National Repository of Grey Literature 89 records found  1 - 10nextend  jump to record: Search took 0.01 seconds. 
Flame retarded polyolefins
Pařízek, Jan ; Poláček, Petr (referee) ; Kučera, František (advisor)
The theoretical part of the bachelor thesis deals with topics related to polyolefins and flammability of polymeric materials. The mechanisms of action of the most common flame retardants and methods of flame characterization are described. In the experimental part, polypropylene samples with flame retardants were prepared. The substances used were based on ammonium polyphosphate, melamine polyphosphate, aluminium hydroxide and expandable graphite. The samples were tested for flammability according to UL 94. Subsequently, the solubility of the polymer/flame retardant mixtures in water was investigated by Soxhlet extraction.
Inflence of Granulation to Sorption Properties of Expanded Graphite
Hladík, Jakub ; Poláček, Petr (referee) ; Kučera, František (advisor)
Expanded graphite is one of the promising sorption materials, but its disadvantage is difficult handling. This thesis deals with the granulation of expanded graphite and the effect of granulation on oil sorption. Samples with a starch and dextrin binder were prepared. Samples filled with cellulose fibers and wood flour were prepared with a starch binder. The strength of the granulate was determined from the sub-sieve fraction. The sorption capacity was determined gravimetrically after 30 minutes of oil immersion. The granulate filled with a lower amount of wood flour achieved the highest sorption capacity. The addition of cellulose fibers substantially strengthened the granulate. Based on the previous results, a granulate of a defined shape and size was prepared. The morphology of the granulate was observed by scanning electron microscopy.
Composite materials with enhanced coefficient of linear attenuation of ionizing radiation
Novotný, Kamil ; Petruš, Josef (referee) ; Kučera, František (advisor)
Ionizing radiation has many useful applications in the fields of healthcare, food industry, nuclear energy and others but poses a hazard to human health in higher doses. In this work, composite materials with enhanced ionizing radiation attenuation properties were prepared. Unsaturated polyester resin was reinforced with inorganic fillers containing elements such as bismuth or barium. Morphology of the samples was studied using scanning electron microscopy. Theoretical values of mass attenuation coefficients were obtained for photon energies 662 keV and 1253 keV using the XCOM software. The attenuation of ionizing gamma radiation was experimentally measured using radioactive sources 137Cs and 60Co. Linear attenuation coefficients and half value layers of the materials were determined using the obtained data. Addition of the fillers improved the shielding properties of the matrix. Composite containing bismuth oxide achieved the highest values of linear and mass attenuation coefficients. The experimental results were found to be in good agreement with theoretical values. Moreover, influence of the fillers on impact toughness has been evaluated.
Butyl Rubber Modified Using Expanded Graphite
Žůrek, Michal ; Petruš, Josef (referee) ; Kučera, František (advisor)
This work deals with the influence of expanded graphite (EG) as a reinforcing filler on the mechanical and tribological properties of vulcanizates of butyl rubber blends. Tensile strength, elongation at break, moduli (M100, M200, M300 a M500), and Young's modulus of elasticity of the prepared vulcanizates were studied by the tensile test method. In addition to the tensile test results, the dispersion of EG particles was studied on scanning electron microscopy (SEM) images of the fracture surfaces of the prepared vulcanizates. The filler-matrix interaction was evaluated using the Kraus model for filled rubber and the results were subsequently compared with SEM images of the EG particle-matrix interface on the fracture surfaces of the vulcanizates. The effect of EG on the properties of the vulcanizates was compared with the effect of common rubber blacks (N220 and N772). It was found that an important factor affecting the mechanical properties of filled vulcanizates is the dispersion of filler particles. EG dosage higher than 5 phr promotes the agglomeration of filler particles in the butyl rubber matrix, which negatively affects the mechanical properties of the blend. Vulcanizates filled only with EG have lower tensile strength than those filled with N220 or N772 blacks. By choosing an appropriate ratio of EG to blacks, higher mechanical strength was achieved than with the use of only one filler.
Biodegradable thermoplastics from renewable resources
Březinová, Štěpánka ; Kučera, František (referee) ; Petruš, Josef (advisor)
The theoretical part of diploma thesis summarizes the state of the art in the field of biodegradable thermoplastic materials, emphasizing polymeric materials made from renewable sources and the possibilities for their processing and for the modification of their useful properties. The experimental part of the thesis is focused on the preparation and characterization of biodegradable polymer blends based on thermoplastic starch (TPS) and poly(butylene adipate-co-terephthalate) (ECX). A suitable type of TPS was selected according to the rheological behavior of the melt for blending with ECX via extrusion technology. The degree of compatibility between TPS and ECX was evaluated by infrared spectroscopy (FTIR-ATR) and by examining the morphology of TPS/ECX blends using scanning electron microscopy (SEM). Affecting the mechanical properties, rheological behavior, and wettability of the prepared TPS/ECX was verified by testing the mechanical properties under tensile stress, determining the melt flow index (MFI), employing the oscillatory rheological test, and determining the maximum wettability. The experimentally obtained results show the possibility of optimizing the mechanical and rheological properties of TPS by blending with ECX. In terms of biodegradability, blends with a majority TPS content can be assumed to be more advantageous.
Copolymeric Acrylamide Gels: Preparation and Properties
Nováková, Pavlína ; Petruš, Josef (referee) ; Kučera, František (advisor)
The bachelor thesis deals with the preparation and properties of copolymer acrylamide gels. The theoretical part is focused on the general characteristics of gels, closer look at copolymeric acrylamide gels – preparation methods, various possibilities of initiation, crosslinking, and use of comonomers. Factors influencing swelling of the gel were described. The experimental level focuses on the preparation of neutral polyacrylamide gel and acrylamide copolymeric gel with anionic component, sodium acrylate. First, the formation of the copolymer and the presence of functional groups were verified by infrared spectroscopy with Fourier transformation. Then gels of different concentrations of sodium acrylate and the crosslinking agent, bisacrylamide, were prepared by radical solution polymerisation. The influence of the gel composition on the swelling degree in distilled water was investigated on the prepared samples. The selected samples were then swelled in environments of different pH and ionic strengths to assess the influence of the external environment on the swelling degree.
Inorganic flame retardants and their application in composites
Bergmann, Ondřej ; Kučera, František (referee) ; Poláček, Petr (advisor)
In the first part of this bachelor thesis frequently used fire retardant additives are described as well as their mechanisms of action and the most common methods of flammability characterization. In the second experimental part the influence of two systems, consisting of a matrix and two fillers in different ratios, on viscosity, thermal stability and flammability were examined. Unsaturated polyester resin was used as the matrix. The first filler was always a fire retardant based on aluminium hydroxide, which was combined with the second filler based on either ammonium polyphosphate, or melamine polyphosphate. Viscosity of these samples was determined and casts for further analyses were made. Casts were analysed with thermogravimetric analysis and by flammability tests. Generally, with higher filler content the samples were more viscous, thermally degraded at lower temperatures and had better fire characteristics.
Electrical behaviour of polymeric composites with expanded graphite
Šimonek, Michal ; Petruš, Josef (referee) ; Kučera, František (advisor)
Electrically conductive thermoplastic composites made from graphene nanoplatelets or graphene precursors are a promising branch of new functional materials. Graphene nanocomposites were prepared via processing in an internal mixer from four extrusion grade polyethylenes (PE) and expanded graphite (EG). As a method of possible improvement of EG dispersion, compounding in presence of various compatibilizers is examined. Melt compounding was performed for 10 min at 200 °C and 60 rpm. The electrical conductivity of compression-molded samples was determined from a current voltage characteristic or direct resistance measurement. Composite morphology was characterized by scanning electron microscopy. Depending on the PE matrix and compatibilizer structure, different electrical conductivities and morphologies were observed, which corresponded in agreement with either percolation theory or the random-resistor network of Miller and Abrahams models. Substantial reduction of percolation threshold was achieved in compatibilized ultra-low density polyethylene where percolation occurred at 3,92 % vol.
Biodegradable seed carriers for large area regeneration of forests
Balej, Marek ; Kučera, František (referee) ; Jančář, Josef (advisor)
This diploma thesis is focused on finding a suitable biodegradable polymer for the construction of mechanically activated forest seed carriers. The subject of the theoretical part of the work is a description of the investigated polymeric materials and characterization of the species composition of trees in domestic forests. Furthermore, the issue of technology to produce these seed carriers for the preparation of prototypes using 3D printing and for high-volume production through plastic injection moulding is elaborated. Finally, in this section, attention is paid to the difference between biodegradable and compostable plastics. The experimental part of the thesis deals with the application of the method of determining the complete aerobic biodegradability of the investigated materials in the soil, measuring the amount of carbon dioxide released and additional DSC, GPC and TGA analysis. It further investigates the saturation of the samples with carbon dioxide, their subsequent temperature-induced batch foaming and SEM analysis of the resulting structure. Finally, it focuses on the preparation of 3D printed prototypes of seed carriers and test specimens, on which the tests of their impact strength and tensile properties are performed. For more detailed analysis, two commercially available bioplastics, NonOilen® and ecoflex® were selected. The test of complete aerobic biodegradability of plastics in soil according to ISO 17556 proved that the biodegradation of NonOilen® and ecoflex® in the soil took place. This was subsequently substantiated by the results of the associated DSC, GPC and TGA analysis. Furthermore, in pressed samples from both materials, it was found by SEM observation that the method of CO2 saturation and subsequent batch, temperature-induced foaming is ineffective in obtaining a porous structure in the given materials. Finally, the impact strength and tensile properties of 3D printed prototypes for the investigated materials (NonOilen® and ecoflex®) were determined using 3D printed test specimens.
Influence of Mixing Line Parameters Adjustment on Mixture´s Properties
Smiřický, Jan ; Kučera, František (referee) ; Petrůj, Jaroslav (advisor)
The main goal of this thesis is to set optimal rubber mixture processing parameters in Barum Continental Ltd. Dispersion is one of the most important tire production steps. Although rubber mixing has been researched by several generations of experts, there are still some unexplored influencing variables. The automotive companies are keen on the reduction of emissions and therefore pushes the tire manufactures as they can contribute to emission reduction, as well as the enhancement of tire toughness. Enhancement of tire toughness causes the decreasing of rolling resistance. Higher toughness is exhibited by tires made of rubber filled by surface modified silica. Silica filled mixtures creates a three-dimensional net which is capable to coexist with a net made by vulcanization reaction. Other goals of this thesis are to understand the process and technologies used for mixing rubber mixtures designated for tire production.

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6 Kučera, Filip
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