Decomposition mechanisms of trinitroalkyl compounds : a theoretical study from aliphatic to aromatic nitro compounds

International audienceThe chemical mechanisms involved in the decomposition of trinitroethyl compounds were studied for both aliphatic and aromatic derivatives using density functional theory calculations. At first, in the case of 1,1,1-trinitrobutane, used as a reference molecule, two primary channels were highlighted among the five investigated ones: the breaking of the C-N bond and the HONO elimination. Then, the influence of various structural parameters was studied for these two reactions by changing the length of the carbon chain, adding substituents or double bonds along the carbon chain. If some slight changes in activation energies were observed for most of these features, no modification of the competition between the two investigated reactions was highlighted and the breaking of the C-N bond remained the favoured mechanism. At last, the reactions involving the trinitroalkyl fragments were highlighted to be more competitive than reactions involving nitro groups linked to aromatic cycles in two aromatic systems (4-(1,1,1-trinitrobutyl)-nitrobenzene and 2-(1,1,1-trinitrobutyl)-nitrobenzene). This showed that aromatic nitro compounds with trinitroalkyl derivatives decompose from their alkyl part and may be considered more likely as aliphatic than as aromatic regarding the initiation of their decomposition process

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Decomposition reactions of trinitrobutane.</p

Assignment of Raman-active vibrational modes of tetragonal mackinawite: Raman investigations and ab initio calculations

International audienceThe mackinawite mineral was prepared as a carbon steel corrosion product in sulfidogenic waters at 90 degrees C after 2 months. The tetragonal crystal structure of the material was confirmed by Rietveld refinement of X-ray diffraction (XRD) data, and vibrational modes were analysed by micro-Raman spectroscopy. Despite a large number of studies on the formation and the stability of tetragonal mackinawite, the interpretation of the Raman spectra remains uncertain. In the present study, we report on the first calculation of the Raman-active vibrational modes of mackinawite using Density Functional Perturbation Theory and direct methods with BLYP + dispersion correction. Based on the comparison between calculated and experimental results, the four fundamental vibrational modes were assigned as 228 cm(-1) (B-1g), 246 cm(-1) (E-g), 373 cm(-1) (A(1g)) and 402 cm(-1) (E-g)

Etude structurale et chimique des effluents gazeux et des résidus de la combustion de nanocomposite à matrice PMMA

International audienceLes nanoparticules sont de plus en plus utilisées en vue de l'optimisation des performances liées à la réaction au feu des matériaux. Dans ce contexte, l'introduction de nanoparticules dans les systèmes retardateurs de flamme de polymères apparait comme une alternative aux retardateurs de flamme usuels employés. Dans le cadre du projet NanoFeu financé par l'ANR, le comportement au feu de polymères comportant des nanoparticules a été étudié ainsi que les produits de dégradation gazeux et les particules ultrafines émises. Pour cela, des matrices à base notamment de polyméthacrylate de méthyle (PMMA) ont été élaborées afin de les étudier sous l'effet de sollicitations thermiques. Plusieurs types de nanoparticules ont pu être testés : nanotubes de carbone, silice et alumine. Ces dernières sont considérées soit seules, soit combinées à un retardateur de flamme : l'ammonium polyphosphate (APP). Un des objectifs poursuivis est d'établir un protocole expérimental permettant de suivre le devenir des nanoparticules dans le processus de dégradation thermique. Des essais de combustion au calorimètre de Tewarson sont présentés, les effluents gazeux émis étant analysés par un spectromètre FT-IR. L'influence marquée de certaines compositions sur le pic de débit calorifique est observée, l'analyse des effluents renseignant sur la composition des gaz émis est réalisée. Celle-ci permet de remonter aux mécanismes de dégradation thermique des composites. Tout au long de la dégradation du matériau, l'analyse du bilan carbone est effectuée, nous informant sur les performances du dispositif expérimental élabor

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

International audienceComposite 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

The NANOFEU project : objectives and tools

International audienceThe NANOFEU project supported by the French Research Agency (ANR) aims to characterise the fire behaviour of nanoparticles filled polymer materials. Day after day, new applications of nanoparticles appear in industry. Among multiple applications in various domains, the role played by nanostructures particularly in combustion and flame retardancy phenomena needs to be quantified by modelling, experimental and numerical validations, since the use of these new components is increasing to upgrade polymer performances. Their employment could represent nowadays a valuable alternative or could be used in synergy with the conventional flame retardants systems. Nanocomposites based on several categories of polymers will be designed, incorporating suitable nanoparticles. Multiscale modelling of material, investigation of thermal degradation processes, and influence of interfacial modifications of nanoparticles, characterisation of effluents, particles released (size and morphology) and smoke toxicity will be made, developing original experimental and numerical means. We will particularly focus on fire performance, smoke toxicity and morphological modification of particles in the effluents, to weight the various impacts of the introduction of these nanofillers. A traceability of nanoparticles affected by combustion will be done through the analysis of effluents. In a first part, this paper includes a detailed presentation of the project by clarifying the partners' roles and objectives expected at the end of the project. In a second part, the foreseen experimental and numerical tools will be developed in order to improve the knowledge of mechanisms involved in combustion

Influence of carbon nanotubes on fire behavior and on decomposition products of thermoplastic polymers

International audienceCarbon nanotubes based poly(methyl methacrylate) and polyamide-6 nanocomposites have been investigated using various techniques within the framework of the Nanofeu project. STEM was used to characterize morphologies of composites, while fire properties were studied using cone calorimeter (CC), fire propagation apparatus (FPA) and pyrolysis combustion flow microcalorimeter (PCFC). The study focused particularly on composition and microstructure of gaseous and aerosol products. Composition of gaseous effluents was analyzed using FTIR coupled with FPA. Morphology of ultrafine particles released from the combustion of nanocomposites was studied using cascade impactors and Atomic Force Microscopy (AFM). Fire behavior has been interpreted in relation with the degradation mechanisms specifically induced by the presence of nanotubes. Molecular modelling simulations, providing molecular insights into the interactions between polymers and nanotubes, aimed to support the analysis of the experimental result