Les cires végétales : sources et applications

Waxes are mixture of long-chain apolar lipids of mineral, synthetic or natural (produced by living organisms) origin. In the plant kingdom, waxes that cover the different parts of the plant play the role of a physical and/or chemical barrier towards the outside thus allowing to control mass transfers and pest attacks. They can have also a storage function as in the Jojoba seeds. Because of their highly variable composition and physical properties, plant waxes (raw, refined or specific fractions) have found numerous applications in the food, cosmetic, candle, coating, polish, polymer and pharmaceutical industries. However, only few of them are currently available at large scale (Candellila, Carnauba, Jojoba) and they represent no more than a few percents of the global waxes market largely dominated by synthetic and petroleum-based products (97 %). In the future, the increase needs for renewable and vegetable-based materials will help to drive the market growth for vegetable waxes and especially those based on vegetable oils (saturated fatty alcohols from fully hydrogenated soybean and castor oils) which have gained importance during the last decade. (Résumé d'auteur

Study of complex carbides obtained after solidification and thermal treatment in High Speed Steels

High-speed steels (HSS) rolls are used in front finishing stands of hot strip mills. Good wear resistance and hardness at high temperature are defining characteristics of HSS. Many carbides are present in these alloys, each having different effects upon the final properties of HSS. As a result, the nature, the morphology and the amount of these carbides are factors of important concern. Optical microscopy combined with electron microscopy lead to quicker identification and characterization of HSS carbides

Are emerging deep eutectic solvents (DES) relevant for lipase-catalyzed lipophilizations?

With the recent interest on green chemistry, the scientists have focused on developing new and more efficiient solvents to carry out enzymatic-catalyzed reactions with emphasis on reduced costs, risks and toxicity while improving biodegradability. Among the new available solvents, the multimolecular-based liquids (such as ionic liquids and eutectic solvents) have been the subject of most recent studies. Currently, and mainly due to its environmental and economic features, DES are arousing much interest and curiosity. Regarding the biotransformations with lipases, the so-called “lipophilization” reactions are of major interest. However, they are complex to implement mainly because it is difficult to find a suitable reaction medium. Thus, this review aimed at providing a presentation of these multimolecular- based solvents with general overview of the recent studies dealing with lipase-catalyzed reactions in DES. In addition, emphasis was placed on their strengths and weaknesses, especially with the perspective to be use as efficient and green medium to implement complex and valuable biotransformation such as lipase-catalyzed lipophilizations. (Résumé d'auteur

Macromolecular engineering of aliphatic polyesters based on macrocyclic units

The last decades have witnessed a steadily increasing progress in the macromolecular engineering of the main families of synthetic polymers. Ring-shaped copolymers show a unique topology due to the absence of any chain-end and exhibit distinct properties from their linear counterparts, such as glass transition temperature, order-disorder transition, reduced viscosity, lower hydrodynamic volumes. This communication aims at reporting on a novel route to biodegradable cyclic polyesters. Our strategy is based on the work of Prof. Kricheldorf who initiated the ring-opening polymerization of ε-caprolactone by cyclic tin dialkoxides, e.g., 2,2-dibutyl-2-stanna-1,3-dioxepane (DSDOP) in order to obtain “living” macrocyclic PCL, still containing two endocyclic tin-oxygen bonds. In this work, the resumption of polymerization by a few units of ε-caprolactone substituted by an acrylic unit, e.g., 1-(2-oxooxepan-3-yl)ethyl prop-2-enoate, followed by intramolecular photo-cross-linking of pendant unsaturations and finally by hydrolysis gave rise to macrocyclic PCL. As a rule, this strategy is very well-suited for the synthesis of high molecular weight PCL. Moreover, tin alkoxides were kept untouched after the cross-linking step and remained thus available for further macromolecular engineering. The process was extended to the synthesis of other architectures such as sun-shaped, two-tail tadpole-shaped, eight-shaped and symmetrical four-tail eight-shaped copolyesters

Measurements of atmospheric and oceanic CO2 in the tropical Atlantic : 10 years after the 1982-1984 FOCAL cruises

Measurements of CO2 parameters in and over the tropical Atlantic ocean have been made during the CITHER 1 cruise (January to March 1993). These observations are compared to the results obtained a decade earlier in the same area during the FOCAL experiment (1982-1984). The increase of atmospheric CO2 (1.3 to 1.5 ppm yr-1) is in agreement with the secular trend. The variation of CO2 fugacity, fCO2, in surface seawater is analysed and compared with variations of hydrographic conditions. The apparent increase of ocean surface fCO2 is somewhat higher than the atmospheric increase: during the 9-year period, the apparent increase of oceanic fCO2 is found to range from 22.5 to 24.9 µatm. A new estimate of air-sea CO2 flux in the Atlantic equatorial belt indicates that the oceanic source is enhanced in 1993 compared to 1984. An interannual change in total inorganic carbon, TCO2, through the accumulation of CO2 in the mixed layer is assessed and analysed in comparison with the fCO2 increase. The agreement between the evolutions of the two parameters of the oceanic CO2 system is acceptable by taking into account the uncertainties to estimate these evolutions. (Résumé d'auteur

Improvement in HSS grade for early stands of hot strip mills - Metallurgical features and mechanical properties assessment

peer reviewedAurora and Kosmos grades are HSS alloys belonging to the complex Fe-Cr-C-X system, where X is a strong carbide former element of the V, Mo or W type. Both alloys were metallurgically characterised prior to their comparison. Metallurgical analyses involved phases identification and carbides quantification by using Scanning Electron Microscopy and Energy Dispersive X rays. Differential Thermal Analysis was performed to allow a better understanding of the solidification sequence of studied alloys while mechanical tests performed were compressive at room temperature and bulk hardness at usual service temperatures. An attempt was made in order to connect experimental results to the good behaviour in operation of Aurora grade. In fact Aurora grade appeared to exhibit strong metallurgical differences when compared to Kosmos grade, especially as concern in nature and amount of carbides