National Repository of Grey Literature 22 records found  1 - 10nextend  jump to record: Search took 0.01 seconds. 
Preparation of Chitosan Based Films for Food Packaging Applications.
Soukup, Karel ; Cruz, G.J.F. ; Hanika, Jiří ; Jandová, Věra ; Hejtmánek, Vladimír ; Šolcová, Olga
In the present study, the effect both of the botanical source and proportion of starch produced from agricultural surplus on the microstructure properties of starch/chitosan/glycerin films was tested. Effective gas transport properties gas diffusion transfer was performed. Starch/chitosan/glycerol biodegradable films were obtained by casting method from giant squid (Dosidicus gigas) pen chitosan mixed with glycerin and starch. Four starch samples were prepared using exceeding or low quality biomass including broken rice grains, hard yellow corn surplus, banana surplus form exportation activity and low quality cassava in three different weight proportion (chitosan/starch) corresponding to 1/1, 2/1 and 5/1. Extraction of starch from the raw material was carried out by mixing it with a water solution of sodium disulfite (5 wt.%). Afterwards, the obtained suspension was filtered and then decanted at 5°C for 24 h. The obtained starch was washed repeatedly with distilled water and ethanol (96 vol.%). Finally, the starch samples were dried at 55°C for 48 h, crushed and sieved. It was found that the gas diffusion transport properties significantly depend on the starch source used. Differences in diffusion transport rates through the films prepared with different starches are related to the size and distribution of granules of starch in the films and/or the amylose conten.
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Preparation of Palladium Catalysts Supported on Activated Carbons from Agricultural Waste Biomass.
Soukup, Karel ; Topka, Pavel ; Cruz, G.J.F. ; Hejtmánek, Vladimír ; Šolcová, Olga
In the framework of the presented study, the low-cost activated carbons from tropical agricultural waste biomass including cocoa pod husks (denoted as CPH-AC) were prepared. The raw materials collected in Tumbes region in Peru were mixed with activating agent based on ZnCl2 in the weight ratio of 1/1. Subsequently, the mixture was put in a ceramic reactor and afterwards in a horizontal oven to be directly carbonized under nitrogen atmosphere. The temperature increased with the rate of 10 min/min until a final carbonization temperature of 600°C was reached and it was kept during 2 h.\n
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Preparation and Characterization of Nanofibrous Catalysts for Environmental Applications
Soukup, Karel ; Topka, Pavel ; Hejtmánek, Vladimír ; Petráš, D. ; Šolcová, Olga
The aim of the study was focused on detailed description of the influence of the preparation of palladium and platinum catalysts supported on polymeric nanofibers based on poly(2,6-dimethyl-1,4-phenylene) oxide on their catalytic performance. The catalytic activity of the prepared electrospun catalysts was investigated by means of model reaction based on total oxidation of methanol. Nanofibrous catalyst supports were prepared by electrospinning technique, which represents currently the most using method to produce polymeric nanofibrous mats. This technique is based on the polymeric fiber elongation under the influence of the electrostatic field between two opposite charged electrodes (capillary electrode and the grounded plate).
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Transport of Gaseous Mixtures in a Porous Membrane Support Modelled Using a Random Three-Dimensional Pore Network
Čapek, P. ; Veselý, M. ; Hejtmánek, Vladimír
In this paper, we developed a pore network model of multi-component mass transport in porous solids. Constitutive equations applied on the pore-scale level were based on the Maxwell-Stefan formulation. Fitting effective transport parameters like tortuosity was completely avoided. Essential information about pore sizes was extracted from the pore network model. It was shown that conditions for unusual phenomena, particularly up-hill flow, can be found quite often in practice. Pore network models also appear to be a very convenient tool for estimation of optimal conditions of diffusion experiments.
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Process-Based Model of Mixed-Matrix Membrane
Čapek, P. ; Hejtmánek, Vladimír ; Veselý, M. ; Sysel, P. ; Kočiřík, Milan ; Brabec, Libor ; Zikánová, Arlette ; Bernauer, B. ; Fíla, V.
The focus of this contribution was on the formulation and verification of a process-based model of the mixed-matrix membrane that consisted of the polyimide matrix synthesized from the monomers 4,4’-(hexafluoroisopropylidene)diphtalic anhydride and 4,4’-oxydianiline, and silicalite-1. When a solution of a polyimide precursor in N,N-dimethylformamide was ready, silicalite-1 particles were dispersed in the solution and the dispersion was subsequently cast on a Teflon support plate. An initial mass ratio of silicalite-1 and polyimide was about 1:1. After solvent removal, the films were heated in subsequent steps up to 230°C for two hour. From a process-based model point of view, a key operation of the entire synthesis was slow sedimentation of silicalite particles in the viscous solution. Preliminary observation of 2D cuts through the solid membrane in a scanning electron microscope revealed that there were a lot of contacts among the silicalite particles. Therefore, a sequential (ballistic) deposition algorithm, well representing sedimentation in a low-energy environment, was used to create an off-lattice model of spatial distribution of the silicalite particles in the polyimide matrix.
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Mass Transport Simulation in Replicas of Porous Material: Effective Transport Properties Estimation
Čapek, P. ; Veselý, M. ; Kolafa, J. ; Hejtmánek, Vladimír ; Brabec, Libor
The purpose of this study was calculation of transport properties of the replicas of some macroporous materials. These trasport parameters such as the effective permeation or diffusion coefficient, respectively, were compared with their experimentally measured counterparts.
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Reconstructed 3D Microstructure and Effective Diffusivity of a Zeolite-Polyimide Mixed Matrix Membrane
Čapek, P. ; Hejtmánek, Vladimír ; Fryčová, M. ; Sysel, P. ; Kočiřík, Milan ; Brabec, Libor ; Zikánová, Arlette ; Bernauer, B. ; Fíla, V.
In our work we focused on a two-phase system consisting of the polyimide matrix synthesized from the monomers 4,4’-(hexafluoroisopropylidene)diphtalic anhydride (6FDA) and 4,4’-oxydianiline (ODA), and silicalite-1 [3, 4]. Its microstructure on the scale capturing the morphology of silicalite particles was reproduced by means of stochastic reconstruction. Then, effective diffusivity of an arbitrary fluid in the reconstructed composite material was determined by exploiting random walk simulation. Resulting values were compared with the corresponding values obtained using two traditional correlations for conductivity of composite materials. Image processing and analysis as the first step of stochastic reconstruction was a bit inexact in terms of an estimation of the volume fractions of both phases.
Advances in Stochastic Reconstruction of Porous Solid Microstructure by the Method of Simulated Annealing
Čapek, P. ; Hejtmánek, Vladimír ; Brabec, Libor ; Zikánová, Arlette ; Kočiřík, Milan
The innovated method of stochastic reconstruction by simulated annealing gives pore space with better connectivity than similar method described in literature. The accomplished analysis of three porous materials proved that differences between replicas, calculated by previous or innovated procedures, prevail on the significance with decreased total porosity of a real solid.

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