National Repository of Grey Literature 161 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
The Crystallization Kinetics in Semicrystalline Nanocomposites
Fiore, Kateřina ; Kučera, Jaroslav (referee) ; Chodák,, Ivan (referee) ; Lesser, Alan (referee) ; Jančář, Josef (advisor)
Růst krystalů zásadně ovlivňuje morfologii a tím také mechanické vlastnosti semikrystalických polymerů. Tato PhD práce přináší alternativní pohled na popis kinetiky krystalizace v polyolefinech plněných slabě interagujícími částicemi. V nanokompozitních materiálech vysoký specifický povrch plniva i při nízkých plněních zásadně ovlivňuje dynamiku řetězců. V blízkosti povrchu plniva začíná hrát významnou roli zpomalená reptace způsobená jak vzájemnými interakcemi plnivo-polymer tak prostorovým omezením mezi nanočásticemi. Růst krystalů byl zkoumán pomocí polarizovaného optického mikroskopu vybaveného horkým stolkem. Výsledky byly korelovány s teoretickými modely a rozsáhlými počítačovými simulacemi na molekulární úrovni. Pozorovaný pokles rychlosti růstu sférolitů v závislosti na obsahu plniva a molekulové hmotnosti matrice je interpretován na základě imobilizační teorie, tedy, zpomalení reptačního pohybu.
DEFORMATION BEHAVIOR OF NANO/MICRO REINFORCED PMMA
Recman, Lukáš ; Nezbedová, Eva (referee) ; Kučera, Jaroslav (referee) ; Jančář, Josef (advisor)
Práce sleduje vliv velikosti částic na elastický modul a deformační chování za mezí kluzu. Bylo pozorováno, že jak elastická oblast, tak oblast za mezí kluzu ukazuje silnou závislost chování na velikosti částic. Cílem této práce je korelovat experimentální data a teoretické předpoklady které bylo odvozeny pro deformační chování v elastické oblasti a v oblasti za mezí kluzu pro amorfní polymery a konkrétně pro PMMA. Vše je motivováno propojit zatím oddělené oblasti kontinuální mikromechaniky a diskrétní nanomechaniky. Deformační chovaní PMMA plněného nano a mikro plnivem bylo pozorováno v elastické a plastické oblasti. Byl zkoumán vliv velikosti částic na velikost modulu a deformačního zpevnění. Mechanizmus vyztužení je interpretován s použitím teorie imobilizace řetězců, nanočástice mají silný vliv na molekulární dynamiku a kinetiku zapletenin. Mým příspěvkem k tomuto tématu je ukázat výraznou závislost na mechanizmu vyztužení v závislosti na velikosti částic. A to jak pod teplotou skelného přechodu tak nad teplotou skelného přechodu. Ačkoli pro velikost modulu byla publikována značná množství dat, která byla následně i interpretována, vliv částic na deformační zpevnění je poskrovnu. Během elastické deformace je primární struktura materiálu neměnná, jedná se o elastickou deformaci, za mezí kluzu již toto neplatí a primární struktura je zde nevratně poškozena. Bylo ukázáno, že obsah nano částic vede ke zvýšení meze kluzu a vyššímu deformačnímu zpevnění. Tento nárůst deformačního zpevnění je v korelaci s Guth-Gold rovnicí. Je předpokládáno, že nanočástice slouží jako další fyzikální zapleteniny a vedou k fyzikálně více zapletenému systému. Stejný efekt jako v elastické oblast tj. vliv velikosti částic na modul, byla pozorována i během deformačního zpevnění.
Physical ageing of polypropylene
Weiss, Jiří ; Kučera, Jaroslav (referee) ; Tocháček, Jiří (advisor)
Physical aging of commercially produced polypropylene homopolymers Mosten was studied. The work is focused on monitoring the changes in physical properties of polymer in the time period 90 days from the date of preparation of the test specimen. The aging of polymers was realized at storage temperatures of 23 and 80 °C. The changes in crystallinity, yield strength, modulus, elongation and impact strength using DSC method, tensile tests and impact tests according to Charpy were monitored. Molecular weight distribution was determined by means of GPC at each polymer. Relationships between the changes in physical properties and polymer molecular weight were sought.
Solubility of polypropylene in hydrocarbon solvents
Urbánková, Radka ; Kučera, Jaroslav (referee) ; Kratochvíla, Jan (advisor)
Polypropylene, on a mass-scale produced polyolefin, shows an excellent combination of end-use properties, eco-friendliness, easy recyclability, and a good processability by different technologies. Key structural parameters of polypropylene are its stereoregularity, molecular weight, and its distribution. A theoretical part of this work compiles a bibliographic search and an experimental part deals with extraction and solubility of polypropylene powder prepared on a highly active Ziegler-Natta polymerization catalyst. Extractions at a boiling point temperature of solvents (pentane - hexane - cyclohexane - hex-1-ene - benzene - heptane - octane - ethylbenzene) resulted in a progressive increase of extracted portions with temperature of extraction. Solvents used within this work were characterised by their physical properties, and steric and electronic parameters such as molecular weight, density, boiling point temperature, dipole moment, refractive index, and Hildebrand´s solubility parameter. Extraction PP at a constant temperature 36°C (boiling point of pentane) at a saturated vapour pressure in a series of hydrocarbon solvents (pentane – hexane – heptane – octane) resulted in practically the same results. Boiling octane extractable fraction at a temperature 36°C was nearly 100 % higher than fractions extracted by the other solvents. The origin of this phenomenon has not been revealed. Polypropylene solubility was determined by a complete dissolving the sample at 140°C in a series of aliphatic and aromatic solvents (pentane - hexane - cyclohexane - hex-1-ene - benzene - heptane - octane - toluene - ethylbenzene - o-xylene - m-xylene - p-xylene - decalin - chlorbenzene - 1,2-dichlorbenzene), followed by cooling the solution down to a laboratory temperature, and separating a soluble fraction, and an insoluble one. The stereoregularity of soluble fractions was characterised by a 13C NMR method, the crystallinity by a DSC method, and a molecular weight distribution by a GPC method. As a result, polypropylene solubility decreases with increasing the Hildebrand solubility parameter of the solvent that corresponds with theoretical expectations. Moreover, PP solubility correlates strongly with a refractive index, and a density of solvent.
CAD systems and design documentation
Kučera, Jaroslav ; Veselka, František (referee) ; Kuchyňková, Hana (advisor)
Project is specialized to work on modern CAD systems. Introduction treats of the development technical drawing and separates it into periods. There are compared two programs from Autodesk – AutoCAD a Inventor in the next part. Program Autodesk Inventor 2008 Suite is shown in more detail and project show innovations in this program compared to last versions. Work on Autodesk Inventor is shown at production of model of elementary electrotechnic equipment, technical documentation and presentation. This model, engineering drawings and presentation are the part of enclosure project. In end of project is attempt at the look to future of technical drawing.
Thermal Dilatation Measurement of Elastomeric Plastic Sheets
Mahel, Jindřich ; Kučera, Jaroslav (referee) ; Petrůj, Jaroslav (advisor)
The aim of the thesis was to design and build an apparatus for measuring linear thermal expansion of plastic waterproofing sheets. In the theoretical part of the thesis the methods used for measuring linear thermal expansion of solids were compared and the principle of thermoelectric cooling was described . For the measuring the Abbe comparator has been chosen , which has been equipped with a tempered chamber with a cascade of thermoelectric Peltier elements for cooling and heating of specimen. The experimental part of the thesis deals with the construction of the device and the actual measuring in the specified temperature range.
Modification of Polyethylene by Reactive Compounding
Horkel, Ondřej ; Kučera, Jaroslav (referee) ; Petrůj, Jaroslav (advisor)
This Master’s thesis deals with the problematics of radically initiated compounding of polyethylene by 1-vinyladamantane. Theoretical part focuses on the theory of grafting processes and how they are influenced by chosen process parameters, as well as the properties of used monomer. In experimental part, two sets of experiments were designed, in both cases the chemicals used were polyethylene LITEN MB 87, (2,5-dimethyl-2,5-bis(tert-butylperoxy) hexane), also called Trigonox 101, as the initiator, and chemicals called Ionol and Irgafos 168 as stabilizers. The experiments were carried out in a Brabender batch mixer, the temperature was 180 – 185 °C, the reaction time was 5 minutes. The analytic methods used to evaluate the prepared samples’ properties were the tensile testing, the Charpy notch test, measuring of the melt flow index, analyzing the torque during kneading and the analysis of infrared spectra of the samples. By carrying out of these experiments it was found that excessive crosslinking was present with mass fraction of initiator being as low as 2 %. It was also concluded that under these conditions the modification does not improve tensile properties of the material, but it does improve the impact strength, albeit slightly. The influence of the modification on flow properties needs to be investigated further. A presence of vinyl groups was observed in infrared spectra, suggesting the presence of ungrafted vinyladamantane.
Description of Failure of the Multilayer Polymer Structure
Zouhar, Michal ; Klusák, Jan (referee) ; Kučera, Jaroslav (referee) ; Hutař, Pavel (advisor)
The aim of this thesis is to describe behavior of cracks in layered polymer materials. Quasi-brittle fracture (through the initiation and subsequent crack propagation mechanism) under low stresses is the most common mode of failure of polymer materials. In this case plastic deformations are localized in the vinicity of the crack tip and linear elastic fracture mechanics description of the crack behavior can be used. The knowledge of fracture parameters change during the crack propagation in multilayer body is a key point for establishing of the maximum load and consequently for the assessment of the residua lifetime. In contrast to homogeneous bodies the estimation of stress intensity factors for multilayer (composite) structure is numerically more elaborated and the fracture mechanics approach is complicated by the existence of interfaces between single layers, where material parameters are changed by a step. Special attention is paid to the configuration of a crack growing close to the material interface and along the interface. For the crack with tip on the material interface the effective values of stress intensity factor based on the crack stability criteria are estimated. It is shown that under special conditions (depending mainly on the elastic mismatch of materials) the existence of material interface has positive influence on the lifetime of the multilayered structure.
Study of conditions influence on the rate of crack propagation in HDPE
Patzelt, Petr ; Kučera, Jaroslav (referee) ; Petrůj, Jaroslav (advisor)
Theoretical part of the thesis is aimed on the summary of material and testing parameters that influence SCG process and also the duration of FNCT test. The experimental part deals with the comparison of time to crack between two used surfactants – 2% Arkopal N110 and 10% sodium dodecylbenzenesulfonate. The temperature during the experiments was 80 °C. The acceleration of the process influenced by solution of sodium dodcelbenzenesulfonate was many times higher against solution of Arkopal. There were tested several HDPE and PP specimens to prove this phenomenon. HDPE specimens used – VB85, VL 20N, PL 10 that were made in UNIPETROL RPA and some other competitive materials were used. PP specimens were developed in labs of Polymer Institute Brno. In additional, another experimental part focuses on evolving the math definition of curves measured within FNCT tests and it is still in progress.
Management Competencies in a Multicultural Environment of the STUDENT AGENCY Ltd.
Kučera, Jaroslav ; Kopřiva, Martin (referee) ; Konečná, Zdeňka (advisor)
This bachelor thesis treat of competency of the manager. About difficulties, which can be in communication in multicultural environment of company. This work includes basic informations about roles of manager. In practical part autor deal with multicultural environment of company STUDENT AGENCY, Ltd. Aim of this work is to identify components intercultural competencies manager bus service in this company.

National Repository of Grey Literature : 161 records found   1 - 10nextend  jump to record:
See also: similar author names
80 KUČERA, Jan
24 KUČERA, Jaroslav
40 KUČERA, Jiří
18 KUČERA, Josef
1 Kučera, J.
16 Kučera, Jakub
80 Kučera, Jan
1 Kučera, Jaromír
1 Kučera, Jiljí
40 Kučera, Jiří
6 Kučera, Jonáš
18 Kučera, Josef
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80 Kučera, Ján
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