Mechanisms of Aging and Release from Weathered Nanocomposites - Safety of Nanomaterials along Their Lifecycle - page 314

US dollars and an annual growth of 49% between 2009 and 2013 (Research and
Markets 2009).
Polymer nanocomposites differ from traditional plastic composites in that they pro-
vide greatly enhanced properties with a minimum effect on mass and without major
processing modifications. Depending on the type of nanofiller used, advantages of
polymer nanocomposites over traditional polymer products include their being stron-
ger, harder, tougher, lighter, more dimensionally stable, less permeable, and more
durable. In coming years, polymer nanocomposites will enter the consumer markets
in large quantities, and they will be increasingly used in essentially every segment
of the industry from textiles, electronics, constructions, sporting goods to aerospace.
Whatever the application, both the long-term performance of the composite and the
fate of the nanofillers in the matrix during the product's lifecycle play a key role in the
commercialization and uses of these nanocomposite products (Kingston et al. 2013).
The reason for that is most common polymers tend to undergo degradation during
exposure to weathering environments. The serious consequence of the degradation
of the host matrix is that the embedded nanofillers could be exposed to the surface
and released to the environment via the effects of rain, condensed water, wind, and
mechanical vibrations. For those nanosize materials that have shown potential risks
to the environment, health, and safety (Nel et al. 2006; Poland et al. 2008; Maynard
2006; Aschberger et al. 2010; Handy et al. 2008; Lee et al. 2010), we need to know
rates and probabilities of release of the nanofillers during the lifecycle of a polymer
nanocomposite to select products and scenarios of safe use.
Weather-induced degradation of the host matrix in a polymer nanocomposite is
inherently a complex process controlled by the exposure environment, materials
properties, and processing. In addition, nanoscale materials possess unique elec-
tronic structure, create a large polymer/particle interfacial volume fraction in the
nanocomposites, and have a tendency to agglomerate. These distinctive characteris-
tics of nanofillers likely affect the rate and mechanism of degradation of the polymer
matrices. Yet, little data is available on (1) the behavior and mechanisms of polymer
nanocomposite degradation under different weathering environments, (2) the fate of
the imbedded nanofillers, (3) how the nanofillers may be released, and (4) the meth-
odology to estimate the release rate as a function of weathering. The lack of this set
of information hinders our ability to understand the nanofiller release mechanisms,
to predict the potential release during the nanocomposite lifecycles and to develop
strategies to mitigate this potentially serious problem. Due to the lack of such data,
the long-term performance of polymer nanocomposites and the potentially harmful
effects of the nanofillers incorporated in polymers on the environment and human
health cannot be correctly assessed.
This chapter will briefly present and discuss recent advances in the weathering
of polymer nanocomposites and release of nanofillers caused by weather-induced
degradation of the polymer matrix.
14.2 WEATHERING OF POLYMER NANOCOMPOSITES
Polymer nanocomposites provide a range of appealing properties such that, in many
applications, they are exposed to harsh conditions. Whatever the application, there is