Release from Composites by Mechanical and Thermal Treatment - Safety of Nanomaterials along Their Lifecycle - page 268

Al 2 O 3 , and SiO 2 ) was employed. In the well-ventilated cases all tested PMMA samples
with fillers and/or fire retardants showed lower effective heat of combustion values and
a lower average mass loss rate compared to PMMA without any additive. The most
significant decrease in heat of combustion was 6% for PMMA with 15 mass% Al 2 O 3 .
In the underventilated case the highest effective heat of combustion was observed for
PMMA with 15 mass% SiO 2 , which is an increase of about 48% compared to neat
PMMA. The highest mass loss rates were determined for samples containing CNT.
Motzkus et al. (2012) investigated the fire behavior and the characterization of solid
and gaseous fire effluents of PMMA and PA6 filled with NPs (silica, alumina, and
CNTs) used to improve their flame retardancy. The impact of these composites on
the emission of airborne particles produced during their combustion in accidental fire
scenarios was determined with an experimental setup, which was developed to mea-
sure the mass distribution in the size range of 30 nm-10 µm, and the concentrations
of submicrometer particles in the aerosol using an ELPI, CPC, and cone calorimeter.
Comparisons were made between unfilled and filled polymers. The influence of filler
surface treatments (silane-based) as well as combinations with a flame retardant (APP)
was also investigated. The results showed that for all samples of PMMA or PA6 modi-
fied or not with and without nanofillers of SiO 2 , MWCNT, or Al 2 O 3 high mass fractions
were seen in the submicrometer particles (close to 80%). A 10% decrease in the mass
fractions of ultrafine particles, due to addition of flame retardant (APP), was noticed.
12.3.3 i nCineration
Incineration differs from thermal degradation and combustion in that it aims at full
combustion to CO 2 and H 2 O by high temperatures in an oxygen sufficient system
with a minimum residence time of the compounds in the incineration zone.
Stahlmecke et al. (2014b) conducted such a study within the German Innovation
Alliance CNT initiative. Therefore, an incinerator was simulated in the laboratory
and two tube furnaces, each with a heated tube length of 550 mm, were used in series
(see experimental setup in Figure 12.15). The test material was polycarbonat (PC),
PA, and PE, each pure and with 5% and 7.5% CNT. Released particle concentration
was measured with an FMPS and particle samples were taken with a NAS for con-
secutive morphological SEM analysis.
The results showed that there was no release of free CNTs and no major differ-
ences in the resulting particle quantities, sizes, and morphologies were found for the
same materials with different CNT contents. During incineration experiments, only
residue of PC materials that remained in the crucible after incineration showed CNT-
like structures embedded in the slag, which was caused by an incomplete combustion
of the material due to experimental deficiencies. Overall, the incineration experiments
showed that burning of the different polymers always released very high particle num-
ber concentrations, independent of the CNT content. However, since none of the mea-
surements revealed any evidence for airborne free CNTs, it can be concluded that under
the given experimental conditions, the CNTs in the materials decomposed completely.
Derrough et al. (2013) investigated in a study the behavior of nanoparticles
during high temperature with a setup of an incineration mounting at a laboratory
scale (Figure 12.16). They selected pure silver, tin, and nickel NP as samples, and