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Viscoelasticity of polymer glasses
Ondreáš, František ; Kučera,, Jaroslav (referee) ; Jančář, Josef (advisor)
This work focuses on polymer glasses relaxation behavior. Polymethylmethacrylate was chosen as a typical representative of polymer glasses. Relaxation processes were studied by dynamical mechanical spectroscopy and differential scanning calorimetry was used as a supplemental analysis. Relaxation process above Tg and high values of rubberlike plateau modulus were observed in thermomechanical spectra. High temperature relaxation transition was studied from the perspective of thermal history, frequency and axial stress dependence and influence of molecular structure was also investigated. Apparent activation energies of studied processes and their axial stress dependence for polymethylmethacrylate were determined. On the basis of obtained data, a hypothesis was developed which connects high temperature relaxation process with molecular process responsible for strain hardening.
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The influence of recycled material on weathering and accelerated aging of high density polyethylene
Borguľová, Eva ; Tocháček, Jiří (referee) ; Bálková, Radka (advisor)
The thesis deals with the testing of moulded high-density polyethylene (HDPE) samples that have been exposed to natural weather conditions for 9 months and accelerated ageing at 65 °C for 1000 hours. One sample was white in colour (made from commercial granulate) and four were black, one of which would have been prepared from 10 year old recycled material (recyclate), the other three were blends of this with white HDPE at 30, 60 and 90 % ratios. Infrared spectroscopy with ATR technique, static and dynamic tensile testing, differential compensation calorimetry and thermogravimetric analysis were used to characterize the changes in composition, structure and mechanical properties. The results showed that photooxidation occurred in all samples after the 1st month of exposure. Inhibition of degradation was noted after 3 months but increased again with time. The change in the mechanistic properties over time is a response of cleavage and recombination, but also of crystallization or crosslinking. The black color proved to be a stabiliser, as the clear samples remained largely tough after accelerated ageing, in contrast to the white sample which became quite brittle, as confirmed by the highest carbonyl index value. Thus, it can be assumed that with moderate UV stabilization the recyclable material is reusable for production, especially the proportion of 30 % (higher proportions caused a decrease in toughness).
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The influence of regranulate on structure and properties of high density polyethylene
Handlíř, Tadeáš ; Poláček, Petr (referee) ; Bálková, Radka (advisor)
The presented diploma thesis deals with the evaluation of the influence of the addition of 30, 60 and 90 % of recycled material on the structure and mechanical properties of high-density polyethylene (HDPE), where recycled material represents both HDPE from a several years old part and material multiple reprocessed by extrusion. The changes of supramolecular structure were examined by calorimetric measurement, which did not indicate degradation of the material due to multiple extrusion. Mechanical properties were investigated by tensile tests and dynamic-mechanical analysis. Both measurements showed the same trend, where the first and second pass of the material through the extruder led to improved mechanical properties, e.g. to increase stiffness, while the influence of the third and fourth passes through the extruder had not a significant effect on the mechanical properties. In terms of the structure and mechanical properties, a positive effect of the combination of material after the second extrusion passing (30%) with virgin material was recorded.
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The influence of recycled material on weathering and accelerated aging of high density polyethylene
Borguľová, Eva ; Tocháček, Jiří (referee) ; Bálková, Radka (advisor)
The thesis deals with the testing of moulded high-density polyethylene (HDPE) samples that have been exposed to natural weather conditions for 9 months and accelerated ageing at 65 °C for 1000 hours. One sample was white in colour (made from commercial granulate) and four were black, one of which would have been prepared from 10 year old recycled material (recyclate), the other three were blends of this with white HDPE at 30, 60 and 90 % ratios. Infrared spectroscopy with ATR technique, static and dynamic tensile testing, differential compensation calorimetry and thermogravimetric analysis were used to characterize the changes in composition, structure and mechanical properties. The results showed that photooxidation occurred in all samples after the 1st month of exposure. Inhibition of degradation was noted after 3 months but increased again with time. The change in the mechanistic properties over time is a response of cleavage and recombination, but also of crystallization or crosslinking. The black color proved to be a stabiliser, as the clear samples remained largely tough after accelerated ageing, in contrast to the white sample which became quite brittle, as confirmed by the highest carbonyl index value. Thus, it can be assumed that with moderate UV stabilization the recyclable material is reusable for production, especially the proportion of 30 % (higher proportions caused a decrease in toughness).
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Mechanical Properties of Hydrogels - Comparison between DMA and AFM Measurements of Elastic Modulus
Hofrichterová, Tereza ; Valentová, Helena (advisor) ; Shukurov, Andrey (referee)
Polymer hydrogels consist of polymer network that is able to absorb large amount of water. They have plenty of real-life applications - for example in medicine and diagnostics. The aim of this thesis is to study elastic modulus of several hydrogel samples by two different methods - dynamical mechanical analysis (DMA) and atomic force microscopy (AFM). Dynamical mechanical analysis represents a traditional method, which is expected to supply very reliable data. On the other hand - there has not been done much research in the field of studying mechanical properties with atomic force microscopy yet. This thesis should result into comparison of these two methods and describing effects that influence the measurement.
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The influence of regranulate on structure and properties of high density polyethylene
Handlíř, Tadeáš ; Poláček, Petr (referee) ; Bálková, Radka (advisor)
The presented diploma thesis deals with the evaluation of the influence of the addition of 30, 60 and 90 % of recycled material on the structure and mechanical properties of high-density polyethylene (HDPE), where recycled material represents both HDPE from a several years old part and material multiple reprocessed by extrusion. The changes of supramolecular structure were examined by calorimetric measurement, which did not indicate degradation of the material due to multiple extrusion. Mechanical properties were investigated by tensile tests and dynamic-mechanical analysis. Both measurements showed the same trend, where the first and second pass of the material through the extruder led to improved mechanical properties, e.g. to increase stiffness, while the influence of the third and fourth passes through the extruder had not a significant effect on the mechanical properties. In terms of the structure and mechanical properties, a positive effect of the combination of material after the second extrusion passing (30%) with virgin material was recorded.
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Mechanical Properties of Hydrogels - Comparison between DMA and AFM Measurements of Elastic Modulus
Hofrichterová, Tereza ; Valentová, Helena (advisor) ; Shukurov, Andrey (referee)
Polymer hydrogels consist of polymer network that is able to absorb large amount of water. They have plenty of real-life applications - for example in medicine and diagnostics. The aim of this thesis is to study elastic modulus of several hydrogel samples by two different methods - dynamical mechanical analysis (DMA) and atomic force microscopy (AFM). Dynamical mechanical analysis represents a traditional method, which is expected to supply very reliable data. On the other hand - there has not been done much research in the field of studying mechanical properties with atomic force microscopy yet. This thesis should result into comparison of these two methods and describing effects that influence the measurement.
|
|
|
Viscoelasticity of polymer glasses
Ondreáš, František ; Kučera,, Jaroslav (referee) ; Jančář, Josef (advisor)
This work focuses on polymer glasses relaxation behavior. Polymethylmethacrylate was chosen as a typical representative of polymer glasses. Relaxation processes were studied by dynamical mechanical spectroscopy and differential scanning calorimetry was used as a supplemental analysis. Relaxation process above Tg and high values of rubberlike plateau modulus were observed in thermomechanical spectra. High temperature relaxation transition was studied from the perspective of thermal history, frequency and axial stress dependence and influence of molecular structure was also investigated. Apparent activation energies of studied processes and their axial stress dependence for polymethylmethacrylate were determined. On the basis of obtained data, a hypothesis was developed which connects high temperature relaxation process with molecular process responsible for strain hardening.
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