Evaluation of risks induced by the incineration of emerging nanocomposites containing polymer matrices
The development of new nanoparticle-based plastic products raises questions regarding their leaching-out over the life cycle. Their possible emissions during the incineration process, coupled with their potential toxicity, may in fact present public health problems that require close attention.
Plastic materials are used in many applications of daily life; consequently, large quantities of plastics and composites are found in solid waste flows (up to 15% of such flows, depending on the countries examined). Moreover, new solutions consisting of adding nanoparticles (Al2O3, TiO2, SiO2, etc.) into these polymer materials are becoming increasingly applied to improve certain properties (e.g. mechanical, barrier effect, fire resistance), yet at the present time no specific marking serves to identify the presence of these types of substances in the products.
Many questions are thus raised regarding the associated risks, whether they be related to the emission of these nanoparticles during the incineration process or to the toxicity of these substances. Various projects involving LNE over the past few years have focused on the first area of concern (NANOFEU, INNANODEP and NANOEMI). An instrumented test bench, built by introducing a cone calorimeter within a controlled atmosphere coupled to various measurement devices (FTIR for gases, DLPI and SMPS for particulates), could thus be developed at LNE in order to simulate the incineration process at the laboratory scale and characterize the gases and particulates being emitted. Extensive metrological validation has, above all, provided assurance that the real-time measurements and sampling conducted for the subsequent characterization using techniques available on LNE's CARMEN platform yield reliable results that accurately depict reality.
The NANOTOX’IN Project is specifically dedicated to two missions: 1) evaluating the toxicity of nanoparticles emitted during the incineration of an EVA matrix widely used in the cable manufacturing industry; and 2) determining the impact of thermal degradation on a potential modification in this toxicity. Various nanoparticles have been taken into account (Aluminum oxide Al2O3, Boehmite AlO(OH), Silica SiO2), with diverse morphology and surface states that highlight a correlation between substance parameters and observed toxicity. An in-depth nanoparticle characterization step is performed prior to introducing the particles into polymer matrices and soot, once incineration has been completed, as well as into the culture medium present during toxicity tests. This step constitutes a key prerequisite to obtaining representative data and thus determining the parameters influencing the observed effects.
LNE's involvement in this project entails providing its partners with the laboratory's expertise and resources to thermally degrade the various mixes under investigation, along with representative samples of the particles emitted and their characterization using all relevant parameters, as described in the ISO/TR 13014 document (size, particle size distribution, shape, crystalline structure, surface charge, specific surface area, etc.). The deployment of several complementary techniques (SCM, AFM, DLS) to determine both particle size and size distribution renders the results obtained more reliable. Also, the reference protocols devised within the scope of the NANOMET Project will be adapted to these highly complex matrices found in soot and the culture media required to carry out toxicity testing.
"Armines" (Ecole des Mines d’Alès, Ecole des Mines de Saint-Etienne)