The crystallization of gypsum (CaSO4·2H2O) from a suspension of calcium sulphate hemihydrate is well-known as the setting of plaster. In this paper we present results concerning the crystallization of gypsum in the presence of different acids. The influence of additives on the crystallization kinetics and on the morphology of gypsum crystal have been studied. The rate retarding effect was determined by recording, versus time, the conductivity of suspension of hemihydrate. The amount of additives adsorbed was measured by capillary electrophoresis. The results are well-related to the amount of adsorbed and incorporated additives during the crystallization. The influence of different additives on the morphology of a crystal of gypsum was also investigated and discussed. Their efficiency is related to the presence of calcium on the faces (120) and (111) and to the correspondence between distances between the carboxylic groups of the additives and between the adsorption sites at the surface of the crystal.
A treatment process for producing implants or prostheses of polymers for controlled release of active ingredients, characterized by a first "pretreatment" step comprising: - a phase of pressurization and heating according to controlled kinetics, - a phase of bringing the polymeric materials into contact with a supercritical fluid in batchwise mode or in continuous mode, and - a phase of depressurization with controlled kinetics, under isothermal conditions.
The present study deals with the determination of optimal values of operating parameters such as temperature and pressure leading to the best yield of a supercritical CO2 extraction of essential oil from local rosemary plants, using the response surface methodology (RSM). The maximum of essential oil recovery percentage relative to the initial mass of leaf powder was 3.52 wt%, and was obtained at 313 K and 22 MPa. A second-order polynomial was used to express the oil recovery and the calculated mass of recovered oil using the RSM was very close to the experimental value, confirming the reliability of this technique. The chemical composition of the Algerian rosemary oil under the obtained optimal conditions (313 K and 22 MPa), determined by GC-MS analysis, revealed the presence of camphor (major compound) (52.12%), 1,8-cineole (9.65%), camphene (7.55%), alpha-pinene (6.05%), borneol (3.52%), aroma dendrene (2.11%), verbenone (1.97%), alpha-caryophyllene (1.71%), and others. (C) 2016 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Many recrystallization processes in supercritical medium utilize CO(2) as antisolvent. This work presents two introduction devices based on the principle of the supercritical antisolvent process: the impinging jets and the concentric tube antisolvent reactor. Those two processes are very simple to develop and allow improving the mixing between the two phases. Some experiments have been conducted for the impinging jets using L-polylactic acid at 10 MPa and 308 K giving spherical particles with average diameter varying from 1.4 to 2.3 mu m. For the concentric tube antisolvent reactor, griseofulvin was tested at 10 MPa and temperatures between 308 and 323 K providing needles with lengths between 25 and 50 mu m. These results combined with previous ones allow comparing these introduction devices with the classical supercritical antisolvent (SAS) process, demonstrating the following improvements: (i) reduction of particle size, (ii) increase in initial solute concentration, and (iii) process intensification.
Silva, Joana M
Araujo, Ana C
Reis, Rui L
Duarte, Ana Rita C
In order to limit bacterial infections during wound treatment, it is interesting to consider the concept of loading medical devices with antibacterial agents. With this in mind, an innovative system with thermosensitive properties was produced: loading a commercially available gauze with a fatty acid eutectic blend based on lauric acid (LA) and myristic acid (MA). This eutectic blend presents a melting point near physiological temperature, which together with its antibacterial properties make an appealing alternative in biomedical applications. At room temperature, the properties and the efficacy of the eutectic blend loaded onto gauzes are preserved, whereas at physiological temperature the eutectic blend undergoes a phase change that facilitates its diffusion from the gauze. The loading of the eutectic blend onto gauzes was performed using two different supercritical fluid technologies, namely, particle from gas saturated solutions (PGSS) and a derived version of rapid expansion of supercritical solution (D-RESS). The PGSS led to a heterogeneous dispersion of the eutectic blend in the gauze, whereas the D-RESS process led to the formation of a homogeneous dispersion along the surface of the gauze. Additionally, with D-RESS no phase separation of the eutectic blend occurred and the cytotoxicity was greatly improved compared with PGSS without compromising the antibacterial properties of the fatty acid eutectic blend. Hence, the present study highlights the potential use of the flexible D-RESS process to load the fatty acid eutectic blend with antibacterial properties onto medical devices in a controllable way. Overall, the effects produced by the loaded gauzes suggest the enormous potential of the developed technology in health-related areas. Copyright =C2=A9 2019 Elsevier B.V. All rights reserved.
To evaluate the potential recovery rate of volatile terpenes from pulp mills, different extraction methods were performed on fir, spruce and maritime pine, and the extracts were analyzed by gas chromatography-flame ionization detector/mass spectroscopy (GC-FID/MS). The results obtained by traditional solvent extraction in the Soxhlet and the accelerated solvent extraction (ASE)(R) apparatus were compared with those of steam distillation technology (Clevenger), and supercritical CO2 (SC-CO2) extraction was also tested as an interesting alternative to extraction with liquid organic solvents. ASE (R)-Dionex applied on freeze-dried samples with successive extraction with n-hexane and acetone/water (95/5) was not suitable for volatile compounds. Steam distillation applied on fresh and ground samples was very specific of volatiles, but did not allow complete extraction. Soxhlet extraction performed on fresh and ground samples with successive application of acetone and acetone/cyclohexane (1/9) gave the most representative quantification of ground wood chips, together for volatile terpenes, resins and fatty-acidtype compounds. SC-CO2 [20 and 30 MPa, 60 degrees C modified by 5% ethanol (EtOH)] is able to extract most of the terpenes, terpenoids and fatty-acid-type compounds, but the extraction rates of volatiles were very limited because of a pre-drying step (freeze-drying and crushing). Other lipophilic extractives were also recovered to a lesser extent.