Chitine et chitosane

International audienc

Cement cake properties in static filtration. On the role of fluid loss control additives on the cake porosity

cited By 24International audienceThe mechanism of the action of fluid loss control additives in cementing oilwell operations is principally the reduction of permeability of the cement filter cake. From filtration equations physical characteristics as porosity of the cement filter cake were investigated and compared with experimental data. A good correlation is observed when no adsorption is involved. The smallest pore diameter for obtaining an efficient control of fluid loss is shown to be of the same order of magnitude as the gyration radius of used macromolecular chains. © 1993

Autoassociative natural polymer derivatives: the alkylchitosans. Rheological behaviour and temperature stability

International audienc

Cement cake properties in static filtration. Influence of polymeric additives on cement filter cake permeability

cited By 36International audienceDuring cementing operations on oil wells, fluid loss control additives are generally used to prevent water loss and to maintain a constant water-to-solid ratio in cement slurries. But their mechanism of action is not yet completely understood. An experimental procedure is described to discriminate between the two predominant phenomena which are the increase of interstitial water viscosity and the decrease of cement cake permeability. The influence of polymeric additives is studied and more particularly the efficiency of fluid loss control additives is related with a threshold concentration corresponding to the overlapping concentration of macromolecular chains in solution. © 1993

Chitin and chitosan [Chitine et chitosane]

cited By 1International audienceChitin is the second natural polymer available at the earth surface. The chemical structure is composed of N-acetylglucosamine units and the physical structure shows three different forms due to the arrangement of the macromolecular chains. The major problem encountered in the chitin chemistry is its preparation and its extraction to obtain a chitin with characteristics similar to the original polymer (molar mass and acetylation degree). The different treatments used for its extraction are discussed. Chitin is poorly valorised due to difficulties to be processed related to a bad solubilisation. Many derivatives are prepared, particularly chitosan obtained from the deacetylation of chitin. This derivative has the particularity to have amino groups and hence to be a cationic polyelectrolyte, in acidic medium, due to protonation of these groups. The degree of acetylation, the molar mass but also the repartition of N-acetylated units along the macromolecular chain are characteristics of the macromolecular chain. These characteristics allow this polymer to have original properties compared with other polysaccharides which are generally anionic. These properties and applications are discussed, demonstrating the large range of domains in which this polymer may be used

Conformation and Rheology of Microbial Exopolysaccharides

cited By 0International audienceno abstrac

Interfacial properties of chitin and chitosan based systems

cited By 20International audienceChitin and chitosan can be modified to obtain amphiphilic systems with controlled structures and architectures. The hydrophile-lipophile balance (HLB, also called hydrophilic-hydrophobic balance) may be modified with respect to different parameters (pH, degrees of substitution of ionic and alkyl groups), and therefore their properties (especially rheological and interfacial) can be adapted to a specific application. The surface activity of ionic derivatives can be improved either by the addition of an oppositely-charged surfactant, which plays the role of counterion by electrostatic interaction (forming a surfactant-polyelectrolyte complex, SPEC), or by N-alkylation. SPECs are found to be more efficient than alkyl derivatives, and the necessary surfactant concentration to reach tensioactive properties is much lower than its critical micellar concentration in the pure solution. The diversity and the control over such structures and architectures make possible their use in numerous domains, strengthening the current interest in these materials. © 2010 The Royal Society of Chemistry

Aqueous gel permeation chromatography of polyelectrolytes and salt exclusion effect

cited By 24International audienceThe dependence of the elution volume of NaCl samples is discussed as a function of the volume and concentration injected and of the ionic strength of the eluent. The same is done with two fractions of polystyrene sulphonic acid in the sodium form. It is concluded that the exclusion depends directly on the screening parameter proportional to μ- 1 2 for NaCl and that a steric parameter has to be added with polyelectrolytes, depending on the molecular weight and on the ionic strength of the eluent. The behaviour is directly correlated to the pore size distribution in the gel. © 1980