Modelling of transport processes in a developing char

A mathematical model, simulation results and laboratory experiments are reported to describe the degradation of fire retardant polymeric materials.The model describes the heat and mass balances of a polymer layer with finite thickness. The degradation is initiated by a constant heat flux at the top of the layer. It is assumed that the polymer degrades to a fixed mass of char and volatile gas in an instantaneous step, at the moment when the temperature reaches a critical value. The most important heat transport mechanism is conduction, which dominates the temperature profile. The mass transport of gas is described by Darcy's law, with a simplifying condition that the overall solid volume is constant during degradation. The transport processes have been modelled in one spatial dimension.Calculations and experiments have been carried out to establish the effects of critical parameters such as layer thickness, heat flux and material properties.     

Structural Characteristics and Permeability of Ethyl Cellulose Films Containing Different Plasticizers

The effect of different type of plasticizers was investigated in ethyl cellulose as coating polymer for manufacturing coated pellets of modified release containing a water soluble model drug. Scanning electron microscopic image analysis (SEM), differential scanning calorimetry (DSC), X-ray photoelectron spectroscopic chemical surface analysis (XPS) were used to study the films, and the dissolution profiles of coated pellets were evaluated. The effect of the different plasticizers and coating levels on the first order dissolution rate constant is determined by statistical experimental design. Correlation was found between the dissolution rate constant and the structural characteristics of the coating layer containing different plasticizers. Partial segregation of the plasticizers was detected especially on the surface of the films, which is in correlation with the differences in the glass transition temperatures. PEG 400 is found to be compatible enough to form continuous, durable EC coating at 5% concentration level, which gave the slowest dissolution.     

Comparison of multivariate linear regression methods in micro‐Raman spectrometric quantitative characterization

Chemical imaging was used in this study as a powerful analytical tool to characterize pharmaceuticals in solid form. The majority of analyses are evaluated with bilinear modelling using only the pure component spectra or just the chemical images themselves to estimate the concentrations in each pixel, which are far from true quantitative determination. Our aim was to create more accurate concentration images using regression methods. For the first time in chemical imaging, variable selections with interval partial least squares (PLS) and with genetic algorithms (PLS‐GA) were applied to increase the efficiency of the models. These were compared to numerous bilinear modelling and multivariate linear regression methods such as univariate regression, classical least squares (CLS), multivariate curve resolution–alternating least squares (MCR‐ALS), principal component regression (PCR) and partial least squares (PLS). Two component spray‐dried pharmaceuticals were used as a model. The paper is shown that, in contrast to the usual way of using either external validation or cross‐validation, both should be performed simultaneously in order to get a clear picture of the prediction errors and to be able to select the appropriate models. Using PLS with variable selection, the root mean square errors were reduced to 3% per pixel by keeping only those peaks that are truly necessary for the estimation of concentrations. It is also shown that interval PLS can point out the best peak for univariate regression, and can thereby be of great help even when regulations allow only univariate models for product quality testing. Variable selection, besides yielding more accurate overall concentrations across a Raman map, also reduces the deviation among pixel concentrations within the images, thereby increasing the sensitivity of homogeneity studies. Copyright © 2015 John Wiley & Sons, Ltd.     

Thermal analysis of fibre forming polymers

Different levels of fibre technologies and application, from synthesis to degradation has been studied using the methods of thermal analysis. Recent results of these studies on synthetic and natural fibres are summarized. The effect of chemical and physical modification of polyolefin fibres as well as the synthesis of polymer emulsion used as additive in fibre technologies could be followed by DSC, DMA, TG methods.     

Use of supercritical CO2‐aided and conventional melt extrusion for enhancing the dissolution rate of an active pharmaceutical ingredient

Dispersing at the molecular level a drug in a polymer matrix is a major challenge to be addressed by the pharmaceutical industry to enhance its bioavailability or to control its release. Melt extrusion and supercritical CO₂‐aided melt extrusion of solid pharmaceutical formulations were performed to enhance the dissolution rate of carvedilol, taken as a model of poorly soluble drug. The presence of the drug improved the processability of the polyacrylate matrix (Eudragit E) through its plasticizing effect. The supercritical method was found gentle compared with melt extrusion owing to the shorter residence time and lower processing temperature and melt viscosity. No traces of decomposition of the drug could be detected after the supercritical extrusion process based on capillary electrophoresis results. This extrusion process resulted in effective homogenization of the components and amorphization of the drug according to Raman mapping, Fourier transform infrared spectrometry, X‐ray diffraction, and polarized light microscopy. The kinetics of dissolution can be dramatically improved. Copyright © 2011 John Wiley & Sons, Ltd.     

Ein neues Doppelsalz, (NH4)2SiF6 · NH4NO3

A New Double Salt, (NH₄)₂SiF₆ · NH₄NO₃. From a aqueous solutions of (NH₄)₂SiF₆ and NH₄NO₃ crystallizes by cooling to room-temperature a new double-salt of the composition (NH₄)₂SiF₆ · NH₄NO₃. Its hexagonal unit containing two molecules has the dimensions: a₀ = 5.868, c₀ = 14.799 Å.     

Thermoanalytical study of nucleating effects in polypropylene composites

Engineering application of polypropylene requires the employment of flame retardants. Reactive compounding of ammonium-polyphosphate and synergist additives with polypropylene is an effective way for forming flame retardant polypropylene. Both the ammonium-polyphosphate and the additives used for improving its performance effect the crystallization and melting behavior of polypropylene. Encapsulation of flame retardant additives with appropriate elastomer, in order to improve their water resistancy, causes further changes in degree of crystallinity and consequently in the mechanical properties.The financial support of the OTKA 014194 is acknowledged with gratitude.