Search results for "swelling"
showing 10 items of 192 documents
An Appraisal by M.I.P of the Changes Induced in the Microstructure of Complex Sulfide Ores by Reactive Thermal Treatments in H2 and N2
1991
Summary Changes in the microstructure of complex sulfide ores resulting from reactive thermal treatments in either H2 or N2 were investigated qualitatively by combined scanning electron microscopy and X ray microanalysis, and quantitatively by mercury intrusion porosimetry (MIP) and mercury pycnometry. With increasing treatment temperature, we successively observed: 1) the development of fractures, preferentially at interfaces between the various mineral components, 2) the development of meso and macropores and the simultaneous swelling of the solids and 3) the crystallization or recrystallization of the metal or sufide phase products. In all cases the specific pore volume and mean pore dia…
Cellulose/Water: Liquid/Gas and Liquid/Liquid Phase Equilibria and Their Consistent Modeling
2007
Liquid/liquid and liquid/gas equilibria were measured for the water/cellulose system at 80 °C using three different polymer samples. For these experiments we prepared cellulose films of approximately 20−25 μm in thickness and determined their equilibrium swelling in water. Thereafter the polymer concentration in the mixed phase was increased by means of a stepwise removal of the volatile component, and the equilibrium vapor pressures were measured using an automated combination of head space sampling and gas chromatography. Contrary to the usual behavior of polymers, the swelling of cellulose increases as its molar mass becomes larger. The Flory−Huggins interaction parameters calculated fro…
Synthesis, characterisation and properties of α,β-poly(N-2-hydroxyethyl)-dl-aspartamide-graft-maleic anhydride precursors and their stimuli-responsiv…
2009
Abstract A family of poly(amino acid)-maleic anhydride hydrogels were designed and synthesized. Water soluble polymeric precursors were prepared by partially substituting the hydroxyl groups of the α,β-poly( N -2-hydroxyethyl)- dl -aspartamide backbone with maleic anhydride, so as to provide double bonds for crosslinking and carboxylic acid groups for pH and electric field responsiveness. Reaction conditions (reactive mixture composition and catalysis) were systematically varied in order to obtain PHEA–MA precursors with different and reliable graft-maleic anhydride levels. PHEA–MA precursors were characterised by titration, Nuclear Magnetic Resonance ( 1 H NMR), Fourier-Transformed Infrare…
Synthesis and characterization of water-swellable?,?-polyasparthydrazide derivatives
1995
α, β-polyasparthydrazide (PAHy) was crosslinked by glutaraldehyde to form water-swellable materials possessing a three-dimensional molecular network. Different crosslinking degrees were prepared varying glutaraldehyde/PAHy ratio and samples containing 5-fluorouracil were obtained by incorporating the drug into the polymer networks during the crosslinking reaction. All samples were characterized by swelling tests, thermal, x-ray and SEM analysis. Their microstructure was observed through scanning electron microscopy. Furthermore, for samples containing the anticancer drug,in vitro release studies were performed in pH 7.4 buffer solution.
Gamma radiation induced maleation of polypropylene using supercritical CO 2 : preliminary results
2000
Abstract The charging of maleic anhydride (MA) and dicumyl peroxide (DCP) into polypropylene matrices has been carried out by CO2 in supercritical conditions. The grafting of MA into polymer chains was done through gamma irradiation in CO2 atmosphere (0.1 MPa, 25°C). The grafting was successful and the amount of grafted anhydride was dependent on the amount of MA and DCP charged into the polypropylene matrix. The presence of grafted succinic anhydride was shown by FT-IR spectroscopy and its amount was determined through a calibration curve derived from standard samples. The effect of swelling due to supercritical CO2, maleic anhydride grafting and gamma irradiation on the molecular structur…
Environmentally sustainable production of cellulose-based superabsorbent hydrogels
2006
The development of new products and materials, especially those which are non-petrolchemical reserves and based on renewable organic resources, using innovative sustainable processes is nowadays of increasing interest and deserves the attention of both academic and industrial research. Cellulose and its derivatives, as renewable organic resources, have been used to synthesize novel superabsorbent hydrogels. Although the production of cellulose is one of the causes connected to deforestation, the production of suitably engineered cellulose superabsorbent hydrogel materials has been proposed to preserve water in typically arid areas in the world. Paradoxically, divinylsulfone (DVS), a small d…
Gamma radiation of EVA-AA/MMA swollen systems to obtain mechanically improved blends
2002
In this work a "new" way to obtain "compatibilised" blends of rubber-glassy thermoplastic components is presented. Polyethylen-vinyl acetate acrylic acid terpolymer is swollen by methylmetacrylate and the system is irradiated through gamma rays in order to induce polymerisation of the monomer. Solubility and dynamic mechanical tests indicate the formation of a two phase system, even though in presence of strong interactions between the two components. Mechanical tensile behaviour is that of a ductile material with appreciable modulus values.
pH-sensitive hydrogel based on a polyaspartamide derivative
2006
A pH-sensitive hydrogel was prepared by UV irradiation technique. Starting polymer was obtained from alpha,beta-poly (N-2-hydroxyethyl)-DL-aspartamide (PHEA) partially derivatized with glycidyl methacrylate (PHG). The PHG copolymer was cross-linked by UV irradiation in the presence of methacrylic acid (MA) to form a pH sensitive hydrogel. The cross-linked matrix shaped as microparticles was characterized by FT-IR spectrophotometry, XPS, X-ray diffraction, SEM and particle size distribution analyses. Moreover, to have information about water affinity of the prepared sample, swelling measurements were carried out in aqueous media mimicking some biological fluids. In order to employ the prepar…
Glial Swelling and Damage by Arachidonic Acid
1994
Arachidonic acid (AA) is a major constituent of membrane phospholipids in brain tissue. Normally, the free fatty acid is present only in small amounts, but it accumulates under adverse conditions such as ischemia (Kinouchi et al. 1990). The release of free fatty acids involves activation of phospholipases and breakdown of membrane phospholipids. A A in particular is considered to mediate pathological processes. It is a polyunsaturated compound and precursor of prostaglandins, leukotrienes, and oxygen-derived free radicals (Wolfe 1982). In cerebral ischemia concentrations of free AA of up to 0.5mM/kg were found (Kinouchi et al. 1990). But also brain injury and seizures cause increased levels…
Mechanisms of Glial Swelling by Arachidonic Acid
1994
The effect of arachidonic acid (AA, 20:4) was analyzed in vitro by employment of C6 glioma cells and astrocytes from primary culture. The cells were suspended in an incubation chamber under continuous control of pH, pO2, and temperature. Cell swelling was quantified by flow cytometry. After a control period, the suspension was added with AA at concentrations of 0.01 to 1.0 mM. Administration of AA induced an immediate, dose dependent swelling in C6 glioma cells or astrocytes. AA-concentrations of 0.01 mM led to an increase of the glial cell volume to 103.0 ± 1.0% of control, 0.1 mM to 110.0 ± 1.5%, and l.0 mM to 118.8 ± 1.5% within 10 min. The swelling response to linoleic acid (18 : 2) was…