Biomedical Engineering Reference
In-Depth Information
their mechanical properties and not by their mass. Although the ranking of
the three options (PUR/CNF and PP/CNF are each compared with steel) in
Figure 11.6b appears the same no matter how the functional unit is defined,
conclusions could still differ if one was to investigate and include uncer-
tainty ranges; for example, the use of an appropriate functional unit accord-
ing to stiffness could lead to the performances of PUR/CNF nanocomposite
ranging within those of steel (not shown in figure).
Adopting a property-based functional unit is also a first step to encompass
the use stage, which is so lacking in many LCA studies performed until now. In
practice, the substitution of an existing product by a nanoproduct occurs because
the latter offers more advantages related to the function it is entitled to fulfill.
Those advantages are primarily expressed during the use stage as well as in
the disposal stage to a lesser extent (e.g., to improve material/thermal recovery).
Including those stages is thus crucial if one strives toward a comprehensive
and accurate overview of the impacts and benefits of nanoproducts over con-
ventional products. On the basis of data from Khanna et al.,
15
Figure 11.7 illus-
trates how conclusions of an LCA can radically change when including the use
stage to a “cradle-to-gate” assessment of automotive components. Relying on
the cradle-to-gate study (black on graph), an LCA practitioner would conclude
on the too large impacts caused by the nanoproducts over the steel-based
Influence of life cycle perspective
15
Highest ranges
10
5
0
-5
-10
Cradle-to-gate
Cradle-to-gate + use
-15
FIGURE 11.7
Change in energy requirements in life cycle of PP/CNF- and PUR/CNF-based automotive
components compared with that of steel, using cradle-to-gate perspective (black) and includ-
ing influence of use stage (light grey; influence is here characterized by fuel consumption sav-
ings due to utilization of lighter materials than steel). Lowest and highest ranges dependent
on percent weight of nanomaterials in product. (Retrieved from Khanna, V. and Bakshi, B.R.,
Environ. Sci. Technol.
,
43,
2078,
2009; Design inspired by Hischier, R. and Walser, T.,
Sci. Total
Environ.
,
425,
271, 2012.)
