Národní úložiště šedé literatury Nalezeno 2 záznamů.  Hledání trvalo 0.01 vteřin. 
Bioresorbable polyurethanes with controlled mechanical properties
Letavaj, Emil ; Žídek, Jan (oponent) ; Kupka, Vojtěch (vedoucí práce)
Presented diploma thesis deals with preparation of bioresorbable polyurethanes (PUR) and their characterization. The theoretical part describes the feedstocks used for the PUR preparation and summarizes the knowledge about PUR used in medical applications. Experimental part presents characterization of bioresorbable PUR films prepared by reactive casting in one step without the use of organic solvents. The absence of solvents represents a great advantage due to their toxicity and subsequent removal from the resulting product. The synthesis of PUR was conducted under an inert atmosphere by polyaddition reaction of hydrophobic poly(e-caprolactone) (PCL) and hydrophilic poly(ethylene glycol) (PEG) with hexamethylene diisocyanate (HDI). Synthesis under an inert atmosphere was necessary due to a side reaction of isocyanate with atmospheric humidity, which causes the formation of porous films instead of continuous ones. Prepared PUR films were characterized for different PCL/PEG ratios and different isocyanate index (ratio of NCO/OH reacted groups). PUR (isocyanate index 1.05) with PCL content 90 wt. % and higher demonstrated tought behavior in mechanical tests. Increase of isocyanate index and decrease of PCL content under 90 wt. % caused fragile sample behavior. The reason of such behavior was the different ability of PCL to crystallize in the structure of the polyurethane network. Increasing the PEG content has improved the ability of PUR films to absorb water and enhanced the rate of hydrolytic degradation. By adjusting the PCL/PEG ratio and the amount of isocyanate, solvent free bioresorbable PUR with suitable mechanical (flexibility, toughness) and physical properties (swelling, degradation) can be obtained. Prepared PUR films could be used in biomedicine e.g. as vascular grafts.
Pultrusion process of composite based on natural fibres
Letavaj, Emil ; Bábík, Adam (oponent) ; Přikryl, Radek (vedoucí práce)
The theoretical part of bachelor thesis is focused on general overview of composite materials, natural fibers and their various modifications. The practical part is based on chemical treatment of flax fibers by two types of silanes, in order to optimize the interface between the phases in the composite material. Such modified fibers were applied to produce composites by pultrusion technological process. In conclusion, the impact of chemical treatment of flax fibers was reviewed on the mechanical properties of the resulting composite profiles.

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