Kinetic Analysis of the Thermal Degradation of Polystyrene-Montmorillonite Nanocomposite

Nanocomposites exhibit a combination of unique properties, such as increased heat distortion temperature, reduced permeability, reduced flammability and improved mechanical properties. In this work, a polystyrene (PS) clay nanocomposite was prepared via bulk polymerization using a novel organically modified montmorillonite (MMT). The organic-modifier is the N,N-dimethyl-n-hexadecyl-(4-vinylbenzyl) ammonium chloride (VB16). The thermal stability of PS–VB16 compared to pure PS is examined in pyrolytic and thermo-oxidative conditions. It is then studied using a kinetic analysis. It is shown that the stability of PS is significantly increased in the presence of clay. The thermal behavior of PS and PS nanocomposite is modeled and simulated. A very good agreement between experimental and simulated curves both in dynamic and isothermal conditions is observed. Using kinetic analysis associated to the reaction to fire of PS nanocomposite simulated in a cone calorimeter, the peak of heat release rate is half that of virgin PS, it is suggested that the clay acts as a char promoter slowing down the degradation and providing a protective barrier to the nanocomposite. The combination of these two effects is an important factor lowering the HRR

Characterisation of the dispersion in polymer flame retarded nanocomposites

Flame retardant nanocomposites have attracted many research efforts because they combine the advantages of a conventional flame retardant polymer with that of polymer nanocomposite. However the properties obtained depend on the dispersion of the nanoparticles. In this study, three types of polymer flame retarded nanocomposites based on different matrices (polypropylene (PP), polybutadiene terephtalate (PBT) and polyamide 6 (PA6)) have been prepared by extrusion. In order to investigate the dispersion of nanoparticles in the polymer containing flame retardant, conventional methods used to characterise the morphology of composites have been applied to FR composites containing nanoclays. XRD, TEM and melt rheology give useful information to describe the dispersion of the nanofiller in the flame retarded nanocomposite. In the PA6-OP1311 (phosphorus based flame retardant) materials, the clay is well dispersed unlike in PBT and PP materials where microcomposites are obtained with some intercalation. The poor dispersion is also highlighted by NMR measurements but the presence of flame retardant particles interferes in the quantitative evaluation of nanoclay dispersion and underestimations are made

Composites on fire at reduced scale: evaluation, characterization and modeling

Composite materials are increasingly being used in the design of aircraft, train, ship and buildings. They are very often structural parts and they must meet the difficult challenge of having adequate structural fire protection. In fire scenarios of particular relevance according to the targeted applications, suitable strategies to control fire hazards are needed for composite structures. There are three main methods available to design composite structures with improved fire resistance behavior: (i) use “normal” structural materials and add surface protection, (ii) use fire retarded versions of “normal” structural materials, and (iii) use structural materials with inherently good fire retardant properties. The first approach is of interest since it does not modify the intrinsic properties of the structural composites and does not lead to processing problems (e.g. incorporation of fillers in the material). It can be achieved with intumescent coatings: when heating beyond a critical temperature, the intumescent material begins to swell and then to expand forming an insulative coating limiting heat and mass transfers. Intumescence will be used in this work On the other hand, the evaluation of fire resistance of intumescent coatings protecting structural composite requires large scale equipment. Due to the complexity of fire phenomenon, full-scale tests are still the main and the most credible tool for investigating fire-related issues but they are however very costly, and generally, the cost significantly increases with scale. For those reasons we have developed reliable, repeatable and fast small scale tests including: (i) a furnace delivering temperature/time curves such as ISO 834, UL-1709 and other curves depending on specific fire conditions (curves ‘on demand’), (ii) a jet fuel fire test (according to ISO 2685 or NextGen) devoted to evaluate the fire resistance of components, equipment and structure located in ‘fire zones’ in aircraft (e.g. compartments containing main engines and auxiliary power units) and (iii) a mini Steiner tunnel (according to ASTM E84). It then permits the ‘high throughput’ development of intumescent coatings protecting composites. Examples using the mini Steiner tunnel and the reduced jet fuel fire test will be presented in the talk. The first example deals with the fire protection carbon fiber reinforced polymer (CFRP) in aircraft structure. Intumescent silicone based-coatings (low and high intumescing coatings) are evaluated on CFRP using a bench mimicking a jet fuel fire occurring at high heat flux (200 kW/m²) (Figure 1). It is shown the development of large intumescence (high intumescing coating) associated with appropriate thermal properties of the coating (heat conductivity measured as low as 0.3 W/m.K) provides efficient protection for the CFRP at the jet fire test. On the other hand, the formation of cohesive ceramic (low intumescing coating) with low heat conductivity (constant heat conductivity as a function of temperature of 0.35 W/m.K) also provides protection but its efficiency is lower than that of intumescent char. It is evidenced that intumescent silicone-based coatings are materials of choice for protecting CFRP in the case of jet fuel fire. Figure 1 – Jet fuel fire at reduced scale on CFRP protected by an intumescent coating In the second example, different intumescent coatings protecting polyethylene terephthalate (PET) rigid foams used in roofing structure are evaluated using the mini Steiner tunnel. Results show good correlation between the two scales and the approach developed at the small scale permits the fast screening of intumescent paints to predict their fire behavior at the large scale. Finally, mechanistic aspects of intumescence based on our small scale tests will be investigated including the chemistry, the physic, the rheology and the modeling of the intumescenc

Investigation of nanodispersion in polystyrene-montmorillonite nanocomposites by solid state NMR

Nanocomposites result from combinations of materials with vastly different properties in the nanometer scale. These materials exhibit many unique properties such as improved thermal stability, reduced flammability, and improved mechanical properties. Many of the properties associated with polymer–clay nanocomposites are a function of the extent of exfoliation of the individual clay sheets or the quality of the nanodispersion. This work demonstrates that solid-state NMR can be used to characterize, quantitatively, the nanodispersion of variously modified montmorillonite (MMT) clays in polystyrene (PS) matrices. The direct influence of the paramagnetic Fe3, embedded in the aluminosilicate layers of MMT, on polymer protons within about 1 nm from the clay surfaces creates relaxation sources, which, via spin diffusion, significantly shorten the overall proton longitudinal relaxation time (T1 H). Deoxygenated samples were used to avoid the particularly strong contribution to the T1 H of PS from paramagnetic molecular oxygen. We used T1 H as an indicator of the nanodispersion of the clay in PS. This approach correlated reasonably well with X-ray diffraction and transmission electron microscopy (TEM) data. A model for interpreting the saturation-recovery data is proposed such that two parameters relating to the dispersion can be extracted. The first parameter, f, is the fraction of the potentially available clay surface that has been transformed into polymer–clay interfaces. The second parameter is a relative measure of the homogeneity of the dispersion of these actual polymer–clay interfaces. Finally, a quick assay of T1 H is reported for samples equilibrated with atmospheric oxygen. Included are these samples as well as 28 PS/MMT nanocomposite samples prepared by extrusion. These measurements are related to the development of highthroughput characterization techniques. This approach gives qualitative indications about dispersion; however, the more time-consuming analysis, of a few deoxygenated samples from this latter set, offers significantly greater insight into the clay dispersion. A second, probably superior, rapid-analysis method, applicable to oxygen-containing samples, is also demonstrated that should yield a reasonable estimate of the f parameter. Thus, for PS/MMT nanocomposites, one has the choice of a less complete NMR assay of dispersion that is significantly faster than TEM analysis, versus a slower and more complete NMR analysis with sample times comparable to TEM, information rivaling that of TEM, and a substantial advantage that this is a bulk characterization method. © 2003 Wiley Periodicals, Inc.* J Polym Sci Part B: Polym Phys 41: 3188–3213, 200

Performance de la nanofiltration pour l'élimination de la matière organique naturelle: essais sur l'usine de Méry/Oise

L'intérêt croissant que les traiteurs d'eaux portent à l'élimination de la matière organique naturelle (MON) a abouti au développement de nouvelles technologies de traitement. Dans ce but, un prototype de nanofiltration à l'échelle industrielle (2 x 1400 m 3 j-¹) est installé à l'usine de Méry sur Oise depuis juillet 1992. Utilisé en traitement de finition après clarification et filtration sur sable, il alimente depuis février 1993 un réseau test de la commune d'Auvers sur Oise (6 000 hbts) en région parisienne.L'objectif de cette publication est de présenter quelques uns des résultats de caractérisation de la MON obtenus pendant 9 mois d'expérimentation (octobre 1992 à juillet 1993), et en particulier ceux concernant les rendements d'élimination de la matière organique naturelle et par voie de conséquence de la demande en chlore.Ces rendements sont généralement supérieurs à 90 % en termes de COD,CODB et d'absorbance UV à 254 et 270 nm éliminés. L'analyse des potentiels de réactivité avec le chlore (taux de chloration: 2,5 mg Cl2/mg C, temps de réaction: 72 heures, pH = 7,5, 20 °C) montre que le perméat est peu consommateur de chlore (demande en chlore < 0,2 mg l-¹ Cl2) et peu précurseur de chloroforme et de trihalométhanes (PFCHC13 < 3 µg l-¹, PFTHM < 11 µg l-¹). Les rendements d'élimination des PFTHM et PFTOX sont généralement supérieurs à 90 %.L'analyse spécifique des constituants majoritaires du perméat montre que les acides aminés totaux (hydrolyse acide puis dérivation à l'OPA/HPLC) constituent une proportion importante du COD (25 à 60 % selon les saisons). Ces composés représentent la quasi totalité de la demande en chlore du perméat si l'on se réfère aux données bibliographiques.Compte tenu de ces résultats, la nanofiltration apparaît comme un excellent procédé de traitement de finition des eaux à potabiliser. En effet, bien qu'elle constitue une barrière de sécurité contre les germes pathogènes, la très faible charge organique du perméat obtenu par nanofiltration (COD~0,15 à 0,3 mg l-¹ C, CODB<0,1 mg l-¹ C) rend plus aisée la maîtrise du résiduel de chlore (lorsqu'une chloration est nécessaire pour maintenir la qualité de l'eau dans les réseaux) et constitue une limitation importante de la formation des sous-produits de chloration.Increasing interest in removing natural organic matter (NOM) has lead to the development of new drinking water treatment technologies. Since July 1992, a nanofiltration demonstration plant (2 x 1400 m3 d-1) has been used to treat sandfiltered water from the Oise river. The permeate has been distributed since February 1993 to the 6000 inhabitants of Auvers/Oise in the Paris suburb. The purpose of this paper is to present and discuss some ofthe results obtained over nine months of operation of this full scale plant, particularly yields of NOM removal and consequently the decreasing of chlorine reactivity (chlorine demand, TTIM and TOX formation potentials).Dissolved organic carbon (DOC) and UV-absorbance were determined using DOC analyser and a spectrophotometer. Biodegradable dissolved organic carbon (BDOC), which represents the biologically assimilable portion of DOC, was determined using the method of JORET et LEVI (1986). Chlorine demand, trihalomethane and total organohalide formation potentials (THMFP and TOXFP) were carried out under the following experimental conditions: applied chlorine dose of 2.5 mg Cl2/mg DOC, pH = 7,5 72 h-contact time and 20°C. Ultrafiltration experiments involved the use ofa laboratory ultrafiltration cell, Total amino-acids were analysed by HPLC after hydrolysis and orthophtaldialdehyde (OPA) derivatization. Aldehyde and ketone determination was based on the method developedby GLAZE et al. (1989) involving pentafluorobenzyl hydroxyl amine (PFBHA) derivatization.Characterization of sand-filtered water (SFW): The sand-frltered water (SFW) upstream of the nanofiItraton membranes has a DOC between 2.4 and 4.l mg l-1, depending on the season (table 1). Its BDOC ranges from 0.7 to l.l mg l-1 C. In fact, a BDOC value higher than 0.3 mg l-1 C has been mentioned by several authors as the limit above which possible bacterial regrowth can take place in the distribution network.The chlorine consumption curves, shown in figure 2 for five sampling campaigns, indicate that the chlorine demand of the SFW can reach 3.4 to 5.2 mg l-1 depending on the season (table 2). The THMFP and the TOXFP are 108-149 ug l-1 and 344-446 ug l-1 Cl- respectively. Note that the ratio of chlorine demand over DOC varies from 1.0 to 1.7 mg Cl2/mg DOC while the THMFP/DOC and TOXFP/DOC ratios present average values of 47.5 ug/mg DOC and 160 ugCl-/mg DOC respectively.The distribution of the SFW (table 3) indicates that the fraction with apparent mo lecular weight Iess than 3 kilodatons contains the major compounds at this stage of the water treatment. This fraction presents the highest chlorine consumption. Specific total amino acids (TAA) analyses demonstrate that TAA represent 3 to 8% of the DOC of the sand-filtered water. The most abundant arnino acids are glycine, aspartic acid, glutamic acid, serine and alanine. The chlorine consumption attributed to these amino acids is evaluated as 1 mg l-1 Cl2, that is to say 1/5 to 1/3 of the SFW chlorine demand. Formaldehyde and acetaldehyde seem to be the major aldehydes present in the SFW with a level of 7 ug l-1 and 20 ug l-1 of formaldehyde and acetaldehyde respectively. They represent only about 0.5 to 0.6 % of the SFW DOC.Characterization of the permeate: The nanofiltration permeate presents a very low NOM level in terms of DOC, BDOC and UV absorbance at 270 nm, that is to say 0.14 to 0.34 mg l-1 C, < 0.1 mg l-1 C and < 0.006 cm-1-l respectively (table 6).The chlorine consumption curves, showt in figure 4 for five sampling campaigns, demonstrate the low permeate reactivity with chlorine. The chlorine demands (table 7) after 72 hours are between 0.12 and 0.32 mg l-1. Moreover chlorine demand/DOC ratios have a value from 0.46 to 0.93 mg Cl2/mg DOC, i.e. half the values measured for SFW. The THMFP and TOXFP (72hours) range from 7 to 11 ug l-1 and 26 to 31 ug l-1 Cl- respectively.Total amino acid (TAA) analyses showed that TAA represent 35 to 60% of the permeate DOC and can account almost entirely for the chlorine consumption. Formaldehyde and acetaldehyde (the major aldehydes analysed) represent 7 to 8% of the permeate DOC.According to the results presented in this paper, nanofiltration appears to be an excellent technolory as a polishing step in surface water treatment. Whereas the level of sand-fïltered water (SFW) DOC varies from 2.4 to 4.1 mg l-1 C (depending on the season), the permeate DOC is consistently lower than 0.3 mg l-1 C. The efficiency of nanofiltration is about 90% for DOC, BDOC and consequently for chlorine demand, THMFP and TOXFP. The high retention of NOM is probably in relation with the percentage (75%) of compounds with apparent molecular weight above 500 daltons in the SFW. In fact the low values of BDOC and chlorine demand justify the use of nanofiltration for the production of a water which represents a very low risk of bacterial regrowth and a low risk of formation of disinfection by product in the network when distributed with a low concentration of residual chlorine

Fire retardant action of mineral fillers

Endothermically decomposing mineral fillers, such as aluminium or magnesium hydroxide, magnesium carbonate, or mixed magnesium/calcium carbonates and hydroxides, such as naturally occurring mixtures of huntite and hydromagnesite are in heavy demand as sustainable, environmentally benign fire retardants. They are more difficult to deploy than the halogenated flame retardants they are replacing, as their modes of action are more complex, and are not equally effective in different polymers. In addition to their presence (at levels up to 70%), reducing the flammable content of the material, they have three quantifiable fire retardant effects: heat absorption through endothermic decomposition; increased heat capacity of the polymer residue; increased heat capacity of the gas phase through the presence of water or carbon dioxide. These three contributions have been quantified for eight of the most common fire retardant mineral fillers, and the effects on standard fire tests such as the LOI, UL 94 and cone calorimeter discussed. By quantifying these estimable contributions, more subtle effects, which they might otherwise mask, may be identified

Development of Bioepoxy Resin Microencapsulated Ammonium-Polyphosphate for Flame Retardancy of Polylactic Acid

Ammonium-polyphosphate (APP) was modified by microencapsulation with a biobased sorbitol polyglycidyl ether (SPE) type epoxy resin and used as a flame retardant additive in polylactic acid (PLA) matrix. The bioresin encapsulated APP (MCAPP) particles were characterized using Fourier transform infrared (FTIR) spectroscopy and Raman mapping, particle size distribution was determined by processing of scanning electron microscopic (SEM) images. Interaction between the APP core and the bioresin shell was revealed by combined thermogravimetric analysis (TGA) FTIR spectroscopy. The APP to SPE mass ratio of 10 to 2 was found to be optimal in terms of thermal, flammability and mechanical properties of 15wt% additive containing biocomposites. The bioresin shell effectively promotes the charring of the APP loaded PLA composites, as found using TGA and cone calorimetry, and eliminates the flammable dripping of the specimens during UL-94 tests. Thus V-0 rating, increased limiting oxygen index and by 20% reduced peak of heat release rate were reached compared to the effects of neat APP. Furthermore, better interfacial interaction of the MCAPP with PLA was indicated by differential scanning calorimetry and SEM observation; the stiff interphase resulted in increased modulus of these composites. Besides, microencapsulation provided improved water resistance to the flame retardant biopolymer system

Hantavirus Pulmonary Syndrome, French Guiana

A systematic serological survey of patients suffering from symptoms suggestive of Hantavirus pulmonary syndrome allowed us to identify a native case in French Guiana. Partial molecular characterization of the implicated hantavirus revealed its close relationship with the Bolivian Rio Mamore virus. We tentatively named it Maripa virus