Biomedical Engineering Reference
In-Depth Information
Life cycle stages included in LCA studies
50
100%
100%
40
30
20
40%
19%
10
0
FIGURE 11.5
Life cycle stages included in inventoried LCA studies.
However, these are just materials to be fed into the manufacture of a finished
product or good. Typically nanomaterials will amount to small percentages,
that is, <5%, relative to the final mass of the nanoproduct. Therefore, compar-
ing for instance 1 kg of steel with 1 kg of carbon nanotubes is inappropri-
ate. Figure 11.6a illustrates the large differences of magnitude that can result
from conducting such an improper assessment; note the order-of-magnitude
differences in the results between the nanomaterial-embedded polymers
(dark grey) and the nanomaterials alone (black).
Yet, comparing results for producing a given mass of nanomaterial-
embedded polymers and those for manufacturing a same mass of steel of
aluminum is still inappropriate—this exemplifies case (ii). These materials
indeed possess different physico-chemical properties that are exploited in
their different applications. For instance, 1 kg of steel is not equivalent to 1 kg
of carbon-nanofiber-embedded polypropylene (CNF/PP nanocomposite)—
and even not to 1 kg of aluminum. Aluminum has a much lower density
than steel; the CNF/PP nanocomposite offers more strength and stiffness
than steel in addition to exhibiting other properties such as electrical con-
ductivity. These properties have a strong influence on the type of application
they will be used in and hence are determinant in the settings of the func-
tional unit if one wants to ensure an adequate comparability of the assessed
products or materials. Figure 11.6b shows how the results can be affected by
the choice of the functional unit. The assessment of the switch from the use
of steel to the use of nanocomposites in automotive body paneling should be
based on the main function of the materials, which is primarily driven by
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