International audienceIt is well known that supercritical carbon dioxide (sc-CO 2) is soluble in molten polymers and acts as a plasticizer. The dissolution of sc-CO 2 leads to a decrease in the viscosity of the liquid polymer, the melting point and the glass transition temperature. These properties have been used in several particle generation processes such as PGSS (particles from gas saturated solutions). It is therefore highly likely that extrusion processes would benefit from the use of sc-CO 2 since the rationale of the extrusion processes is to formulate, texture and shape molten polymers by forcing them through a die. Combining these two technologies, extrusion and supercritical fluids, could open up new applications in extrusion. The main advantage of introducing sc-CO 2 in the barrel of an extruder is its function as a plasticizer, which allows the processing of molecules which would otherwise be too fragile to withstand the mechanical stresses and the operating temperatures of a standard extrusion process. In addition, the dissolved CO 2 acts as a foaming agent during expansion through the die. It is therefore possible to control pore generation and growth by controlling the operating conditions. This review focuses on experimental work carried out using continuous extrusion. A continuous process is more economically favourable than batch foaming processes because it is easier to control, has a higher throughput and is very versatile in the properties and shapes of the products obtained. The coupling of extrusion and supercritical CO 2 technologies has already broadened the range of application of extrusion processes. The first applications were developed for the agro-food industry twenty years ago. However, most thermoplastics could potentially be submitted to sc-CO 2-assisted extrusion, opening new challenging opportunities, particularly in the field of pharmaceutical applications. This coupled technology is however still very new and further developments of both experimental and modelling studies will be necessary to gain better theoretical understanding and technical expertise prior to industrial use, especially in the pharmaceutical field

In the pharmaceutical industry, an even greater number of products are in the form of particulate solids. Their formation, formulation and the control of their user properties are still not well understood and mastered. Since the mid-1980s, a new method of powder generation has appeared involving crystallisation with supercritical fluids. Carbon dioxide is the most widely used solvent and its innocuity and ''green'' characteristics make it the best candidate for the pharmaceutical industry. Rapid Expansion of Supercritical Solutions (RESS), Supercritical Anti Solvent (SAS) and Particles from Gas Saturated Solutions (PGSS) are three families of processes which lead to the production of fine and monodisperse powders, including the possibility of controlling crystal polymorphism. For the RESS process, the sudden decompression of the fluid in which a solute has been dissolved is the driving force of nucleation. CO 2 is, however, a rather feeble solvent and this is obviously the main limitation of the development of RESS. In the SAS process, CO 2 acts as a non-solvent for inducing the crystallisation of a solute from an organic solution. The versatility of SAS (there is always a proper solvent-antisolvent couple for the studied solute) ensures future developments for very different types of materials. PGSS uses the fact that it is much easier to dissolve CO 2 in organic solutions (or melted compounds) than the contrary. It presents very promising perspectives of industrial development. After almost 20 years of active research, and more than 10 years of process development, this technology is reaching maturity, and very soon commercial drug produced by these techniques are likely to appear.

International audienceThe upcoming depletion of fossil fuels calls for the development of alternative energies produced from renewable resources. Particularly, energy valorisation of agriculture and food processing wastes is one of the most promising tools for renewable energy production. The amount of food wastes is rapidly increasing due to urbanisation, industrialisation and population growth worldwide. They consequently represent a widely available resource, and their use as a raw material allows reducing the environmental cost associated with their disposal. These resources usually have high moisture content, making dry valorisation processes unattractive because of a costly drying step prior to conversion. Hydrothermal processes are conversely particularly well suited for the valorisation of wet organic wastes in an economical way, since they use water as the reaction medium. More specifically, liquid fuels can be produced using hydrothermal liquefaction (HTL). The process converts wet biomass into a crude-like oil with higher heating values up to 40 MJ/kg using subcritical water (T=250-370 degrees C, P=10-30 MPa). Though this is an active research area, the mechanisms of hydrothermal liquefaction still remain unclear today. Some processes have already been developed at the pilot scale for valorising food processing wastes. However, the development of HTL processes at industrial scales is facing technological and economic challenges. This paper discusses the two main issues to address for development of the process at large scales. On the one hand, hydrothermal conversion of food processing residues and model compounds is necessary to better understand the fundamentals of hydrothermal liquefaction. As well, technological and process integration issues have to be addressed to ensure economic viability of commercial HTL processes

Calcium phosphate cements can be handled in paste form and set in a wet medium after precipitation of calcium phosphate crystals in the implantation site. Depending on the products entering into the chemical reaction leading to the precipitation of calcium phosphates, different phases can be obtained with different mechanical properties, setting times and injectability. We tested a cement composed of a powder, containing beta-tricalcium phosphate (beta-TCP) and sodium pyrophosphate mixed with a solution of phosphoric and sulphuric acids. The cement set under a dicalcium phosphate dihydrate (DCPD)-based matrix containing beta-TCP particles. This was injected with a syringe into a defect drilled in rabbit condyles, the control being an identical defect left empty in the opposite condyle. The condyles were analysed histologically 2, 6 and 18 weeks after implantation. After injection into the bone defect the cement set and formed a porous calcium phosphate structure. Two different calcium phosphate phases with different solubility rates could be identified by scanning electron microscopy (SEM) observation. The less-soluble fragments could be degraded by cell phagocytosis in cell compartments of low pH or integrated in the newly formed bone matrix. The degradation rate of the material was relatively high but compatible with the ingrowth of bone trabeculae within the resorbing material. The ossification process was different from the creeping substitution occurring at the ceramic contact. Bone did not form directly at the cement surface following the differentiation of osteoblasts at the material surface. The trabeculae came to the material surface from the edges of the implantation site. Bone formation in the implantation site was significantly higher than in the control region during the first week of implantation. In conclusion, this material set in situ was well tolerated, inducing a mild foreign-body reaction, which did not impair its replacement by newly formed bone within a few weeks.

7th Intenatioanal Symposium on Agglomeration, ALBI, FRANCE, MAY 29-31, 2001International audienceThe hydration of semolina particles is an essential step in couscous processing which leads to binding between particles for the formation of agglomerates. Despite this importance, the hydration properties of such food products are rarely studied and in particular, durum wheat semolina has never been investigated. Here we present,a study of the hydration properties of durum wheat semolina by determination of water sorption isotherms, and other characterisation techniques to obtain a better understanding of hydration mechanisms. Equilibrium and dynamic sorption properties, have been measured as a function of relative humidity by means of a controlled atmosphere microbalance. It is found that durum wheat semolina presents a type II isotherm [F. Rouquerol, J. Rouquerol, K. Sing, Adsorption by Powders and Porous Solids-Principles Methodology and Applications, Academic Press, 1999] indicative of multi-layer adsorption. The Guggenheim-Anderson-de Boer (GAB) model is used to describe the isotherm and obtain a better understanding of hydration mechanisms and liquid/solid interactions. The effects observed are related to physical properties of the semolina. In particular, the size of the semolina particles is found mainly to influence sorption kinetics: the finer the particles, the faster their sorption kinetics. Increasing temperature in the range 25-45 degreesC accelerates sorption kinetics. Furthermore, hydration causes no irreversible transformation of semolina components. Thus, absorption kinetics seem to be influenced by physical mechanisms, while the biochemical composition determines the amount of water sorbed. (C) 2003 Elsevier Science B.V. All rights reserved

Extrusion assisted by supercritical CO 2 (sc-CO 2) is an emerging method for the microcellular foaming of polymer. Instead of batch foaming, which requires formation of single-phase polymer/CO 2 solution in long cycle times, the extrusion assisted by supercritical fluids overcomes this issue by providing rapid mixing and dissolution of CO 2 in the polymer melt. Because the sc-CO 2 is soluble in many molten polymers and acts as a removable plasticizer, its introduction in an extruder will permit a decrease of the processing temperature. This technic allows the use of fragile component like active molecule or starchy and proteinaceous materials. At the end of the extruder, the pressure drop will create instability and phase separation with the creation of porosity. This review is dedicated to the extrusion assisted by sc-CO 2 with different types of biopolymer. Industrial application domains include agro-food, biomedical, pharmaceutical, packaging and many others.

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