Degree Of Reticulation Research Articles

Synthesis, Characterization, and Catalytic Properties of Cationic Hydrogels Containing Copper(II) and Cobalt(II) Ions

Here, we report the synthesis and characterization of a hydrogel based on ethylene glycol diglycidyl ether (EGDE) and 1,8-diamino-3,6-dioxaoctane (DA). Chemically stable Co(II) and Cu(II) coordination complexes were prepared with this nonsoluble polyelectrolyte, poly(EGDE-DA), and studied by ss-NMR, FT-IR, thermogravimetry, and microscopy. Mesopores were found in all the samples, the thermal stability of the polymer matrix was highly affected by the presence of metal ions, and the (13)C CP-MAS spectrum for the Cu(II)-complex evidenced a significant increase in the reticulation degree by Cu(II) ions. The catalytic activity of these materials on H2O2 activation was studied by electron spin resonance (ESR). The Co(II)-poly(EGDE-DA)/H2O2 heterogeneous system produced O2, an anion superoxide (O2(•)¯), and a hydroxyl radical (OH(•)), which diffused into the solution at the time that a decrease in pH was detected. In the same way, the Cu(II)-poly(EGDE-DA)/H2O2 heterogeneous system produced O2 and OH(•). H2O2 activation by the poly(EGDE-DA) complexes with Co(II) and Cu(II) were applied on the decolorization of solutions of the azo-dye methyl orange (MO). In the presence of 63 mM H2O2, 87% of MO was removed in 10 min with Cu(II)-poly(EGDE-DA) and in 110 min with Co(II)-poly(EGDE-DA). In addition, the pharmaceutical product epinephrine was partially oxidized to adrenochrome by the O2(•)¯ released from the Co(II)-poly(EGDE-DA)/H2O2 heterogeneous system.

Reticulação de plastissóis de PVC utilizando resina epóxi polifuncional: Síntese e caracterização

PVC plastisols, crosslinked in the presence of a polyfunctional epoxy resin, were obtained via spread coating. It was possible to infer that the presence of an amine type accelerator, at least in the conditions used in this study, proved to be essential for crosslinking. The results of reticulation degree showed that gel formation only happened in samples where the amine type accelerator has been used concomitantly with the epoxy resin. The results of Young’s modulus seem to confirm the hypothesis of formation of a three dimensional network between the molecules of PVC and epoxy resin, but it was not possible to confirm a chemical reaction between these two polymers because of the large number of molecules present in the formulation. Evidence that crosslinking actually occurred may come from more detailed studies and the use of complementary characterization techniques, which are underway.

Gastrointestinal delivery of glipizide from carboxymethyl locust bean gum–Al3+–alginate hydrogel network: In vitro and in vivo performance

AbstractSodium alginate and carboxymethyl locust bean gum (CMLBG) were reticulated in an aqueous solution of AlCl3, and this novel interpenetrating network (IPN) hydrogel encapsulated about 93–98% glipizide. The degree of reticulation in the spherical IPN beads was confirmed by Fourier transform infrared spectroscopy, elemental analysis, neutralization equivalent determination, tensile strength testing, and differential scanning calorimetry analysis. An increase in the CMLBG weight ratio and the degree of crosslinking in the IPN was found to increase mean dissolution time of the encapsulated drug. The dissolution efficiency was found to be much higher in the medium at pH 7.4 than at pH 1.2. The swelling of IPN depended on the pH of the medium, and accordingly, monitored the drug release for a period of 8 h. The anomalous drug transport mechanism was presumed to be operative. High performance liquid chromatography (HPLC) analysis showed the drug's stability in the IPN during encapsulation. The IPN showed significant hypoglycemic activity on male Wistar rats for up to 10 h. This could be beneficial for diabetic patients for achieving control over blood glucose levels. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Novel etherified locust bean gum-alginate hydrogels for controlled release of glipizide

On many occasions, homopolysaccharide hydrogel networks alone are not suitable for controlled drug delivery. In this study, interpenetrating networks (IPNs) of sodium alginate (ALG) and etherified locust bean gum (ELBG) were developed through ionotropic gelation with Al3+ ions, tested for glipizide release, and were compared with homopolymer hydrogel networks. The degree of reticulation in IPNs was explained by the neutralization equivalent, tensile strength measurement, and drying kinetics of drug-free hydrogels. IPNs afforded a maximum of 94.40 ± 0.35% drug entrapment efficiency and exhibited slower drug release profiles up to 8 h. Al3+-ALG network almost completed the release of embedded drug in 3.5 h; however, the homopolymer Al3+-ELBG network discharged their content at a slow, uniform rate up to 8 h like the IPNs. All the networks appeared spherical under scanning electron microscope. In all cases, a faster drug release rate was assumed in phosphate buffer (pH 7.4) than in KCl/HCl buffer (pH 1.2) solution. The pH-responsive swelling of the beads was responsible for the variable drug release rate in different media. NonFickian diffusion mechanism was operative for the transport of drug from the IPNs. Moreover, IPNs gained appreciation for their better mechanical strength (63.79 ± 1.59 MPa) than Al3+-ELBG network. Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry, and X-ray diffraction analyses indicated a compatible environment for drug encapsualtion and release from the IPNs. The drug release curves of Al3+-ELBG and IPNs were found similar to a reference product. Hence, Al3+-ELBG and IPNs could be useful in controlling diabetes over longer periods.

Cytopathological findings in the vitreous of patients with retinal detachment

AbstractPurpose Proliferative vitreoretinopathy (PVR) is the leading cause of failure in retinal detachment surgery. The migration of retinal pigment epithelial cells and the occurrence of extracellular matrix changes have been associated with PVR. The purpose of this prospective study was to analyze the cellular contents of the vitreous in patients with retinal detachment.Methods The vitreous samples of patients with epiretinal membrane and rhegmatogenous retinal detachment were obtained at the initial phase of surgery without previous intraocular infusion. A cytopathological analysis and staining of the vitreous was performed in all cases. The vitreous of 40 patients with retinal detachment and 49 patients undergoing epiretinal membrane peeling (control group) were included.Results The preparations displayed a variable cellularity. A higher amount of epithelial cell clumping was observed in retinal detachment specimens compared with controls. Furthermore, in the retinal detachment group, more free pigments were encountered and a higher degree of reticulation of the extracellular matrix was noted. In the vitreous of patients with retinal detachment, there is some cytopathological evidence for a higher concentration and an increased activity of retinal pigment epithelial cells compared with controls.Conclusion The predictive value of cytopathological changes for the occurrence of postoperative proliferative vitreoretinopathy in patients undergoing retinal detachment surgery remains to be demonstrated.

Effect of EPDM Particles Size on its Thermo-Mechanical Regeneration

This work presents the effect of EPDM powder particles size on its thermomechanical regeneration process in a batch mixer. The recycled material was decomposed into six particle groups (125, 250, 355, 500, 710 and 1000 μm) to be treated separately under controlled temperature and rotor speed to determine the relation between specific surface area and bulk regeneration. In each case, EPDM crosslink density was measured using the polymer-solvent interaction described by Flory-Rehner's equation. The results showed that not only regeneration can be achieved (crosslink density reduction), but specific conditions also led to increased reticulation degree. Images of the particles before and after treatment were also analyzed and showed that aggregates presence may distort the sieving and treatment processes of the rubber particles.

Bond-graph description and simulation of membrane processes: Permeation in a compartmental membrane system

AbstractNetwork and numerical analysis of permeation through a membrane under non-stationary, stationary, and pseudo-stationary conditions is described. A compartmentalized membrane system (feed solution|membrane|stripping solution) was represented by a linear network of capacitances, diffusion, and sorption/desorption graphs. Reticulation degree of diffusion layers sufficient for quantitative modeling of the diffusion through a homogeneous membrane was estimated. It was found that for membranes of the thickness from 0.001 cm to 0.1 cm and the diffusion coefficients from 1 × 10−7 cm2 s−1 to 1 × 10−5 cm2 s−1, the membrane (or other diffusion layer) partition into ten slices leads to simulated time lags and stationary fluxes differing from the theoretical ones by less than 0.5 % and 1 %, respectively. Extended model with two unstirred interfacial layers and the feed and stripping solution of finite volumes was applied to characterize the effects caused by possible membrane heterogeneity.

Liberação de benzoato de cálcio de filmes de alginato de sódio reticulados com íons cálcio

Biofilmes confeccionados à base de alginato de sódio foram reticulados com íons Ca++ provenientes de duas fontes, cloreto e benzoato de cálcio, e continham glicerol como plastificante. Inicialmente, devido ao alto poder gelificante do Ca++, um filme de baixo grau de reticulação foi confeccionado por casting (1º estágio). Esse filme sofreu uma reticulação complementar por imersão em uma solução contendo de 3 a 7% de CaCl2.2H2O, além de glicerol (2º estágio). A liberação de benzoato de cálcio foi avaliada em diferentes concentrações de agente ativo no filme e dois níveis de reticulação do alginato. O mecanismo envolvido no processo de difusão foi investigado usando o modelo da Lei de Potência. Os resultados indicaram que a difusão de benzoato de cálcio em filmes de alginato apresenta características de comportamentos Fickiano e não-Fickiano. Os coeficientes de difusão efetivos obtidos usando a solução em série derivada da 2ª Lei de Fick são próximos aos valores obtidos pela solução em tempos curtos, com valores de difusividade efetiva do benzoato variando de 3 a 5.10-7 cm²/s. Os valores de difusividade diminuíram com o aumento da intensidade de reticulação e aumentaram com a concentração de benzoato no filme.

Comparison between measurements of elasticity and free amino group content of ovalbumin microcapsule membranes: Discrimination of the cross-linking degree

An inverse method is used to characterize the membrane mechanical behavior of liquid filled microcapsules. Cross-linked ovalbumin microcapsules are flowed and deformed into a cylindrical microchannel of comparable size. The deformed shape is compared to predictions obtained numerically when modeling a capsule under the same flow conditions. The unknown shear modulus value corresponds to the best fit. The degree of reticulation is estimated in parallel by determining the free amino groups remaining on the microcapsules after the cross-linking reaction. We characterize microcapsule populations fabricated at different reaction pH (5–8) and times (5–30 min) to study different cross-linking degrees. The capsule shear modulus and the amino groups are nearly constant with the reaction pH for the capsules fabricated after 5 min of reticulation. The shear modulus increases with the reaction time, while the NH 2 content decreases with it. A global increase in shear modulus with pH is also observed, together with an unexpected increase in NH 2 content. The study shows that the inverse method is capable of discriminating between various cross-linking degrees of microcapsules. Moreover, for this type of microcapsules, the mechanical method appears more reliable than the chemical one to obtain an estimation of their cross-linking degree.

Network genealogy of 195-bp satellite DNA supports the superimposed hybridization hypothesis of Trypanosoma cruzi evolutionary pattern

Trypanosoma cruzi is highly diverse genetically and has been partitioned into six discrete typing units (DTUs), recently re-named T. cruzi I–VI. Although T. cruzi reproduces predominantly by binary division, accumulating evidence indicates that particular DTUs are the result of hybridization events. Two major scenarios for the origin of the hybrid lineages have been proposed. It is accepted widely that the most heterozygous TcV and TcVI DTUs are the result of genetic exchange between TcII and TcIII strains. On the other hand, the participation of a TcI parental in the current genome structure of these hybrid strains is a matter of debate. Here, sequences of the T. cruzi-specific 195-bp satellite DNA of TcI, TcII, TcIII, TcV, and TcVI strains have been used for inferring network genealogies. The resulting genealogy showed a high degree of reticulation, which is consistent with more than one event of hybridization between the Tc DTUs. The data also strongly suggest that TcIII is a hybrid with two distinct sets of satellite sequences, and that genetic exchange between TcI and TcII parentals occurred within the pedigree of the TcV and TcVI DTUs. Although satellite DNAs belong to the fast-evolving portion of eukaryotic genomes, in >100 satellite units of nine T. cruzi strains we found regions that display 100% identity. No DTU-specific consensus motifs were identified, inferring species-wide conservation.

Interactions H.I.F.U. / polymer films

In order to obtain the modification of a defined volume of a polymer layer, preliminary tests of sonication (HIFU 0.75 and 3 MHz) were carried out to obtain an accurate characterization of the acoustic fields as well as convective flow velocities measured close to the surface by Particle Image Velocimetry and luminol mapping. Then, sonication of a delimited zone of an acrylic resin deposited upon a stainless steel thin substrate highlighted a strong dependence of the polymerization or reticulation degree, with different exposure times and different power thresholds for the same final modification. The point was to examine the ability of the thin polymer film to absorb ultrasonic energy or to act as a perfect reflector which induces asymmetric cavitation and therefore violent collapses to take place close to the surface. In the first case, the wave absorption by the film is converted into heat and then acts for the polymer alteration under the high convective flow velocities. For the highest acoustic intensities and for the hardest films, cavitation occurs and the produced microbubbles oscillated and grow close to the surface. Then, the shocks resulting of the bubble collapse eroded mechanically the film.

A Numerical Model for the Optimal Vulcanization of 2D Polar Rubber Compounds Using Microwaves

AbstractA numerical model is presented for the optimal vulcanization of 2D extruded polar rubber with microwaves and peroxides. Magnetron power and curing time are used as the input production parameters, and the output mechanical property selected for optimization is the average tensile strength of the item. A 2D thick weather strip is analyzed to validate the model. The electric field is evaluated by means of Yee cells (FDTD approach) and suitably inserted in Fourier's heat transmission law, thus allowing point‐by‐point temperature profiles to be determined. The temperature is then used to evaluate the degree of peroxidic reticulation, and thus the final tensile strength. A so‐called alternating tangent approach based on the bisection method is finally proposed to estimate the optimal magnetron power and curing time.magnified image

Structural parameters of polyacrylamide hydrogels obtained by the Equilibrium Swelling Theory

In this paper, the synthesis and structural characterization of a series of polyacrylamide hydrogels with different degrees of reticulation are reported. Although the Equilibrium Swelling Theory was recognized as a simple and reliable tool for the determination of structural hydrogels network parameters like equilibrium degree of swelling, cross-link ratio and mesh size, this is the first application of this methodology for polyacrylamide hydrogels. By changing the total monomer content in the synthesis solution (% T) from 5 to 30%, at a fixed value of cross-linker content in the total monomer amount (% C) of 5%, the final parameter obtained, the mesh size, can be tuned from 2 to 0.3 nm. It was also possible to change the mesh size (0.19–0.35) by varying % C from 5 to 12% (at % T = 20%). Scanning Electron Microscopy images for the most different formulations are shown and corroborate data obtained from the theory.

Polymer Microstructures: Modification and Characterization by Fluid Sorption

Polymer micro-organisation can be modified by combination of the three constraints, thermal, hydrostatic and fluid sorption. In selecting the fluid's nature, chemically active or inert, and its physical state, liquid or supercritical, new “materials” can be generated. In addition, the interplay of temperature and pressure allows tailoring the obtained material structure for specific applications. Several complementary techniques have been developed to modify, analyze and characterize the end products: scanning transitiometry, vibrating wire (VW)-PVT coupling, thermoporosimetry, temperature modulated DSC (TMDSC), sorptometry. The great variety of possible applications in materials science is illustrated with different polymers which can produce materials from soft gel to rigid foams when submitted to fluid sorption, typical fluids being methane, or a simple gas (CO2 or N2). Absorption of an appropriate fluid in a cross linked polymer leads to a swelling phenomenon. Thermoporosimetry is a calorimetric technique developed to measure the shift by confinement of thermal transition temperatures of the swelling fluids, which can be currently used solvents or mercury. Application of thermoporosimetry to a swollen cross linked polymer allows to calculate the mesh size distribution and to evaluate the degree of reticulation of the polymer. The same technique can be applied to characterise the pore size distribution in a foamed polymer.

Compressive Behavior of Al2O3—SiC Ceramic Composite Foams Fabricated by Decomposition of Aluminum Sulfate Aqueous Solution

In recent years, a new class of ceramic foams with porosity levels up to 95% has been produced by the chemical method with aeration of a suspension containing foaming agents. The method of foamed suspensions has originated from the chemical reactions of water-soluble salts. In this study, sintered cellular ceramic composites with varying degrees of reticulation are prepared using coarse and fine silicon carbide (SiC) powder. A new process has been developed in order to produce SiC particles containing alumina (Al2 O3) foam by chemical route. An aqueous solution of aluminum sulfate and ammonium sulfate plus SiC particles is fired to prepare ceramic foams up to 1200°C in a ceramic crucible. During heating, the viscous suspension is foamed, sulfate ions are volatilized, and an Al 2O3—SiC composite cake is obtained. The resulting Al2O3 are in networking morphology with flaky struts whereas SiC particles are encapsulated in the flaky alumina. These 3D connections of the struts are responsible for macropores and Al2O3 and SiC grains within the struts are responsible for micropores. Thus, a ceramic composite foam containing bimodal pore distribution is obtained. After sintering at 1550°C, compression tests are applied for the ceramic composite foams. High compressive strength is achieved after post sintering. Both sintering temperature and addition of SiC particles increase the compressive strength of the foam. Both SEM image and XRD analyses are carried out to examine composite microstructures and properties.

When polymers fail: A case report on a defective epoxy resin flooring

A case of failure of an epoxy flooring is presented. The cause of the damage has been found in a wrong formulation of one of the layers, that contained an anomalous quantity of solvents, which produced a plasticization of the resin with a consequent loss in mechanical properties. Differential scanning calorimetry, solid phase micro-extraction–gas chromatography–mass spectrometry and wide angle X-ray diffraction were employed. No significant difference in the degree of reticulation was detected between the defective samples and a reference specimen coming from the manufacturer. After evaporation of the solvents in excess, the resins completely recovered their mechanical properties. The responsibility of the failure was charged to the negligence of the manufacturer in the formulation of the resins.

Polystyrene Resins Incorporating BINOL Units: New Materials For Asymmetric Catalysis

The radical crosslinking polymerization of styrene with (R)-divinyl-BINOL derivatives results in the formation of reticulated polystyrene networks containing protected (R)-BINOL entities at each junction of the polystyrene chains. The generation of polystyrene-immobilized free (R)-BINOL was performed by cleaving the protecting ether groups under acidic conditions. The resulting materials containing optically active BINOL units were tested as chiral ligands in the enantioselective addition of diethylzinc to benzaldehyde. The catalytic properties of the polymer gels were shown to be highly dependent on the degree of reticulation: in the best cases, the resins incorporating (R)-BINOL units showed activities and selectivities similar to those of molecular (R)-BINOL. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Microstructure of ceramic foams

This paper describes the preparation of ceramic foams by expansion of a ceramic suspension based on a polyurethane system. The microstructure and degree of reticulation of the foamed ceramic were examined and analysed with the help of a simple geometrical model. Like the porous ceramics prepared by the replica processing method, these foamed ceramics possess open cells in a nearly equiaxed shape but the cell size is much finer. The ratio of the window size to the cell size is a useful parameter for characterising the geometry of the foam and is related to the qualitative concept of degree of reticulation. For a face centred cubic array of cells it is related geometrically to the volume fraction of porosity and this relationship is tested using microstructural measurements for a range of ceramic foams.

Factors affecting the microstructure of a fine ceramic foam

Sintered cellular ceramics with varying degrees of reticulation were prepared using coarse and fine alumina powders and a 70/30 mixture thereof. The ceramic foams had fine cell size (about 150 μm diameter ) in each case. The method of preparation involved the free expansion of suspensions of these powders at 20 vol.% in a polyurethane foaming system. In order to modify the microstructure, the expansion was opposed using a die, and this reduced the void fraction and window size. In addition, directional rising was achieved by expanding the foam in a long cylindrical vessel and this modified the cell shape of the final foam. These foams have potential use in a range of applications including catalysis, but the main aim of the present work was to prepare preforms for metal matrix composites.

A study of the preparation and mechanism of the ambient temperature curing of acrylic latex with epoxy resins

A method for the ambient temperature curing of acrylic emulsions with epoxy resins has been developed. The results show that an acrylic resin can be effectively cured at room temperature through the addition of between 5 and 20 wt% of epoxy resin to the acrylic monomers. The resulting cured polymers have a degree of reticulation of the order of 75%. It is shown that the tensile strength, and water and alkali resistance are greatly increased compared to those of uncured resins, while the elongation rate decreases sharply. The reticulation reaction was demonstrated to be a result of a reaction between epoxy and carboxyl groups, and was favoured when the amine concentration (curing agent) was low with respect to the concentration of epoxy groups, and when the amine was carboxylated by the acrylic monomers. It was also found that a grafting reaction took place between the acrylic monomers and the epoxy resins via an esterification of the carboxyl groups during the emulsion polymerization step.