National Repository of Grey Literature 6 records found  Search took 0.00 seconds. 
Preparation and characterization of lightweight polymer materials with hierarchical cellular structure
Režnáková, Ema ; Ondreáš, František (referee) ; Lepcio, Petr (advisor)
The asymmetrical arrangement of cellular structure allows for an accurate functional adaptation at all levels of hierarchy, which derives excellent features for the development of new materials. The main objective of introducing a hierarchy into cellular structures is to improve the mechanical behaviour of the material while maintaining its elastic properties. A part of this work is devoted to the literature review related to the lightened cellular polymeric materials with hierarchical cellular structure. The rest is focused on the preparation of PLA based polymer structures using 3D printing, followed by a saturation in CO2 and a foaming in a silicon oil at elevated temperature. Samples were prepared from natural and white PLA filaments. Based on a series of experiments, optimal conditions for the saturation and foaming process were identified. Through 3D printing and foaming, a one-, two- and three-level hierarchy was introduced into the beam-shaped samples and the effect of the internal cell arrangement on the strain response of the material was examined by the means of a mechanical three-point bending test. Increasing the level of the hierarchy led to an increase in material resistance, which resulted in high values of strength and strain energy (toughness) based on the samples density. The best results were achieved by samples with “sandwich” structure with three levels of hierarchy and 30% filling. Despite the shorter plateau, there was a significant increase in strength and strain energy compared to gradient structures. At the same time, the contribution of the polymer structures prepared in this field of research was demonstrated by comparison with the theoretical model.
Processing optimalization of biodegradable starch based packaging and its characterization for adaptation on production technology
Krahulová, Veronika ; Ondreáš, František (referee) ; Lepcio, Petr (advisor)
This diploma thesis focuses on the problematics of preparation of biodegradable starch based packaging. The aim of the thesis is to optimize the preparation and verify the characteristics for further adaptation and production technologies. The films consisted of starch, PVA and glycerol. Four types of starches, three types of PVA and different ratios of glycerol were tested. Films were prepared by casting with glycerol as a plasticizer, instead of distilled water, to reduce the energy cost of the preparation. The mechanical properties of the films were tested as well. The experimentally determined values of elongation at break and tensile strength of the wheat starch films were compared with a semiempirical model. Results revealed that the preparation of thermoplasticization of starch with glycerol leads to a considerable increase in elongation at break but at the same time to a marked decrease in tensile strength compared to the preparation from solution. The rheological properties of the prepared films were also investigated. Infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to study the structure of the films.
Structure and properties of physically foamed polymer nanocomposites
Kotoučková, Simona ; Ondreáš, František (referee) ; Lepcio, Petr (advisor)
This work deals with physically foamed polymer nanocomposites. The theoretical part of the thesis deals with various possibilities of preparation of polymer foams. Another important problematics on which the theoretical part focuses is the ability to control the spatial organization of nanoparticles in a polymer matrix. For the experimental part, polymethyl methacrylate (PMMA) was used as a model system, and it is assumed that it will be possible to based on the obtained conclusions on research in more complicated systems with a wider practical application potential such as polypropylene impact-copolymer (ICPP). The experimental part focuses on optimalization of the process of preparing nanocomposite foam. The object of optimization is to determine the appropriate saturation time when maximum carbon dioxide saturation is achieved under a given pressure. The effect of nanoparticles on the process of saturation and foaming was analyzed by comparing nanocomposites with the preparation of pure polymer foams. On the prepared foam samples, the shape stability during foaming and the dimensional stability after foaming at elevated temperature were evaluated. The effect of nanoparticles on the resulting structure of porous material was evaluated. This effect was demonstrated by the preparation and evaluation of acquired SEM images of a laminar structure sample containing a composite and a pure polymer layer.
Effect of sub-micrometer structural features on rheology of polymer nanocomposites
Lepcio, Petr ; Chodák,, Ivan (referee) ; doc.Ing.Marián Lehocký, Ph.D. (referee) ; Jančář, Josef (advisor)
Polymerní nanokompozity (PNCs) mají slibnou budoucnost jako lehké funkční materiály zpracovatelné aditivními výrobními technologiemi. Jejich rychlému rozšíření však brání silná závislost jejich užitných vlastností na prostorovém uspořádání nanočástic (NP). Schopnost řídit disperzi nanočástic je tak klíčovým předpokladem pro jejich uplatnění ve funkčních kompozitech. Tato práce zkoumá přípravu polymerních nanokompozitů v modelové sklotvorné polymerní matrici roztokovou metodou, technikou schopnou vytvářet prostorové uspořádání nanočástic řízené strukturními a kinetickými parametry přípravného procesu. Prezentované výsledky popisují rozdíly mezi změnami rheologického chování roztoku polystyrenu při oscilačním smyku s vysokou amplitudou (LAOS) vyvolanými nanočásticemi. Výsledky vedou k závěru, že vysoce-afinní OP-POSS nanočástice při nízkých koncentracích dobře interagují s PS a tvoří tuhé agregáty, zatímco nízko-afinní OM-POSS nanočástice za těchto podmínek neovlivňují deformační chování polymerních řetězců. Dále byla pozornost zaměřena na vliv použitého rozpouštědla na uspořádání nanočástic v SiO2/PMMA a SiO2/PS nanokompozitech, který je v literatuře prezentován jako parametr řídící prostorové uspořádání nanočástic v pevném stavu. Důraz byl kladen na kvalitativní rozdíly mezi „špatně dispergovanými“ shluky nanočástic, které byly na základě rheologie a strukturální analýzy (TEM, USAXS) identifikovány jako polymerními řetězci vázané nanočásticové klastry a dva typy agregátů, jeden termodynamického a druhý kinetického původu. Jednotlivé druhy agregátů se vyznačují odlišnými kinetikami vzniku a rozdílnými vlastnostmi jak mezi sebou, tak v porovnání s dispergovanými nanočásticemi. Pozorované typy disperze nanočástic byly kvantitativně posouzeny podle svých rheologických vlastností během roztokové přípravy, podle kterých byla vyhodnocena míra adsorpce polymeru na povrch nanočástic a atrakce ve vypuzeném objemu. Výsledky byly porovnány s teorií PRISM. Důležitost uspořádání nanočástic byla demonstrována na porovnání teplot skelných přechodů různých struktur při stejném chemickém složení.
Preparation and characterization of self assembled polymer nanocomposites
Lepcio, Petr ; Žídek, Jan (referee) ; Jančář, Josef (advisor)
Polymerní nanokompozity na bázi polyhedrálních oligomerních silsesquioxanů (POSS) představují slibnou oblast výzkumu, která potenciálně může využít samouspořádávní při navrhování nových materiálů. Tato diplomová práce popisuje postup přípravy oktafenyl-POSS/PS, oktafenyl-POSS/PMMA a oktamethyl-POSS/PS systémů a charakterizaci jejich termomechanických vlastností v pevné fázi a reologických vlastností v roztoku. Získané výsledky jsou diskutovány s přihlédnutím k teoriím zabývajících se stavem disperze nanočástic.
Adhesion of a-SiOC:H films on planar substrates
Lepcio, Petr ; Salyk, Ota (referee) ; Čech, Vladimír (advisor)
This bachelor thesis deals with preparation of thin films of plasma polymers prepared by plasma-enhanced chemical vapor deposition. Tetravinylsilane was used as a monomer. Two sets of samples were prepared. Samples of the first set were prepared at different effective powers from pure tetravinylsilane and samples of the second set were prepared from deposition mixture of tetravinylsilane with different oxygen content at constant effective power. The film thickness was evaluated by spectroscopic ellipsometry and chemical structure by infrared spectroscopy. A scratch test was used to determine adhesion characterized by the critical normal load. An appearance of performed scratches was obtained by atomic force microscopy (AFM). Film adhesion influenced by the effective power and oxygen content in deposition mixture was discussed based on the received data.

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