Biomedical Engineering Reference
In-Depth Information
unfortunate absence of LCA application at the early stages of the nanoprod-
uct development, which is one of the major intended uses of LCA.
11.2.3 Review of LCA Applied to Nanomaterials and Nanotechnologies
In spite of being a standardized tool (ISO 14040
3
and ISO 14044
13
), the use
of LCA undergoes many distorted interpretations and uses, which can be
encountered in the scientific literature. The overview of the 43 LCA studies
presented in
Table 11.1
embraces studies where the authors have claimed
conducting a “life cycle analysis” or “life cycle assessment.”
Taking these LCA studies as a whole, a number of general findings can be
drawn. A substantial amount of studies shares the conclusion that, on a same
produced mass basis, the manufacture of nanomaterials is found to be more
energy intensive than the production of conventional materials such as alu-
minum or steel. Although large discrepancies exist between figures reported
for a same type of nanomaterial, higher energy requirements of one up to
several orders of magnitude have been reported for carbon nanoibers,
14 -16
carbon nanotubes,
1 7, 1 8
fullerenes,
19-21
titanium dioxide,
22
and nano silver.
23,24
In contrast, the production of other nanomaterials such as nanoclays appear
to be low energy demanding,
25,26
which still calls for a case-by-case treat-
ment of nanomaterials.
However, nanomaterials are not final products as such and are often used
in small quantities in order to improve the functionalities of a given product,
such as an increased stiffness or a lighter weight. The low percentage of mass of
nanomaterials over the total mass of the product, mainly ranging below 5 wt.%,
thus tends to reduce the contribution of nanoparticles to the whole product
environmental burden. However, it does not make it negligible. In a study
assessing fullerene used in organic solar cells, Anctil et al.
21
showed that, while
only the mass of fullerene accounted for 0.3% in the total weight, its embodied
energy accounted for 19% of the total embodied energy of the solar cells. As
concluded by the authors, this demonstrates the need for overruling the typical
5 wt.% cutoff rules when setting up inventories for assessing nanoproducts.
These high energy requirements, mainly stemming from the large use of
solvents or other chemicals for the purification and functionalization of the
nanomaterials, drive many nontoxic impact categories. In studies assessing
a broad range of impact categories, nonrenewable resource depletion, global
warming, acidification, and impacts caused by airborne inorganics were
found to be dominating after performing normalization and weighting of
the results.
17,22,28,33
A very limited number of studies attempted to investigate the toxicity-
related impacts caused by the releases of nanoparticles into the environment.
Walser et al.
24
and Meyer et al.
37
performed the assessments of nanosilver-
embedded T-shirts and socks, respectively. To estimate the releases of nanosil-
ver to the freshwater environment during the washing process (use stage),
Walser et al.
24
used literature sources and measurements and evaluated the
