LEE- Polimer Bilim ve Teknolojisi-Doktora

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  • Öge
    Manufacturing and characterization of polymer composites by using selective laser sintering 3D printing method
    (Lisansüstü Eğitim Enstitüsü, 2021) Özbay, Burçin ; Serhatlı, İ. Ersin ; 709840 ; Polimer Bilim ve Teknolojisi
    From the early invention of Additive Manufacturing (AM) from the 1960s to the 1990s, it has been rapidly developing worldwide within the last fifteen years. Studying this fast-growing technology has great importance for many application areas. Additionally, Selective Laser Sintering (SLS) is one of the improved methods of additive manufacturing and is crucial to develop thermoplastics and their composites. The thermoplastic material and thermoplastic matrix composite materials produced by this method have great potential to be used in the automotive and biomedical industries, aerospace and electric electronic sectors, and many others. In this area, hollow featured additives can be used to achieve lightweighted polymer composite structures. The density reduction is significant in enhancing fuel efficiency and reducing CO2 emissions in the aerospace and automotive industries. In the first part of the study, a Hollow Glass Microspheres (HGM) additive amount (10 wt. %, 15 wt. %, 20 wt. %) effects on Polyamide 12 (PA 12) polymer composite sintered parts as a means of the final density and mechanical properties of the composite structures were investigated. As the result of the study, the optimum HGM addition amount was detected as 20 wt. %. After that the second part of the study has been started with the detected optimum amount of HGM addition to PA 12. The study aims to determine the effects of different types and the same amount of hollow featured additives on polyamide polymeric structures, which have been produced by SLS-AM technology. This part of the research covers the comparison of the same amount, and different types of Hollow Glass Microspheres (HGMs) filled Polyamide 12 (PA 12) polymer composites. In the third part of the study, the metal additive effects on PA 12 polymer matrix were investigated. The electrical, thermal and mechanical effects of copper fillers on the PA 12 polymer matrix were examined. Two various types of Cu particles (spherical and dendritic) were introduced to the PA 12 polymer matrix in the same proportion (15 wt. %) as fillers. The thermal stability and thermal behaviors, crystallization kinetics, and heat capacities of copper-filled mixes and unfilled PA 12 were also analyzed. And the electrical conductivity of unfilled PA 12 and produced Cu-filled polymer composites were analyzed. In the last part of the research, the flame retardancy properties of polymer composites that were produced by SLS, were investigated. Different types and the same amount of fire retardant additives were added to PA 12 polymer matrix. And unfilled PA 12 and produced polymer composites were analyzed in terms of mechanical characteristics and flame retardancy features. For the SLS-AM processing EOS P 110 (EOS GmbH) SLS production machine with 100 microns of layer height was used in the study. To prepare polymer composite powder mixtures, a rotary tumbler was used. For powder and sintered samples, material characterization tests were performed. All mechanical tests (tensile, 3 point bending, notched Charpy impact tests, and DMA) were performed according to the related ISO standards. On the other hand, the sintering window area detections were obtained by DSC graphs. They were used to determine optimum laser sintering process parameters, which are laser power, scan speed, and scan spacing.
  • Öge
    Studies on suspension of some inorganic nanoparticles as additive in motor engine/lubrication oils
    (Lisansüstü Eğitim Enstitüsü, 2021) Tanrıseven, Zulhice ; Gül, Ahmet ; 709893 ; Polimer Bilim ve Teknolojisi
    Nanoparticles have very wide range applications. They are used for in almost every field, from medicine to coatings. Nanomaterials have very large surface area and very small particle sizes. Since they have very larger surface area than macroscale materials, nanomaterials are choosen to achieve desired properties with less amount of substances. There are nanomaterials which is known with their intrinsic lubrication efficiencies. Some of these materials, like graphene or hexagonal boron nitride or boric acid, have lamelar structure. These platelets, the layers, slide over each other when they are squeezed into two sliding surfaces to help reducing the friction between these two surfaces. There is another type of nanomaterials that have lubrication effect like titanium dioxide; these types of nanomaterials have spherical geometrical shapes. These nanomaterials act like marble and third body substance between two sliding surfaces. All nanomaterials have huge tendencies to agglomerate to form aggregates. In order to dispers them into targeted media, they should have gone certain stages before introducing into the targeted media. The aim of this study is to suspend nanomaterials that have lubrication properties in nonpolar media. In this study, multiwall carbon nanotubes, expandable graphene, graphene oxide, hexagonal boron nitride, boric acid, zinc oxide and titanium dioxide were used. All nanoparticles' morphologies were characterized by SEM or TEM and other proper characterization methods were used to characterize them; for instance, RAMAN for carbon based nanomaterials and XRD for crystal structure analyses. In order to suspend these seven nanomaterials in nonpolar media, two different methods were used through the study. One of these methods is called two step method which indicates first synthesizing the material then suspend it into targeted media. All seven nanoparticles were tried to be kept suspended in nonpolar media by two step method first. In order to prepare nanoparticles by two step method, nanoparticles were supplied and dispersed in different amphiphilic several base fluids by ultrasonic horn to have nanofluids. Diisononyl adipate (DiNA), diisodecyladipate (DiDA), nonylphenol etoxylate (NP), diisononyl phthalate (DiNP) and nonanol were examined to be base fluid. Nonanol is determined as the most appropriate base fluid to have stable suspension of nanoparticles in nonpolar media. It is a liquid fatty alcohol. It has both lipophilic long hydrocarbon chain and a hydrophilic hydroxy group at the end of this chain. It helps nanoparticles remain suspended in a nonpolar medium. In order to model nonpolar media, fully formulated commercial engine oils and poly alpha olefin oils were used. Prepared nanofluids were added to oils and added oils were examined by their suspension stability by two methods, turbidimetry and sedimentation photography. Turbiscan instrument was used to perform turbidimetry characterization method. This instrument sends a light (880 nm) to the sample by varying time and records the transmittance and backscattering intensities comes from different height levels of sample holder. Changes of transmittance or backscattering intensities over time indicates the unstability of the suspension. Furthermore, viscosity effects of nanofluid addition were examined by viscosimeter. All seven nanoparticles were examined to suspend in nonpolar media by two step method. MWCNT, expandable graphene, GO, boric acid had low TSI values that indicates stable suspention in nonpolar media. Other three nanoparticles did not have low TSI values; so, they were encapsulated by liposome structure to have stable suspension in nonpolar media. Characterization methods mentioned above were also implemented to nanofluids that have been prepared by liposoming method. Liposomes are spherical structures made by PC (Phosphotidyl Choline). These structures are biomimetic structures; thus, they are used as drug delivery agents. They have difficult and expensive preparation steps; so, they have not been used for suspending a nanoparticle in an engine oil. However, as the liposome preparation technology is developing, more practical agents and ways are developed to prepare liposomes; therefore, today it is easier and cheaper to prepare these liposomes. In this study, one-step and easy way is used to prepare liposomes of nanoparticles. In addition, unlike to previous liposome preparation methods in literature, chosen base fluid is used as preparation medium in liposome method, nonanol. Fatty alcohols were used as stabilizing agents for liposomes. Using a stabilizing agent as preparation medium enables us to have very stable liposomes (more than three months). Hexagonal boron nitride, titanium dioxide and zinc oxide were encapsulated by liposome structure. First time in the literature, in this study, these nanoparticles were encapsulated by liposome structure with proposed method and these liposomes were photographed by TEM. These liposomes were also characterized by zeta sizer instrument for their particle sizes and their polydispersity indexes. TEM and particle size analyses conducted showed results confirming each other and demonstrating the stability of liposomes. It was observed the fact that the proposed liposome preparation method facilitates to dispers and suspend any nanoparticle in the lipophilic medium. Suspending nanoparticles with chemicals that have not been used for this purpose and by encapsulating them by liposome structure by proposed one-step and easy method is a new and alternative way for literature. Nanoparticles have very wide usage areas. These easy-prepared suspendable nanofluids can also be implemented to other areas.
  • Öge
    Development of new generation, high performance polypropylene composites
    (Lisansüstü Eğitim Enstitüsü, 2021) Kaymakçı, Orkun ; Uyanık, Nurseli ; 723063 ; Polimer Bilim ve Teknolojisi
    Thermoplastic polypropylene (PP) composites have been extensively used in different industries such as appliances, automotive, construction and furniture due to their balanced mechanical performance and cost, high chemical resistance, low moisture absorption, recyclability and ease of processability. Depending on the application and the requirements, many different fillers and reinforcers have been used to tailor the properties of the PP matrix. These fillers and reinforcers include calcium carbonate, talcum, mica, glass beads, glass fibers, carbon fibers, wood powder, jute fibers and hemp fibers. However, because of the availability and the cost constraints, only a limited number of different fillers and reinforcers are widely used to prepare thermoplastic PP composites. The properties of the composites depend on the characteristics of the polymer resin, properties of the fillers/reinforcers and the adhesion strength of the interface between the polymer matrix and the filler. To improve the adhesion strength between the polar fillers and non-polar polymer matrices, compatibilizers that show both hydrophilic and hydrophobic properties are used. Maleic anhydride grafted PP (MA-g-PP) is a compatibilizer widely used in industry to produce thermoplastic PP composites. Microfibrillar reinforced polymer composites (MFCs) are relatively newer class of thermoplastic composites. MFCs are in-situ produced during compounding process of incompatible polymer blends with different melting temperatures with the help of hot/cold drawing. In contrast to traditional fiber reinforced composites, MFCs are lightweight and easy to recycle. Furthermore, cost effective, environmentally friendly and high-performance polymer blends can be obtained using recycled resources through in-situ microfibrillar polymer composites. In this thesis, novel, cost-effective, green and high-performance composites are developed through compounding PP with new generation fillers / reinforcers and through in-situ formation of microfibrillar recycled hybrid composites. The work done in this thesis is presented as a collection of six different studies that are categorized in different sections in results and discussion section. Firstly, novel, environmentally friendly and relatively cost efficient in-situ microfibrillar recycled PET fiber/carbon fiber/PP matrix composites with high mechanical properties were discussed. The effect of the in-situ microfibrillar rPET and MA-g-PP compatibilizer on the morphological, mechanical and physical properties of the composites were studied. Different formulations with rPET content up to 15 phr and MA-g-PP content up to 5% were prepared. Through SEM and EDX studies, the formation of the in-situ microfibrillar PETs were confirmed. It was found that the optimum mechanical properties are obtained with 5 phr rPET content. It was shown that adding MA-g-PP significantly improves the mechanical properties as it improves the interfacial adhesion strength between carbon fibers, microfibrillar rPETs and PP matrix. In addition, MA-g-PP was affected the morphology of the rPET microfibrils due to the steric stabilization effect of the compatibilizer. In this study, it was shown that it is possible to further improve the properties of the carbon fiber PP composites with in-situ microfibrillar PETs in a cost-effective way. Secondly, the similar microfibrillation concept was adapted into glass fiber (GF) filled PP composites to decrease the GF content of the materials without sacrificing their performance. 34% GF filled PP is used in large amounts in home appliance industry to produce washing machine tubs via injection molding. High performance cost effective and environmentally sustainable composites were produced by incorporation of rPET microfibrils into the composites. Effects of rPET content and MA-g-PP coupling agent on the tensile, flexural and viscoelastic properties were extensively characterized. Formation of the rPET fibers in the hybrid composite is confirmed in morphological characterization. The optimum properties were obtained with 10% rPET and 24% GF composites. Despite the popularity of the fiber reinforced PP composites both in academia and industry, the research on basalt fiber (BF) reinforced thermoplastic PP composites is quite limited. In the third section of the study, silane coupled PP/BF composites were investigated. The effect of the BF content and the effect of the MA-g-PP coupling agent on the thermal, mechanical and morphological properties of silane coupled PP/BF composites were investigated. Tensile tests have shown that BF content remarkably affects the modulus of the composites. Strength and strain values were highly dependent on the presence of the coupling agent. Both BF and coupling agent were considerably affected the impact resistance of the composites. Composites with higher BF contents also have shown higher storage modulus and lower viscoelastic energy dissipation. The morphological studies explained the increased interfacial adhesion between the fibers and the PP matrix. The improved interfacial adhesion was also affected the crystallization PP matrix in the composites. Similar to the first and second sections, in the fourth section, hybrid BF, microfibrillar rPET and PP composites were investigated. The properties of the composites that are produced in the previous section was further improved through incorporation of in-situ microfibrillar PETs into the composite system. For 10% BF loaded samples, highest mechanical properties were obtained with the formulation with 15 phr rPET. Because of the limited microfibrillation efficiency, addition of more than 15 phr rPET to the composites was not further improved the material properties. In the fifth section of the thesis, hybrid composites of in-situ microfibrillar rPET, silane coupled halloysite nanotube (HNT) and PP were developed. The effect of the rPET content on the viscoelastic and morphological characteristics of the HNT/PP nanocomposites were studied in detail. Mechanical properties of the materials were improved with the addition of up to 10 phr rPET into the nanocomposites. Morphology studies confirmed the homogenous distribution of the HNT particles along the composites. In addition, the formation of the PET fibers from rPET flakes were verified. Dynamic mechanical test results have shown that the reinforcing effect of the rPET weakens at temperatures over the polymer's glass transition temperature. Finally, the effects of multilayer graphene nanoplatelet (GNP) type and content on the morphological and mechanical properties of the PP nanocomposites were investigated. GNPs were greatly improved the mechanical properties of the PP, only addition of 1% GNPs was improved tensile modulus, flexural modulus and Izod impact strength by 10%, 23% and 16% respectively. Morphological studies have shown that only GNPs in nanocomposites with lower graphene loading levels are uniformly distributed along the PP matrix. At higher loading levels of GNPs, agglomeration was observed on SEM images. GNPs with different flake thicknesses and different number of layers have shown similar impact on the mechanical properties of the composites.