Claire Longuet

Behavior and Fate of Halloysite Nanotubes (HNTs) When Incinerating PA6/HNTs Nanocomposite

Nanoclay-based nanocomposites have been widely studied and produced since the late 1990s, and frequently end up in waste disposal plants. This work investigates the behavior of PA6/HNTs nanocomposites (nylon-6 incorporating halloysite nanotubes) during incineration. Incineration tests were performed at lab-scale using a specific tubular furnace modified in order to control the key incineration parameters within both the combustion and postcombustion zones. The combustion residues and combustion aerosol (particulate matter and gas phase) collected downstream of the incinerator furnace were characterized using various aerosol analysis techniques. Time tracking of the gas and particle-number concentrations revealed two-step char formation during combustion. HNTs transformed into other mineral structures which were found in both the aerosol and the residues. During combustion of the polymer, it appears that HNTs contribute to the formation of a cohesive char layer that protects the residual material.

Gaseous effluents from the combustion of nanocomposites in controlled-ventilation conditions

Composite materials are more and more used every day. In order to further enhance their attractive mechanical and physico chemical performances, the last generation of these materials largely makes use of nanomaterials. Various nanofillers are eligible for such a purpose, the best ones depending on the associated matrices. One favorite field of application of these nanomaterials is fire retardancy and fire behavior of nanocomposites. In the context of the ANR research project NanoFeu, various technical analyses have been performed [1]. One focuses on the characterization of the dispersion of nanofillers in the matrix; another deals with the characterization of the fire behavior of samples including the study of the composition of the gaseous effluents, the characterization of the emitted soot [2]. A third part of the work focused on molecular modeling of observed phenomena within the matrices. This paper focuses mainly on the combustion of nanocomposite samples under various ventilation conditions. Tests have been performed with the Fire Propagation Apparatus (FPA). Samples are based on poly(methyl methacrylate); various nanofillers were used: carbon nanotubes, alumina and silica. Efficiency of fillers is compared to the classical ammonium polyphosphate in equal proportions. During testing, the ventilation-controlled conditions were obtained by adjusting the combustion air flow rate entering the apparatus. Gaseous effluents were analyzed by Fourier Transform Infra-Red spectrometer. Fire behavior is characterized in terms of fire parameters and chemical composition of gaseous effluents. The influence of ventilation conditions is especially significant in terms of amount of gases released: much more important production of specific gases is generally observed in case of under ventilation regime as compared to the well ventilated case.

Comparison of Surface and Bulk Properties of Pendant and Hybrid Fluorosilicones

The most common fluorosilicone polymer commercialized to date is polymethyltrifluoropropylsiloxane. However, the low content of is the perfluorinated groups in the polymer 36.5 wt% does not fulfill the requirements of some high tech applications, particularly when swelling properties or degradation at high temperatures are concerned. A number of strategies have been employed to increase the fluorine content of fluorosilicone polymers. One elegant way is to introduce into the silicone chain, either as a pendant group or inside the backbone, perfluorinated groups of increasing size (typically C6 or higher). We refer to silicones with perfluorinated chains introduced as side groups as “pendant silicones” whereas those carrying fluorine atoms in the main backbone are called “hybrid silicones”. The most popular synthesis techniques of such polymers are briefly discussed here. A full fuller comparison is given of the two classes of polymers in terms of surface, mechanical, swelling and thermal properties.

Thermal degradation, flammability, and potential toxicity of polymer nanocomposites

Abstract: Many new nanomaterial-based products have been developed recently, due to advances in nanotechnology. These are designed to offer new functionalities or to modify existing products. This chapter examines the thermal degradation and flammability of various nanocomposite polymers and the potential risks of burning them. Different fire scenarios have been simulated with a cone calorimeter coupled with FTIR, condensation nuclei counter (CNC) analysers, and/or cascade impactors in order to produce aerosols emitted at different radiation levels and flammable atmospheres. The testing conditions and influential parameters are presented. Combinations of pristine ultrafine particles with soot or other ultrafine particles during thermal degradation can directly affect human health. Hence, more research is needed into the morphology and composition of the released nano-objects and ultrafine particles.

Physical, morphological and chemical modification of Al-based nanofillers in by-products of incinerated nanocomposites and related biological outcome

The number of products containing nanomaterials is increasing this last ten years. Information and literature about the end-of-life of nanocomposites often remains partial and does not address the overall fate and transformations of nanoparticles that may affect biological responses. This paper underlines that the physico-chemical features of nanoparticles can be modified by the incineration process and the available toxicological data on pristine nanofillers might not be relevant to assess the modified nanoparticles included in soot. Combustion tests have been performed at lab-scale using a cone calorimeter modified to collect fumes (particulate matter and gas phase) and have been characterized using various techniques. Nanocomposites selected were poly(ethylene vinyl acetate) containing Al-based nanoparticles, i.e. boehmites or alumina. Evaluations of in vitro cytotoxicity responses on pristine nanofillers, soot and residual ash, show that safe boehmite nanoparticles, become toxic due to a chemical modification after incineration process.

Radical crosslinking during polyhydrosilylation between fluorinated and silicone molecules: a model study

Abstract The present study deals with an explanation for crosslinking reactions that occur during the polyhydrosilylation of telechelic Si-H silicones with divinylperfluoro molecules. For a better understanding of the chemical process, a model reaction was performed and characterized by a full battery of techniques, including the different nuclei NMR analyses. Even if hydrosilylation occurs, side methyl groups on the silicon atoms also react with tert-butoxy radicals. Abstraction of a hydrogen radical from the methyl side group of the silicone chains allows the vinyl fluorinated molecules to add on polydimethylsiloxane and to bridge chains together.