Search results for "fluid"
showing 10 items of 5513 documents
Phase Behavior of the System Linear Polyglycerol + Methanol + Carbon Dioxide
2011
To compare the phase behavior of linear and hyperbranched polymers, the phase envelopes of the ternary system linear polyglycerol + methanol + carbon dioxide were determined for polymers of varying molar mass. Phase changes were detected by a static synthetic method using the Cailletet setup for temperatures between 331 K and 421 K and pressures up to 13.1 MPa. Besides the vapor–liquid and liquid–liquid equilibria, also the vapor–liquid to vapor–liquid–liquid and vapor–liquid–liquid to liquid–liquid phase boundaries are reported. The experimental results are similar to systems with hyperbranched polymers (rather than linear polymers). For the systems with linear polymers, however, the bubbl…
Carboxylation of a linear low density polyethylene via gamma irradiation in presence of carbon dioxide in subcritical and supercritical conditions
1994
Abstract In this work the molecular modifications induced in a linear low density polyethylene gamma irradiated in presence of carbon dioxide both in subcritical and supercritical conditions are presented. The obtained results indicate that this process can be a new and interesting way in order to graft oxidized groups in the polyethylene chains. Moreover it is worth noting that, together with these functionalization reactions, also a significant crosslinking occurs, with improvement in some mechanical tensile behaviour.
Scattering function and the dynamics of phase separation in polymer mixtures under shear flow
1988
The phenomenological mean-field theory describing concentration fluctuations and spinodal decomposition of binary mixtures of long flexible macromolecules is generalized to mixtures under steady shear flow. This shear flow leads to a partial orientation and stretching of the coils, as well as to an anisotropic deformation of concentration fluctuations. Generalizing the approach of Onuki and Kawasaki, we obtain the collective scattering function describing these concentration fluctuations in the mixture under shear flow. Both the steady-state situation in the one-phase region and the initial stages of spinodal decomposition for concentrations inside of the spinodal curve are considered.
Investigation of Multicomponent Sorption in Polymers from Fluid Mixtures at Supercritical Conditions: The Case of the Carbon Dioxide/Vinylidenefluor…
2008
The simultaneous sorption of carbon dioxide and vinylidene fluoride (VDF) in poly(vinylidenefluoride) from their supercritical (sc) mixtures was studied using an experimental method, already described in a previous publication, based on the gas-chromatographic determination of the equilibrium composition of the fluid phase in contact with the polymer. Argon was added to the system as a nonabsorbable molecular probe in the polymer to take into account the effect of the volume swelling on the measurement. Sorption behavior has been studied at 50 °C by changing the composition and the density of the supercritical phase. We have found that VDF dissolves in its polymer with concentrations much l…
Transient birefringence of polymer melts in intermittent shear flow: Model analysis of the non-linear viscoelastic behaviour
1977
A non-linear viscoelastic model has been used to interpret transient flow birefringence in changing shear flow for a polymer melt. It is shown how the new model is consistent with the basic hypothesis of the linear stress-optical law. Stress growth in shear flow and relaxation after different amounts of shearing are compared with the predictions of the non-linear model. A good agreement between experimental data and theoretical predictions is found.
Irradiation of low density and high density polyethylenes in presence of carbon dioxide in subcritical and supercritical conditions
1998
Abstract The grafting of carboxylated and oxygenated functions on low density and high density polyethylenes is carried out by gamma irradiation in the presence of carbon dioxide. Both crosslinking and grafting of oxidised groups occur. The extent of these molecular modifications depends on the physical conditions of the gas phase and on the nature of the polymer matrix.
Oxidation of Sulfides with a Silica-Supported Peracid in Supercritical Carbon Dioxide under Flow Conditions: Tuning Chemoselectivity with Pressure
2010
Supercritical carbon dioxide is a convenient medium for performing the selective oxidation of sulfides 1 to either sulfoxides 2 or sulfones 3 with [2-percarboxyethyl]-functionalized silica (4) under flow conditions. The chemoselectivity of the reaction, which results from the different diffusion rates of sulfide and sulfoxide over the reagent bed, can be controlled by adjusting the pressure and the hydration of the silica surface as both the solvating power of the mobile phase and the surface activity of the stationary phase determine the migration rates of sulfide 1 and sulfoxide 2 over the supported peroxide. The results elucidate the impact of surface phenomena on the course of chemical …
Comparative effect of supercritical carbon dioxide and high pressure processing on structural changes and activity loss of oxidoreductive enzymes
2019
Abstract Due to the CO2 specific characteristics, it has been used as supercritical (Sc) fluid for several applications, including enzyme inactivation. The influence of Sc-CO2 (10–65 MPa/10–30 min/35–65 °C) on mushroom polyphenol oxidase (PPO) and horseradish peroxidase (POD) was evaluated and the results were compared with those found using high pressure processing (HPP) (200–900 MPa/5–45 °C/1–15 min). The free ion concentration was also studied to compare the enzymatic activity and changes in electrical conductivity. Additionally both enzymes, untreated or treated using either Sc-CO2 or HPP, were used as additives in the CuCl2 crystallization method. The resulting additive-specific CuCl2 …
Viscometric behaviour of polymer blends based on poly (vinylidene fluoride)
1994
The viscosity behaviour of dilute dimethylformamide solutions of poly(vinylidene fluoride)-poly (methyl methacrylate) and poly(vinylidene fluoride)-polystyrene has been studied at 25°C. The polymer concentration ranges are such that neither phase separation nor microgel formation occurs, although we are very close to theta conditions. The intrinsic viscosity and viscosity interaction parameter of the ternary mixtures have been calculated. The estimation of the compatibility of the above polymer pairs has been studied based on: a) specific viscosities; b) viscosity interaction parameters, according to Krigbaum and Wall formalism, and c) viscosity interaction parameters of a system formed by …
Nonisothermal elongational behavior of blends with liquid crystalline polymers
1994
Measurements of melt strength and breaking stretching ratio of several blends of thermoplastic polymers with liquid crystalline polymers are presented. The melt strength behavior depends not only on the viscosity of the blends but also on the temperature dependence of the viscosity. In particular, even if the viscosities of the blends are, at the extrusion temperature, lower than that of the thermoplastic matrices, the melt strength can be larger than that of the pure thermoplastics if its viscosity-temperature curve exceeds that of the matrices far from the solidification temperature. This behavior allows one to spin or film blow these blends despite the low viscosity.