Development of mono and multilayer antimicrobial food packaging materials for controlled release of potassium sorbate

In this study, cellulose acetate (CA) based mono and multilayer films including potassium sorbate (Psb) as an antimicrobial agent were prepared using dry phase inversion technique. To achieve appropriate controlled release of Psb, the structure of the films was changed by manipulating the film preparation conditions. In particular, the initial casting composition, wet casting thickness and drying temperature were varied. Results indicate that Psb release rate decreased as the CA content in the casting solution, the wet casting thickness and the drying temperature for both mono and multilayer films were increased. Compared to the results for the monolayer films, a significant decrease of Psb release rate through the multilayer films was recorded. Drying-induced crystallization was observed in the monolayer films. As a consequence of this, a fast initial release of Psb, controlled by Fickian diffusion, was followed by a slower release controlled by dissolution of Psb crystals. In multilayer films, no crystals were detected in the structure and the release rate was regulated only by diffusion of Psb through the film. The results suggest that the films prepared in this study can be used as food packaging materials for achieving controlled and extended release of Psb.     

Solvent sorption in a polymer-solvent system - Importance of swelling and heat effects

Sorption experiments are often conducted in gravimetric sorption columns where several deviations from ideal conditions could potentially occur. For example, heat effects due to solvent sorption, errors introduced due to concentration dependent diffusion coefficients and swelling are unavoidable. In this study, we develop a model to study the importance of the combination of these effects in obtaining diffusion coefficients from sorption experiments. The model is used to explore a wide range of operating conditions and physical parameters.     

Payne cell gravimetric measurements in polymer-solvent systems for diffusion coefficients and isotherm data

The discussion focuses on the application of a Payne cell to the measurement of diffusion and solubility coefficients in polymer/solvent systems. Payne cells have, thus far, been used exclusively to measure steady-state permeation rates of solvents. An analytical model has been developed to describe transient gravimetric sorption and desorption measurements performed with a Payne cell. The model has been validated by a complementary numerical simulation and has been applied to evaluate diffusion and solubility coefficients in two different toluene-silicone rubber systems. The data measured using the Payne cell are found to compare very well with diffusion coefficient and isotherm data measured by traditional gravimetric sorption experiments.     

The effects of urease immobilization on the transport characteristics and protein adsorption capacity of cellulose acetate based hemodialysis membranes

In this study, cellulose acetate (CA) based hemodialysis membranes were prepared by a dry phase inversion method and the influences of urease immobilization on the clearing performance and protein adsorption capacity of the membranes were investigated. Permeation experiments have shown that modification of CA membranes with urease immobilization not only enhanced the transport rate of urea but also increased the permeation coefficients of uric acid and creatinine by changing the structure of the membrane. Furthermore, the protein adsorption capacity of the CA membranes decreased. On the other hand, the mechanical strength of the modified CA membrane did not change significantly compared with that of the unmodified one. A mathematical model was derived to determine the rate of mass transfer of urea through modified CA membranes. Model predictions along with the experimental data suggest that urease immobilization can be used as an alternative method in preparing CA based hemodialysis membranes with improved transport characteristics and biocompatibility through reduced protein adsorption capacities.     

Development of cellulose acetate based antimicrobial food packaging materials for controlled release of lysozyme

Antimicrobial packaging materials were obtained by incorporation of lysozyme into cellulose acetate (CA) films. In order to achieve controlled release of lysozyme, the structure of the films was changed from highly asymmetric and porous to dense by modulating the composition of the initial casting solution. The highest release rate, soluble lysozyme activity and antimicrobial activity were obtained with the film prepared from 5% CA solution including 1.5% lysozyme. Increasing CA content in the casting solution decreased the porosity of the films, hence, reduced the release rate, maximum released lysozyme activities and the antimicrobial activities of the films. In contrast, immobilized lysozyme activities and the tensile strength of the films increased. The incorporation of lysozyme did not cause significant reductions in tensile strength and elongation at break values except in films prepared with 15% CA. This study showed the good potential of asymmetric CA films to achieve controlled release in antimicrobial packaging.     

DRYING OF SOLVENT COATED POLYMER FILMS

ABSTRACT

The ability to predict the drying behavior of coating is of great importance to the coating industry. For this purpose, the model developed by Vrentas and Vrentas has been used to predict the concentration profile as well as the thickness and the temperature change of the polymer film as a function of time. The model incorporates the coupling between heat and mass transfer and diffusion induced convection which occurs when a single layer of a binary polymer solution is dried in a convection heated oven.

The model was solved numerically by using the finite difference approximation and it was applied to the well characterized polyvinylacetate(PVAC)-toluene system. The effects of operating conditions on     

Square-wave adsorptive stripping voltammetric determination of candesartan cilexetil in pharmaceutical formulations

A sensitive, simple and rapid square-wave adsorptive stripping voltammetric method was developed and validated for the determination of candesartan cilexetil in pharmaceutical formulations. The proposed method was based on electrochemical reduction of candesartan cilexetil at a hanging mercury drop electrode in phosphate buffer at pH 5.0. A well-defined reduction peak was observed at −1340 mV with 30 s of accumulation time and −1100 mV of accumulation potential. Under these optimized conditions, the square-wave adsorptive stripping voltammetric peak current showed a linear correlation on drug concentration over the range of 0.25–1.34 μg mL⁻¹ with a correlation coefficient of 0.9986 for the proposed method. The detection and quantitation limits for this method were 1 × 10⁻² and 2.5 × 10⁻¹ μg mL⁻¹, respectively. The results obtained for intra-day and inter-day precision (as RSD%) were between 1.10 and 3.90%. This method was applied successfully for the determination of candesartan cilexetil in its tablet dosage forms with mean recoveries of 101.13 ± 0.78% with RSD of 2.06% for 8 mg tablet and 99.84 ± 0.89% with RSD of 2.36% for 16 mg tablet. The results obtained from the developed square-wave adsorptive stripping voltammetric method were compared with those obtained by the analytical method reported in the literature.     

Characterization of waterborne acrylic based paint films and measurement of their water vapor permeabilities

Recently, production of waterborne coatings has increased significantly as a consequence of strict pollution regulations. Waterborne coatings are sensitive to humidity, thus, their barrier properties with respect to permeation of moisture needs to be determined. Among various coating constituents, binder represents the matrix structure and its amount relative to the amounts of pigments and fillers can significantly affect the structure, hence the barrier property of the coating. In this study, waterborne acrylic based paints applied as protective coating on interior and exterior wall of the buildings are studied. The paint samples formulated with four different binder contents by a commercial paint company are used in the experiments. We first determine unknown ingredients of the paint samples using different characterization tools and then investigate the effect of the binder content on the structure of the paint films. In addition, water vapor permeability of the paint films is measured using a permeation cell. Results show that the barrier property of the waterborne acrylic based paint films against humidity decreases with decreased binder content due to uneven distribution of the pigments, consequently, porous structure formation in the films.     

Multi-Zone Drying Schemes for Lowering the Residual Solvent Content during Multi-Component Drying of Semicrystalline Polymers

The development of a glassy skin in multicomponent semicrystalline polymer systems limits the diffusion of solvents out of the system and increases residual solvent levels. Based on the results of a mathematical model that we had previously developed, we have proposed a multi-zone drying scheme aimed at lowering the residual solvent levels by taking into account the effect of interactions between the various solvents as predicted by the model. This article focuses on the application of this model to develop optimal drying schemes and to verify the effectiveness of these predictions using experimental techniques. The mathematical model developed previously to study the diffusion of multiple solvents and changes in the crystallinity of semicrystalline polymer systems during drying incorporates many features including Vrentas-Duda diffusion theory, solvent-induced crystallization kinetics, as well as glass transition effects and skinning of the film. The multi-zone drying system was developed by varying the drying temperature in each zone as well as changing the partial pressure of individual solvents during the drying process. The effectiveness of the multi-zone drying schemes predicted by the model was validated experimentally using thermogravimetric methods. The polymer-solvent system chosen was a poly(vinyl alcohol)-water-methanol system. Our experimental data suggested that the multi-zone drying schemes were superior to a single-zone drying system through direct comparison. Further examination of the mathematical model yielded individual solvent profiles and these data reaffirmed our conclusions that a multi-zone drying scheme has the ability to reduce the effect of solvent trapping and thus lower the overall residual solvent content.