Effect Of Aerosil Research Articles

Formation of polymers in the presence of dispersed mineral phase

The adsorption of oligomeric peroxide of sebacic acid on aerosols was studied. The parameters of the adsorption process were found. The effect of aerosil on the polymerization of styrene (ST), methyl acrylate (MA), butyl acrylate (BA), methyl methacrylate (MMA) and butyl methacrylate (BMA) was studied. The initiators used were oligomeric sebacic acid peroxide (OPSA), benzoyl peroxide (BP), lauryl peroxide (PL) and didecanoyl diperoxy adipinate (DP). The mineral filler increases the polymerization rate of MMA, BMA, MA, BA initiated by OPSA. Under the same conditions, the polymerization rate of ST decreases with an increase in the aerosil content in the polymerization system. BP practically does not affect the polymerization rate of vinyl monomers in the presence of aerosil. The reaction of thermal decomposition of OPSA, DP, PL and BP in styrene in the presence of aerosol was studied. An increase in the content of aerosil leads to an increase in the effective decomposition constant of OPSA, DP, PL. in the case of BP, aerosil has practically no effect on the decomposition rate.

Effect of Aerosil and Oleic Acid on Sedimentation of Magnetorheological Fluid

Magnetorheological Fluids (MRFs) are considered as smart fluids because they control viscosity using external magnetic field. It contains ferro-magnetic powder which are aligned in magnetic flux lines. The magnetic force between particles are controlled by magnetic field intensity. This controllable viscosity makes them acceptable in many mechanical applications, but due to difference in density between suspended particles and carrier fluid sedimentation is bound to occur. This thus creates the need of some additives. In our study, silica Nano particles (commercially known as Aerosil 200) is used as stabilizer and Oleic Acid is used as surfactant and their effect on sedimentation is studied in this article. Some other synthesis parameters like particle concentration, stirring duration and material loading also cause some change in sedimentation rate.

Development of Spray Dried Ritonavir Microparticles for Dissolution Rate Enhancement

The purpose of the present investigation was to develop microparticles of Ritonavir to improve its solubility and rate of dissolution and oral bioavailability. Solid dispersions of Ritonavir (BCS-II, anti-HIV drug) with varying contents of Poloxamer 188 were prepared by spray drying technique. The effect of Aerosil 200 on microparticle performance was also investigated. Drug-excipient compatibility and the amorphous state of the drug in microparticles were confirmed by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and x-ray powder diffraction (XRPD) studies, respectively. The surface morphology of microparticles was studied by scanning electron microscopy (SEM). The prepared microparticles were characterized for solubility, drug content, encapsulation efficiency, micromeritic and in-vitro dissolution properties. Use of Poloxamer 188 at an equal ratio with drug resulted in high drug content in microparticles. However, encapsulation efficiency was increased with increase in Poloxamer 188 ratio. FTIR revealed no any chemical changes in drug during spray drying process. Phase transitions and formation of the amorphous state was confirmed by DSC and XRPD studies. SEM photomicrographs showed the formation of uniformly sized Ritonavir microparticles without aggregation in presence of Aerosil 200. However, a strong influence of Poloxamer 188 on solubility and rate of Ritonavir dissolution was observed. In the present research, a spray drying technique was successfully developed for the preparation of free-flowing Ritonavir microparticles exhibiting improved solubility and rate of dissolution and hence, oral bioavailability. The developed technique could be successfully applied for dissolution enhancement of other BCS-II drugs including anti-retroviral drugs.

Effect of Aerosil® on the properties of lipid controlled release microparticles

Theophylline-loaded microparticles of a lipid carrier, Precirol® ATO 5, were prepared by the ultrasonic spray-congealing method. The goal of the work was to investigate the effect of different concentrations and kind of colloidal silicon dioxide (Aerosil® 90, 200 and 300) on the microparticle characteristics (particle size, drug loading, morphology and kinetics of release). The results showed that the introduction of Aerosil® improved the drug distribution in the different particle sizes and that the mean diameter of the microparticles decreased with the viscosity of the suspension to be nebulized, especially that with Aerosil® 300. Whatever the microparticles formulation is, SEM and image analysis did not reveal any remarkable difference of the microparticle shape and surface area, suggesting that other parameters could influence the dissolution behaviour. Actually, the dissolution profiles of all the formulations appeared to be closely related to the physico-chemical properties of Aerosil®, especially to its gelation properties, which are a function of its specific surface area. In particular, microparticles having high concentration of Aerosil® 200 and 300 approached a zero order release kinetics, while Aerosil® 90 microparticles followed a first order release kinetics. Therefore, the drug release rate is controlled by the extent and rate of water absorption/swelling of the Aerosil® employed. Finally, DSC, HSM, XRD and FT-IR evidenced the permanence of the drug in its original state.

Modification of Crystal Habit of Ibuprofen Using the Phase Partition Technique: Effect of Aerosil and Tween 80 in Binding Solvent

A ternary diagram, representing the solubility of binding solvent (chloroform) in a mixture of ethanol and water, was constructed. For this study, the solvent mixture that gave the best ibuprofen pellets (IPs) was composed of chloroform:ethanol:water at a ratio of 1.5%:8%:90.5%. The suitable agitator speed, temperature, and mixing time were found to be 1500 rpm, 25°C ± 2°C, and 20 min, respectively. In addition, suitable stirring time when the phase partition process of IPs began was 15 min. IPs obtained from these conditions were small and round, approximately 1 mm; surface determination by scanning electron microscopy (SEM) indicated that the IPs were composed of drug microcrystals rearranged on the surface. For the dissolution, IPs showed lower drug release when compared with pure ibuprofen crystal (IC) (f2 analysis). An attempt to modify the dissolution property of IP by incorporating various concentrations of Aerosil and Tween 80 in the binding solvent was made. Microscopic appearance showed that both Aerosil and Tween 80 gave less spherical pellets when compared with the use of binding solvent alone. For both the Aerosil and Tween 80 employed, the results indicated a change in rearrangement of drug microcrystals and a change in crystal habit. However, Tween 80 gave more change of the crystallographic direction of drug microcrystals than Aerosil. In term of dissolution, the results showed that employing Tween 80 at 1.2% gave the highest drug release compared to the use of Aerosil and IC alone (f2 analysis). These pellets had a good flow property, as indicated by Carr's compressibility, flow rate, and angle of repose, and they can be compressed into a tablet, encapsulated by suitable polymer, or pulverized to obtain micronized crystals. In the case of compression into tablets, the dissolution profiles of these tablets compared with those of commercial product meet the USP 24 requirement (Q ≥ 80% at 60 min).

Effect of aerosil on the hydrothermal modification of porous structure of silica gel adsorbents

The effect of pyrogeneous silica (aerosil) on hydrothermal treatment (HTT) of narrow and mesoporous silica gels possessing various sizes of primary globules was studied. The HTT process was carried out in the autoclave at 200°C (6 h) in the liquid and gaseous phases. In the systems studied, aerosil was in the form of mechanical mixture with silica gel or constituted a separate phase in the aqueous suspension form. It was stated that the presence of pyrogeneous silica during the hydrothermal modification of silica gels affects the size of their specific surface area, average pores size and curves of pores volume distribution based on their radii. The extent of observed changes depends on the porous structure of initial adsorbents. The investigations show that it is possible to transfer the silica mass through the gaseous phase during the hydrothermal treatment. It was also pointed out that intensity of silica mass transfer observed during the hydrothermal modification in the gaseous phase does not differ from the mass transfer in the liquid phase systems. It was observed that for both modified silica gels relative efficiencies of the hydrothermal treatment are similar. This makes it possible to predict the extent of structural changes in the silica matrix, for silica gels of different porous structure, under the similar hydrothermal treatment conditions.

Sustained release of nitrofurantoin from inert wax matrixes

Sustained release nitrofurantoin granules containing stearic acid and glyceryl monostearate (matrix) were prepared using fusion, solvent evaporation or melt granulation techniques. The effect of Aerosil, Avicel, dibasic calcium phosphate dihydrate (Emcompress) and sodium chloride as channeling agents on the in vitro release of nitrofurantoin was investigated. The results obtained revealed that, with the granules prepared by the fusion method a sustained release pattern could be achieved contrary to those prepared by the other techniques. Moreover, all the selected channeling agents increased the extent of the drug release but with different rates depending upon their concentration and nature. The release of the drug was found to follow the Higuchi model with granules containing 0 and 5% channeling agents while, it followed first-order kinetics with those containing 10% of channeling agent. In vivo studies in humans revealed that the urinary excretion of nitrofurantoin from the test granules occurred over a sustained period from 2–8 hours after oral administration.

Effect of aerosil on radical polymerization in media with crosslinked structures

The effect of Aerosil on the three-dimensional polymerization of triethanolamine trimethacrylate was studied by EPR. It was shown that the introduction of the filler leads to an increase of the rate of radical accumulation because of an increased rate of initiation; in the filled system, the rate of macroradical termination increases due to the defects of the three-dimensional network formed in the presence of Aerosil.

The effect of film-inducing substances on the characteristics of binary powder mixtures

Compaction of a brittle material, phenacetin, could be improved by proper choice of the diluent and film-inducing agent. Aspirin, potassium chloride and sodium chloride were used owing to their ability to relieve stresses by plastic flow. The effect of Aerosil, Eudragit-E and magnesium stearate on the characteristics of these binary mixtures as well as their mechanism were presented. In almost all Systems the results of the repose angle and bulk density were consistent with those obtained from tensile strength measurement. Phenacetin tablets needed higher ratios of potassium chloride or sodium chloride to produce satisfactory compacts than in the case of aspirin. A linear relation was obtained by plotting log packing fraction of various potassium chloride to phenacetin binary mixtures versus log tensile strength. At a given pressure the tensile strength of phenacetin alone could be estimated.

The effect of aerosil on the properties of polyformaldehyde fibre

The effect of aerosil on the properties of polyformaldehyde fibre

Effect of aerosil on the course of thiuram accelerated sulfur vulcanization

AbstractTetramethylthiuram disulfide (TMTD)‐accelerated sulfur vulcanization of natural rubber has been investigated at temperatures from 100°C to 145°C. Continuous measurements in a Vuremo curemeter were used to estimate the extent of crosslinking, which was plotted against cure time. The cure curves as well as their linearized forms (dependences of the logarithm of the extent of vulcanization on the cure time) clearly show that at lower cure temperatures the course of the vulcanization differs significantly from the first‐order rate law. These digressions have been removed by the addition of a highly dispersed silica gel, Aerosil, which simultaneously speeds up the course of the vulcanization up to the value corresponding to the rate of zinc dimethyldithiocarbamate (ZnDMDC)‐accelerated sulfur vulcanization. These results are in accordance with our recent theory supposing that ZnDMDC is the actual accelerator in TMTD‐accelerated sulfur systems. In the presence of Aerosil, the formation of ZnDMDC from TMTD is catalyzed via dispersed silica gel. Support for this view derives from the temperature dependences of vulcanization reactions. The activation energies of TMTD‐accelerated sulfur vulcanizations in the absence (31 kcal/mole) and in the presence of Aerosil (23.5 kcal/mole) correspond exactly to the values calculated from the rate constants of the thiuram decrease in TMTD‐accelerated vulcanization (30 kcal/mole) and from the rate constants of crosslinking in the dithiocarbamate‐accelerated sulfur vulcanization (23 kcal/mole), respectively.

Vulcanization of Elastomers. 24. The Effect of Fillers on the Course of Vulcanization Reactions. I

Abstract The effect of Aerosil on the chemical reactions and the kinetics observed in thiuram vulcanizations was subjected to closer scrutiny. Results now available show: 1. Aerosil does not alter the chemical mechanism of thiuram vulcanizations. It also has no qualitative effect on the kinetics of the various reactions involved. Thiuram disappearance and dithiocarbamate formation over by far the greatest range of conversions are first order reactions. Nevertheless, the limiting value of dithiocarbamate formation is somewhat higher than in the absence of Aerosil. 2. Quantitatively speaking, essential differences are involved. The rate constants for both thiuram loss and dithiocarbamate formation rise considerably when Aerosil is used; in both cases there is a dependence on the Aerosil content of the rubber compound. Yet the activation energies of thiuram disappearance and dithiocarbamate formation are practically the same as in Aerosil-free thiuram vulcanizations, amounting to about 21 kcal/mole. 3. Measurements of the limiting equilibrium swelling reveal that adding Aerosil does not result in additional crosslinking, so that in thiuram vulcanizations the catalytic action displayed by silica gel is the outstanding feature.