Current understanding of cellulose ethers impact on the hydration of C3A and C3A-sulphate systems

International audienceThe impact of cellulose ethers (CE) on C3A hydration was examined to support the understanding of the retarding effect of CE on cement hydration. In this sense, we successively studied the CE adsorption on ettringite and calcium hydroaluminates, and then the CE influence during C3A hydration in presence or absence of calcium sulphate. We emphasized a phase-specific adsorption of CE depending on CE chemistry. Besides, in addition of CE, we highlighted a gradual slowing down of C3A dissolution as well as ettringite and calcium hydroaluminates precipitation. Again, a great impact of CE chemistry and CE adsorption behaviour were noticed. Thus, HECs induce always a stronger adsorption on calcium hydroaluminates and a longer C3A hydration delay that HPMC

Changes in C3S hydration in presence of cellulose ethers

International audienceThe influence of cellulose ethers (CE) on C3S hydration processes was examined in order to improve our knowledge of the retarding effect of cellulose ethers on the cement hydration kinetics. In this frame, the impacts of various cellulose ethers on C3S dissolution, C-S-H nucleation-growth process and portlandite precipitation were investigated. A weak influence of cellulose ethers on the dissolution kinetics of pure C3S phase was observed. In contrast, a significant decrease of the initial amount of C-S-H nuclei and a strong modification of the growth rate of C-S-H were noticed. A slowing down of the portlandite precipitation was also demonstrated in the case of both cement and C3S hydration. CE adsorption behavior clearly highlighted a chemical structure dependence as well as a cement phase dependence. Finally, we supported the conclusion that CE adsorption is doubtless responsible for the various retarding effect observed as a function of CE types

Some aspects of cellulose ethers influence on water transport and porous structure of cement-based materials

International audienceThis paper evaluates and compares the impact of cellulose ethers (CE) on water transport and porous structure of cement-based materials in both fresh and hardened state. Investigations of the porous network (mercury intrusion porosimetry, apparent density, 2D and 3D observations) emphasize an air-entrained stabilisation depending on CE chemistry. We also highlight that CE chemistry leads to a gradual effect on characteristics of the water transport. The global tendencies brought by CE are: higher water retention, lower capillarity water absorption, lower liquid water permeability as well as higher water vapour permeability. All things considered, we demonstrate that CE chemistry is an important controlling factor on water transport and porous structure evolution

Impact des éthers de cellulose sur l'hydratation du silicate tricalcique

National audienceLes mécanismes d'hydratation du ciment en présence de molécules organiques restent assez mal élucidés. Les éthers de cellulose sont systématiquement introduits dans les formulations des mortiers industriels. Leurs conséquences macroscopiques sur la réaction d'hydratation du ciment sont parfaitement connues, notamment en terme de ralentissement de la cinétique d'hydratation, mais elles n'en restent pas moins inexpliquées. Par conséquent, l'interaction des éthers de cellulose avec la matrice cimentaire a été examinée. Les résultats tendent à montrer que les éthers de cellulose ont un impact mineur sur la dissolution des différentes phases anhydres. Au contraire, ces adjuvants présentent un effet important sur la germination-croissance de certains hydrates comme l'hydrosilicate de calcium et la portlandite

Study of the toxicity of inhaled ultrafine engineered powder: example of boehmite nanoparticles

International audienceBoehmite nanoparticles (NP) can be used as a vector for vaccines, replacing conventional adjuvants but also in industry as abrasives, catalysts, substrates for electronic circuits, refractory materials. Thus, the boehmite NP constitutes a good model of study taking into account its various applications: in the industry as well as in the nanomedecine field. This important use of boehmite NP makes particular interest of the evaluation of its potential toxicity. Some toxicological works have been yet performed, the health risk induced by boehmite NP is still not completely characterized. Nevertheless, some authors have shown from In vitro experiments that the boehmite can cause an inflammation characterized by production of IL-8 and a certain cytotoxicity associated with a LDH release. As a result, the boehmite NP must be considered as potential risk factors for health

Water transport in freshly-mixed mortars containing cellulose ethers

Groupe de travail n°2 : Interactions éther de cellulose-ciment du CEReM (Consortium d'Etudes et de Recherches sur les Mortiers)Polysaccharides are polymers frequently introduced into mortar formulations in order to improve the workability and water retention capacity of the fresh materials [1]. Among all the polysaccharides, cellulose ethers seem to be the most suitable molecules to obtain a mortar with pretty good water retention ability (i.e. higher than 94%). On the other hand, polysaccharides such as starch ethers or starches generally induce a low increase in water retention (i.e. up to 85%). Mortar consistency may contribute to its water retention capacity but this hypothesis should be checked by further investigations. Indeed, cellulose ethers could induce excellent water retention thanks to the possible superposition of two phenomena [2]: - a rheological effect similar to the one caused by other polysaccharides; - an effect that could be specific to cellulose ethers, which remains to be defined. It could be caused by a modification of the porous network in the fresh state, osmotic pressure or the presence of a cellulose ether film playing the role of diffusion barrier. The molar mass distribution of polysaccharides has been determined by size exclusion chromatography. Using such well-known molecules, it should be possible to understand the functioning of three types of cellulose ethers (HEC, HPMC and HEMC) on mortar water retention. Then, the influence of mortar consistency on water retention has been studied in order to verify if there is a relationship between these two parameters. To complete the panel, the impact of starch ethers on water retention and mortar consistency has also been investigated

Study on the toxicity of inhaled alumina nanoparticles: impact of physicochemical properties and adsorption artifacts on the measurement of biological responses

International audienceThis work aims at developping a multidisciplinary approach to highlight the correlation between the toxicity of alumina engineered nanoparticles (NP) and their physicochemical characteristics. Accuracy of measurements depends on cell production after contact with particles, but also depends on the ability of biomolecules to get adsorbed on the NP [1]. That's why, mechanisms of biomolecules adsorption on NP must be fully understood to avoid misinterpretation of data

A new Strategy to Improve Drug Delivery to the Maxillary Sinuses: The Frequency Sweep Acoustic Airflow

International audiencePurpose Enhancement of intra-nasal sinus drug deposition involves nebulization of a drug superimposed by the acoustic airflow characterized by a specific frequency. We investigated the impact of fixed frequency versus frequency sweep acoustic airflow on the improvement of aerosolized drug penetration into the maxillary sinuses.Methods Fixed frequency and frequency sweep acoustic airflow were generated using a prototype of variable frequency nebulizing system, and their effect on the intra-nasal sinus aerosol deposition in a ‘nasal replica’, a transparent, water-resistant, non-porous resin replica of the human plastinated cast created using a stereolithography technique, was tested. Sodium fluoride and gentamicin were chosen as markers. In addition to this, the effect of sweep cycle and intensity variation was also studied. Results Studies performed using fixed frequency acoustic airflow showed that each of the maxillary sinuses of the ‘nasal replica’ required specific frequency for the optimal intra-nasal sinus aerosol deposition; depending on the ostia of the left and right maxillary sinuses which are different. Intra-nasal sinus drug deposition experiments under the effect of the frequency sweep acoustic airflow showed an optimal aerosol deposition into both maxillary sinus of the ‘nasal replica’. Studies on the effect of the duration of the sweep cycle showed that the shorter the cycle the better the deposition.Conclusion Our study demonstrates the benefit of frequency sweep acoustic airflow on the drug deposition into maxillary sinuses of the ‘nasal replica’ characterized by ostia of different geometry. However, the delivery rates of the ‘nasal replica’ cannot be directly applied to real human chronic rhinosinusitis condition; further in vivo studies have to be conducted

Impact of cellulose ethers on the cement paste microstructure

ISBN = 3-87264-022-4 7 pagesInternational audienceComplementary investigation tools (2D and 3D observations by optical microscopy and fast X-ray microtomography and then image analysis) were developed in order to examine the effects of cellulose ethers on the cement paste microstructure. The obtained results show that the presence of cellulose ether may induce an increase of both 50-250 µm-diameter air voids. The chemistry of the cellulose ethers appears as a main controlling factor of this porous media modification. In particular, cellulose ethers seems to play an important role on the air bubbles morphological characteristics, the content of air volume and the stabilisation of the porosity from the fresh cement paste to the hardened cement paste

New insight into artifactual phenomena during <i>in vitro</i> toxicity assessment of engineered nanoparticles: Study of TNF-α adsorption on alumina oxide nanoparticle

International audienceBiomolecules can be adsorbed on nanoparticles (NPs) and degraded during in vitro toxicity assays. These artifactual phenomena could lead to misinterpretation of biological activity, such as false-negative results. To avoid possible underestimation of cytokine release after contact between NP and cells, we propose a methodology to account for these artifactual phenomena and lead to accurate measurements. We focused on the pro-inflammatory cytokine tumor necrosis factor TNF-α. We studied well-characterized boehmite engineered NP [aluminum oxide hydroxide, AlO(OH)]. The rate of TNF-α degradation and its adsorption (on boehmite and on the walls of wells) were determined in cell-free conditions by adding a known TNF-α concentration (1500 pg/ml) under various experimental conditions. After a 24-h incubation, we quantified that 7 wt.% of the initial TNF-α was degraded over time, 6 wt.% adsorbed on the walls of 96-well plates, and 13 wt.% adsorbed on the boehmite surface. Finally, boehmite NP were incubated with murine macrophages (RAW 264.7 cell line). The release of TNF-α was assessed for boehmite NP and the experimental data were corrected considering the artifactual phenomena, which accounted for about 20-30% of the tota