|
|
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.
|
|
|
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.
|
|
|
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.
|
|
|
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.
|
guest ::
