Release from Composites by Mechanical and Thermal Treatment - Safety of Nanomaterials along Their Lifecycle - page 246

processing or use of nanomaterials with hazard potential for workers, consumers,
and the environment. The most straightforward way to avoid risks is by minimizing
exposure. Therefore, detailed knowledge is important to understand how and when
a possible release of particles from products with nanoparticles or nanocomposites
may occur. Harmonized approaches are needed for various processes along the life-
cycle to enable risk assessors, regulators, and product developers to assess possible
risks of exposures for humans and the environment. The focus of this chapter is on
the methods of testing and characterizing various mechanical and thermal release
processes along the lifecycles of nanocomposites. The possibility and need for a
standardized release test method will be discussed. The review of the different test
methods shows that release testing is feasible, but also that not all test setups can
deliver the data needed to assess the exposure risk for a given release scenario.
12.1.2 i introduCtion to r elease t esting
Nanocomposites have been used in commercial products for more than a century
as can be seen by the use of carbon black and precipitated amorphous silica in rub-
ber tires. The use of carbon black in tires, invented by the B.F. Goodrich Company
in 1910, led to a more than 100-fold increase in strength and durability of rubber
tires. * This nanofiller is still used today. But nowadays nanocomposites are also used
more and more in other products such as construction and insulation materials (Van
Broekhuizen et al. 2011; Lee et al. 2010) or as components in cars, air planes, and
ships to, for example, strengthen the construction by keeping or even reducing their
weight. Here, nanocomposites are understood as a solid material containing nano-
materials, phases, or structures with one to three dimensions smaller than 100 nm.
The increased use of nanocomposites has raised the concern on possible risks
stemming from their production and use. One of the main concerns here is the use of
nanomaterials as fillers in composites, which potentially leads to the release of nano-
materials into the environment. The risk that nanomaterials may pose for humans
and nature was identified at the end of the last century and since then investigations
have been conducted to assess the probability of release and exposure. It has to be
noted that nanocomposites with pores in the nanoscale but no dispersed nanomate-
rial, as used in insulation materials, cannot lead to the release of original nano-
objects added to the matrix.
To be able to assess potential exposure and consequently, when linked with the haz-
ard potential, the risk of the use of a nanomaterial in a composite, detailed knowledge
on the release is needed. Different approaches may be pursued to derive the infor-
mation needed for exposure assessment. It is essential to recognize though that mea-
surements allow the assessment of only one case study at a time while more general
knowledge is needed to ensure safe use of nanocomposites. One tiered approach was
introduced by Schneider et al. (2011), where source-related studies are used to derive
information on release rates and the characteristics of the released material. Modeling
of the transport and transformation of the released material can then be used to derive
* M. Bellis, History of tires, www.inventors.about.com, and D. Hiskey, Making tires black,
www.todayifoundout.com, 1. Nov. 2013.