Formulation factors affecting drug release from poly(lactic acid) (PLA) microcapsule tablets

A sustained-release (SR) formulation of phenobarbital (PB) microcapsule tablet was prepared using low molecular weight (MW) DL- and high MW L-poly(lactic acid) (PLA) polymer. Microencapsulation of PB showed a unimodal size distribution (375 to 550 microns) of the microcapsules with high loading capacity (> 84%). Drug release from the microcapsule was influenced by the polymer ratios and increased with an increase in L-PLA amount. Microcapsules and physical mixtures of PB and the PLA were directly compressed independently to form microcapsule and matrix tablets, respectively. Drug release from the microcapsule tablets was significantly lowered (p < .001) compared to matrix tablets or free microcapsule (free microcapsule > matrices > microcapsule tablets). We also investigated the effect of tablet adjuvants, compression pressures, and microcapsule loading on the tablet performance in terms of friability, hardness, porosity, tensile strength, and the release kinetics of PB. The drug release rate increased with increasing compression pressure in the case of Emcompress or lactose, but not Avicel. The drug release rate was three- to fivefold increased with sodium starch glycolate compared to tablets without a disintegrant. With an increase in microcapsule loading, a decrease in the drug release rate was observed; however, the tablet performance remained satisfactory. The morphology of the microcapsules was monitored microscopically after the dissolution and the disintegration of tablets. The drug release accelerated with compression pressures and microcapsule loading from the tablets due to mechanical destruction of the microcapsule wall, which was more clearly seen after disintegration and dissolution of the tablets. Our data suggest that the PLA microcapsule can be tableted to make a SR product without significantly affecting its release kinetics.     

Complete electrochemical dechlorination of chlorobenzenes in the presence of naphthalene mediator

Electrochemical dechlorination of chlorobenzene in organic solutions was studied. Electrolysis of chlorobenzene in acetonitrile solution in a one-compartment cell fitted with a platinum cathode and a zinc anode at 60mA/cm(2) and 0 degrees C was found to be the optimum conditions, which gave complete dechlorination of chlorobenzene. However, similar result could not be achieved when applying these conditions to 1,3-dichlorobenzene and 1,2,4-trichlorobenzene. We found that the use of naphthalene which reacted as a mediator in the appropriate system could accelerate the reduction and gave complete dechlorination of those chlorobenzenes. Moreover, in the presence of naphthalene the reaction time could be shortened by half compared to dechlorination in the absence of naphthalene.     

Advanced modeling techniques for micromagnetic systems

We present a review of micromagnetic and magnetotransport modeling methods which go beyond the standard model. We first give a brief overview of the standard micromagnetic model, which for (i) the steady-state (equilibrium) solution is based on the minimization of the free energy functional, and for (ii) the dynamical solution, relies on the numerical solution of the Landau-Lifshitz-Gilbert (LLG) equation. We present three complements to the standard model, i.e., (i) magnetotransport calculations based on ohmic conduction in the presence of the anisotropic magnetoresistance (AMR) effect, (ii) magnetotransport calculations based on spin-dependent tunneling in the presence of single charge tunneling (Coulomb blockade) effect, and (iii) stochastic micromagnetics, which incorporates the effects of thermal fluctuations via a white-noise thermal field in the LLG equation. All three complements are of practical importance: (i) magnetotransport model either in the ohmic or tunneling transport regimes, enables the conversion of the micromagnetic results to the measurable quantity of magnetoresistance ratio, while (ii) stochastic modeling is essential as the dimensions of the micromagnetic system reduces to the deep submicron regime and approaches the superparamagnetic limit.     

Morphological studies of (polyamide‐6)/(silane‐grafted high‐density polyethylene)/nanoclay ternary nanocomposites

In this work, the influence of organoclay incorporation along with silane grafting of high‐density polyethylene (HDPE) on compatibilization and morphology of HDPE/(polyamide‐6) (PA6) blends was investigated. Analysis by Fourier‐transform infrared spectroscopy was done for the investigation of grafting efficiency of specimens. Scanning electron microscopy and thermal properties (diffraction scanning colorimetry) were examined to study the effect of silane grafting as well as adding organoclay in compatibilizing blends. Small‐angle X‐ray scattering, transmission electron microscopy, and dynamic rheology (Rheometric Mechanical Spectrometer) were also used to explain morphological changes. The results of scanning electron microscopy indicated that silane‐grafted HDPE had hydrophilic characteristics and therefore was more compatible with PA6 than neat polyethylene. Furthermore, in the same way, adding nanoclay to this blend resulted in more uniform and finer morphology. Results of diffraction scanning colorimetry confirmed the compatibilizing effect of both silane grafting of polyethylene and use of organoclay in blends by showing a strong deviation of separate melting peak of PA6 in the composites to reduced intensity and shift to lower temperatures. J. VINYL ADDIT. TECHNOL., 21:191–196, 2015. © 2014 Society of Plastics Engineers     

The impact of viscoelastic behavior and viscosity ratio on the phase behavior and morphology of polypropylene/polybutene‐1 blends

In this study, the influence of the viscosity ratio on the rheology, morphology, and interfacial interaction of polypropylene and polybutene‐1 (PB‐1) resins with various melt flow behaviors in the blend are investigated. A droplet‐matrix morphology is observed in the scanning electron microscope images for all formulations and the size of particles increased proportionally by increasing the viscosity ratio. Viscoelastic parameters of blends at various viscosity ratios and compositions are measured by small‐amplitude oscillation rheometry in the linear viscoelastic region. The Cole‐Cole plots showed a nearly semicircular arc for all compositions. This semicircular arc is observed while the viscosity ratio is lower than 1, and the Cole‐Cole plots deviated from the semicircular shape at PB‐1 content higher than 10 wt%. It is emphasized that, in addition to compatibility, the semi‐circularity of Cole‐Cole plots affects the size of the dispersed particles, which is under the influence of the viscosity ratio. It is found that the interfacial tensions of polypropylene and PB‐1 are not significantly different when changing the viscosity ratio and coarsening the morphology. The form relaxation times in the blends with lower viscosity ratios are shorter than the form relaxation times of the blends with higher viscosity ratios. J. VINYL ADDIT. TECHNOL. 21:94–101, 2015. © 2014 Society of Plastics Engineers     

Sulfur dioxide removal by calcium-modified fibrous KCC-1 mesoporous silica: kinetics,thermodynamics, isotherm and mass transfer mechanism

Journal of Porous Materials - The removal of sulfur dioxide from industrial flue gas through dry flue gas desulfurization method commonly involves the use of adsorption process with porous sorbent....     

Molecular dynamics simulation of diffusion and permeation of gases in polystyrene

Molecular dynamics simulations are performed to study the diffusion and permeation of gases, including argon, nitrogen, methane, carbon dioxide, and propane, in polystyrene over a wide range of temperatures. A jumping mechanism is observed for the diffusion of diffusants in polymer. The calculated diffusion coefficients agree well with the experimental data and with the results of former simulation studies. The relation between the diffusion coefficient and the molecular diameter is confirmed by the results. Our calculated results on the temperature-dependence of diffusion coefficients show that for some gases a break is seen, at the glass transition temperature, in the Arrhenius plot of ln (D) versus 1/T, while for some other light gases, argon and nitrogen, the plot is linear over the whole temperature range. We have also calculated the permeability coefficients, using the diffusion coefficients calculated in this work and our recently published solubility coefficients [Eslami and Müller-Plathe, Macromolecules 2007; 40:6413]. Our results show that the calculated permeability coefficients are higher than the experimental data by almost the same trend observed in the solubility calculations, but the ratios of calculated permeabilities are in a very good agreement with experiment.     

Premixed filtration combustion of micron and sub-micron particles in inert porous media: A theoretical analysis

An analytical model for one-dimensional premixed filtration combustion of volatile fuel particles-air mixture is presented. It is presumed that fuel particles first vaporize and a gaseous fuel with definite chemical structure is formed, which is subsequently oxidized in the gas phase. Flame structure is considered in the three zones. In the preheating vaporization zone, the mixture is heated until it reaches ignition temperature. In the reaction zone, the combustible mixture burns and the post flame zone is occupied by the combustion products. The temperature and mass fraction profiles are obtained of gaseous fuel in these three zones at a semi-infinite inert porous media. Thereafter, the effects of various parameters such as gas velocity, porosity, fuel particles diameter, number density of fuel particles, and heat of chemical reaction on the temperature and mass fraction profiles are investigated.     

Effects of Nano‐SiC on Silane Grafting and Curing of Polyolefin Elastomer: Mixing Order,Physical, and Mechanical Properties

The objective of this article was preparation of curable silane‐grafted poly(ethylene‐1‐butene) nanocomposite. The poly(ethylene‐1‐butene) was a polyolefin elastomer with random high comonomer content. Two preparation methods were investigated. The method of preparing nanocomposites significantly affected the mechanical properties of the resulted nanocomposites. So that, with the same formulation and different preparation methods, silane grafting with the first was 94% (PVDS3), while with the second was 33% (PS3VD). It was shown that the tensile strength of the cured nanocomposite prepared with the method 1 (PVDS3) increased four times higher than the pure resin. The effects of different factors such as the amount of silane and also the amount of silicon carbide on the physical, mechanical, and thermal properties of the cured and uncured nanocomposites were investigated. The rate of curing was depended on the silicon carbide concentration and 5 phr (part per hundred resin), and nano‐SiC was a concentration where the tensile properties were optimum. Thermal stability and the impermeability of the cured samples improved in the presence of nano‐silicon carbide. J. VINYL ADDIT. TECHNOL., 26:244–252, 2020. © 2019 Society of Plastics Engineers