Release from Composites by Mechanical and Thermal Treatment - Safety of Nanomaterials along Their Lifecycle - page 267

loading showed a 12 K higher onset temperature for degradation compared to that
for neat PA6. The onset temperature for degradation remained almost unchanged
for samples with higher clay loading (5, 7.5, and 10 mass% clay). These results are
related to the morphological observations that showed an optimal exfoliated struc-
ture only for the nanocomposite with 2.5 mass% clay, and distinct clay agglomera-
tion in those with higher clay loadings.
Zanetti et al. (2004) found that during the thermal degradation of polyethylene
(PE)/clay nanocomposites by means of TGA in the oxidant atmosphere, the forma-
tion of a protective layer on the polymer surface was observed caused by a charring
process of PE. But PE is normally a nonchar-forming polymer.
Chrissafis et al. (2007) studied the thermal degradation mechanism of polycap-
rolactone (PCL) and its nanocomposites containing different nanoparticles (two lay-
ered silicates, SiO 2 , and MWNT) through TGA using nonisothermal conditions at
different heating rates. The results showed that modified montmorillonite and fumed
silica accelerate the decomposition of PCL due to respective aminolysis and hydro-
lytic reactions that the reactive groups on the surface of these materials can induce.
On the other hand, CNTs and unmodified montmorillonite can decelerate the ther-
mal degradation of PCL due to a shielding effect.
Overall, quite a few studies investigating the thermal degradation and release of
nano-object containing material were conducted. The test setups for thermal degra-
dation are comparable to each other because of the general use of thermogravimetric
analyzer and are therefore advanced for harmonization and standardization.
12.3.2 C omBustion
Combustion is an exothermal process not entirely different from thermal degrada-
tion. The main difference is the uncontrolled high energy release in the form of heat
during explosion or fire leading to mainly oxidized compounds as the final product.
This also means that different from thermal degradation, combustion may lead to
partial or total oxidation and hence release of the embedded nano-objects.
Bouillard et al. (2013) used a home-made demonstrator combustion system to
assess nano-object release during combustion. Therefore, a high-performance nano-
composite polymer (acrylonitrile-butadiene-styrene, ABS) mixed with 3 mass%
of MWCNTs was tested. An oven was developed to simulate specific combustion
regimes (mainly in low-temperature substoichiometric conditions) and conceived
with proper mass and heat-transfer controls to assess favorable conditions for the
release of nano-objects. To detect the potential release of CNTs during the com-
bustion, the particle size distribution in the fumes was measured using an ELPI.
Additionally, particles were sampled using an aspiration-based TEM grid sampler.
The study showed release of MWCNT at about 400°C, the combustion temperature
of ABS with 3 mass% of MWCNTs. CNTs of about 12 nm diameter and 600 nm
length were observed in the combustion emissions.
Calogine et al. (2011) focused on the combustion of nanocomposite samples under
various ventilation conditions. The tests were performed with the fire propagation
apparatus according to ISO 12136:2011, and PMMA with various nanofillers (CNTs,