LEE- Polimer Bilim ve Teknolojisi Lisansüstü Programı

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http://hdl.handle.net/11527/19428

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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.
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.
Development of new generation, high performance polypropylene composites

(Lisansüstü Eğitim Enstitüsü, 2022) 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.
High internal phase emulsion template method for fast and selective mercury adsorption

(Graduate School, 2022-01-06) Yıldırım, Melis Şeval ; Yavuz, Erdem ; 515171009 ; Polymer Science and Technology ; Polimer Bilim ve Teknolojisi

There are many template methods for designing porous polymers. Porous polymers have become highly preferred in the industry due to their easy processability and properties. In this study, it was polymerized using a high internal phase emulsion template (HIPE). HIPE is named by looking at the ratio of the external phase volume to the total volume. If this ratio is greater than 0.74, it can be called HIPE.Macroporous polymers prepared by the HIPE method were used. The main disadvantage of PolyHIPE polymers is that they have a low high area (SBET ~9 m2g-1). To overcome this disadvantage, a hypercrosslinking reaction was performed. High surface area polymers were obtained with the Fiedel Crafts reaction (SBET ~ 594 m2g-1). After the hypercrosslinked polymer was obtained, three different functionalization steps were applied. These are respectively; aldehyde, carboxylic acid and amide functionalization. The main purpose of this study is to obtain a selective, fast adsorbent on mercury. It is amide groups that provide selectivity to mercury. The -CONR2 group was obtained from the -Cl groups. In this study, amide group was obtained from carboxylic acid by using four different amides as propylamine, ethanolamine, aniline, diethylamine and DIC/NHS. With the emulsion templating strategy, hypercrosslinking polymers with different hyper-crosslinking times (15 minutes, 30 minutes, 60 minutes, 22 hours) were obtained, increased to amide groups and adsorption studies were carried out. While the main product, HXL-30min-PHP-CONR2, adsorbs 28 mg/g mercury in the first 2 minutes, it is 40.5 mg/g in the 180th minute when it reaches equilibrium. For these studies, different pH ranges were tried (pH 3, pH 4, pH 5, pH 6, pH 7) and the optimum pH was found to be 7.Isotherm (Langmuir, Freundlich, Dubinin- Radushkevich) and kinetic (pseudo-first order, pseudo-second order, intra-particle diffusion) models were made for HXL-30min-PHP-CONR2. Window and void diameter were calculated by using SEM images with Imagej program. Reuse studies were performed for HXL-PHP-CONR2 using 0.1 M HNO3, and 90% capacity was observed up to the 5th cycle.
Production of special resins for use in polyurethane

(Graduate School, 2022-01-18) Hüten, Tibet ; Kızılcan, Nilgün ; 515191015 ; Polymer Science and Technology ; Polimer Bilim ve Teknolojisi

Polyurethane prepolymers, generally reaction products of diols and diisocyanates, are considered an important part of polyurethane chemistry due to their direct contribution to final properties. Isocyanate and polyol react and form a strong, reinforcing urethane bond. Prepolymers are generally prepared with a 2/1 ratio of isocyanates to polyols to ensure an NCO (isocyanate) terminated structure. NCO terminated structure later reacts with chain extenders and crosslinkers to produce polyurethane structure with larger molecular weight. In prepolymer chemistry, isocyanate is considered a reactive component of the reaction medium. Apart from their role as a reactive component, they also arrange the mechanical properties of polyurethane. Therefore, a proper type of isocyanate should be considered for its application. In microcellular elastomeric shoe sole polyurethane chemistry, diphenylmethane diisocyanate (MDI) has high consumption. Crude 4,4'- MDI has been chosen as the core of formulation for its highly reactive para-positioned NCO groups to form more reinforcing urethane bonds. However, a phenomenon called dimerization creates a dilemma on its high consumption in prepolymers. The reactivity of isocyanate is proportional to its rate of dimerization. Since crude MDI is a highly reactive material it has more tendency for dimerization. Dimerization is a phenomenon occupying a reaction between two isocyanates. The formation of dimers in the reaction medium reduces the free isocyanate components to react with polyols, creating a different reaction profile. Remaining free isocyanates in the reaction medium will react with a polyol to form a polyurethane structure with less frequent reinforcing urethane bonds. Therefore, fewer urethane bonds result in weaker mechanical properties. Changes in mechanical properties and reaction profiles are known symptoms of dimerization. Apart from these symptoms, dimers are known for their high melting and freezing points. According to this phenomenon, optimal operation and storage temperature of prepolymer will be in a more narrow spectrum. Prepolymer with a higher melting point will take a longer time to melt. Therefore, a more complicated pathway of processing should be considered. Storage conditions of prepolymers are also affected by dimerization. Dimerization rate is faster in 5 to 40 °C and above 50 °C . Therefore, prepolymers should be stored under 0 °C to evade dimerization. When the freezing point of a prepolymer is high and closer to the dimerization area, its stability during storage will dropdown. Freezing temperature is a key element to observing the storage stability of prepolymers. Isomers of crude MDI (2,4'- MDI and 2,2'- MDI) can be mixed with crude MDI to lower its melting and freezing temperatures for better operation and storage temperatures. Today, two forms of isocyanates named OP50 (50% - 50% mixture of 2,4'- and 4,4'- MDI) and carbodiimide modified MDI used for storage stabilization and improvement on melting of the prepolymer. Isomers of crude MDI have orto positioned NCO groups with low reactivity due to steric hindrance and show less tendency to dimerization. In literature, there is no concise study on the effect of OP50 and carbodiimide modified MDI in both melting and freezing points of prepolymers. Our study aims to investigate the effects of change in isocyanate and polyol components on freezing and melting points of prepolymers while preventing a dramatic change in mechanical properties. Prepolymers with carbodiimide modified MDI in 7-12 % show the lowest freezing temperature, the starting point of freezing, melting temperature, the starting point of melting. Its projections on mechanical properties in polyurethane (PU2) show improvement on elongation at break, tensile strength. Modulus shows a decrease due to loss of crystallinity. Besides from the best formulation, the mechanical properties of polyurethanes made from the other two best prepolymers are also investigated. PU3 which was made from PREP5 did not show a significant loss in mechanical properties same as the PU2. However, PU4 where PREP6 was used, show losses in compression set and tear resistance due to a lower amount of hydrogen and urethane bonding. It has the highest elongation at break value for its low level of crystalline hydrogen bonds. From shelf life observations in jars at 21 °C, found formula withstand freezing for 38 days while reference formula withstands for 19 days. Freezing showed a faster propagation in PREP1 than PREP4. At the end of 150 days, PREP1 completely frozen while PREP4 stayed in liquid form. For this reason, the formulation was found successful to be used in standard polyurethane applications and increasing the shelf life of prepolymers.
Investigation of mechanical, physical and flame retardant properties of polypropylene compounds using synergisticcombination of minerals and intumescent flame retardants

(Graduate School, 2022-02-10) Kahraman, Merve ; Kızılcan, Nilgün ; 515122004 ; Polymer Science and Technology ; Polimer Bilim ve Teknolojisi

In daily life, polymeric materials can be used in many different applications because of their low price, processability and also good features. Polypropylene is very important polymer of polyolefins. Especially, polypropylene material is used in home appliances and automotive sector due to its constructive properties. Beside good properties, polypropylene has also negative properties to use in industry therefore some additives need to be compounded with plastics depending on the application fields to achieve the desired features. In order not to lose desired functional properties, additive can be added to polymers at optimum quantity. Due to fires in the world, increasing the flame retardant properties of materials becomes even more important so the usage of flame retardant additives and smoke suppresants are increasing day by day in polymeric materials. These materials have important role on improving flame retardancy properties of polymeric materials but enviromental friendly materials have to be used due to toxicological properties of halogenated flame retardant additives so environmental friendly systems like halogen free and mineral based flame retardant materials have to be used inside polymeric materials. Polypropylene has been choosen as main polymer due to usage of home appliances sector. The main goal of this study is to increase flame retardancy features of polypropylene and create synergistic effect with using intumescent flame retardant system, mica, colemanite and expandable graphite. Commercially available materials like IFR, mica, colemanite and expandable graphite have been choosen not to face any production restriction. IFR is environmental friendly and halogenated flame retardant additive Mica and colemanite minerals are abundant materials on the earth and their price is lower compared to IFR system. Expandable graphite is promising flame retardant material to increase flame retardancy properties of polypropylene. In this research, concentration of flame retardant additives was adjusted at 30 wt% mass of overall volume of compound. Potential flame retardant additives were added with mass fractions of 2, 4, 6, 8, 15 wt.%. Flame retardant additives were also added to the polypropylene at a rate of 30 wt% and its effect also were observed. Flame retardant additives filled compouds were prepared in the co-rotating twin screw extrusion at 100 rpm screw speed and at 185 ℃. After production of compounded materials, standard testing specimens were prepared in the injection molding machine. Density and melt flow index(MFI) tests were carried out to define physical properties of sampling parts. Mechanical testing were conducted to define mechanical features of sampling materials. Thermal gravimetric analysis(TGA) and heat deflection temperature(HDT) tests were used to measure thermal properties of compounds. Investigation of char layer was evaluated using scanning electron microscopy(SEM). Furthermore, limiting oxygen index(LOI), UL 94 vertical flammability test, and glow wire test were used to determine flame retardancy performance of compounds. In the first stage of this thesis, IFR was added to polypropylene material at 20-25-30 wt% loading levels to evaluate the influence of the IFR system on polypropylene and to determine ideal formulation to catch desired mechanical, physical and flame retardancy properties. The blend compounds were designated as PP80/IFR20, PP75/IFR25, PP70/IFR30 respectively. In this terminology, the letters "PP" and "IFR" were used to indicate the plastic polypropylene and flame retardant additive intumescent flame retardant. The numbers following the sample same were used to represent the loading level of materials by weight percent. According to flame retardancy test results, IFR has an important effect on flame retardancy, LOI values reached to 37.9% with loading level of 30 wt% IFR. PP75/IFR25 and PP70/IFR30 passed to UL 94 vertical tests and all compounds passed glow wire tests both 750 and 850℃. TGA results showed that thermal stability of compounds enhanced by adding IFR to the polypropylene. In the second stage of thesis, IFR and mica were mixed with PP material in co-rotating twin screw extrusion to increase flame retardancy of PP. The blend compounds were designated PP70/IFR28/M2, PP70/IFR26/M4, PP70/IFR24/M6, PP70/IFR22/M8, PP70/IFR15/M15, PP70/IFR0/M30 respectively. In this therminology, the letters "PP", "IFR" and "M" were used to indicate the plastic polypropylene, flame retardant additive intumescent flame retardant and mineral mica. The LOI, UL 94 and glow wire test results represented that mica had a considerable effect on flammability and LOI rate which can reach to 37.5 % with loading level of 2 wt% mica at the overall quantity of flame retardant ingredients fixed constant at 30 wt.%. Additionally, the PP/IFR compounds passed UL 94 V0 rating and both 750 °C and 850 °C glow wire tests and with 2-8 wt% mica loading. According to TGA analyses, the results indicated that mica improved the thermal uniformity of PP/IFR compounds and also promoted formation of char layer. When mica mineral added to polypropylene without IFR system, it has no influence on flammability of polypropylene. Mica content can be used up to 8 wt.% in polypropylene compound with IFR material. In the third stage of thesis, synergistic action between IFR and EG in PP compounds was observed. The blend compounds were designated PP70/IFR28/EG2, PP70/IFR26/EG4, PP70/IFR24/EG6, PP70/IFR22/EG8, PP70/IFR15/EG15, PP70/IFR0/EG30 respectively. In this therminology, the letters "PP", "IFR" and "EG" were used to indicate the plastic polypropylene, flame retardant additive intumescent flame retardant and additive expandable graphite. The LOI, UL 94 and glow wire test results represented that EG had prominent effect on flammability and LOI rate which can reach to 37.2 % with loading level of 4 wt.% EG at the overall quantity of flame retardant ingredients fixed constant at 30 wt.%. Additionally, the PP/IFR compounds passed UL 94 V0 grade and both 750 °C and 850 °C glow wire tests and with 2-6 wt.% EG loading. These tests demonstrated that the addition of EG into PP/IFR system improved the flame retardancy properties of PP compounds. It means that synergistic is available between IFR and EG additives. HDT values can be increased with addition of EG as a result, the load carrying ability will be increased during fire. Furthermore, it is difficult to process EG with PP material at 30 wt% loading level of EG. It is not suitable in terms of processability. In terms of mechanical properties, elastic modulus values increased with addition of EG to PP/IFR compound. In the fourth stage of thesis, IFR and colemanite were mixed with PP material in corotating twin screw extrusion to create flame retardant system and increase flame retardancy of PP. The blend compounds were designated PP70/IFR28/C2, PP70/IFR26/C4, PP70/IFR24/C6, PP70/IFR22/C8, PP70/IFR15/C15, PP70/IFR0/C30 respectively. In this therminology, the letters "PP", "IFR" and "C" were used to indicate the plastic polypropylene, flame retardant additive intumescent flame retardant and mineral colemanite. The LOI, UL 94 and glow wire test results represented that colemanite had a valuable influence on flammability and LOI grade which can reach to 37.6 % with loading level of 2 wt.% colemanite at the overall quantity of flame retardant ingredients fixed constant at 30 wt.%. Additionally, the PP/IFR compounds passed UL 94 V0 grade and both 750 °C and 850 °C glow wire tests and with 2-6 wt.% colemanite loading. Tensile strength value of polypropylene homopolymer decreased when IFR and colemanite added to polymeric system. The stiffness of PP70/IFR0/C30 sample was higher than PP70/IFR30/C0 sample when temperature increased. When all properties have been taken into consideration, colemanite can be used up to 4 wt% in IFR filled PP compound. In the fifth stage of thesis, IFR, colemanite, mica and expandable graphite were compounded with PP material in the different combinations and loading levels to create synergistic flame retardant system and increase flame retardancy properties of final compound. Combinations and loading levels were determined according to test results of binary mixtures of IFR and other potential flame retardant materials. The blend compounds were designated PP70/IFR20/M8/C2, PP70/IFR22/M6/C2, PP70/IFR22/M4/C4,PP70/IFR22/EG6/C2,PP70/IFR22/EG4/C4,PP70/IFR22/EG6/M 2,PP70/IFR22/EG4/M4, PP70/IFR22/EG2/M6, PP70/IFR20/EG2/M8 respectively. In this therminology, the letters "PP", "IFR", "C", "EG", "M" were used to indicate the plastic polypropylene, flame retardant additive intumescent flame retardant, mineral colemanite, expandable graphite and mica. The LOI, UL 94 and glow wire test results indicated that mica and colemanite created synergistic effect with IFR in PP compound when they used at reasonable amount. The LOI achieved up to 33%, and UL 94 test attained V0 rate for PP/IFR/mica/colemanite samples at the total amount of flame retardant additives kept constant at 30 wt.%. Additionally the PP/IFR/mica/colemanite compounds passed UL 94 V0 rating and both 750 °C and 850 °C glow wire tests. According to TGA analyses, it is obvious that the char residue increased by the increasing loading of mica. Colemanite gives their structure water to the system and they create cooling effect on the surface. PP70/IFR30 and PP70/IFR20/M8/C2 samples indicated the same mechanical properties in terms of elastic module value. Increasing of mica content increased elastic module but decreased tensile strengh and strain values. PP70/IFR20/EG2/M8 and PP70/IFR20/M8/C2 showed the same tensile strength and strain values but the formula containing expandable graphite indicated lower elastic modulus. Consequently, it is observed that the usage of colemanite, mica and expandable graphite in certain proportions instead of IFR into the PP compound doesn't adversely affect the mechanical properties of final compound. Flame retardant additives don't improve impact resistance and also don't create a synergistic effect in terms of izod impact properties. In the mica, colemanite and IFR mixtures, when mica used at 8 wt% loading level, HDT value reached to 94.5℃. When colemanite amount started to increase in the compound with mica and IFR, HDT values decreased. In the expandable graphite mixtures, expandable graphite filled flame retardant compound reached to 96.2 ℃. According to all test results, mica and colemanite materials can show synergistic effect when they used with IFR in PP compound at reasonable amount. Especially, colemanite is abundant and commercial available material in Turkey. Usage of this material with reduction of IFR amount in the final compound will bring cost reduction and national resource will be used.
Production and characterization of thermoplastic elastomer foams based on styrene-ethylene-butadiene-styrene and polypropylene

(Graduate School, 2022-05-30) Kıroğlu, Ceren ; Kızılcan, Nilgün ; 515142010 ; Polymer Science and Technology

Bu çalışmada, köpürtme teknolojisi yüksek darbe dayanımı ve sönümleme özelliklerine ve aynı zamanda düşük yoğunluk ve sertlik değerlerine sahip malzeme özelliklerini karşılamak üzere etkin bir yöntem olması sebebiyle seçilmiştir. Köpürtme teknolojisi ve termoplastik elastomerlerin bir araya gelmesi pek çok yeni ve potansiyel uygulama alanına zemin hazırlamaya devam etmektedir. Bu çalışmanın kapsamında, SEBS/PP köpüklerin farklı bileçimleri iki farklı köpürtücü ajanın üç farklı oranı kullanılarak hazırlanmıştır. Buna ek olarak, SEBS/PP bileşimlerinin üç farklı tipteki inorganik dolgu ile, üç farklı SEBS/PP oranıyla numuneleri hazırlanarak, elastomer ve termoplastik oranının ve inorganik dolguların köpük ve TPE malzemeler üzerindeki etkisi araştırılmıştır. Bu çalışma kapsamda hazırlanan malzemelerin elektronik ev eşyalarında kullanılmakta olan elastik conta malzemelerine alternatif olması beklenmektedir.
Double layer thermoplastic polyurethane-gelatin electrospun wound dressings for biomedical applications

(Graduate School, 2022-06-23) Yıldırım, Arzu ; Güner, F. Seniha ; Taygun Erol, Melek Mümine ; 515191019 ; Polymer Science and Technology

Electrospinning is the technique to produce nano or micro scale fibers. Since this technique offers high surface area to volume ratio and porous structure, the dressing mimics the extracellular matrix (ECM). This technique gives the opportunity to use synthetic and natural polymers, active agents or essential oils, for that reasons it is a commonly preferred technique to produce wound dressings. Besides, to be able to add more features to the wound dressings double layer electrospun dressings have been made recently. Therefore, top layer which basicly includes synthetic polymers and active agents mimicks the epidermis layer, wheras sublayer with natural polymers and active agents mimicks the dermis layer of the skin. In this study, double layer nanofiber mats were produced by electrospinning technique. Each layer had a St. John's Wort oil (Hypericum perforatum oil) to provide a curative effect on the wound healing process. Top layer, which includes thermoplastic polyurethane (TPU) and Hypericum Perforatum Oil, was elastic, prevented water and pathogen transition and gave mechanical strength to the electrospun mat. On the other hand, the bottom layer which basically includes cold water fish gelatine and Hypericum Perforatum Oil firstly aimed to repair by being a source of collagen. With these properties the top layer and bottom layer mimic the epidermis and dermis layers of the skin, respectively. Besides, plasma treatment was applied as a surface activation technique for the TPU electrospun mat to have better adhesion to hydrophilic gelatin electrospun layer. By this way, better packing was obtained between the layers. Morphological and chemical characterization, water vapor transmission rate, absorption tests and antibacterial property test were done to the dressings. According to the result, a homogenous fiber structure was obtained. The Sample 2 showed antibacterial property and suggested for moderate to highly exudative wounds. On the other hand, Sample 3 which was a plasma treated sample also had homogenous, bead free fiber structure, showed antibacterial activity and suggested for moderately exudative wounds, but it had lower active agent release during the test period due to better packing between the layers with plasma treatment. Sample 3 had lower active agent release during the test period. Therefore the sample could be suggested for long term remedies. Overall results indicated that obtained nanofiber dressings can be a good candidate as a wound dressing material.
Development of adhesive resin systems with low formaldehyde emission for the wood based panel industry

(Graduate School, 2022-06-23) Alkan, Ümran Burcu ; Kızılcan, Nilgün ; 515172005 ; Polymer Science and Technology

Industrial products that are obtained by mechanically chopped, shredded and ground log wood into fiber, chip or layer and bonding these structures with a resin at high temperature and pressure are named as wood based board or composite wood based panel. Particleboard, medium density fiberboard, plywood, oriented particle board can be listed as the most important wood-based panel types. Formaldehyde is a chemical that has been the subject of a wide variety of industrial processes and is a raw material in the production of urea formaldehyde (UF), phenol formaldehyde (PF), melamine formaldehyde (MF) and melamine urea formaldehyde (MUF) resins. These resins have also been used for years to bind wood fibers and chips in the production of wood-based composite panels. In particular, urea formaldehyde (UF) resin is the most preferred one in the wood-based panel industry due to its cheap, transparent color, fast curing, low viscosity and easy application. However, wood-based composite panels that are produced with formaldehyde containing resins cause free formaldehyde emissions that negatively affect the environment and human health. Emission release can continue for long periods after the production of the panel product, especially under variable temperature and relative humidity conditions. Strict regulations have been imposed on the formaldehyde emissions to be released by wood-based boards produced with binders containing formaldehyde. Emission classes have been defined and the limitations have begun to be secured by legal sanctions. The ultimate aim of the thesis is to press wood-based particleboards with low formaldehyde emission without sacrificing quality. In this thesis, two different studies were carried out with urea glyoxal and urea formaldehyde resins and particleboards pressed with these resins were evaluated. In the first study, glyoxal, an aliphatic dicarbonyl aldehyde was employed instead of formaldehyde for resin synthesis. Urea glyoxal (UG) and urea melamine glyoxal (UMG) resins were synthesized without using formaldehyde and the effects of melamine content were determinated by substituting melamine instead of urea (10% and 20%). The reaction mechanism of urea with glyoxal in acidic environment at elevated temperature is based on two stages. In first step, the nitrogen atom of urea is bonded to the carbon atom of glyoxal, forming the carbon-nitrogen bond. The latter is based on transfer of the hydrogen atom on nitrogen to oxygen atom and forming the hydroxyl bond. The reaction of melamine and glyoxal proceeds as same steps. Usage of melamine within the scope of this thesis study was evaluated in order to increase the cross-linking on the resin due to containing benzene ring and three amine groups on the ring. In order to act as a hardener for urea glyoxal and urea melamine glyoxal resins, an acid ionic liquid that called as N-methyl-2-pyrrolidone hydrogen sulfate was synthesized.Ionic liquids are defined as organic salts that contain a small molecule inorganic/organic anionic structure and a relatively larger cationic structure. These salts have a wide range of uses as polymerization media in various polymerization processes, separation techniques for polymer gel electrodes, and also as catalysts. Ionic liquids are also important for green chemistry as they have low toxicity and volatility properties. FTIR-ATR, DSC, TGA, 13C NMR, SEM and SEM-EDAX studies were carried out for the characterization studies of the synthesized resins. FTIR-ATR spectroscopic experiments, showed characteristic peaks of the resins were determined separately as UG, UMG10% and UMG20%. The temperatures at which resins start to cure, with and without catalyst, were determined with DSC analysis. A small endothermic peak was seen non catalyst resins due to glyoxal, which does not initially react. This peak was not observed in the resins with catalyst due to the ionic liquid reacting with glyoxal. The initial temperature of curing started at 180-200oC and melamine allocation caused decreasing of temperature. Furthermore, decreases were observed in terms of both curing temperatures and enthalpy with the usage of catalyst. Resins that contained melamine, this decrease was more sharply. In this way, it is concluded that both melamine and ionic liquid usage caused the curing reaction to take place more easily. The thermal degradation behavior of the resin samples is determined by TGA and it has been observed that this degradation occurs between 180-300oC.13C NMR, the sequence of carbon atoms of the resin was determined. Resin appearances and elemental compositions were obtained with SEM and SEM-EDAX. The presence of melamine further clarified the crystalline appearance on the surface, while a smooth and homogeneous surface is observed of the system cured with ionic liquid. Particleboards that were pressed with UG, UMG10%, and UMG20% with N-methyl-2-pyrrolidone hydrogen sulphate as a hardener, in 12 mm thickness and density of 700 kg/m3, were evaluated in terms of both mechanical properties and formaldehyde emission. The test specimens, which were subjected to internal bond, bending strength, elastic modulus and surface strength tests, were classified according to the EN 312 standard. All samples fulfilled the P1 classification. According to particleboard results, the best mechanical properties of internal bond and elastic modulus were obtained with 10% melamine substitution, flexural strength and surface toughness values that decreased depending on the amount 20% usage of melamine. Formaldehyde emission was determined according to EN 12460-5 and all particleboard samples were fit with European E1 norms. In addition, using the approaches that given in literature, all of the particleboards fulfill CARB II, E0 and F**** classifications. In this study, UMG10% with acid ionic liquid was recommended as non-formaldehyde resin system. In the second study, urea formaldehyde resin was synthesized and in-situ usage of lignosulfonate and/or 1,4 butanediol diglycidyl ether was investigated. Lignosulfonates are defined as lignin polymers that contain water-soluble sulfonate groups. Glycidyl ethers are chemicals that ended with mono or poly functional oxirane groups with low viscosity. In this study, four different resin syntheses, namely UF, UF-LS, UF-GE and UF-LS-GE, were conducted. Synthesis of UF resin was done by the traditional three stage alkaline-acid-alkaline method. For UF-LS, the same method was followed and calcium lignosulfonate was hydroxymethylated in an alkaline medium to react with excess formaldehyde in the first stage and to participate the polymerization by condensation. For UF-GE, resin synthesis was started in an alkaline environment such as UF, and polymerization was advanced by adding 1.4 butanediol diglycidyl ether in the second step. Polymerization was advanced as a result of ring opening of oxirane rings in an acidic medium and reaction with hydroxymethylated urea. FTIR-ATR, DSC, XRD, 1H NMR, 13C NMR, SEM, and SEM-EDAX analyses were carried out for characterization. FTIR-ATR spectroscopic experiments, the characteristic peaks of the resins were determined separately for UF, UF-LS, UF-GE, and UF-LS-GE. No distinctive peak was observed in the modified resins for this study, apart from the peaks that were seen in UF resin; For this reason, 1H NMR and 13C NMR studies were carried out to determine the structural formulas of the resins, the positions of hydrogen and carbon atoms. The curing temperatures and enthalpies of the resins were determined by DSC analysis. A single exothermic peak seen in a wide range of UF resin showed two different peak structures relatively narrow in the presence of LS or GE. The second peak was attributed to the degradation of the methylene ether bridges. On the other hand, single usage of LS or GE decreased the cure temperatures and significantly lowered the enthalpies. Combinated usage of LS and GE, curing temperature had an increasing trend and a single curing peak was observed. In addition, the combination of LS and GE reduced the enthalpy value by nearly half compared to the standard UF resin. The crystalline structures of the resins were examined and the crystalline regions specific to UF resin were determined by XRD analysis. In this analysis, it can be said that GE had a decreasing effect on crystallinity. Resin appearances and elemental compositions were obtained with SEM and SEM-EDAX. Different agglomeration properties were observed for UF, UF-LS, UF-GE, and UF-LS-GE. Particleboards pressed with NH4Cl as a catalyst on synthesized resins (UF, UF-LS, UF-GE, and UF-LS-GE) with thickness of 16 mm and density of 650 kg/m3 were evaluated in terms of both mechanical properties and formaldehyde emission. The test specimens, which were subjected to internal bond, bending strength, elastic modulus and surface strength tests, were classified according to the EN 312 standard. Particleboards pressed with UF, UF-LS and UF-GE fulfilled the P2 class by meeting the requirements for boards that are used in interior equipment (including furniture) in dry conditions. Especially LS or GE had a positive effect on the internal bond compared to the standard UF resin. Usage of GE for flexural strength, flexural modulus and surface strength tests; for internal bond, the use of LS provides the optimum effect. On the other hand, particleboard samples pressed with the UF-LS-GE met P1 class that is named as the board used in dry conditions for general use. Although the boards show a decreasing trend in flexural strength, flexural modulus and surface durability tests for UF-LS-GE, these properties fulfilled with P2 class however, for internal bond, these particleboards only met the P1 class due to the resin's insufficient bonding with wood. The reason for this situation is considered as relatively high temperature and time required for the bonding of LS and GE during panel formation. In the wood-based panel industry, panels are generally pressed at 180-200oC and 3-5 minutes. During hot press, this temperature reaches only 100-110oC for core layer. These parameters were not fully sufficient for full curing of particle board pressed with UF-LS-GE; however, it is evaluated as P1. Formaldehyde emission was determined according to EN 12460-5 and all particleboard samples comply with E1 norms. Especially, LS modification gave the formaldehyde reduction effect. The effect of GE on formaldehyde emission for particleboard is determined as relatively low. In the combination of LS and GE, it caused an increase in emission as a result of not full curing compared to the standard UF resin. In this study, it can also be interpreted that UF-LS provides F** and CARBI classes by using the approaches that were determined in the literature.
Fabrication of caffeic acid grafted poly(lactide)-b-poly(hydroxyethylmetacrylate) films

(Graduate School, 2022-09-19) Düz, Gamze ; Kahveci, Muhammet Übeydullah ; 515191004 ; Polymer Science and Technology

In this study, we aimed to prepare an antimicrobial, PLA-based partially degradable caffeic acid functionalized film that has the potential to be used in active food packaging. We report a synthetic route for the functionalization of poly(D, L-lactide)-b-poly(2-hydroxyethyl methacrylate) copolymer grafted with caffeic acid. First, we synthesized a dual initiator, namely 2-Bromo-N-(5-hydroxyphenyl)2-methylpropanamide (BNMP) (yield = %58), bearing ATRP initiator and ring opening polymerization. The initiator was synthesized via an amidation reaction between 5-amino-1-pentanol and 2-bromoisobutyryl bromide in the presence of triethyl amine. Firstly, ring-opening polymerization of D, L-lactide was achieved via the hydroxyl group of BNMP using tin(II) 2-ethyl hexanoate (Sn(Oct)2) as catalyst (Mn = 9800 g/mol). This polymerization was carried out by the melt polymerization method. Secondly, 2-hydroxyethyl methacrylate (HEMA) was polymerized through atom transfer radical polymerization (ATRP) using poly(D, L-lactide) macroinitiator yielding the block copolymer, PLA-b-PHEMA. Eventually, the block copolymer was functionalized via a Steglich esterification reaction between caffeic acid and hydroxyl groups of the PHEMA segment to obtain PLA-b-PHEMA-g-CA. The polymers were characterized by size exclusion chromatography (SEC), nuclear magnetic resonance spectroscopy (NMR), ultraviolet-visible (UV-Vis), and infrared (IR) spectroscopies. The grafting degree was calculated by using the regression line of caffeic acid standards at known concentrations and was found 60.7%. The bioactivity of the caffeic acid-functionalized block copolymer was investigated with DPPH for radical scavenging activity and antimicrobial activity against gram-positive (S. aureus.) and gram-negative (E.coli) bacteria. The films were prepared by mixing different amounts of PLA-b-PHEMA-g-CA with a high molecular weight of commercial PLA via solvent casting technique. The mechanical properties of the films obtained from the mixture of copolymer with high molecular weight PLA were also examined. To gain further insight, the thermal and surface properties of the films were evaluated with differential scanning calorimetry (DSC) measurements and water contact angle measurements(WCA), respectively. According to the results, the synthesized PLA-b-PHEMA-g-CA polymer showed bioactivity.
Development of cornstarch and tannin-based wood adhesives for interior particleboard production

(Graduate School, 2022-09-22) Oktay, Salise ; Kızılcan, Nilgün ; 515182005 ; Polymer Science and Technology

Wood-based panel industry is an important industry that produces wood-based panels such as furniture and parquet, which we frequently use in our daily lives, on an industrial scale. Particleboard is one of the most important products frequently produced in the wood-based panel industry. Particleboard is a composite product. It is made by turning the logs into chips and pressing the formed chips in a hot press by mixing with a thermoset resin. Therefore, the thermoset resin used in particleboard production, as well as the wood raw material, is of great importance in terms of the final properties of the final product. Thermoset resins, which are frequently used in the wood-based panel industry, are based on formaldehyde such as urea formaldehyde and melamine formaldehyde. Cost advantage and high reactivity of formaldehyde-based resins are the most important reasons for their frequent preference. Today, one of the most important problems of the wood-based panel industry is formaldehyde emission. Formaldehyde is classified as a carcinogenic substance and threatens human and environmental health. Therefore, there are formaldehyde emission limits that become more restrictive day by day. Some of the factors affecting the formaldehyde emission of wood-based panels are the formaldehyde found in the natural content of the wood raw material, the type of wood raw material used, and hot press conditions. Apart from these, it is known that one of the most important factors affecting plate formaldehyde emission is formaldehyde-based thermoset resins used as binders. It is known that the formaldehyde content of these resins, which are not involved in polymerization and released, and especially when the urea formaldehyde resin is exposed to moisture and temperature, hydrolysis and release of formaldehyde increase the formaldehyde emission values of the boards. In addition to the fact that formaldehyde-based resins cause formaldehyde emission, they are produced from petrochemical raw materials. Formaldehyde emission caused by formaldehyde-based resins and their synthesis from petrochemical raw materials has pushed the industry and academia to resins that can be synthesized with the use of sustainable raw materials that can be an alternative to formaldehyde-based resins in terms of performance and cost. In the doctoral dissertation conducted in cooperation with Kastamonu Integrated Wood Industry, which is a global power in its sector, and Istanbul Technical University, it was worked on the development of resin formulations containing corn starch - tannin to be used in the production of particleboard suitable for internal applications. Physical and chemical properties of synthesized resins were determined. In order to examine the performances of suitable resin formulations, paticleboard production was carried out in laboratory scale. In addition to the physical and mechanical tests of the particleboards, formaldehyde emission tests were performed. The formaldehyde emission of the produced boards was determined by the perforator method. The physical and mechanical results obtained were evaluated by taking into consideration the particleboards for use in interior applications and their properties standard TS EN 312 standard P2 class limit values. Production of laboratory scale particleboards and physical, mechanical and perforator tests of the produced particleboards were carried out with the support of Kastamonu Integrated Wood Industry R&D department.
Electrospun polyacrylonitrile based composite nanofibers containing polyindole and graphene oxide

(Graduate School, 2023-03-06) Gergin Bozkaya, İlknur ; Saraç, Sezai A ; 515092003 ; Polymer Science and Technology

Studies on the conductive polymers has gained great interests when the Nobel Prize in Chemistry was awarded by discovery and development of the conductivity of polyacetylene in 2000. Conductive polymers are also called organic metals. They conduct electricity thanks to the conjugated chain structure consisting of consecutive single and double bonds in their structures. Conductive polymers, which are insulating in neutral state, gain conductivity by doping. Polyacetylene, polypyrrole, polythiophene, poly(3,4-ethylenedioxythiophene) (PEDOT) are some of the conductive polymers that have been studied extensively. These polymers can be used in solar cells, super capacitors, chemical and biosensor application areas. Polyindole (PIN) is one of the conductive polymers which can show electrochromic properties with high redox activity, good thermal stability, slow degradation rate and good air stability. Polyindole containing studies have been increasing in recent years and this polymer can be used in the pharmaceutical field, anticorrosion coatings, photovoltaic batteries, supercapacitor applications or anode material in batteries. On the other hand, with the advancement of nanotechnology, it has been found that materials in nano scale show physical and chemical property differences compare to the bulk form. Nanoscale generally includes the range of 1-100 nm. When the size of the particle in the material becomes too small, the electronic structure of the material can change. For example; gold normally does not react, but can be active at the nano level. Nanofibers are fibers with a high length/volume ratio with average diameters in the order of nanometers. In addition to their chemical properties also depending on the surface properties such as morphology and topography, materials can improve and can be used various areas. Due to their low densities, large surface areas with porous structures, it has a wide range of research and application areas of nanofibers such as filtration, tissue engineering, drug release systems, biomedical, textile, energy storage and sensor. Especially in recent years, electrospinning technique has attracted interests by scientists to generate nanofibers because of it is extremely simple, cheap and practical usage. On the other hand, scientists have great expectations since discovering a few atoms thick materials. Graphene oxide (GO) is a two dimensional material with high surface area. It can be semiconductor or insulating material which depends on the degree of oxidation, sheet size, microstructure and among many other factors. Moreover, graphene oxide contains some functional groups (epoxy, hydroxyl, carbonyl, etc.) on the structure which makes the dispersive ability in the solvent. These oxygen containing functional groups enable the development of GO-based composites, especially due to their ability to disperse in the solvent. Unfortunately, nanofiber production from conductive polymers and GO like materials can be limited or not possible by electrospinning method. For this reason, nanofibers of conductive polymers and GO are produced by making blend or composite with a different polymer called as carrier polymer, whose nanofibers can be easily obtained by electrospinning. Polyacrylonitrile (PAN) is one of the carrier polymer which is a very common usage area especially in the textile manufactory and carbon fiber production. Also, PAN fibers are the precursor of high quality of carbon fibers. PAN is choosen as a carrier polymer and PAN based composites are studied in this thesis. In the first part of the study; the oxidative chemical reaction of polyindole has taken place in the presence of FeCl3. Nanofibers were produced by mixing polyindole with polyacrylonitrile in N, N-Dimethylformamide (DMF) solvent at different weight / volume ratios. Polyacrylonitrile and polyindole blends were generated in different proportions of polyindole. Composite fibers were produced from the solutions by adjusting the optimum conditions using electrospinning method. Morphological, thermal properties, spectral analysis of these fibers were investigated by Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (FTIR-ATR) and Differential Scanning Calorimetry (DSC). Electrochemical characterization of fibers has been studied by Electrochemical Impedance Spectroscopy (EIS). The experimantal data was used to fit the equivalent circuit with Zsimpwin Software. In addition, it was found that the electrochemical properties (such as double layer capacitance, solution resistance and charge transfer resistance) of composite fibers were effected by surface tension and conductivity of solution. Iron, is an important element in the industry, environment, medical applications areas, biological studies and human health. Different methods such as electron spin coulometry and ion selective electrodes are used in the determination of Fe(II). Differently, in this study, Electrochemical Impedance Spectroscopy is presented as an alternative technique to determine Fe(II) concentration. Electroactive behavior of the fiber electrode was investigated by Cyclic Voltammetry (CV). Electroactivity of the nanofiber selected depending on the impedance and morphological properties of the nanofibers was measured with the help of K3Fe(CN)6/K4Fe(CN)6 electrolyte. It was discussed that the presence of Polyindole (PIN) content showed an electrocatalytic activity against K3Fe(CN)6/K4Fe(CN)6. The lowest Fe(II) ion analyte concentration detection limit for the selected electrode was calculated as 1x10-4 mol.l-1. In the second part of the study which is different from the first part, graphene oxide (GO) is choosen as a material to improve the capacitive property of Polyacrylonitrile. Polyacrylonitrile / Graphene oxide (GO) nanofibers were produced by using a rotary collector instead of a fixed collector in the electrospinning device. Thus, thinner, more aligned nanofibers with higher young modulus were acquired. Oxidative stabilization and carbonization applied to composite nanofibers through the thermal process. In particular, the stretching applied to the nanofiber during oxidation determines the mechanical strength and structure of the final product carbon nanofiber to be formed. Therefore, understanding of the oxidation mechanism is an essential part of the production of carbon nanofibers (CNFs). The stress, temperature and application time utilized to the material in oxidation affect the structure of the carbon nanofiber. Oxidation step of electrospun polyacrylonitrile based composite nanofibers was studied and morphological, spectral and electrochemical properties of composite nanofibers were investigated. Morphological and spectral characterizations of composite nanofibers were performed by FTIR-ATR and Raman Spectroscopy, SEM, AFM and Transmission Electron Microscopy (TEM). Mechanical tests were performed with Dynamic Mechanical Analysis (DMA). Thermal behaviours of composite nanofibers were investigated by Thermal Gravimetric Analysis (TGA). Capacitive behavior of nanofibers were performed by EIS and CV. When there is GO in the structure, the ions in the solution can penetrate into the pores which cause the double layer capacitance (Cdl) value increasement. Average pore diameters have been measured with the ImageJ program to be around 38.5 nm and it has been found that the double layer capacitance (Cdl) of PAN nanofibers containing GO is 0.600 µF which is the highest value. Also, it was observed that the capacitive behaviour of carbon nanofiber formed in the presence of graphene oxide improved. PAN/GO carbon nanofibers exhibit potential for capacitive applications in the light of these results. In the third part of the study, X-ray Photoelectron Spectroscopy (XPS) and FTIR analysis methods were used to understand the oxidative stabilization deeply. The thermal oxidative stabilization of polyacrylonitrile has a complex mechanism with the cyclization and dehydrogenation steps. Polyacrylonitrile (PAN) composite nanofibers with GO were fabricated, and thermal oxidation were performed to these nanofibers. The oxidation process were applied at various temperatures (250 0C, 280 0C, and 300 0C) during 1h and 3h. Nanofibers were significantly effected by high temperature with during long duration time. The effect of GO addition into the nanofibers were analyzed by XPS, FTIR-ATR and, EIS. After heat treatment, change in C1s spectra and development of sp2 carbon was detected by XPS. It was concluded that the presence of GO accelerated the oxidation mechanism and developed the final structure.
Rigid polyurethane foams with improved reaction to fire and low emission properties

(Graduate School, 2023-03-16) Değirmenci, Berrin ; Köken, Nesrin ; Salatelli, Elisabetta ; 515112009 ; Polymer Science and Technology

In this work, different combustion modifiers were evaluated in rigid polyurethane/polyisocyanurate foam with regard to their reaction to fire and emission performance. Terminology of combustion modifiers cover both flame retardants and smoke suppressants. The difference between flame retardants and smoke suppressants derive from the action they exhibit during the combustion. Flame retardants delay the combustion action whereas smoke suppressants aid lowering the smoke and harmful compounds generated during the burning of the substance. Having said that it in the research or in the application area, it is possible to see that combustion modifiers and flame retardants definitions can be used interchangeably. Initially, a literature screening was completed to choose the right flame retardants that are commercially available for rigid polyurethane foams. While most of the found candidates are phosphorous based, few examples such as Hexion TL 91-805D polyol that is nitrogen based, was also in scope. In the flow of the study, flame retardants were then classified according to being reactive or not towards isocyanates. This classification is particularly important when evaluating emission performance of the said substances. On the smoke suppressants side, Zinc borate and ferrocene represent non-phosphorous substances that are suitable to incorporate in this particular application. Performance examination of each combustion modifier was completed using 2 methodology. First methodology was determined as the incorporation of one combustion modifier each time at the same weight in the selected formulation. It was then followed by the incorporation of a combination of one flame retardant and one smoke suppressant in rigid Polyurethane foams. DIN 4102 small scale flame device and NBS smoke chamber instruments were chosen to perform the analysis. This method was useful to reveal synergy between different candidates in the foams. Results showed that among the candidates, interaction of Triethyl phosphate and Zinc Borate as well as Triethyl phosphate and Ferrocene created a synergic impact and greatly improved combustion properties in Polyisocyanurate foams. For the investigation of the found results, thermogravimetric and scanning electron microscope characterizations were carried out. It was revealed that Zinc borate creates a thermal barrier and prevents the cell from a complete destruction once the foam is exposed to ignition. While reaction to fire performance was improved, it was detected that addition of Zinc borate has an impact on the reactivity and free rise density of the foams. Gel time occurred to be longer and density of the foams were measured to be higher with respect to reference. This might be explained by Zinc borate acting as an inert filler. Triethyl phosphate-Ferrocene study also put forward interesting results. While addition of a little amount of Ferrocene provided the best fire performance in rigid Polyisocyanurate foams, more than certain amount of Ferrocene incorporation has led the complete burning of the foam. Therefore, for an enhanced smoke and fire performance, Ferrocene amount should be optimized in the formulations. In the latter step, three compound combustion modifier combinations were examined. Loading of oligomeric Triethyl phosphate into the Triethyl phosphate and Zinc borate combination aided to provide superior performance in fire properties with respect to Triethyl phosphate and Zinc borate containing foam. To confirm the results with the same amount of combustion modifiers loading, the second methodology was used: Analyses were successively repeated by adjusting the foams to the same molded density and P% content in the final material. A cone calorimeter was selected to perform the ultimate combustion test and displayed additional parameters such as Total Heat Release, Peak Heat Release Rate, and Total Smoke Production in 11 formulations. The outcome of the cone calorimeter study was evaluated using Triethyl phosphate (mod 1) containing formulation as the reference. In this way, it was possible to confirm the synergism in other formulas. Formulations that surpassed the performance of reference foam were found to be the same as those completed in the laboratory: Triethyl phosphate-zinc borate (mod 3), Triethyl phosphate-ferrocene (mod 12), and Triethyl phosphate-oligomeric Triethyl phosphate-zinc borate (mod 9) combinations. These 3 combinations displayed either a lowered Total Heat Release or Total Smoke Production Rate or both than the reference. In the final stage, further analysis was completed to check the emission properties of these 3 foams and reference using the Headspace gas chromatography-mass spectrometry characterization method. While Triethyl phosphate showed an elevated pique especially in the reference foam due to the high addition amount, Ferrocene also confirmed to migrate because of the sublimation at high temperatures. Cone calorimeter and headspace analysis confirmed that the Triethyl phosphate-oligomeric Triethyl phosphate-zinc borate combination proved to be the most efficient combination with regards to both reactions to fire and emission properties in rigid Polyisocyanurate foams. This result is also proof of how oligomeric substances can enhance the emission properties of end material. As a final word, this study showed that the fire and emission properties of rigid Polyurethane Polyisocyanurate foams can be enhanced through the addition of the right combustion modifiers at the right amount. Said properties are not only governed by the P% content but also synergism and molecular structure might play an important role in improving the properties in polyurethane formulations.
Post-polymerization modification of poly(vinylene sulfide)s

(Graduate School, 2023-08-09) Kakaş, İbrahim Ethem ; Günay, Ufuk Saim ; 515211008 ; Polymer Science and Technology

The demands for the fast synthesis of a significant number of target compounds could not be met by conventional chemical synthesis. The "click chemistry" was presented as a solution to this problem based on the biosynthesis pathways and the synthesis of natural products. It is revealed in 2001 by a team of chemists at The Scripps Research Institute, led by K. Barry Sharpless. Click reactions are defined as a group of reactions function well in a variety of environments, which are simple to carry out, produce their intended products in extremely high yields with few to no byproducts, are unaffected by the nature of the groups' connections to one another and exhibit great stero- and regio-selectivity. Additionally, click reactions allow for facile product separation ways. The copper (I)-catalyzed azide-alkyne cycloaddition, an enhanced variant of the Huisgen azide-alkyne dipolar cycloaddition, is the most used click technique. Cu(I) toxicity was yet another disadvantage; it is still unsuitable for biological uses. To address this issue, numerous metal-free "click" reactions were developed to polymer chemistry. Among them, thiol-yne click and thiol-ene click reactions became popular for polymer chemists. The Michael addition reaction is a flexible synthesis technique for the effective coupling of a wide range of nucleophiles with electron deficient olefins. When Michael donors are thiols and Michael acceptors are α-β unsaturated carbonyl compounds, the reaction is called as thiol-yne or thiol-ene addition. Thiol-yne and thiol-ene are robust click reactions that are unaffected by water and produce few and harmless byproducts that can be easily removed. Recent developments of base catalysis enabled high yields with high reaction specificity. The heteronucleophilic conjugate addition reaction involving sodium thiophenolate and propiolates to produce unsaturated esters was first found by Ruhemann shortly after Arthur Michael's initial study on the conjugate addition of carbon nucleophiles to unsaturated substrates. Under ambient reaction conditions, quantitative conversions may be seen, which is undoubtedly made possible by the strong nucleophilicity of the thiolate anion and/or the utilization of highly electrophilic alkynes. The synthesis of acetylenic polymers containing heteroatoms presents considerable importance. One method employed to synthesize these polymers is alkyne hydrothiolation, which involves the combination of alkynes and sodium thiolates to produce vinyl sulfides. The concept of the "hydrothiolation" reaction was initially introduced by Truce and Simms in the 1950s. Alkynes can be hydrothiolated with aryl/aliphatic thiols to form vinyl sulfides by radical, nucleophilic or metal-catalyzed routes. By the nucleophilic and metal-catalyzed alkyne hydrothiolation processes both anti-Markovnikov (linear) and Markovnikov (branched) products are produced, while only anti-Markovnikov (linear) products are produced by the radical alkyne hydrothiolation method. The drawback of metal catalyzed route is the requirement of heat and for the radicalic route, the inorganic bases were not suitable to aryl thiols. While the radicalic reaction can be initiated by thermal or UV irradiation, the nucleophile-catalyzed pathway requires an electron-deficient alkyne or alkene with an adjacent electron-withdrawing group, such as an ester, amide, or cyanide. The nucleophilic thiol-ene addition is constrained by the availability of the activated alkenes, but it also benefits from mild reaction conditions, no detectable byproducts, and high conversion is possible under ideal reaction conditions. The development of organobases such as diethylamine, triethylamine, diphenylamine, DABCO enabled the efficient reaction conditions for hydrothiolation of activated alkynes. Thus, it is demonstrated that the hydrothiolation reaction may be carried out under ideal conditions with high yields by using the nucleophilic pathway catalyzed by organobases and adapting it to the polymer science. Tang and colleagues applied the hydrothiolation procedure to polymer science. In the presence of several secondary and tertiary amines, such as diethylamine, triethylamine, diphenylamine, triphenylamine, and morpholine in high concentrations, they carried out polyhydrothiolation of aryl dithiols with arylacetylenedicarboxylates in the presence of organobases. They also discovered that poly(vinylene sulfide)s had molecular weights up to 32.3 kDa in high yields. For organobase selection part a study conducted by Durmaz and coworkers was taken as a reference. Durmaz and colleagues investigated the systematic and selective modification of the electron-deficient triple bond using thiols via nucleophilic thiol-yne interactions. They developed a polyester with an internal electron-deficient alkyne molecule, and on this scaffold, they investigated amino-yne and thiol-yne processes. The effectiveness of several amidine and guanidine bases, as well as various nitrogen and phosphorus-based catalysts, was examined in nucleophilic thiol-yne reactions. In-depth 1H NMR investigations showed that when the nucleophilic catalysts 1,4-diazabicyclo[2.2.2]octane (DABCO) and 4-(dimethylamino) pyridine (DMAP) were utilized in the reactions, only mono thiolation was seen even though 1.2 equivalents of thiols (per alkyne) were applied. High efficiencies, such as 90 and 84%, were demonstrated by DABCO and DMAP. Additionally, the end products showed mixed stereoregularities. The catalysts were then tested using the amidine base 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) and the guanidine bases 1,1,3,3-Tetramethylguanidine (TMG) and 1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD). For DBU, TMG, and TBD, respectively, the efficiency for the mono additions was determined to be 83, 86, and 74%. These bases effectively facilitated the thiol-yne reaction. It is interesting that although using the same amount of thiol for each alkyne repeating unit, these catalysts, as measured by 1H NMR, also generated the double addition products (8%, 4%, and 15% for DBU, TMG, and TBD, respectively) in addition to the mono addition products. According to this study, TBD was preferred for double addition of thiols onto electron deficient vinylene sulfide units during the thiol-ene click reaction due to its efficiency and DABCO was preferred for mono addition of thiol onto the electron deficient alkyne moieties during the thiol-yne polymerization reaction due to its efficiency. Poly(vinylene sulfide)s possess activated double bonds. These double bonds can be crosslinked and functionalized with thiols in the presence of organobases. There are several studies about functionalization of electron deficient alkyne units. In this manner, the synthesis of a polymer with electron-deficient alkyne groups was the subject of research by Thayumanavan and colleagues. On this polymer, they applied thiol-yne and thiol-ene addition processes using reversible addition-fragmentation chain-transfer (RAFT) polymerization. The electron-deficient alkyne groups were modified with thiols in their work using Et3N as an organocatalyst. The thiol vinyl ether functional groups of the resultant homopolymer were modified using a potent base, TBD, to introduce thioacetal linkages in the pendant group as well. This work was an example of post-polymer modification of pendant electron deficient alkene units. Post-polymer modification of electron deficient alkene units was also conducted by Durmaz and coworkers. They employed unsaturated polyester (UP) scaffold for this purpose. By esterifying maleic anhydride with 1,4-butanediol an unsaturated polyester (UP) scaffold was created. Then, in the presence of TBD in CHCl3, this polyester scaffold was altered using different thiols. This was an illustration of post-polymer functionalization of electron-deficient alkene units in the main chain. Truong and Dove conducted a separate study on the functionalization of electron-deficient alkene units. In their research, they initiated the reaction between dodecane-1-thiol and PEG32-bispropiolate using a catalytic amount of Et3N. Then, they modified vinylene sulfide with benzylmercaptan in the presence of TBD. The purpose of this study is to synthesize polymers with electron deficient vinylene sulfide units in the main chain and modifying them with various thiols in the presence of an organocatalyst. In this work firstly, propiolic acid and ethylene glycol were reacted in the presence of p-toluenesulfonic acid monohydrate at 105 ℃ in benzene to obtain a symmetrical ester with two activated alkyne moieties. The product, ethane-1,2-diyl dipropiolate was reacted with 1,6-hexanedithiol in the presence of an organocatalyst DABCO at room temperature which yielded poly(vinylene) sulfide. Activated double bonds of the synthesized poly(vinylene) sulfide were modified with various monothiols (1-octanethiol, 2-mercaptoethanol, 2-furanmethanethiol, benzylmercaptane, 2-propanethiol, 1-propanethiol, cyclopentanethiol, methylthioglycolate, 3-nitrobenzylmercaptan, allyl mercaptan and 2-methyl-2-propanethiol) in the presence of a strong basic and nucleophilic organocatalyst TBD, in CHCl3 with various efficiencies at room temperature. Synthesized polymers were characterized with GPC, 1H NMR and 13C NMR.
New methods in the synthesis of single-chain polymeric nanoparticles

(Graduate School, 2023-12-12) Alkan, Burcu ; Durmaz, Hakan ; Temel, İsmail Gökhan ; 515202002 ; Polymer Science and Technology

Nanoparticles can be described as nanometer-sized colloidal particles, possessing exceptional optical, electrical, and magnetic properties. Although numerous types of nanoparticles have been utilized, polymeric nanoparticles with controlled characteristics have recently drawn significant attention as a promising research topic within the field of nanoscience. The design of polymeric nanoparticles having controlled size and functionality is essential for application areas such as drug delivery, microelectronics, and catalysis. A variety of conventional methods including emulsion polymerization, interfacial polymerization, self-assembly, solvent evaporation, or supercritical fluid technology have been employed to prepare polymeric nanoparticles. However, size control and the pre-determination of the functional groups remain challenging by utilizing the above-noted methods. To address these problems, single-chain nanoparticles (SCNPs), also known as single-chain polymeric nanoparticles, have emerged as a crucial class of versatile nanomaterials by the contributions of scientists who are inspired by nature. Ever since the intramolecular crosslinking strategy was first introduced, a variety of approaches has been exploited to yield well-defined SCNPs comprising characteristic features. The intramolecular interactions enable the formation of collapsing or folding of an individual polymer chain via various physical or chemical crosslinking reactions. Due to their unique characteristics resulting from nanometer-sized dimensions (1.5-20 nm), self-crosslinked nanoparticles are of considerable scientific value for particular applications such as drug delivery, bioimaging, biosensors, and catalysis. In this regard, this thesis aimed to demonstrate the synthesis of SCNPs by utilizing intramolecular crosslinking approaches conducted under straightforward and robust reaction conditions. The structure of the precursor polymers was prepared using both polycondensation and controlled/living polymerization techniques and the in-chain crosslinking reactions were established by external addition of crosslinking agent under dilute reaction conditions. In the first study, the synthesis and the functionalization of polyester-based SCNPs are demonstrated utilizing Michael addition reactions. For this purpose, condensation polymerization was first performed to yield a polyester precursor containing reactive alkyne units in the main chain. It is widely accepted that the reactive nature of alkyne units is due to the bonding of two electron-withdrawing carbonyl groups, which renders the triple bond highly electron-deficient and thus suitable for Michael addition reactions. Hereby, linear polymer precursor was intramolecularly crosslinked to generate SCNPs through aza-Michael addition reaction in short durations and without using any catalyst. Piperazine, a secondary diamine compound was utilized as a crosslinking agent with varying ratios to adjust the folding degree and thus the size of the self-crosslinked nanoparticles. The folding procedure was conducted at dilute conditions (c = 1.0 mg mL-1 ) to prevent intermolecular interaction between the polymer chains under mild reaction conditions. Later, the feasibility of the functionalization reaction was investigated via thiol-Michael addition since the remaining alkyne units were still reactive toward the nucleophiles. It has been previously shown in the study that the utilization of a nucleophilic catalyst namely, 1,4-diazobicyclo [2.2.2]octane (DABCO) is required to perform the addition reaction of thiol compounds efficiently to the reactive triple bond. Therefore, the obtained SCNPs were functionalized with a thiol nucleophile in the presence of DABCO for 2 minutes at room temperature. In the second study, not only intrachain collapsing but also the further modification reaction was demonstrated by utilizing nucleophilic aromatic substitution reaction. Firstly, a well-defined precursor polymer with controlled molecular weight has been synthesized via ring-opening metathesis polymerization (ROMP) of oxanorbornene monomer comprising dichlorotriazine (DCT) moiety. By taking the benefits of the electrophilic feature of the chlorine atoms on DCT, intramolecular crosslinking has been performed via nucleophilic aromatic substitution reaction with the addition of a dithiol compound as a crosslinker. Double folding strategy and the post-modification reaction of obtained SCNPs were demonstrated by introducing a different dithiol and a thiol compound, respectively, since unreacted chlorine atoms were still present along the structure. Multiple characterization techniques, including NMR, GPC, DLS, and TEM were used to confirm the formation and modification of SCNPs.

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