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Hybrid gellan hydrogels
Borovský, Martin ; Přibyl, Jiří (referee) ; Krouská, Jitka (advisor)
The subject of this bachelor thesis was the preparation of hybrid gellan hydrogels based on the combination of physical crosslinking and ionic interaction of the functional groups of gellan with multivalent ions of selected metals. These materials were subsequently characterized by analysis on their mechanical properties, ability to swell in aquatic environment, and by studying of their rate of drying using drying scales. The results of the study indicate that hybrid crosslinked hydrogel networks provide better mechanical properties, thus these hydrogels have high application potential. From the obtained data it was found that hydrogels with the addition of multivalent ions exhibit a higher degree of crosslinking of their hydrogel network, which positively affects the resulting properties of the hydrogels. By using different types of ions at variable concentrations, the hydrogels with a wide range of properties can be prepared. In conclusion, the experimental findings are summarized and an overview of the influence of multivalent ions on the mechanical properties of hydrogels is provided.
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Effect of surface finish on degradation of wood-based structural board due to influence of moisture
Kratochvílová, Erika ; Schmid, Pavel (referee) ; Petro,, Marek (referee) ; Šlanhof, Jiří (advisor)
The aim of this dissertation is the optimisation of surface finishes for application to oriented strand board (OSB) in order to increase its moisture resistance. This is a summary of research focused on experimental verification that the application of surface finish could have significant influence on reducing thickness swelling, increasing weight of OSB due to water absorption and slowing down the rise of water in OSB. There was also verified if application of surface finishes only on the cutting edges could significantly affect the penetration of water into the OSB board. Some of used test methods were based on European technical standards, but were modified in order to determine influence of surface finishes in the long term. Alternative test method was also designed and implemented. The essence of this test method was to determine how high the water can rise in OSB. The research covered 8 different types of surface finishes available on the market. The selected finishes did not require any special treatments to be applied to the surface of the OSB itself. Based on the results, a mutual comparison and evaluation of their effects was carried out.
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Innovative wood-based materials
Buriánek, Vlastimil ; Brožovský, Jiří (referee) ; Vaněrek, Jan (advisor)
This bachelor’s thesis deals with the issue of optimizing the modification process for plywood boards. Optimization consists mainly in evaluating different densification methods with different parameters of plasticization and stabilization. Psychical parameters (bulk density, swelling, water absorption) and strength parameters (bending strength, modulus of elasticity) of modified plates were chosen for the evaluation parameters. The practical part involved the verification of two thickening treatments on birch plywood.
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The frost susceptibility of soils and materials for subgrade of pavements
Puda, Adam ; Pácha, Petr (referee) ; Stehlík, Dušan (advisor)
The bachelor thesis deals with the theoretical part of the deformation caused by frost action, but primarily frost heave, their gradual development and factors affecting their final formation. Furthermore, different ways of measuring the frost susceptibility in the Czech Republic and their comparison. Introduction to the different methods of measuring frost susceptibility in selected countries within the European Union. The practical part is focused on the process of frost heave samples with and without thermal insulation material.
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Structural and transport properties of hybrid hydrogels with application utilization
Zhurauliova, Darya ; Pekař, Miloslav (referee) ; Smilek, Jiří (advisor)
The presented diploma thesis deals with the preparation and subsequent characterization of structural and transport properties of hybrid hydrogels based on polyvinyl alcohol and sodium alginate concerning their application potential. The thesis aims to study the current state of the solved issue on the topic of characterization of structural and transport (release) properties of hybrid hydrogels about their use in various branches of human activity and also based on literature research to propose and optimize a suitable preparation procedure and to carry out a series of experiments for their characterization. With regard to the literature research, suitable polymers capable of gelation, such as polyvinyl alcohol (PVA) and natural polysaccharide – sodium alginate, were selected for the preparation of hydrogels. The preparation of this hybrid network involved the physical cross-linking of PVA by freezing and thawing and ionic cross-linking of sodium alginate with calcium ions. By combining these polymers, viscoelastic, swelling and transport properties were determined by using physicochemical methods. Rheological measurements were performed to study the mechanical properties - specifically oscillation and amplitude tests. The structural properties of hydrogels (or xerogels) were determined, by scanning electron microscopy. The transport (release) properties of gel systems were determined by diffusion experiments with the UV-VIS spectrometry detection method, in which an organic dye (methylene blue) was used as a model probe. Another aim of this diploma thesis is to modify the internal structure of hybrid hydrogels with suitable reagents, ie., lecithin. The presence of lecithin in the hybrid hydrogel three-dimensional network serves as a model of the phospholipid bilayer, forming the cell membrane or occurring in tissues, and thus has a significant effect on rheological and transport properties. Physicochemical methods also determined the mechanical, swelling and transport properties of hybrid hydrogels with the addition of lecithin. The conclusion of this work is a summary of measured data to provide a comprehensive overview of this issue. The results suggest that the presence of sodium alginate in the PVA structure reduces the mechanical properties, although the presence of lecithin increases the strength of the hybrid hydrogels. However, by comparing all measurement results, it is possible to determine that sodium alginate, resp. lecithin affects the properties and structure of the hydrogel, which makes it possible to correct the properties of hybrid gel systems according to the required applications.
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Foundations in Volume Unstable Soils
Legut, Dana ; Weiglová, Kamila (referee) ; Hauser,, Jaroslav (referee) ; Zdražil, Karel (referee) ; Vašina,, Josef (referee) ; Paseka, Antonín (advisor)
This dissertation is concerned with the foundations in volume unstable soils and objects disorders which are related to this. The thesis was focused on the study of clay and loess soils which are abundant in the geological profile of the Czech Republic. First, the formation of the two groups of soils is introduced, then their properties are examined and finally the influence of vegetation on the former type and the influence of collapsibility in the latter type are investigated. The conclusion is, in fact, a recommendation on the design of structures so that the system of clay / structure is not damaged and that structures are not subject to renovations. Several instance of problems with structures are discussed which were subject to structural repairs employing both a civil and geotechnical engineers.
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Preparation and Characterization of Mixed Hydrogels Based on the System Hyaluronan-Albumin
Hájovská, Pavla ; Kráčalík, Milan (referee) ; Kalina, Michal (advisor)
This diploma thesis deals with preparation and subsequent characterization of albumin (BSA) and mixed hyaluronan-albumin (HA+BSA) hydrogels. The experimental characterization was based on the rheological measurements of the influence of ionic strength, pH and molar mass of HA on the gelation process and the properties of formed gels, as well as the time stability of these properties. Following object of the study was swelling of hydrogels in water and buffers with different pH value. Characterization was extended by thermal analysis, morphology description using scanning electron microscopy (SEM) and study of transport properties of hydrogels for selected model substance. Due to increasing ionic strength, the gel point was shifted towards higher temperature values and the resulting gels exhibited higher values of complex moduli. In case when pH was lower than isoelectric point of BSA, attractive electrostatic interactions between albumin and hyaluronan took place and the faster gelation occurred, compared to the case when pH was higher than isoelectric point of BSA. On the contrary, values of complex moduli increased with increasing pH. The gel samples prepared in the presence of low molecular weight HA reached higher values of complex moduli, compared to samples with the high molecular weight HA. Rheological properties of BSA gels were stable over time, whereas the mixed HA+BSA were characterized by significant decrease of complex moduli during the first three days of storage. Due to heating up to 100 °C, more than 80 % of the weight of studied samples was lost, as a result of water evaporation. Further heating of hydrogels, up to 250 °C, did not cause other changes associated with weight loss, in contrast with crystalline powder BSA, in which another weight loss at 220 °C was observed, as a result of the beginning degradation. Swelling studies, as well as SEM images, indicated higher crosslink density of BSA gels, compared to HA+BSA samples, which exhibited higher values of swelling ratio. The lowest values of equilibrium swelling ratio were observed at pH 4, which is close to the isoelectric point of albumin. Calculated diffusion coefficients relative to diffusivity of methylene blue in water ranged between the order of 10E-2 for diffusion into physiological solution and the order of 10E-3 for the diffusion into water. Ongoing transport of model dye from gel to solution was significantly slower, compared to its diffusion in water, as a result of gel porosity and electrostatic immobilization of positively charged molecules of methylene blue on the negatively charged BSA and HA chains.
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Vliv chemické modifikace na vybrané vlastnosti dřevěné pružiny
Novák, Filip
This thesis focuses on the influence of chemical modification on a wooden spring.The spring was made of beech wood (Fagus sylvatica, L.). Bending ratio was chosen 1:4 thickness to radius. The effectiveness of the chemical modification with acetic anhydride was measured by weight percentage gain (WPG). Acetylation was made with 18 % WPG (at full acetylation 25 % WPG was observed damage of bent wood mostly by compression stress). Chosen spring properties was evaluated in four moisture states (dry, in condition of 65 %, 85 % and 99 % relative humidity and temperature 20 °C). Influence of acetylation on mechanical properties was proven. In wet condition acetylated samples proved higher shear modulus of elasticity a higher rigidity of spring. In dry condition acetylated samples proved lower shear modulus of elasticity a lower rigidity of spring. Influence of acetylation on dimension stability was proven. Acetylated samples proved reduction of equilibrium moisture content (46-56 %) in comparison to reference samples. Acetylated samples proved swelling reduction in radial direction (41-56 %) and in tengential direction (46-59 %). More regular swelling (ratio of radial and rangential) was observed at acetylated samples. Influence of acetylation on shape stability was proven. Shape stability of acetylated spring was evaluated by change in diameter of spring in different moisture states. Wet conditions caused enlargement of acetylated spring diameter (5-16 %) and of reference spring diameter (10-40 %). Reduction of shape changes was observed (57-75 %).
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