Degradation kinetics of thiamine hydrochloride in directly compressed tablets iii water vapour transmission through free and applied eudragit films

Abstract

Water vapour transmission through free and applied film of four Eudragit resins namely, E₁₀₀, L₁₀₀ and RS₁₀₀ to directly compressed thiamine hydrochloride tablets was investigated. The type of Eudragit film influenced both water vapour transmission and moisture absorption characteristics of the tablets compressed with either single or binary blend of vehicles. The moisture absorption rate constant K_a, for a given batch was found to be a function of vapour pressure, P, and film thickness, L. The relationship between K_a and either of these parameters is exponental and may be expressed as K_a = A exp (x/P) and K_a = K*_a exp (-x*L). In general, film coating with Eudragit resins affected the physical characteristics of the tablets. The rate of drug release, K has an exponentially relationship as K_e K_o exp (-c/L).     

Comparison of directly compressed vitamin B12 tablets prepared from micronized rotary-spun microfibers and cast films

Fiber-based dosage forms are potential alternatives of conventional dosage forms from the point of the improved extent and rate of drug dissolution. Rotary-spun polymer fibers and cast films were prepared and micronized in order to direct compress after homogenization with tabletting excipients. Particle size distribution of powder mixtures of micronized fibers and films homogenized with tabletting excipients were determined by laser scattering particle size distribution analyzer. Powder rheological behavior of the mixtures containing micronized fibers and cast films was also compared. Positron annihilation lifetime spectroscopy was applied for the microstructural characterization of micronized fibers and films. The water-soluble vitamin B₁₂ release from the compressed tablets was determined. It was confirmed that the rotary spinning method resulted in homogeneous supramolecularly ordered powder mixture, which was successfully compressed after homogenization with conventional tabletting excipients. The obtained directly compressed tablets showed uniform drug release of low variations. The results highlight the novel application of micronized rotary-spun fibers as intermediate for further processing reserving the original favorable powder characteristics of fibrous systems.     

Influence of pharmacotechnical design on the interaction and availability of norfloxacin in directly compressed tablets with certain antacids

Norfloxacin is a fluorquinolone that can interfere with antacids that contain aluminum and magnesium salts by complexation and modification of its solubility, which reduces its absorption and may lead to therapeutic failures. The purpose of this work was to evaluate the effect of the pharmaceutical design on this interaction and to develop a formulation of norfloxacin tablets in which this process could be avoided. Norfloxacin tablets were designed in 28 formulations. The interaction was studied in terms of in vitro dissolution behavior (USP 23, apparatus 2) in simulated gastric fluid with different doses of four commercially available antacid preparations. It was observed that dissolution rates were markedly reduced in the presence of all antacids studied. This phenomenon was practically avoided with some formulations of norfloxacin tablets in which a disintegrant (sodium starch glycolate or crospovidone) was included. These results indicated that the chelation among metal ions and norfloxacin could be affected by the delivering ability of the drug in the tablet. It was demonstrated that the pharmacotechnical design could modify an interaction process. Some formulations of tablets, in which the reduced dissolution rates in the presence of nonsystemic antacids in vitro was practically avoided, were developed by direct compression.     

Nucleation and growth of poly-Si films deposited directly on glass substrate in reactive thermal-chemical vapour deposition

We prepared device-grade polycrystalline silicon thin films on glass substrates at 450 °C, by reactive thermal-chemical vapour deposition employing Si₂H₆ and F₂ as source gases. The nucleation and growth of the poly-Si thin films were investigated, and the process pressures were varied from 533 to 933 Pa. Thin films with thickness of 2 to 200 nm were prepared and their crystallinity and morphological properties were characterized. The incubation time is shorter than 30 s; 533 Pa yields higher crystallinity. However a trade-off exists between growth rates and grain sizes. We proposed a model for comparing our technique with conventional low- pressure chemical vapor deposition.     

Optical transmission through hexagonal arrays of subwavelength holes in thin metal films

We have studied the light transmission through hexagonal arrays of subwavelength holes in thin gold and aluminum films, varying the film thickness between 20 and 120 nm while the hole diameter as well as the interhole distance have been kept constant at approximately 300 and approximately 500 nm, respectively. The films were characterized by means of UV-vis spectroscopy and scanning near-field optical microscopy (SNOM).     

Optimization of the mechanical properties and water-vapor transmission properties of free films of hydroxypropylmethylcellulose

Free films of hydroxypropylmethylcellulose were prepared by a spraying technique. Methocel E5 and Methocel E15 were used in varying proportions in the preparation of films. The free films were studied for their mechanical properties and moisture permeability characteristics. A 2² factorial design was used to quantitate the effect of each polymer on the tensile strength and permeability constant of the films.     

The dynamic water vapour sorption behaviour of natural fibres and kinetic analysis using the parallel exponential kinetics model

Hygroscopic behaviour is an inherent characteristic of natural fibres which can influence their applications as textile fabrics and composite reinforcements. In this study, the water vapour sorption kinetic properties of cotton, filter paper, flax, hemp, jute, and sisal fibres were determined using a dynamic vapour sorption apparatus and the results were analyzed by use of a parallel exponential kinetics (PEK) model. With all of the fibres tested, the magnitude of the sorption hysteresis observed varied, but it was always greatest at the higher end of the hygroscopic range. Flax and sisal fibres displayed the lowest and highest total hysteresis, respectively. The PEK model, which is comprised of fast and slow sorption components, exhibited hysteresis in terms of mass for both processes between the adsorption and desorption isotherm. The hysteresis derived from the slow sorption process was less than from the fast process for all tested fibres. The fast processes for cotton and filter paper dominated the isotherm process; however, the hemp and sisal fibres displayed a dominant slow process in the isotherm run. The characteristic time for the fast sorption process did not vary between adsorption and desorption, except at the top end of the hygroscopic range. The characteristic time for the slow process was invariably larger for the desorption process. The physical interpretation of the PEK model is discussed.     

A mathematical model for the prediction of water vapour transmission rate at different temperature and relative humidity combinations

A simple mathematical procedure for the estimation of water vapour transmission rate under different conditions is presented and discussed. The ASTM dynamic and gravimetric methods were used for measuring the water vapour transmission rate of four thin plastic films (PET 19 μm, PVC 16 μm, EVA 15 μm and LDPE 23 μm) under 38 different conditions of temperature and relative humidity and the corresponding permeance values were drawn. On the basis of the Clausius Clapeyron's relationship between temperature and water vapour pressure, a simple equation was derived for a rapid transformation of water vapour transmission rate data. The mathematical procedure was applied to the data collected for the four thin films and good agreement was found between observed and predicted values for the PET and LDPE films, while for the PVC and EVA films the equation developed led to an overestimate of water vapour transmission at the lower temperatures.     

Influences of deposition and crystallization kinetics on the properties of silicon films deposited by low-pressure chemical vapour deposition from silane and disilane

The paper deals with the properties of silicon films obtained by low-pressure chemical vapour deposition (LPCVD). Two gaseous sources characterized by different deposition temperatures, i.e. disilane Si₂H₆ (420-520 °C) and silane SiH₄ (520-750 °C), was studied in order to understand the influences of deposition and crystallization kinetics on silicon film properties. Thus, the deposition of amorphous, semi-crystallized and polycrystalline silicon films was related to “volume random” and “surface columnar” crystallization phenomena, highlighting a linear relationship between the refractive index and the polysilicon volume fraction and, showing complex residual stress dependency with process conditions. Finally, by introducing the ratio V_d/V_c between the deposition and crystallization rates as a major parameter, different deposition behaviours and related semi-empirical relationships were defined in order to characterize fully the various properties of LPCVD silicon films (microstructure, polysilicon volume fraction, refractive index and residual stress) according to the chosen gaseous source, silane or disilane.     

A simple model for the interaction between water vapour and oxygen transmission in multilayer barrier materials intended for food packaging applications

The above article (DOI: 10.1002/pts.799) was published online on 26 October 2007 in Wiley Interscience ( www.interscience.com ), and in print in Packaging Technology and Science 21 (4): 207–216. The following errors were subsequently identified. On page 208, in the ninth line of text in the right hand column, p_w should not have had the upper indices o. The first equation on page 208 is incorrect and should read: The publisher accepts full responsibility for this error and would like to apologise for any confusion caused.     

Conductivity threshold and kinetics of the phase transition in Fe2O3-Fe3O4 thin films made by chemical vapour deposition

Iron oxide films were made by chemical vapour deposition and annealing post-treatment. Optical and d.c. electrical measurements probed the Fe₂O₃ Fe₃O₄ transition. It could be understood as a thermally activated process, with an activation energy equal to the band-gap of Fe₂O₃. A.c. electrical data gave evidence against the transition being percolative.     

Influence of film thickness on the optical transmission through subwavelength single slits in metallic thin films

Silver and gold films with thicknesses in the range of 120-450 nm were evaporated onto glass substrates. A sequence of slits with widths varying between 70 and 270 nm was milled in the films using a focused gallium ion beam. We have undertaken high-resolution measurements of the optical transmission through the single slits with 488.0 nm (for Ag) and 632.8 nm (for Au) laser sources aligned to the optical axis of a microscope. Based on the present experimental results, it was possible to observe that (1) the slit transmission is notably affected by the film thickness, which presents a damped oscillatory behavior as the thickness is augmented, and (2) the transmission increases linearly with increasing slit width for a fixed film thickness.     

Oxidation of nickel-based alloys in dry and water vapour containing air

Abstract

Ni-based alloys are widely used in power generation and their oxidation behaviour in the uncoated state is of interest, especially the impact of water vapour in the air on the formation of a protective underlying alumina scale. High-temperature X-ray diffraction was applied to investigate in situ the oxide scale formation in the initial state on the alumina formers CM247DS and CMSX4 in comparison to the chromia formers IN792 and SCA425+. Post-oxidation analysis was performed by field emission scanning electron microscopy. The samples were oxidised for 100 h at 950°C in dry air and in air with 20% relative moisture in the high temperature device on the X-ray diffractometer. In dry air, CM247 and CMSX-4 form α-Al₂O₃ from the beginning simultaneously with spinels and nickel oxide. The alumina scale underlies the spinels which spall partially on cooling. When adding water vapour, the same oxides were formed simultaneously resulting in a comparable oxide scale. IN792 forms in dry air mainly NiAl₂O₄ and transitionally CrO₂ under laid by an alumina scale. With water vapour, Cr₂O₃ forms and the underlying alumina scale shows a non coherent dendritic structure. SCA425+ forms in dry air Cr₂O₃ and Cr containing mixed oxides and with water vapour a more coherent alumina scale than IN792.     

Development of a mathematical model for the effect of temperature and relative humidity on the water vapour permeability of plastic films

The water vapour permeability constants of three flexible films (LDPE, PET and a laminate of both films) were determined at 20, 30 and 40 °C and from 55 to 90% relative humidities. The relationship between permeability and temperature followed the Arrhenius model for the three films. The relative humidity also influenced the permeability of the films. A mathematical model describing permeance (P/X - the permeability of laminates or films) as a function of external relative humidity and temperature was developed. The model can be used to predict the permeance of the three films at different temperatures and relative humidities.     

Diffusion kinetics of Au through Pt films about 2000 and 6000 Å thick studied with Auger spectroscopy

The diffusion kinetics of Au through Pt films were studied because of the frequent use of PtAu metallizations in semiconductor technology and because Au is often undesirable in active semiconductor regions etc. that are in contact with the Pt. PtAu couples with approximately 2000 Å and 6000 Å Pt films were heat treated between 250° and 350°C in 1 atm N₂ ambient. Surface composition and depth profiles were measured using Auger spectroscopy and ion milling. Au was found to diffuse initially through thin Pt films (< 6000 Å) by grain boundary migration and more than 10¹⁵ atoms cm^?2 of Au crossed the Pt film when the bulk of the Pt contained very little Au (?1 at.%). For 2250 Å Pt films on Au, the time t(X = 0.5) for half-saturation of the Pt surface with Au was given by t(0.5) = 1.2 X 10^?7X exp (0.96 eV/kT) min, where X is the fractional Au concentration in the first 7 Å of the surface. This diffusion rate is relatively fast; e.g.t(0.5)≈7 min for a 2250 Å Pt film at 350°C. At t(0.5) the bulk of the Pt contained less than 1 at.% Au and t(0.5) was proportional to Pt film thickness near 2000 to 6000 Å.     

Effects of annealing temperature on crystallisation kinetics and properties of polycrystalline Si thin films and solar cells on glass fabricated by plasma enhanced chemical vapour deposition

Solid-phase crystallisation of Si thin films on glass fabricated by plasma enhanced chemical vapour deposition is compared at different annealing temperatures. Four independent techniques, optical transmission microscopy, Raman and UV reflectance spectroscopy, and X-ray diffraction, are used to characterise the crystallisation kinetics and film properties. The 1.5 μm thick films with the n+/p−/p+ solar cell structure have incubation times of about 300, 53, and 14 min and full crystallisation times of about 855, 128, and 30 min at 600 °C, 640 °C, and 680 °C respectively. Estimated activation energies for incubation and crystal growth are 2.7 and 3.2 eV respectively. The average grain size in the resulting polycrystalline Si films measured from scanning electron microscopy images gradually decreases with a higher annealing temperature and the crystal quality becomes poorer according to the Raman, UV reflection, and X-ray diffraction results. The dopant activation and majority carrier mobilities in heavily doped n+ and p+ layers are similar for all crystallisation temperatures. Both the open-circuit voltage and the spectral response are lower for the cells crystallised at higher temperatures and the minority carrier diffusion lengths are shorter accordingly although they are still longer than the cell thickness for all annealing temperatures. The results indicate that shortening the crystallisation time by merely increasing the crystallisation temperature offers little or no merits for PECVD polycrystalline Si thin-film solar cells on glass.