LEE- Polimer Bilim ve Teknolojisi-Yüksek Lisans
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ÖgeEnhancement of interfacial properties for high performance polyethylene fibers produced via gel spinning(Graduate School, 2023)Fibers are materials with high length/diameter ratios, having adjustable fineness, mechanical properties. High performance fibers exhibit excellent mechanical properties such as high modulus, high strength, high abrasion resistance, thermal resistance, low density. One of the methods used to produce high performance fibers is gel spinning, in which the chains are partially entangled in liquid-gel form and connection with each other , rather than solution or melt unlike other methods (dry spinning, wet spinning, melt spinning). In this thesis, ultra high molecular weight polyethylene (UHMWPE) was dissolved in paraffin oil and high performance UHMWPE fibers were obtained by gel spinning method. The gel obtained by dissolving UHMWPE in paraffin oil is formed into filaments by passing through the spinnerettes after extrusion, then passes through the quenching and extraction bath, drying and winding in the final stage. High tensile strength, low specific density, great impact resistance, and exceptional chemical resistance are just a few of the excellent qualities of ultra-high molecular weight polyethylene (UHMWPE) fiber. It is frequently utilized in fishing, aircraft, biomedicine, and ballistic, among other things. UHMWPE fiber has a very high degree of crystallinity (>99%) and macromolecular orientation (>95%), which leads to a high modulus and tenacity of UHMWPE fiber. Gel spinning is a difficult and advanced engineering process. UHMWPE concentration is one of the parameters that determine fiber strength which was kept as 8% wt in this study. For this research, n-hexane was used in the extraction bath to remove paraffin oil from spun UHMWPE fibers. Following the solvent extraction procedure, the fibers undergoing hot drawing with different drawn ratios. The differential scanning calorimeter is used to analyze the thermal and crystallization properties of the fibers in their drawn, undrawn, and gel-state forms. Two newly peaks are observed when DR reached to 40. These peaks shows orthorombic-hexagonal transition. An orthorhombic structure represents a prism-like crystal structure with three unequal edges and internal angles, whereas a hexagonal structure resembles a hexagon with six equal edges. The tensile test was used to reveal the effect of drawn ratios on performance and it was revealed that with the increase in drawn ratio, the mechanical strength would increase by a maximum of 322.71%. Simultaneously, this thesis also focuses on investigating the enhancement of interface properties in UHMWPE fiber/epoxy composites.There are numerous surface treatment methods used to improve the coaction between fibers and composite materials, chemical etching and corona discharge are two commonly used methods to enhance the fiber- epoxy interaction. In this thesis study, the optimum corona discharge result was revealed by experiments performed at different voltage and time parameters. Then, the obtained results from corona discharge method were compared with the results obtained when the surface was modified via chemical etching, and it was seen that hydroxyl and carboxyl groups were formed on the surface more effectively in the chemical etching method. Glutaraldehyde, which is used as a cross-linking agent in chemical etching method, can form bonds with OH functional groups due to its chemical structure. Thus, the hydroxyl groups formed on the UHMWPE fibers become able to cross-link with the hydroxyl groups in the epoxy. Tests have shown an increase in both mechanical performance and adhesion.
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ÖgeThe synthesis and characterization of a novel flame retardant containing rigid polyurethane foam(Graduate School, 2024-07-04)Rigid polyurethane foams are one of the most preferred thermal insulation materials due to their excellent thermal insulation properties, mechanical strength, lightness, and applicability. They are used in various fields from household appliances to pipes, cladding, and insulated panels, and are commonly encountered in daily life. However, these materials pose a risk to human life and health due to their weak characteristic of being easily flammable and capable of intensifying fires. This risk has created a need for flame retardant materials. Flame retardants are added to polyurethane to prevent the flames from rapidly intensifying in the event of a fire, providing people with an escape time. Traditional flame retardants contained halogens such as bromine and chlorine, but their use has been restricted due to the release of toxic gases during a fire. As a result, there has been a need for alternative flame retardants with different chemical structures. Currently, commonly used flame retardants include phosphorus-based compounds such as tris(2-chloroethyl) phosphate and triphenyl phosphate; phosphonates such as dimethyl propyl phosphonate; ammonium polyphosphate (APP) and DOPO derivatives like phosphaphenanthrene oxide; nitrogen-based compounds such as melamine, melamine cyanurate, and melamine polyphosphate; polymeric silicone derivatives; and inorganic flame retardants like magnesium hydroxide and aluminum trihydroxide. This thesis was carried out in two stages: the synthesis of a flame retardant containing fluorine and nitrogen, and the addition of the flame retardant to rigid polyurethane foam. The synthesis process was carried out in three stages, successfully synthesizing a fluorine-containing, hydroxyl-terminated compound with a triazole structure through a copper-catalyzed azide-alkyne cycloaddition reaction, an example of click chemistry. Techniques such as fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopies were used to elucidate the structural properties of the resulting compound. The flame retardant, incorporated into the rigid polyurethane formulation by mechanically mixing in various percentages, was aimed to react with isocyanates, through its OH groups as a polyol, which are the components of polyurethane, thus exhibiting chemical flame retardant functionality. Consequently, the structural properties of the RPUF samples were examined using techniques such as FTIR, thermal and flammability properties with cone calorimeter, limiting oxygen index (LOI), thermogravimetric analysis (TGA), and thermal conductivity meter, and morphological properties with scanning electron microscopy (SEM). The impact of the flame retardant on the mechanical properties was investigated through compression testing and foam density measurements of the RPUF samples. The hydrophobic contribution of the flame retardant to the foam samples due to its fluorine content was measured with a contact angle meter. All analyses were carried out on foam samples containing no flame retardant and those containing 5%, 10%, and 15% flame retardant. Test results show significant improvement in the flame retardancy of rigid polyurethane foam with enhanced LOI values and reduced peak heat release rates. Additionally, it was observed that the flame retardant successfully bonded chemically to the foam structure, did not deteriorate its mechanical properties and cell structure, maintained excellent thermal insulation, and increased contact angle values imparted hydrophobicity due to its fluorine content. This thesis demonstrates the potential of nitrogen and fluorine-containing flame retardants for providing superior fire protection, indicating that they are promising candidates for future applications in fire-resistant materials.
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ÖgeExtraction of polysaccharides from waste seaweed and examining their film forming properties(Graduate School, 2024-08-16)Biomaterials produced from seaweeds are used by many industries such as pharmaceuticals, cosmetics, medical, fertilizers, textiles, food and packaging. These materials come from living things that are renewable, such microbes, plants, and animals. They lessen our reliance on finite resources and have a minimal negative impact on the environment by providing a sustainable substitute for fossil fuels and synthetic materials. Turkey, with its agricultural potential and biodiversity, has a significant potential for the production and use of bio-based raw materials. Studies and policies implemented in our country to support the transition to a more sustainable economy in the future. Numerous species can be found in the oceans, which covers an important part of the planet's surface. These organisms are rich in biological materials that, with the help of biotechnology, could find application in a wide range of industrial applications. This area of study, known as marine biotechnology, investigates the potential use of these compounds derived from marine animals in a variety of industries. Marine resources are a renewable and limitless resource. Reducing dependence on fossil fuels and facilitating the shift to a more sustainable economy can be accomplished in this way. Turkey has enormous potential in the field of marine biotechnology because it is surrounded by seas on three sides. It is impossible to say, though, that this potential has yet to be fully fulfilled. Our nation needs to invest more money and conduct more studies in the field of marine biotechnology. There is a wide range of marine biomaterials. One of the most important of these biomaterials is seaweed, which is rich in protein, vitamins and minerals. The industrial utilization of seaweeds has a history dating back thousands of years and is still of great importance today. Today, when issues such as sustainability and efficient use of natural resources are on the agenda, the use of renewable resources such as seaweeds has become even more important. The seas in our country are home to a wide variety of algae species as they have different water temperatures, salinity ratios and depths. The coastline, especially rocky areas, is an ideal habitat for seaweeds. Various types of algae are frequently seen in these areas, which are constantly oxygenated by the waves. For some reasons, seaweeds collect on coasts. These are factors such as waves and currents, wind, tidal movements, the natural life cycle of seaweeds. Seaweeds of different species are collected at certain times of the year on the shores of the Marmara Sea, which is home to a wide variety of seaweed species. When these collections are on the shore, they can be disturbing in terms of odor and appearance. At the same time, it can restrict the usage areas of people on the coast. When waste seaweeds do not wash up on the shore, they accumulate on the sea surface, and since these accumulations reduce the contact of the sea with the air, they reduce the oxygen level in the sea and reduce the efficiency of the oxygen source needed by the creatures living in the sea. This, in turn, reduces the quality of life of the creatures living in the marine ecosystem, shortens their lifespan and may jeopardize the continuity of species. Collecting these algae accumulated on the sea surface and coasts to be transformed into various materials can both clean the sea and the coast and provide a cheap raw material source to the industry. Some similar studies are being carried out in different parts of the world. The structural and quantitative diversity of the chemical components found in the structures of these seaweeds, which are found in thousands of different species, may cause us to see these seaweeds as a very special resource. Seaweed is produced and used as a raw material nowadays all over the world. High-value applications of algal-extracted biopolymers are becoming more and more necessary as the algae industry and algae biorefinery expand. The polysaccharides in the structure of these seaweeds can be seen as a source of raw materials for different applications. Seaweeds can grow and reproduce in conditions that cause minimal damage to the environment. Since seaweed farming does not require fresh water, chemical fertilizers or land, which are some of the most important environmental constraints associated with land-based agriculture, marine farming appears to be more sustainable than land-based agriculture. Seaweed can absorb carbon dioxide from the atmosphere, contributing to efforts to mitigate climate change. Even though we think that terrestrial plants are the source of the oxygen we breathe, photosynthesis by marine algae produces over 75% of the oxygen on the globe. Seaweed is consumed directly in many cultures, often as a source of nutrients and dietary fiber. Seaweeds are not only a great source of food, but also an important raw material for animal feed, biomass and biofuel synthesis and are currently being utilized in these fields. Seaweed can be used to remove pollutants from water and soil, a process known as bioremediation. The concept of this project is to collect different seaweed samples from the coasts of the Marmara Sea to isolate the polysaccharide components in their structure and to investigate the possible utilization of these polysaccharides as a source of feedstock. The first focus of the study is to determine the proportion of polysaccharides in the composition of different types of seaweed waste, the next step is to convert these polysaccharides into polymeric films using different film agents. This innovative approach not only addresses the problem of accumulation of marine waste on the coasts, but also allows us to see the possibilities for the proper utilization of this bio-waste material.
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ÖgeCatalyzing the inverse vulcanization reaction via 1,3-benzoxazines(Graduate School, 2023)High-performance polymers take a vital role in our daily life by their commercial manufacturing and extensive range of applications in various areas like structural materials, aerospace, electronics, printed circuit boards, coatings and adhesives. Polymeric materials can be categorized as thermosets and thermoplastics according to their behavior against temperature. Thermoplastics are a resin which is solid at the room temperature, but becomes softer by increasing the heat and showing fluid behavior or properties due to the melting point or passing the glass transition temperature. Some of thermoset polymers can be consider as a high-performance polymers because of their unique features such as flame resistance, decent mechanical strength, dimensional stability and durability against many solvents. Although these remarkable advantages, they have some disadvantages like shorth shelf life, being brittle, water adsortion and etc. The common members of thermoset resins are phenol-formaldehyde, urea-formaldehyde, melamine-formaldehyde and etc. Phenol-formaldehyde resins are well-known, the most and wide produced in the thermoset resins family. In the 20th century it has been found that the drawbacks of phenolic resins can overcome by polybenzoxazines via their excellent properties: high char yield, high thermal resistance and stability, zero volumetric change and low toxic substance releasing during curing, cost-effective, low moisture absorption, without any requirement for catalyst and etc. Additionally, the easy synthesis procedure of polybenzoxazines is also one of their striking advantages. Because there are corresponding monomers as a polybenzoxazine precursors which can be prepared from cost-effective raw materials such as primary amines, formaldehyde and phenols. In this study, it is aimed to catalyze the reaction of vinylic monomers with sulfur, known as reverse vulcanization. In general, for reverse vulcanization to occur, elemental sulfur must be heated up to the homolytic bond breaking temperature of 160 °C. The resulting sulfur radicals react with the double bond and trigger the polymerization from there. Although the required temperature for reverse curing is high, side reactions increase at this temperature. Therefore, it is important that inverse vulcanization can be catalyzed at more reasonable temperatures. In this study, benzoxazines with different functionalities will be used as catalysts. All the benzoxaiznes acted as catalyst to reduce inverse vulcanization. Among the benzoxazine monomers pyridine containing benzoxazine reduced inverse vulcation temperature better compared to other benzoxazines. It is known that pyridine-type systems contribute to the homolytic decomposition of sulfur, and that sulfur generates radicals by removing hydrogen from benzoxazines. An effective catalytic system was designed by combining these two approaches in a single structure. In this thesis, the development of benzoxazine-based high-performance catalysts by utilizing the flexibility of benzoxazine chemistry is described. The designed benzoxazine will contain the pyridine structure on it. Thus, it is thought that the catalytic performance for reverse vulcanization will increase. With a design benzoxazine catalyst, an attempt will be made to reduce the required minimum temperature of 160 oC to 130 oC for inverse vulcanization.
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ÖgePreparation of porous polymers by emulsion template method and their use in biodiesel production(Graduate School, 2024-01-18)High Internal Phase Emulsions were prepared to obtain highly porous polymers as solid catalysts for esterification of oleic acid with methanol. High internal phase emulsion method enables preparing porous polymers with interconnectivity. However, the surface area of these polymers is extremely constrained as a result of very large pores. This drawback was overcome through hypercrosslinking reaction. PolyHIPEs were prepared using VBC as a monomer and DVB as a crosslinker, followed by a hypercrosslinking process to produce high-surface-area polymers. The hypercrosslinking reaction was applied through Friedel-Crafts alkylation reaction catalyzed by a Lewis acid FeCl3 where chloromethyl group acts as an internal electrophile, and DCE as solvent and external crosslinker. Because DCE has a boiling point of 80°C, it enables the reaction to take place at high temperatures while simultaneously acting as an external crosslinker for the hypercrosslinking process. This reaction produces micro/meso pores and high specific surface area within the framework of polyHIPE precursor. The hypercrosslinking reaction is a controlled reaction that allows an increase of the surface area in a controlled way leaving some unreacted pendant groups. The unreacted pendant groups were employed for additional functionalization on the polymer surface, resulting in acid groups. The catalytic acitivity of the functional unhypercrosslinked and hypercrosslinked solid catalysts were validated through the esterification of oleic acid with methanol for biodiesel production. In addition, this study showed that it is possible to control the amount of sulfonic acid groups and the hydrophobicity of the polymer surface by attaching the sulfonic acid groups in PolyHIPE to the polymer via a methylene bridge. The morpholgy of the polymer surfaces were charactrized by SEM and BET surface area measurements were used to determine the surface area, pore size, and pore size distributions. The surface functionality was characterized by FT-IR and acid-base titration. The good yields were obtained for the esterification reaction with 10% of the solid catalyst at 90oC. Furthermore, the application of the hypercrosslinked solid acid catalyst resulted in enhanced reaction kinetics when compared to the unhypercrosslinked equivalent. The high-surface-area solid acid catalysts can be reused at least four times with relatively negligible activity loss.