National Repository of Grey Literature 98 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Hybrid Composites Combining Short Deformable Fibers and Particulate Fillers in Polymeric Matrix
Smrčková, Markéta ; Pavelka,, Vladimír (referee) ; Poláček, Petr (advisor)
In this work, the effect of adding short deformable polyvinylalcohol fibers into dimethacrylate resins on mechanical properties of composite materials was investigated. Furthermore, micro- or nano-fillers were added into the matrix. The effect of filler/short fibers combination on mechanical properties of so-called hybrid composites was studied. Composites were characterized by differential compensation photocalorimetry (DPC), termogravimetric (TGA) and dynamic mechanical (DMA) analysis. The fracture surfaces were examined using scanning electron (SEM) and confocal laser (CLSM) microscopy. Elastic modulus and strength, the critical value of stress intensity factor and strain energy release rate and the viscoelastic properties of composite materials were measured. The mechanical properties of composite materials are affected not only by the type of filler/reinforcement, but also by properties of the matrix. These properties also depend on the way of network formation during photo-initiated polymerization. For this reason, heat of polymerization, degree of conversion and the maximum polymerization rate of mixture of dimethacrylate monomers were determined.
Lightweight composite materials for automotive applications
Sousedík, Jan ; Poláček, Petr (referee) ; Přikryl, Radek (advisor)
This bachelor thesis investigated the influence of lightening filler in the form of hollow glass microbeads on the mechanical properties of composite material. The method chosen for the preparation of composite material was pultrusion. Two types of composite material were prepared as part of the bachelor thesis, specifically epoxy-vinyl ester resin-based composites and unsaturated polyester resin-based composites. Special bulked glass fibres were used as reinforcement. The final composite material was subjected to a three-point flexural test where mechanical properties were monitored. In addition, control of the distribution and adhesion of the filler was performed by using light microscopy and scanning electron microscopy (SEM).
Optimization and characterization of dimethacrylate-based resin
Baradzina, Lizaveta ; Petruš, Josef (referee) ; Poláček, Petr (advisor)
This diploma thesis was focused on the optimization and characterization of resins based on dimethacrylate monomers. The polymerization process was also monitored depending on the type and molar ratio of monomers used, on the content of barium glass filler and the presence of glass fibers. Changes in the viscoelastic properties of materials during polymerization were also investigated. The following methods were used to characterize the prepared dimethacrylate resins and composite materials based on them: viscosimetry, differential scanning photocalorimetry (DPC), photoreology, dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). The dynamic viscosity of the prepared dimethacrylate matrices was determined by viscometry. Based on the results of DPC analysis of the tested resins, the dependences of heat flow on time, conversion on time and polymerization rate on conversion were created. With photoreology, the course of curing, the onset of the gelation point and changes in the viscoelastic properties of the systems were monitored. The viscoelastic properties of the cured composite materials were then determined by DMA in the three-point arrangement. TGA was performed to accurately determine the composition of the tested samples
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.
Flame retarders of polymeric materials
Winkler, David ; Poláček, Petr (referee) ; Kučera, František (advisor)
Bachelor thesis focuses on the study of expanded graphite as flame retardant added to low density polyethylene and it´s potential synergistic effect with ammonium polyphosphate. Additive and non-additive dog-bone samples were prepared by compounding and injection. Crystalization, melting point and thermal decomposition of the samples were monitored by TGA and DSC thermal analysis methods. The effect of expanded graphite on the mechanical proporties of the materiál was monitored by a tenssile test. The effect of expanded graphite as a flame retardant and its synergistic effect with ammonium polyphosphate was confirmed by a flame test in the horizontal position of the sample.
Ceramic nanofiber-reinforced composites
Bocian, Luboš ; Přikryl, Radek (referee) ; Poláček, Petr (advisor)
This thesis investigated how the addition of unsilanized and silanized ceramic SiO2 nanofibers into particle reinforced composite affects flexural strength, fracture toughness, total fracture work and temperature dependence of viscoelastic properties. Fracture surfaces were analyzed with SEM. Flexural strength always decreased with addition of nanofibers. Composites with silanized nanofibers showed higher flexural strength than those with unsilanized nanofibers. Fracture toughness was higher with addition of nanofibers. Fracture toughness of composites with silanized nanofibers was always lower than that of systems with unsilanized nanofibers. Total fracture work was lower with addition of nanofibers, but sharply increased in composites with 5 % of nanofibers. Glass transition temperature almost always increased with addition of nanofibers. Storage modulus increased with addition of nanofibers. Storage modulus was always lower in composites with silanized nanofibers.
Photopolymerization study of composites
Baradzina, Lizaveta ; Petruš, Josef (referee) ; Poláček, Petr (advisor)
This bachelor thesis investigated the influence of ceramic nanofibers and particle filler on the curing kinetics of composite materials with dimethacrylate matrix. Changes in viscoelastic properties of materials during polymerization were also monitored. Within this work, four types of materials were prepared: particle composite, fiber composite, hybrid composite and pure matrix. Composite systems of different compositions were characterized by photorheology, differential photocalorimetry (DPC), and dynamic-mechanical analysis (DMA). The effect of light intensity and irradiation time on changes in the rheological properties of materials that occur during photopolymerization were investigated using photorheology. Based on the results of DPC analysis of the tested samples the dependencies of conversion on time and polymerization rate on conversion were created. The viscoelastic properties of the cured composites were determined by DMA analysis in a three-point arrangement.
Short fiber reinforced composites in dental applications
Matysová, Dorota ; Vladimír, Pavelka (referee) ; Poláček, Petr (advisor)
This diploma thesis deals with short-fibre reinforced composites for dental applications. Particulate barium filler, short polyacrylonitryle fibres or short glass fibres were added to the dimethacrylate matrix to study their effect on the composite material properties. Methods used for this study were thermogravimetric analysis (TGA), differential compensation photocalorimetry (DPC), dynamic mechanical analysis (DMA), three point bending, scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). The matrix curing was defined by heat of polymerisation, degree of conversion and polymerisation rate. Composite materials were characterized by the glass transition temperature, storage moduli at 35 °C and 100 °C, elastic modulus, strength, the critical value of stress intensity factor and the critical value of energy release rate. Fracture surface investigation is also included in this thesis.
Preparation and characterization of highly filled composite materials for dental applications
Gavroňová, Ivana ; Bystřický, Zdeněk (referee) ; Poláček, Petr (advisor)
Master thesis deals with highly filled particulate composite materials for dental applications. In the practical part, the dimetacrylate matrix was filled with a mixture of particles of different types and different sizes to achieve the maximum possible packing. Moreover, filler content and the influence of filler on composite material was studied. Hydrolytic stability was also tested on composite materials. The methods used to characterize composite materials were bending test, thermogravimetric analysis (TGA), differential scanning photocalorimetry (DPC), dynamic-mechanical analysis (DMA) and scanning electron microscopy (SEM). Curing of the matrix was characterized by the degree of conversion, the heat of polymerization and the polymerization rate. Furthermore the polymerization shrinkage was measured. The glass transition temperature, the dynamic modulus at 40 °C and 100 °C, the modulus of elasticity, the strength, the critical value of the stress factor and the critical energy release rate were found in the tested samples.
Short fiber reinforced composite for dental use: preparation and characterization
Henkrichová, Jana ; Přikryl, Radek (referee) ; Poláček, Petr (advisor)
This diploma thesis studies short fiber reinforced composites for dental applications. Barium particulate filler, nanosilica and short glass and polyvinylalcohol fibers were added to the matrix consisting of four dimethacrylate types of monomers. The effect on material properties was observed. For characterization of different types of composite materials following methods were used: thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), three point bending test for notched and un-notched samples and scanning electron microscopy (SEM). Viscoelastic properties, modulus of elasticity and strength, critical values of stress intensity factor and strain energy release rate and polymerization shrinkage of composite materials were determined. It is possible to improve these properties of composite materials by adding short fibres to particulate reinforced composite. To make this modification more efficient, it is necessary to change surface treatment of fibres and preparation method of short fiber reinforced composites. Viscosity of material has raised after adding short fibers and processing of these types of dental material in dental laboratory is considered difficult to provide.

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