Release from Composites by Mechanical and Thermal Treatment - Safety of Nanomaterials along Their Lifecycle - page 271

mechanical mechanisms. Further release processes not tackled in this chapter are
exposures of nanomaterials to reactive gases or liquids, for example, ozone or hydro-
gen peroxide in water. Simulations of weathering combine thermal processes and
exposure to reactive chemical compounds. Yet, going another step further is the
combination of weathering followed by mechanical stress like sonication as reviewed
in Hirth et al. (2013). Especially, this combination of matrix degradation by weather-
ing and mechanical stress by sanding and abrasion mechanisms is seen as a possible
mechanism releasing single or agglomerated nano-objects.
Another methodology for grouping was, for example, discussed by Le Bihan et al.
(2013). They list different test methods, the release scenario simulated by this method
and the wear energy linked to it. In a first assessment some correlation between
released concentrations and the energy input was identified by Le Bihan et al. (2013).
Current status in view of harmonization: The review presented here shows that
some test methods, for example, dustiness, abrasion, and sanding, can be viewed as
quite advanced and ready for standardization while others are more in their infancy.
A simple grouping of release test scenarios into three levels for harmonization maybe
(see Table 12.4): Level 1—ready for standardization; Level 2—basic information on
mechanisms and release rates is available but several test setups are available or
some basic information is missing; and Level 3—nearly no information and test
methods are available. This type of evaluation linked to the need of standardization,
for example, due to exposure risk is a feasible way to prioritize future developments.
Comparison of material behavior to different stress conditions: First tests of
the same nanomaterial using different test methods have been conducted (e.g.,
Wohlleben et al. 2011 and 2013). This type of tests, once evaluated and established,
will allow complete assessment of release probabilities facilitating safer design and
thus a reduction in likeliness of exposure.
Release to exposure: The ultimate aim for release testing is to ensure the safety of
workers, consumers, the population, and the environment. Hence, a good robust link
from release to exposure or even dose is needed. Due to the high physical and chemical
variability, the interaction with the environment during transport, the homogeneous
interaction at high concentrations, and uptake probabilities can vary significantly so
that models are needed to simulate the processes and interactions well enough for, for
example, exposure assessments. Some computational fluid dynamic (CVD) models
are available for specific workplace scenarios. Extensions to other exposure scenarios
and the environment are urgently needed. This will facilitate the safe implementation
of the use of nanomaterials for the benefit of humans and nature.

TABLE 12.4
Readiness for Standardization

Level Release Scenario

1 Dustiness, abrasion, sanding, and drilling

2 Milling, grinding, sawing scratching, dropping, cutting/shredding, thermal stress, incineration,

and mixed processes (e.g., weathering)

3 Reactive liquids, reactive gases, and fire/explosion