area)5

In the course of the case study "Nanotechnological Process Innovation in the Production of Styrene," we took as our example for investigation the ecological potential of nanotechnology-based catalytic applications. Specifically, the deployment of a nanostructured catalyst based on nano-tubes for the chemical production (synthesis) of styrene. Since no detailed

5 Source: authors (base data: authors, Harsch and Schuckert 1996)

life cycle assessment data for this alternative styrene production process was available, data on the energy use for this process were derived from descriptions of the technology.

The alternative styrene production process, based on a nanotube catalyst, thus yielded potential energy savings of almost 50% at the process stage. Two special effects are responsible for this improvement in efficiency: first, the previously endothermic reaction could be converted to an exothermic one; second, the reaction temperature could be lowered considerably, the reaction medium altered, and the plant power input minimized. With regard to the overall styrene product life cycle, this means an increase in efficiency of about 8-9%. Furthermore, the new catalyst makes possible considerable reductions in heavy metal emissions during the product life cycle. Possible risks from the deployment of nanotubes could negatively offset this; this still needs to be further investigated and taken into consideration in possible facility planning.

The goal of the case study "Nano-innovations in Display Technology" was the investigation of possible eco-efficiency potentials in the transition to new nanotechnology-based displays that just now are in the early stages of development. In this case study, OLEDs as well as CNT FEDs were compared to conventional CRT and modern LCD and plasma displays.

This case study likewise suggests that increases in material and energy efficiencies are possible, although due to the various stages of development of the technology, the resulting eco-efficiency estimates come with a certain degree of uncertainty. After overcoming the problem of long-term stability of the organic luminescent materials, the lower production costs of OLEDs as compared to those of the prevailing LCDs could stand in their favor. OLEDs also promise a greater degree of energy efficiency in the use phase (by a factor of two as compared to the LCD). The successful implementation in mass production of these material and energy increases in efficiency will make possible significant eco-efficiency potentials. A minimum twenty-percent savings in life-cycle energy use as compared to the LCD seems possible.

The development of higher eco-efficiency potentials for CNT FEDs will also be possible once energy efficiencies in the manufacturing phase, particularly the highly complex production of nanotubes for field emitters, becomes comparable to current production processes. Risks from these new technologies are unlikely.

Our goal in the case study "Nano-applications in Lighting" was to investigate possible eco-efficiencies by means of the application of new nanotechnological products in the field of illumination. White LEDs were compared to conventional incandescent and compact fluorescent lamps; furthermore, the future potential of quantum dots was also investigated.

With light sources in use today, 97-99% of the life-cycle energy consumption occurs in the use phase. Materials consumption, in comparison, is of much lesser consequence. The crucial measure for the environmental assessment of light sources used as illumination, therefore, is energy consumption and associated emissions during the use phase. The current white LED, it turns out, compares favorably to the conventional incandescent lamp, but is at a disadvantage by a factor of three when compared to the compact fluorescent. Only with the further development of nanotechnol-ogy-based products with a significantly higher light efficiency, i.e., white LEDs with an efficiency above ca. 65 Im/W, will the LED become environmentally comparable to the compact fluorescent and useful in non-specialized lighting applications, i.e., for everyday lighting purposes.

The use of quantum dots as source of illumination will someday make possible even greater increases in energy efficiency. Quantum-dot technology is expected to find long-term application in the area of video displays, particularly in combination with OLEDs. However, the commercial application of quantum dots is still some years away.

The case study "Risk Potentials of Nanotechnological Applications" specifically focuses on the analysis and consideration of the potential risks of nanoparticles. In this study we explore the hazards that could arise due to the properties of the structures, substances, and materials utilized in the field of nanotechnology. We also give an account of the problematic effects for humans and the environment of selected nanoparticle structures and materials as already described in the scientific literature.

The behavior of nanoparticles is, in part, quite different from that of the same materials at the macro level; this is true even for identical compounds. Some extremely surprising effects and properties of nanoparticles and nanostructured surfaces can be found in many of the studies analyzed. They document a series of suspicious factors with respect to the possible toxic effects of nanomaterials and - particularly nanoparticles - on the environment and human health, all of which need to be seriously addressed. In addition to the essentially structureless nanoparticle, nano-structured materials such as nanotubes and buckyballs are of particular significance here.

However, the scientific results so far are preliminary in most cases and in part contradictory and they often consider only a small fraction of possible effects. The degree to which generalizations can be made or knowledge carried over from these individual studies is extremely questionable. The current state of knowledge is far too sketchy for a thorough risk assessment. Generalizations and toxicity classifications for nanoparticles appear to be possible in, at best, a medium-term time span.

Furthermore, the previous results relate principally to human-toxicological questions. We still know almost nothing about the ecotoxic-ity and behavior of nanoparticles in the environment. Much broader research is sorely needed. Taking into consideration production processes and the majority of applications, the issue of risks today, with respect to nanoparticles, does appear to be pressing, but of possibly limited scope if releases into the environment can be avoided. A point in favor of this is that many production processes occur in either an aqueous solution or in a closed system and, in many products, the particles or nanostructures are firmly bonded in a matrix. Nevertheless, over the course of the entire life cycle there still exist large gaps in our knowledge with respect to risk potentials.

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