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Influence of selected agents on crystallization power of polylactide
Kurakin, Yuriy ; Přikryl, Radek (referee) ; Bálková, Radka (advisor)
The influence of seven additives on the crystallization ability of polylactide (PLA), melt flow index (MVR) and mechanical tensile properties was studied. Pressed plates with a thickness of 0.8 mm were tested. Selected additives added in amounts of 0.5 and 1.0% were as follows: talc, sodium benzoate, mixtures of organic salts with amorphous SiO2 and zinc stearate, metal salt, phosphate salt, and potassium salt of 5-dimethylsulfoisophthalate (LAK-301 - nucleating agent developed for PLA). Non-isothermal crystallization measurements were performed at different cooling rates (0.3; 0.5; 0.7; 1.0 and 1.5 ° C). All nucleation agents increased the MVR of PLA except talc; the largest increase (9-fold and 24-fold) was the addition of metal salt. The additives did not fundamentally change the mechanical properties. All samples were rather brittle (the most brittle with LAK-301), the modulus of elasticity was around 1.2 GPa for all samples, the strength of PLA was increased the most by the addition of 1% talc (by 12%) and the elongation at break was increased by organic salt with SiO2. All samples with nucleating agents content of 1% were amorphous (crystalline content did not exceed 2%). Thus, the addition of reagents did not support the crystallization process during rapid cooling, even in the case of LAK-301. However, LAK-301 was acting as an excellent nucleating agent at slow cooling rates (1.5 °C / min and below). The nucleation activity of the additives decreased in the following order: LAK-301, organic salt with zinc stearate, talc, organic salt modified with amorphous SiO2 and phosphate salt. Samples with sodium benzoate and metal salt were crystallizing on cooling in several steps and it was not possible to use the method of Dobrev and Gutzow to evaluate the nucleation activity.
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The influence of detergents on time to failure of high density polyethylene by full notch creep test performed in corrosive bath
Kotoučková, Simona ; Tocháček, Jiří (referee) ; Bálková, Radka (advisor)
The thesis deals with the study of the influence of concentration and different types of surfactants (Igepal CO-520, Arkopal N110, Igepal CO-890, sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, dodecyltrimethylammonium bromide and Dehyton PL) on the environmental stress cracking resistance of high-density polyethylene by means of Full Notch Creep Test. Furthermore, the influence of ligamental stress (3,5; 4,0 a 4,5 MPa), pH of the prepared active environment and type of the water used as a solvent for the surfactants on the time to failure was monitored. An accelerating effect was observed at increased concentration, stress and molecular weight. Faster failure was achieved after exposure to ionic types compared to nonionic. The rate of the notch opening was determined. The brittle and ductile behavior during the process of failure was evaluated by microscopic analysis of the morphology of the fracture surfaces. Based on the pH change after the test, the stability of the active environment was evaluated. Deteriorating quality of surfactant solutions was observed. Raman spectroscopy and Fourier transform infrared spectroscopy were used to detect the surfactant on the surface of the test specimen after the test.
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Crystallization of binary polylactide blends and their morphology
Debnáriková, Michaela ; Poláček, Petr (referee) ; Bálková, Radka (advisor)
Master thesis deals with the influence of polyvinylacetate, polycaprolactone, poly(butylene-adipate-co-terephtalate) and talc, ethylenevinylacetate, polyethylene glycol and monosodium citrate on the flow properties, mechanical properties and crystallization ability of PLA. The flow properties were studied using the melt flow index and mechanical properties were studied using a tensile test. The crystallinity was studied by differential scanning calorimetry and on a polarization optical microscope equipped with hot stage. Isothermal crystallization was performed at 95 and 105 °C for 3 h and non-isothermal crystallization was performed with a calorimeter at two cooling rates (1 and 10 °C/min). Upon the isothermal crystallization at 95 °C, the formation of denser crystalline structure was observed and the content of crystalline phase increased in most of the samples. The formation of spherulitic structure was observed at 105 °C in samples with 30 % PVAc, 30 % EVA and PEG. Reducing the cooling rate to 1 °C/min at non-isothermal crystallization had nearly no effect on the crystallization process of the most samples; the content of crystalline phase increased in the samples containing PBAT and PEG, which revealed double melting peak during subsequent heating. The crystalline fraction was the most significantly affected by the addition of PEG. All added polymers except PVAc affected the mechanical properties; PBAT, PCL, EVA and PEG increased the strain and decreased the strength and modulus of elasticity. The samples containing monosodium citrate showed unsatisfactory mechanical properties and could not be measured. The samples containing higher concentration of EVA copolymer showed the phase separation.
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Properties of pultruded composites based on epoxy matrix
Huljak, Pavel ; Bálková, Radka (referee) ; Přikryl, Radek (advisor)
The theoretical part of this bachelor thesis deals with research of composite materials, especially based on polymer epoxy and polyester resins, using as reinforcement a glass fiber bundles. The practical section includes the production of composite materials and their components along with the most important testing methods. The main goal of the experimental part is to characterize the optimal conditions pultrusion production of epoxy composite material. Another point is characterization of mechanical and chemical properties of the produced composite at a number of test methods. Finally the optimized epoxy composite materials are compared with composites based on polyester resins.
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Morphology of Polyamide 12 and Polyamide 11 formed at overpressure and underpressure
Bělašková, Marie ; Tocháček, Jiří (referee) ; Bálková, Radka (advisor)
In this master thesis it was studied morphology of polyamide 12 (PA12), polyamide 11 (PA11) and their blends in the percent ratios 95/5, 75/25, 50/50, 25/75 and 5/95 formed at pressure 7 MPa in a calorimeter both after continual heating and cooling and after annealing and isothermal crystallization. Neat polyamides and blends were further characterized by thermogravimetric analysis, differential scanning calorimetry at atmospheric pressure, Fourier-transform infrared spectroscopy in attenuated total refection, and X-ray diffraction analysis. The increased pressure improved level of polyamide chains ordering in crystal lamellae. Thermal annealing improved especially ordering of PA12, isothermal crystallization led to considerable increase of crystallinity, whereas PA11-rich blends supported perfection of PA12 crystals. Partial transformation of - to -structure occurred in case of neat PA12 at high pressure, the change of the chain conformation into the closer one occurred in neat PA11 without transformation of the type of crystal structure.
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Weathering and accelerated aging of high density polyethylene mixtures with regranulate
Bruzl, Dominik ; Tocháček, Jiří (referee) ; Bálková, Radka (advisor)
This master thesis deals with the effect of multiple extrusion (1, 2, 3) and the addition of 30, 60 and 90 % of this recycled material on the weathering and accelerated ageing of high density polyethylene (HDPE) copolymer. The weathering lasted 9 months and the accelerated ageing 1000 h at 65 °C. The degree of material degradation was assessed from changes in mechanical and physical properties and compositional changes using dynamic mechanical analysis and tensile testing, differential compensation calorimetry, thermogravimetric analysis and infrared spectrometry in the full attenuated reflection mode. The measurements showed that repeated extrusion as well as the addition of recycle material to the original one (R0) slightly slows down the photo-oxidative degradation during first month, but after that it does not have a negative or significant positive effect on the progress and rate of overall material degradation. A certain exception was the recycled material after the 3rd extrusion (R3), where the original properties comparable to R0 did not change much during ageing. The mechanical properties of the blends were better or comparable to R0 during ageing, but after months 6 and 9 the breaking strength of most of them decreased substantially as a result of the shortening of the chains. Accelerated ageing caused significant embrittlement in all samples, resulting in a reduction in yield strength by about half and almost immediate failure.
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Polymer nanocomposites for interior car body parts
Miškolci, Michal ; Bálková, Radka (referee) ; Jančář, Josef (advisor)
This bachelor’s thesis is interested in the problem of scratch resistance of interior car body parts. In this thesis, the solution is seen in using polycarbonate – based nanocomposites. In theoretical part, a literature search of this theme was made. In experimental part, the samples based on polycarbonate were prepared, and their tensile modulus was tested, as one of the main parameter affecting the scratch resistance.
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Kinetics of non-isothermal crystallization of polylactide with selected agents
Červený, Ľuboš ; Tocháček, Jiří (referee) ; Bálková, Radka (advisor)
The aim of submitted diploma thesis is the study of non-isothermal crystallization kinetics of polylactide (PLA) with selected agents (1 %) and observation of the emerging crystalline structure under polarizing optical microscope. The agents were talc, a mixture of organic salts with the addition of amorphous SiO2 (HPN 68L) and zinc stearate (HPN 20E) and LAK-301 (potassium salt of 5-dimethylsulfoisophtalate), which is a nucleating agent developer for PLA. The PLA matrix served as a reference. Non-isothermal crystallization took place on a differential scanning calorimeter at cooling rates () 0,3; 0,5; 0,7; 1; 1,5; 2 °C/min After non-isothermal crystallization, the crystalline fraction (Xc) od PLA was evaluated from X-ray diffraction analysis, and the supramolecular structure was observed after chemical degradative etching using confocal laser scanning microscope. The crystallization kinetics were evaluated by the methods of Jeziorny and Mo and the activation energy of the crystallization was determined according to the Friedmann method. All prepared materials were amorphous (Xc 40 % for up to 1,5 °C/min). However, for LAK-301, Xc decreased to 30 % already at the = 2 °C/min and it can be assumed that with increasing its nucleation activity will decrease. A spherulitic structure was observed in all samples, but the number and size of spherulites decreased with increasing and the appearance varied according to the type of agent. Both kinetic models proved to be unsuitable for materials with low Xc and the highest because the rate of crystallization did not change. With the Jeziorny method, it was possible to evaluate the kinetics only for the relative crystallinity Xt = 29–50 % and with the Mo method it was not possible to evaluate the data for the highest for PLA matrix and sample with HPN 68L. The samples with LAK-301 and HPN 68L showed the lowest activation energy.
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Flow properties of coolants for metal cutting
Blašková, Daniela ; Poláček, Petr (referee) ; Bálková, Radka (advisor)
The flow properties of two types of operating and clean coolants (A and B) were measured, both used in metalworking. Four samples of both operating liquids were sampled from the process monthly (from the beginning to the end of its use). All liquids were measured at 25 °C with an oil emulsion content of 4%. In addition, flow curves of pure cooling emulsions with concentration of coolant 2, 4, 6 and 8% were measured at 30, 35, 40, 45 and 50 °C. Rheological measurement was performed at geometry of concentric cylinders. Microbial activity and content of additives (Thermogravimetry) was determined in operating liquid A. Both operating liquids exhibited non-Newtonian behavior. Viscosity increased with the shear rate (10–100 s-1) and impurity level. Although the amount of impurity was approximately the same in both liquids, viscosity varied. For pure liquids, the viscosity increased with increasing concentration and decreased with increasing temperature, except for liquid A with concentration of coolants 6 and 8%, which, depending on the temperature, exhibited both shear thinning, shear thickening and Newtonian behavior. The results shown that impurity level of operating liquids has only minor effect on viscosity and flow properties, but it had an effect on cooling effect. Impurities diluted operating liquids, partial decomposition of the oil component may occur, but in particular, microbial activity causes skin problems of staff. Recommended is to introduce a specific control test for the presence of bacteria.
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Durability of Polyehtylene Ribbons from Netwrap
Huljak, Pavel ; Poláček, Petr (referee) ; Bálková, Radka (advisor)
This diploma thesis deals with the measurement of mechanical properties and accelerated aging of monoaxially stretched polyethylene strips coming from three types of polymeric mesh, which serves to pack hay on baling machines. The strength of the strips is evaluated from two points of view. The first one is static tensile strength measured before and after accelerated aging at 23 °C and 40 °C, the second one determines the strength as the weight that causes the strip failure on a simple machine at 23, 40, 60 and 80 ° C. The results show that the smallest static strength has the least stabilized strip, which, on the other hand, revealed the highest strength in a dynamic loading. The change of supermolecular structure was evaluated by calorimetric measurements. The data shown only very little change of inner structure due to the average response of the whole crystalline phase comprising relatively wide distribution of crystallites. It is more than probable that supermolecular structure had been changed but the method is not sensitive to see the change of orientation of lamellae and macromolecular chains in them.
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