LEE- Polimer Bilim ve Teknolojisi Lisansüstü Programı

Bu topluluk için Kalıcı Uri

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

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4D printing of body temperature responsive hydrogels with self-healing and shape-memory abilities

(Graduate School, 2024-06-25) Aydın, Gamze ; Okay, Oğuz ; Abdullah, Turdimuhammad ; 515211007 ; Polymer Science and Technology

The power of additive manufacturing (AM), also known as three-dimensional (3D) printing, is being continuously expanded by researchers who are pushing the boundaries of this transformative technology. This technique, which is a cornerstone of the fourth industrial revolution allows for the creation of complex, customised objects directly from computer-aided designs. In recent years, a revolutionary advancement within AM has emerged: four-dimensional (4D) printing. 4D printing integrates smart materials with 3D printing, enabling objects to change properties over time. The fourth dimension in the name refers to the time parameter, which arises from the change in the properties of the printed material over time. Leveraging the inherent design freedom and moldless fabrication of 3D printing, this thesis utilized stereolithography, a high-precision photopolymerization technique, for rapid, low-volume, and customized manufacturing applications. In this thesis, a hydrophobic hexadecyl acrylate (C16A) and hydrophilic N, N-dimethyl acrylamide (DMAA) and methacrylic acid (MAA) monomers were polymerized in the presence of diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide (TPO) photoinitiator using a commercial stereolithography (SLA) device without any solvent or crosslinker. In this wise, the possible toxic side effects of solvent and chemical crosslinker were avoided which are critical concerns for a potential medical application. Among the materials employed in 4D printing, smart hydrogels are highly promising. Hydrogels are particularly attractive for biomedical applications due to their biomimetic properties, which enable them to resemble the structure and function of natural tissues. However, traditional hydrogels exhibit shortcomings, including low mechanical strength and slow response times. Consequently, the development of printable hydrogels that are mechanically robust, capable of actuation at body temperature, and capable of maintaining their actuated form represents a key area of ongoing research. In this study, mechanical characteristics of hydrogels were enhanced by the synergic effect of hydrophobic interactions in C16A and hydrogen bonding in between DMAA and MAA monomers. The mechanical behavior of these physically crosslinked hydrogel was governed by the DMAA:MAA mole ratio, denoted as x_DMAA. Rapid temperature-induced actuation were also achieved successfully in less than 30 seconds. These actuations were based on the melting of the hydrophobic domains formed by the C16A units.
Applying different surface treatments on different plastic materials, examining the effect on paint test performance and developing a high-performance painting process

(Graduate School, 2022-06-23) Çetin, Elif Burcu ; Kızılcan, Nilgün ; 515181007 ; Polymer Science and Technology

Nowadays, the standard plastic part painting process which is used in the automotive industry today, consists of surface cleaning, surface pre-treatment, primer, base coat and clear coat applications. Although high performance engineering polymers have high mechanical & chemical properties and atmospheric resistance, their use in various applications is limited due to their low surface energies. For this reason, the research and development activities of surface pretreatment applications that increase the surface wetting ability in the automotive industry have increased significantly in recent years. Flame, mechanical and chemical etching, corona and plasma application methods are among the actively used and newly developed surface activation processes. In this study, test plates were prepared from polyamide (PA GF15), Acrylonitrile Butadiene Styrene (ABS), Polycarbonate/Acrylonitrile Butadiene Styrene (PC/ABS), Polypropylene (PP TD10, PP TD17, Primerless PP) polymeric materials that are used in the automotive industry. Various variations of surface pre-treatment, primer, base coat and clear coat were applied to the test plates. These variations were divided by two categories as related to surface pretreatment and primer application.Three different methods were used for surface pretreatment; (1) flame application, (2) atmospheric plasma application, (3) no surface pretreatment application. There are two conditions for primer application; (1) primer application, (2) no primer application. Application distance was determined as a variable parameter in surface pretreatment methods. Other process parameters were kept constant. This application distance was defined as 10 and 20 cm for flame application, 7 and 10 mm for atmospheric plasma application. After each surface treatment, the surface wetting abilities were analyzed by contact angle measurement and the both morphological and roughness paramter change on the surface were examined with scanning electron microscope (SEM) and 3D optical microscope device. The effect of both surface pretreatments and primer applications on paint performance tests was analyzed. Examined paint performance tests were adhesion resistance, water resistance, humidity resistant, thermal cycle resistance, impact resistance and stone impact resistance. The results of these paint performance tests were evaluated for each material as separately and the optimum painting process steps were determined as special to each polymeric material.
Catalyzing the inverse vulcanization reaction via 1,3-benzoxazines

(Graduate School, 2023) Shafizada, Ahmad ; Kışkan, Barış ; 807401 ; Polymer Science & Technology Programme

High-performance polymers take a vital role in our daily life by their commercial manufacturing and extensive range of applications in various areas like structural materials, aerospace, electronics, printed circuit boards, coatings and adhesives. Polymeric materials can be categorized as thermosets and thermoplastics according to their behavior against temperature. Thermoplastics are a resin which is solid at the room temperature, but becomes softer by increasing the heat and showing fluid behavior or properties due to the melting point or passing the glass transition temperature. Some of thermoset polymers can be consider as a high-performance polymers because of their unique features such as flame resistance, decent mechanical strength, dimensional stability and durability against many solvents. Although these remarkable advantages, they have some disadvantages like shorth shelf life, being brittle, water adsortion and etc. The common members of thermoset resins are phenol-formaldehyde, urea-formaldehyde, melamine-formaldehyde and etc. Phenol-formaldehyde resins are well-known, the most and wide produced in the thermoset resins family. In the 20th century it has been found that the drawbacks of phenolic resins can overcome by polybenzoxazines via their excellent properties: high char yield, high thermal resistance and stability, zero volumetric change and low toxic substance releasing during curing, cost-effective, low moisture absorption, without any requirement for catalyst and etc. Additionally, the easy synthesis procedure of polybenzoxazines is also one of their striking advantages. Because there are corresponding monomers as a polybenzoxazine precursors which can be prepared from cost-effective raw materials such as primary amines, formaldehyde and phenols. In this study, it is aimed to catalyze the reaction of vinylic monomers with sulfur, known as reverse vulcanization. In general, for reverse vulcanization to occur, elemental sulfur must be heated up to the homolytic bond breaking temperature of 160 °C. The resulting sulfur radicals react with the double bond and trigger the polymerization from there. Although the required temperature for reverse curing is high, side reactions increase at this temperature. Therefore, it is important that inverse vulcanization can be catalyzed at more reasonable temperatures. In this study, benzoxazines with different functionalities will be used as catalysts. All the benzoxaiznes acted as catalyst to reduce inverse vulcanization. Among the benzoxazine monomers pyridine containing benzoxazine reduced inverse vulcation temperature better compared to other benzoxazines. It is known that pyridine-type systems contribute to the homolytic decomposition of sulfur, and that sulfur generates radicals by removing hydrogen from benzoxazines. An effective catalytic system was designed by combining these two approaches in a single structure. In this thesis, the development of benzoxazine-based high-performance catalysts by utilizing the flexibility of benzoxazine chemistry is described. The designed benzoxazine will contain the pyridine structure on it. Thus, it is thought that the catalytic performance for reverse vulcanization will increase. With a design benzoxazine catalyst, an attempt will be made to reduce the required minimum temperature of 160 oC to 130 oC for inverse vulcanization.
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.
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.
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.
Development of novel biopolyamide compounds as a green and sustainable alternative to petroleum derived polymers and their applications in medical field

(Graduate School, 2024-06-27) Gülel, Şebnem ; Güvenilir, Yüksel ; 515162001 ; Polymer Science and Technology

Polyamides, widely known as nylons, represent a crucial category of polymers renowned for their versatile properties and extensive applications. With exceptional strength, durability, and heat resistance, polyamides like polyamide 6 (PA6) and polyamide 6.6 (PA66) have become highly preferred materials across various industries. However, their petroleum-derived nature poses significant environmental challenges, including the depletion of finite resources and the accumulation of plastic waste. Therefore, the global need for sustainable alternatives to petroleum-derived polymers has led to extensive research into polymer materials derived from renewable resources and those that are biodegradable. In response, the development of bio-based polyamides, such as polyamide 5.6 (PA56), and their biocomposites have gained great importance in polymer research. The primary objective of this thesis was to develop novel biopolyamide compounds as green and sustainable alternatives to petroleum-derived polymers. Specifically, the research aimed to achieve the enzymatic synthesis of bio-based polyamide 5.6 using monomers from renewable feedstocks, develop novel PA56 composites that can replace petroleum-derived composites currently used in various industrial applications, and introduce antimicrobial activity to bio-based PA56 for its potential applications in the medical field. The thesis focuses on finding sustainable alternatives to overcome the environmental issues caused by the extensive use of petroleum-derived polymers. It underlines the increasing global demand for polymers and the urgent need to prevent the environmental problems arising from this trend, such as finite resource depletion and plastic waste accumulation. Furthermore, the thesis highlighted the present scarcity of PA66 due to the limited production of its key monomer, hexamethylenediamine. This scarcity has driven researchers to explore innovative solutions to meet the growing demand for durable and high-performance polymers. The thesis discusses the potential of utilizing bio-based diamines derived from renewable biomass sources in polymer synthesis. It proposes the development and adoption of bio-based polyamides, particularly focusing on bio-based polyamide 5.6 synthesized from renewable sources like cadaverine, to address these concerns and fulfill the emerging material scarcity in the polymer industry. The first part of the study focused on the properties of bio-based polyamide 5.6 (PA56). A comprehensive investigation of the physical, mechanical, rheological, thermal, and flammability properties of bio-based polyamide 5.6 identified the unique properties of PA56 by highlighting its strong points compared to those of its petroleum-derived counterparts, such as polyamide 6 (PA6) and polyamide 6.6 (PA66). PA56 exhibited the highest water absorption among these polyamides. This high water absorption capacity of PA56 makes it advantageous for textile applications. Additionally, PA56 demonstrated similar mechanical properties to PA66, making it suitable as a high-performance engineering thermoplastic. Its rheological and thermal properties further suggest its potential in applications requiring high flowability and thermal stability. Overall, a detailed investigation of the properties of PA56 revealed its potential as a sustainable alternative to its petroleum-derived counterparts across various industrial applications. In the second part of the study, enzymatic synthesis reactions, catalyzed by enzymes like lipases, were presented as an efficient and environmentally friendly method for producing polyamides. The enzymatic synthesis of bio-based polyamide 5.6 from dimethyl adipate and cadaverine (pentane-1,5-diamine) monomers was achieved using lipase enzyme as a catalyst. This solvent-free, single-step process produced PA56 without intermediates or by-products. Successful enzymatic synthesis of bio-based polyamide 5.6 by utilizing immobilized lipase from Candida antarctica as a biocatalyst, along with a renewable monomer like cadaverine showed their potential for sustainability. The enzymatic synthesis reactions were conducted at 60 °C, 70 °C, and 80 °C for 8, 16, 24, and 48 hours, with lipase enzyme concentrations of 5%, 10%, and 20% (w/w) to evaluate the effects of temperature, time, and enzyme concentration on the synthesis process. The effects of these parameters were investigated through the monomer conversion rate. The study observed that higher monomer conversions were achieved with the higher enzyme concentration, suggesting a positive relationship between enzyme concentration and monomer conversion rate. However, polymerization periods exceeding 24 hours at temperatures above 60 °C adversely affected monomer conversion. The decrease in monomer conversion at high temperatures and prolonged reaction times is attributed to factors such as enzyme denaturation and product inhibition. The average molecular weights of the synthesized polyamide 5.6 were determined using gel permeation chromatography (GPC). To facilitate this analysis, the polyamide 5.6 was modified through N-trifluoroacetylation reaction, which involved reacting its amine groups with trifluoroacetic anhydride to form N-trifluoroacetylated polyamide 5.6 (N-TFA-PA56). This modification improved the solubility of PA56 in tetrahydrofuran (THF), the eluent used for GPC analysis. The highest number average molecular weight (Mn) and weight average molecular weight (Mw) were obtained as 11,900 Da and 20,300 Da, respectively for the reaction with enzyme concentration of 20% (w/w), a temperature of 70 °C, and a reaction time of 24 hours. Therefore, these reaction conditions were identified as optimal for lipase catalyzed synthesis reaction of bio-based polyamide 5.6. Instrumental analysis techniques including Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) were applied to the enzymatically synthesized polyamide 5.6 products for further characterization. These analytical methods verified the successful enzymatic synthesis of PA56 and highlighted its potential as a bio-based alternative to petroleum-derived polyamides. The third part of the study involved developing novel PA56 and PA66 composites with improved properties. Polymer compounding by extrusion method was performed to tailor the properties of polyamide 5.6. Formulation studies employing glass fibers and flame retardants led to the development of novel bio-based composites with improved properties desired for specific applications in various industries. In these formulations, glass fibers and flame retardants enhanced the mechanical and flammability properties of polyamide 5.6, respectively.
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.
Effect of polylactide molecular weight on cellulose nanocrystal dispersion quality

(Graduate School, 2022-01-28) Dündar, Anıl ; Nofar, Mohammad Reza ; 515181001 ; Polymer Science and Technology

Today, plastics are materials that are frequently used for all sectors, especially as a part of daily life, and their consumption is increasing rapidly with a continuous increase, and these materials are often obtained from petroleum-derived fossil resources. The demand for plastic materials is increasing due to reasons such as the excessive use of plastics, the increasing population, the desire of the society to reach higher quality products, and the increase in standards. Especially with the covid 19 pandemic, rapid consumption has inflated this demand. As the usage increased, plastic pollution increased rapidly and studies have been carried out on this subject due to the limited fossil resources. Instead of these petroleum-derived polymers, biodegradable polymers have come to the fore. At this point, one of the the most ideal candidate is the polylactic acid (PLA) polymer since the physical and mechanical properties of PLA are comparable to some petroleum-derived polymers used in the industry. However in spite of all these good and superior features of PLA, it has some shortcomings too such as low viscoelastic properties, slow crystallization rate, brittleness, low thermal stability. For this reason, improving these drawbacks are the main problems that must be overcome in order to use them instead of petroleum-derived polymers. Various studies are carried out in the literature. Copolymerizing using different monomers in the polymerization stage, blending with different polymers without changing their biodegradability, strengthening with micro or nano additives are the methods frequently applied by researchers in the literature. In this study, it was tried to improve the rheological properties of PLA by using a nano additive, and at the same time, how the concept of molecular weight affects the dispersion of this nano additive was investigated. Cellulose Nanocrystals (CNC), which has become popular recently and can improve both the rheological and morphological properties of PLA without affecting its biodegradability, have been used as nanoadditives. CNCs are biopolymers with only crystalline regions after hydrolysis of the amorphous regions in the structure produced from cellulose with acids. Considering its chemical structure, it shows hydrophilic properties because it contains plenty of oxygen and hydroxyl groups. PLA, on the other hand, is a hydrophobic polymer in the ester structure, consisting of long carbon-hydrogen chains and without hydroxyl molecules in its structure. Therefore, they are incompatible with CNC due to their characteristics and their interaction is too weak. In PLA/CNC nanocomposites produced by the melt mixing method, which is the most preferred in the industry, bad results were obtained due to this incompatibility between matrix and the CNC. Thus, nanocomposites with the expected good properties could not be achieved. In order to increase the interactions of CNC and PLA, interface development was achieved by using surface modifiers and the properties of the nanocomposite improved positively. However, nanocomposites produced by the melt mixing method are also very sensitive to high heat due to the ester structure of PLA and can be easily degraded. For this reason, solvent casting is the method used both to avoid this degradation and to produce PLA/CNC nanocomposite without using any surface modifying chemicals. By choosing a suitable solvent that can dissolve both phases, it is possible to better disperse the hydrophilic CNC in the hydrophobic polymer matrix and achieve better results. The solvent chosen for this study is Dimethyl Sulfoxide. Studies in the literature have reported that it disperses CNC better in PLA matrix than solvents such as THF and DMF. In the literatue percolation threshold values were obtained generally between 0.12% - 3%. Based on these results, 0.5% -1% CNC amounts were selected to examine for this thesis. It was also investigated how CNCs would disperse in three different types of PLA: high molecular weight PLA2500HP, medium molecular weight PLA 3001D, and low molecular weight PLA3251D. The mutual point of these polymers is that all of them are semi-crystalline structure leading better results in CNC containing composites compared to amorphous PLAs according to studies and findings in the literature. Within this context, this thesis searches the effect of PLA's molecular weight on the dispersion level of PLA/CNC nanocomposites through the matrix and network formation which is the main stone to get maximized reinforcing effect. When the preparation method was examined, first of all, CNCs were mixed in DMSO solvent for 2 hours in a water bath mixer, so that the CNCs were thoroughly dispersed. Afterwards, PLA granules were added to the prepared DMSO-CNC mixture and the magnetic stirrer was mixed for 4 hours at 90C. The mixtures were poured into petri dishes and kept at room temperature for 2 days, then dried as a film in an oven under vacuum at 85oC for 5 days. Afterwards, the nanocomposites, which were pulverized with the help of a grinder, were kept under vacuum in an oven for 2 more days. In the light of rheology measurements, viscoelastic properties of all molecular weight PLAs improved dramatically with the addition of 1% CNC. The shear thinning behavior of PLA improved with the increase of the complex viscosity. At the same time, this increase can be interpreted that the CNC is well dispersed in the polymer matrix and a network structure is formed with each other. The viscous-like character of unadulterated PLA has turned into an elastic -like material. This significant increase in the storage module with the 1% CNC additive corresponds to the percolation threshold amount, which is the minimum amount required to improve the rheological properties of PLA . In the studies conducted in the literature, these increases are experienced after the CNC is well dispersed and networked in the PLA matrix. On the other hand, 0.5% CNC amount did not give good results for medium and high molecular weight PLA. The reason for this is that because the CNC is not well dispersed in these structures, no network structure can be formed and the viscoelastic properties cannot change. CNCs, which could not enter the longer chains of medium and high molecular weight PLAs, interacted with each other and acted as a foreign substance in the polymer matrix, thus reducing the usual properties. In low molecular weight PLA, on the other hand, it can be interpreted that viscoelastic properties can still improve and this improvement occurs because CNC can more easily disperse between short PLA chains. Similar results were observed for other rheological results. Considering the apparent yield stress of PLA nanocomposites, those containing only 1% CNC showed yield stress, which is in line with the results obtained in other graphs. TGA results showed that the thermal stability was mostly affected with the medium molecular weight PLA. As the CNC amount increased, the degradation temperature of high and low molecular weight PLAs improved by 11oC and 4oC, respectively. No significant change was observed for medium molecular weight PLA. Non-isothermal DSC results showed that the presence of CNC has remarkable effect on the crystallization of PLA. Especially in medium molecular weight PLA, the presence of CNC decreased the cold crystallization temperatures. In high molecular weight PLA, 1% CNC decreased the melting temperature, while it increased the melting temperature in medium molecular weight. No significant difference was observed in low molecular weight PLA.
Effects of crosslinking and nanosilica on waterborne polyurethane dispersions

(Graduate School, 2022-02-08) Erkahraman, Yunus ; Köken, Nesrin ; 515181034 ; Polymer Science and Technology

Waterborne polyurethane dispersions (WPUDs) are versatile materials that are a type of waterborne polymer colloids, utilize water as a dispersing medium, and contain little or no organic solvent. WPUDs are increasingly replacing solventborne polyurethanes thanks to their superior properties such as very low or no volatile organic compound (VOC), low viscosity, excellent film properties, ease of use, good adhesion, high abrasion resistance, and flexibility. WPUDs are preferred in a wide range of applications and industries, including coatings, binders, adhesives, sealants, automotive, inks, biomaterials, paper, wood, footwear, textiles, and many more. Different ways are used to improve the weak properties of WPUDs, such as poor mechanical strength, poor water and alkali resistance, relatively low heat resistance, and high raw material costs. The most common of these ways are, using crosslinkers in various structures, hybridization with polymers that contain different groups such as acrylics and silicones, and the creation of composites by adding nano or micron size inorganic fillers to the dispersion such as silica, clay, graphene oxide, SiO2, TiO2, Al2O3, Fe2O3, CaCO3. Nanosilicas, which have different types such as colloidal silica, precipitated silica, fumed silica, are widely preferred for making composite materials with WPUD because of different properties such as superior hardness, low toxicity, good stability and dispersion, and low cost. The main purposes of producing WPUD/nanosilica composites using various techniques including in-situ polymerization, blending, and the sol-gel process are to develop composite materials with superior mechanical, thermal, optical, chemical, rheological, or electrical characteristics than pure WPUDs. This study aims to obtain new waterborne PU dispersion (WPUD)/nanosilica composites by using various nano silicas and crosslinkers with different types such as isocyanate, aziridine, and waterborne PU dispersion, and investigate the effects of crosslinkers and nano silica by forming a film from these WPUD/nanosilica composites. Various tests were carried out to determine the thermal properties, crystallization behaviors, optical properties, swelling degrees of the obtained WPUD/nanosilica composite films, and it was aimed to gain the properties such as high water resistance, homogeneous distribution, and mechanical strength to the films and using them as a surface coating material in the future. In this study, we prepared various formulations using polyether-based aliphatic waterborne polyurethane dispersion with different amounts and types of nanosilicas (hydrophobic fumed silica and aqueous silica dispersion) and different crosslinkers such as polyether modified HDI--based polyisocyanate and polyfunctional aziridine. WPUD ratio was determined as 75% by weight, polyisocyanate ratio of 5%, and polyaziridine ratio of 2%, if present in the formulation. While fumed silica ratio ranged between 0.1 and 3% by weight aqueous silica dispersion ratio ranged between 1% and 25% by weight in the prepared formulations. WPUD/silica nanocomposites were prepared using the blending method by mechanical stirrer. Crosslinkers were added just before the tests due to the limited pot life. After pouring the prepared WPUD/silica nanocomposite dispersion into Teflon molds, cured for 4 hours at room temperature and at 50 °C for 8 hours in the oven to form films with a thickness of approximately 150μm. Fourier transform infrared spectroscopy (FTIR) was used to examine the chemical structure of the waterborne polyurethane dispersion, silicas, and crosslinkers used in the formulations, as well as the films formed after curing, to determine the changes in the peaks with the addition of crosslinker and silica, and to compare with the pure WPUD film. Differential scanning calorimetry (DSC) was used to examine the thermal properties of the films and X-ray diffraction (XRD) was used to examine the crystallization behaviors. Scanning electron microscopy (SEM)-EDX spectrometry was used for the morphological and elemental analysis of the films. The transparency of the films was observed with an optical microscope (OM) under the same conditions. The swelling degrees of the films in water were evaluated over weight changes. Finally, the hardness values of the films were measured with the Shore D Durometer. Characteristic polyurethane peaks were seen in the FTIR spectral analysis of the neat WPUD film. New characteristic peaks formed as a result of crosslinking reactions were determined. In addition, the presence of nano silica in the structure was determined by the appearance of characteristic Si-O-Si peaks. According to the DSC results, it was determined that the films contained crystalline structures, and the thermal stability of the films increased with the addition of fumed silica and aqueous silica dispersion. According to XRD data, it was determined that the crystallinity increased slightly with the addition of polyisocyanate, but the crystallinity decreased significantly with the addition of polyaziridine. In addition to these, nano silica additions were also found to reduce crystallinity. Also, It was determined that the films with the lowest crystallinity were the films containing polyaziridine crosslinker and fumed silica. In the neat WPUD film SEM images, it was observed that the surface was a rough surface consisting of nano and micron-sized polyurethane particles, and phase separations were observed on the surface. While the phase separations decreased and the surface became more uniform with the addition of polyaziridine, the phase separations increased with the addition of polyisocyanate. Also, it was observed that the surface became rougher with the addition of silica, as the silica ratio increased in the samples containing fumed silica, the silica agglomerations increased and the uniform structure did not occur. In the EDX measurements, carbon, oxygen, and nitrogen atoms were determined, and the silicon atom was also included in the structure with the addition of silica. According to the swelling measurement results, it was found that crosslinking and the addition of a certain amount of nanosilica reduced the degree of swelling. It was determined that the films with the lowest swelling degree were the films containing polyaziridine crosslinker and fumed silica. As a result of the transparency tests performed with an optical microscope, it was seen that the transparency of the films decreases as the amount of silica increases. In the hardness test results, it was seen that the hardness of the films increases with the addition of a crosslinker and certain amount silica. Also, It was observed that the addition of polyaziridine increased the hardness more than the polyisocyanate.
Electromagnetic shielding and acoustic properties of recycled carbon black enhanced polyurethane

(Graduate School, 2025-01-03) Özçelik, Ethem Gökhan ; Karagöz, Bünyamin ; 515211019 ; Polymer Science and Technology

Polyurethanes are a group of polymers with various forms, that can be easily modified according to their usage area and are widely preferred in the industry. They are materials that can meet the needs of the industry for various application areas thanks to their superior mechanical properties, insulation performance, durability, low density, and easy production capabilities. In recent years, the automotive industry has been transitioning to systems that can operate with more environmentally friendly resources, in line with the sustainability targets accepted by the world and the net zero carbon emission targets accepted by the Paris 2050 agreement. Electric vehicles are designs that most automotive companies put on their agenda and offer in the markets to achieve these determined goals. Still, like every new technology, these technologies have some points that are open to improvement. The goal of increasing the driving range of electric vehicles is one of the main issues open to development. According to research, weight reduction achieved by using materials with lower density but the same properties in cars leads to fuel savings and decreased emission values while also allowing for increased driving range. Studies indicated that every 10% weight reduction in automotive results in 7% automobile fuel savings. One of the main issues discussed is vehicles N.V.H. (Noise, Vibration, Harshness) problem. Due to the operating principles of traditional vehicles, they produce sounds at low and medium frequencies and thus dampen sounds at the same and lower frequencies coming from outside the car. Since electric vehicles do not have a sound source at these frequencies, materials with acoustic barrier properties have become very important in electric vehicle designs so that the sounds originating from the wheels and traffic coming from outside the vehicle do not disrupt the comfort of the drivers. The negative effects that arise with the electrification of vehicles are another problem that is tried to be eliminated with the right material choices. Frequencies produced by electrical devices can interfere with the frequencies of other devices and thus potentially cause loss of function in devices and pave the way for data leakage, which is one of today's biggest problems. Not only the functions of the devices but also exposure to these frequencies for a very long time affects human health physically and psychologically. While materials with electromagnetic shielding properties minimize these effects, they have become another material group used in electric vehicles. These materials eliminate negative effects by damping the frequencies produced by electronic devices, thanks to the conductive metal or carbon-based additives they contain in their structures. Generally, carbon-based additives (Carbon Fiber, Carbon Black, Graphene, Carbon Nanotube, etc.) can be preferred with polymer matrixes instead of metal additives due to their high density and dispersion problems. In this thesis, the study aims to develop a polyurethane material that can be an alternative to the problems mentioned above. The semi-integral skin of the polyurethane material creates a thick surface on the outer layer, providing the low-density material with a transmission loss feature against sound waves while also providing electromagnetic shielding properties thanks to the carbon black it contains. The carbon black used in this study was obtained from ICARBON company and was obtained by pyrolysis of end-of-life automotive tires at 550C for 2 hours under the N2 atmosphere. In the first phase of the study, the electromagnetic performances of semi-integral polyurethane materials containing 2% and 5% recycled carbon black by weight, mixed with standard type mixer, were examined and compared with semi-integral polyurethane material which has 0.5% recycled carbon black by weight which was dispersed with stator type homogenizer reaching high speeds, to understand the importance of dispersion of additives in the polymer matrix. Electromagnetic shielding properties were analyzed by the waveguide method, and by determining the S21 properties of the materials, shielding efficiency in the 12.4-18 GHz Ku band was calculated for each material group. The result pointed out that the electromagnetic properties of the material produced by stator-type homogenizer were better than the other experimental groups. In the second phase of the study, the ratio of 0.5% by weight was constant, and semi-integral polyurethane materials were mixed by stator-type homogenizer with a constant amount of conductive PANI additive with the same process parameters. DSC, TGA, FTIR, mechanical, acoustic, and electromagnetic shielding properties were compared for each sample group.
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.
Energy dissipation and rate-dependent deformation behavior of STF-integrated PU foam nanocomposites

(Graduate School, 2023-06-08) Gündüz, Emre ; Karagöz, Bünyamin ; 515191022 ; Polymer Science and Technology

Designing energy absorptive structures is crucial for safety and these structures withstand several loads such as compression, bending, and impact. Beside to honeycombs as a core material for sandwich structures, polymeric foams receive great attention as structural components with their outstanding effective stress transfer, viscoelastic properties, and increased surface area. Among several polymeric foams, rigid polyurethane (PU) foams are good candidates presenting high strength and lightweight characteristics and tailorability. PU is a particular polymer group that stands out with its unique chemistry, typically synthesized from polyol and isocyanate, which also has a potential to fill the vacancies between rubbers and plastics based on their mechanical thermal and viscoelastic properties. PU foams can have densities that range from 20 to 3000 kg/m3 which provide a wide range of application areas and properties. The physical and mechanical properties of PU foams are closely correlated to their morphological characteristics, which are mainly determined by several key parameters such as foam density, cell density, cell edge length, wall thickness, and thickness to length ratio (t/l). PU foams could be customized by incorporating nano and/or micro-sized reinforcing agents to obtain unique functionality and properties. Combining nanoparticle inclusion with process parameter optimization can result in improved mechanical properties and multifunctionality. Nanoparticles can act as nucleation points and lead to narrow cell edge length, increased cell wall thickness, and higher cell density, yielding advanced mechanical properties. Despite the considerable research into carbon-based nanostructures such as carbon nanotubes (CNTs) and graphene as reinforcing agents in polymeric foams to maximize their energy absorption capabilities and strength, further efforts are required to investigate the potential role of other nanomaterials, such as shear thickening fluids (STFs), which exhibit extraordinary energy absorption properties. STFs as colloid suspensions, at elevated shear rates, form hydroclusters due to particle interaction yielding a drastic viscosity increase. Thus, rapid viscosity change results in an excellent energy absorption characteristic. This study is aimed to improve the compressive and energy absorption properties of PU foams with STF integration while discussing the microstructure/mechanical property relationship. Initially, STFs were fabricated with up to 30 wt.% fumed and spherical silica content, using a mechanical stirrer at 300 rpm and horn sonicator with 30% amplitude, then investigated by a plate rheometer in order to understand the effect of particle geometry and weight fraction on the flow characteristics. The results revealed that 26 wt.% of fumed silica was the optimum suspension for integration to PU foam with the excellent thickening ratio, and viscosity values increased after critical shear rate up to 67.66 times. The 26 wt.% STFs were successfully integrated into rigid PU foams, using a mechanical stirrer prior to the foaming reaction, at 0.5, 1, and 3 wt.%, and the morphological analysis, compression, and cyclic compression tests at various strain rates up to 0.2 s-1 and 10, 40, 80% strains xxii in order to understand rate dependent properties under different deformation region such as plateau and densification, were performed. According to morphological characterizations, cell edge lengths decreased and cell wall thickness increased with increasing until 1 wt.% STF. The maximum t/l ratio, which is a favorable indicator for mechanical strength prediction, was observed with 1 wt.% STF integration into PU foam. The results showed that 1 wt.% STF presented the highest compressive strength and specific compressive strength with 33% and 10.4% increments, respectively. For the energy absorption properties, 1 wt.% STF demonstrated up to 9.4% higher loss factor and 46.9% total absorbed energy regarding cyclic compression tests strain and strain rate parameters. Dynamic mechanical analyses were also carried out, under bending loads with dual cantilever clamps, to develop the microstructure-mechanical property relationship and to examine the viscoelastic properties. Linear viscoelastic region and storage and loss moduli increased with 1 wt.% STF integration. The results were consistent with both the compression and cyclic compression tests, despite differences in the direction and frequency of the applied force. Integration of 1 wt.% STF resulted in a significant increase of approximately 50% in both storage and compression modulus, while no significant changes in loss factor were observed. By enhancing the storage modulus and broadening the linear elastic regime, STF/PU foams can effectively withstand higher levels of load and displacement without permanent deformation. Excessive STF integration, such as above 1 wt. %, caused deterioration in the foam morphology and cellular structure, resulting in lower mechanical properties and strengths, however the 3 wt.% STF integrated foam still exhibited better properties than neat foam. This study showed that the flow properties of STFs are significantly influenced by the silica surface geometry and weight fraction. Furthermore, the study demonstrated that the addition of an optimized amount of STF enhanced the compressive strength, viscoelastic properties, and energy absorption capabilities of PU foams. With the addition of STF, PU foams could be used in a wider range of application areas and their superior mechanical properties could be used to build safer and reliable structures.
Enhancement of interfacial properties for high performance polyethylene fibers produced via gel spinning

(Graduate School, 2023) Ünlü, Oğuz Kağan ; Kılıç, Ali ; 515211011 ; Polymer Science and Technology Programme

Fibers are materials with high length/diameter ratios, having adjustable fineness, mechanical properties. High performance fibers exhibit excellent mechanical properties such as high modulus, high strength, high abrasion resistance, thermal resistance, low density. One of the methods used to produce high performance fibers is gel spinning, in which the chains are partially entangled in liquid-gel form and connection with each other , rather than solution or melt unlike other methods (dry spinning, wet spinning, melt spinning). In this thesis, ultra high molecular weight polyethylene (UHMWPE) was dissolved in paraffin oil and high performance UHMWPE fibers were obtained by gel spinning method. The gel obtained by dissolving UHMWPE in paraffin oil is formed into filaments by passing through the spinnerettes after extrusion, then passes through the quenching and extraction bath, drying and winding in the final stage. High tensile strength, low specific density, great impact resistance, and exceptional chemical resistance are just a few of the excellent qualities of ultra-high molecular weight polyethylene (UHMWPE) fiber. It is frequently utilized in fishing, aircraft, biomedicine, and ballistic, among other things. UHMWPE fiber has a very high degree of crystallinity (>99%) and macromolecular orientation (>95%), which leads to a high modulus and tenacity of UHMWPE fiber. Gel spinning is a difficult and advanced engineering process. UHMWPE concentration is one of the parameters that determine fiber strength which was kept as 8% wt in this study. For this research, n-hexane was used in the extraction bath to remove paraffin oil from spun UHMWPE fibers. Following the solvent extraction procedure, the fibers undergoing hot drawing with different drawn ratios. The differential scanning calorimeter is used to analyze the thermal and crystallization properties of the fibers in their drawn, undrawn, and gel-state forms. Two newly peaks are observed when DR reached to 40. These peaks shows orthorombic-hexagonal transition. An orthorhombic structure represents a prism-like crystal structure with three unequal edges and internal angles, whereas a hexagonal structure resembles a hexagon with six equal edges. The tensile test was used to reveal the effect of drawn ratios on performance and it was revealed that with the increase in drawn ratio, the mechanical strength would increase by a maximum of 322.71%. Simultaneously, this thesis also focuses on investigating the enhancement of interface properties in UHMWPE fiber/epoxy composites.There are numerous surface treatment methods used to improve the coaction between fibers and composite materials, chemical etching and corona discharge are two commonly used methods to enhance the fiber- epoxy interaction. In this thesis study, the optimum corona discharge result was revealed by experiments performed at different voltage and time parameters. Then, the obtained results from corona discharge method were compared with the results obtained when the surface was modified via chemical etching, and it was seen that hydroxyl and carboxyl groups were formed on the surface more effectively in the chemical etching method. Glutaraldehyde, which is used as a cross-linking agent in chemical etching method, can form bonds with OH functional groups due to its chemical structure. Thus, the hydroxyl groups formed on the UHMWPE fibers become able to cross-link with the hydroxyl groups in the epoxy. Tests have shown an increase in both mechanical performance and adhesion.
Extraction of polysaccharides from waste seaweed and examining their film forming properties

(Graduate School, 2024-08-16) Demirci, Hatice ; Ünlü, Cüneyt Hüseyin ; 515191007 ; Polymer Science and Technology

Biomaterials produced from seaweeds are used by many industries such as pharmaceuticals, cosmetics, medical, fertilizers, textiles, food and packaging. These materials come from living things that are renewable, such microbes, plants, and animals. They lessen our reliance on finite resources and have a minimal negative impact on the environment by providing a sustainable substitute for fossil fuels and synthetic materials. Turkey, with its agricultural potential and biodiversity, has a significant potential for the production and use of bio-based raw materials. Studies and policies implemented in our country to support the transition to a more sustainable economy in the future. Numerous species can be found in the oceans, which covers an important part of the planet's surface. These organisms are rich in biological materials that, with the help of biotechnology, could find application in a wide range of industrial applications. This area of study, known as marine biotechnology, investigates the potential use of these compounds derived from marine animals in a variety of industries. Marine resources are a renewable and limitless resource. Reducing dependence on fossil fuels and facilitating the shift to a more sustainable economy can be accomplished in this way. Turkey has enormous potential in the field of marine biotechnology because it is surrounded by seas on three sides. It is impossible to say, though, that this potential has yet to be fully fulfilled. Our nation needs to invest more money and conduct more studies in the field of marine biotechnology. There is a wide range of marine biomaterials. One of the most important of these biomaterials is seaweed, which is rich in protein, vitamins and minerals. The industrial utilization of seaweeds has a history dating back thousands of years and is still of great importance today. Today, when issues such as sustainability and efficient use of natural resources are on the agenda, the use of renewable resources such as seaweeds has become even more important. The seas in our country are home to a wide variety of algae species as they have different water temperatures, salinity ratios and depths. The coastline, especially rocky areas, is an ideal habitat for seaweeds. Various types of algae are frequently seen in these areas, which are constantly oxygenated by the waves. For some reasons, seaweeds collect on coasts. These are factors such as waves and currents, wind, tidal movements, the natural life cycle of seaweeds. Seaweeds of different species are collected at certain times of the year on the shores of the Marmara Sea, which is home to a wide variety of seaweed species. When these collections are on the shore, they can be disturbing in terms of odor and appearance. At the same time, it can restrict the usage areas of people on the coast. When waste seaweeds do not wash up on the shore, they accumulate on the sea surface, and since these accumulations reduce the contact of the sea with the air, they reduce the oxygen level in the sea and reduce the efficiency of the oxygen source needed by the creatures living in the sea. This, in turn, reduces the quality of life of the creatures living in the marine ecosystem, shortens their lifespan and may jeopardize the continuity of species. Collecting these algae accumulated on the sea surface and coasts to be transformed into various materials can both clean the sea and the coast and provide a cheap raw material source to the industry. Some similar studies are being carried out in different parts of the world. The structural and quantitative diversity of the chemical components found in the structures of these seaweeds, which are found in thousands of different species, may cause us to see these seaweeds as a very special resource. Seaweed is produced and used as a raw material nowadays all over the world. High-value applications of algal-extracted biopolymers are becoming more and more necessary as the algae industry and algae biorefinery expand. The polysaccharides in the structure of these seaweeds can be seen as a source of raw materials for different applications. Seaweeds can grow and reproduce in conditions that cause minimal damage to the environment. Since seaweed farming does not require fresh water, chemical fertilizers or land, which are some of the most important environmental constraints associated with land-based agriculture, marine farming appears to be more sustainable than land-based agriculture. Seaweed can absorb carbon dioxide from the atmosphere, contributing to efforts to mitigate climate change. Even though we think that terrestrial plants are the source of the oxygen we breathe, photosynthesis by marine algae produces over 75% of the oxygen on the globe. Seaweed is consumed directly in many cultures, often as a source of nutrients and dietary fiber. Seaweeds are not only a great source of food, but also an important raw material for animal feed, biomass and biofuel synthesis and are currently being utilized in these fields. Seaweed can be used to remove pollutants from water and soil, a process known as bioremediation. The concept of this project is to collect different seaweed samples from the coasts of the Marmara Sea to isolate the polysaccharide components in their structure and to investigate the possible utilization of these polysaccharides as a source of feedstock. The first focus of the study is to determine the proportion of polysaccharides in the composition of different types of seaweed waste, the next step is to convert these polysaccharides into polymeric films using different film agents. This innovative approach not only addresses the problem of accumulation of marine waste on the coasts, but also allows us to see the possibilities for the proper utilization of this bio-waste material.
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.
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.
Induced crystalline fiber-like structure as reinforcement in PLA products through applied shear in injection molding

(Lisansüstü Eğitim Enstitüsü, 2022-06-27) Eraslan, Kerim ; Nofar, Reza M. ; 515201009 ; Polymer Science and Technology

In recent years, there has been a growing interest in sustainable, biobased, and biodegradable polymers due to the rise of public awareness towards petroleum-based polymers, the requirement to comply with new environmental laws, and the considerations about the ecological impacts of the product over the entire life cycle. Polylactic acid (PLA) is a biopolymer produced from renewable resources, considered an alternative to commodity and engineering applications due to its high strength, stiffness, and production capacity. However, PLA suffers from high brittleness, low melt strength, and slow crystallization, hampering processing and applicability. To improve the mechanical and thermal properties of PLA, methods such as PLA-based nanocomposite development, fiber modification methods, fiber reinforcement, mixing with rigid polymers or plasticizers, and chain branching have been applied. Although these attempts could eliminate the disadvantages of PLA, the biodegradability and natural advantages of PLA should be preserved while also reducing the end-product cost. Furthermore, the additives or fibers must be compatible with the mechanical and thermal recycling processes applied to the PLA products after use. Self-reinforced PLA composites (SR-PLAs) have been introduced to provide high strength and stiffness without traditional reinforcements. Furthermore, the absence of foreign reinforcements such as glass or carbon fiber can contribute to the complete biodegradability and easy recyclability of the composite. Self-reinforced composites are comprised of identical or similar types of polymers in the matrix and reinforcement phases. This concept aims to obtain a solid and stable matrix-fiber interface using polymers with similar chemical structures in both phases. However, the matrix and the reinforcement phases must have a certain melting temperature difference to produce these composites. Thus, while the matrix will be completely molten, the structure of the reinforcing polymer will be preserved. This study aims to determine the manufacturability and mechanical and thermal properties of in-situ SR-PLAs prepared through injection molding. Different types of PLAs were used to provide the required melting temperature difference in the matrix and reinforcement phase. The matrix was formed by an amorphous PLA (aPLA). The reinforcement phase was created by three semi-crystalline PLA grades (cPLA1, cPLA2, and cPLA3) with different crystallizability and molecular weight. To induce isothermal cold crystallization, the cPLAs were initially annealed at 90 oC, between the glass transition and melting temperature of PLA. Then, the aPLA/cPLA blends with different cPLA types and compositions with a weight ratio of 95/5, 90/10, 85/15, and 80/20 were prepared using a dry mixer. Finally, the aPLA/cPLA blends were dehumidified at 50 oC overnight and injection molded. Before processing, an aPLA/cPLA3 blend with a weight ratio of 85/15 was injection molded in different barrel and mold temperatures to determine the process parameters. The differential scanning calorimetry (DSC) analysis revealed non-isothermal cold crystallization peaks for aPLA/cPLA3 samples processed at an average barrel temperature of 160 oC. This was mainly due to the stretching and unfolding of some cPLA crystals during processing. In addition, the tensile results showed slightly lower mechanical properties for aPLA/cPLA3 samples processed at a mold temperature of 20 oC. Therefore, the barrel and mold temperatures were determined as 150 and 40 oC. Next, the thermal and mechanical behavior of neat PLA and aPLA/cPLA blends were studied. The neat PLA did not exhibit crystallinity due to the absence of the cPLA phase. On the other hand, the aPLA/cPLA blends with cPLA contents below 5 wt% also did not exhibit crystallinity. The aPLA/cPLA blends with cPLA contents above 10 wt% showed crystallinities due to unmelted cPLA crystals during processing as the process was carried below the melting temperature of cPLA crystals. Moreover, the crystallinities of aPLA/cPLA3 blends were more pronounced than aPLA/cPLA1 and aPLA/cPLA2 blends due to the higher melting temperature and crystallizability of cPLA3. The single glass transition around 60 oC indicated miscibility between aPLA and cPLAs. The tensile test results revealed that the tensile strength and modulus values of the aPLA/cPLA samples were significantly greater than those of the neat aPLA. Moreover, this reinforcing effect became even more prominent when cPLA3 was used. These enhancements were due to the induced fiber-like structure obtained through the inherent high shear rate of the injection molding process. The strain at break values did not reveal substantial improvements, although aPLA/cPLA samples were slightly more ductile than neat PLA. Finally, the HDT and impact strength analysis of aPLA/cPLA were investigated to improve the processability and applicability of PLA. While the cPLA addition slightly increased the heat deflection temperature (HDT) to 60 oC, it unaltered the impact strength at 12 kJ/m2. Therefore, polybutylene adipate terephthalate (PBAT) was selected to improve the tensile toughness of SR-PLA blends. cPLA3 was chosen as the reinforcing phase in SR-PLAs due to its most prominent enhancement effect on thermal and mechanical properties. The SR-PLA/PBAT blends with a fixed 15 wt. % PBAT was prepared similarly to SR-PLA preparation methods. In addition, 85 wt. % SR-PLAs contained different cPLA3 compositions with a weight ratio of 90/10, 80/20, and 70/30 to observe the effects of cPLA content on the material properties of SR-PLA/PBAT blends. The thermal analysis revealed that the SR-PLA/PBAT had higher crystallization than SR-PLAs. Moreover, the crystallinity was further increased with increasing cPLA3 content. The melting temperature of SR-PLA/PBAT blends was lower than SR-PLAs. This was attributed to the fact that the PBAT droplets could have penetrated between the cPLA crystals, resulting in a less ordered structure. The SR-PLA(80/20)/PBAT and SR-PLA(70/30)/PBAT blends exhibited non-isothermal cold crystallization due to the higher crystallizability of cPLA3. Furthermore, the cold crystallization in PLA(70/30)/PBAT occurred earlier than in PLA(80/20)/PBAT as the higher cPLA3 contents further enhanced the orientation of fiber-like crystals and supported heterogeneous cold crystallization. Finally, the two distinct glass transitions around -35 and 60 oC indicated immiscibility between PLA and PBAT. The stress-strain behavior of SR-PLA/PBAT blends showed that the PBAT addition resulted in a transition from ductile to brittle behavior. The tensile strength and modulus of SR-PLA/PBAT blends were lower than neat PLA. The maximum losses in terms of percentage for tensile strength and modulus were 15 and 25%, respectively. On the other hand, the strain at the break of the SR-PLA/PBAT blends was significantly greater than neat PLA. Moreover, this reinforcing effect was even more significant in higher cPLA3 contents due to the formation of a more uniform blend morphology. As a result, the ductility of neat PLA was increased from 3.9 to 44.6% in SR-PLA(70/30)/PBAT. Furthermore, the impact strength of neat PLA was enhanced to 16 kJ/m2 in all SR-PLA/PBAT blends. Finally, the improvements in blend morphology were demonstrated by SEM images. The microstructure of SR-PLA/PBAT blends revealed that the PBAT droplets were finely dispersed within the SR-PLA. Moreover, higher cPLA3 contents improved the blend melt strength, promoting the breakup of PBAT droplets. Therefore, a more uniform blend morphology corresponded to enhancements in ductility and impact strength.
Industrial scale sustainable nanocomposite production by melt mixing technique

(Graduate School, 2022-08-12) Avcıoğlu, Nesrin ; Nofar, Reza M. ; Doğu, Mustafa ; 515191011 ; Polymer Science and Technolog

Scientists are in search of new biopolymers as alternatives for petroleum-based polymers due to environmental concerns. Polylactic acid (PLA) is a biopolymer that is produced from renewable feedstock and has high performance with biodegradable and sustainable nature. This is while PLA suffers from brittleness, poor processability, and impact strength. The development of PLA composites and blends are possible ways to overcome such drawbacks. Cellulose nanocrystals (CNCs) are good alternative nanoparticles to improve some of these drawbacks compared to other reinforcements for not only providing good mechanical and physical properties but also being low density, biobased and biodegradable filler. Unfortunately, the production of nanocomposites on a large scale with good CNCs dispersion is still a challenge. This study is aimed to develop sustainable polymer nanocomposites by direct melt-mixing on an industrial scale through two approaches that are with and without masterbatch preparation. For this purpose, a corotating twin-screw extruder (Gülnar 1101402) was used and its specifications are 25 mm screw diameter and L/D ratio of 42. This extruder has 8 barrels with volumetric feeders. PLA was reinforced with CNC (1, 2, and 4% (w/w)) in this industrial-scale co-rotating twin-screw extruder. Polyethylene glycol (PEG) was used as an agent that could enhance the interfacial interaction between PLA and CNC to promote dispersion and acts as a plasticizer to overcome the brittleness of PLA. PEG concentration was kept constant at 10%(w/w) throughout all formulations. In this process, PLA was fed in the main feeder and solvent casted (distilled water was used as a solvent) PEG/ PEG-CNC after shredding was fed into the side feeder. For all trials, the vacuum pump that is located after the side feeder was set as on and the screw speed was set as 130 rpm. The temperature profile for each heating zones was 40°C, 170 °C, 175°C, 180°C, 185°C, 180°C, 185°C, 190°C and 185°C. Obtained granules from this process were dried at 50°C in a vacuum oven overnight both for injection molding and compression molding. In the compression molding process, the mold was set at 190°C for 5 minutes and pressure was gradually enhanced to 1.5 tons. At the end of the heating process under pressure, the mold was cooled quickly with water circulation. Samples for rheological characterization, SEM analysis, XRD analysis were prepared with this method. For the injection molding process temperature of the cylinder and temperature of the mold were set as 190°C and 70°C, respectively and residence time was optimized as 15 seconds. Dog-bone samples for the tensile test were obtained with this processing technique. Fabricated nanocomposites were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), rheological analysis, scanning electron microscopy (SEM) and tensile test. It was seen that from the DSC cooling thermogram, the addition of CNC resulted in non-isothermal crystallization behavior and improvement of crystallization capacity and crystallization temperature. When the consideration of the second heating cycle of normally compounded particles, the addition of CNC resulted in decreasing melting temperature. This means that crystal nucleation is improved with the addition of CNC and small crystals tend to reduce of melting point. The highest change of degree of crystallinity and melting temperature in comparison to the neat PLA were observed for PLA/PEG/CNC2 from 39% to 59% and from 177 oC to 172 oC, respectively. Whereas, for the masterbatch preparation method, the crystal growth observed instead of nucleation. This might be related to the agglomeration of the nanoparticles in the MB preparation technique, but the agglomeration could not be understandable from the SEM results. Besides, low melting shoulders are observed for the only normally compounded particles due to the existence of small crystals in the structure. DSC first heating thermograms were only considered for comparison of the results of XRD because of the thermal history of the materials. The neat PLA shows two distinct peaks in 2θ= 16.8 and 19.2. The different amounts of CNC in the nanocomposites result in some changes in diffraction patterns. This shift in the diffraction patterns means some structural changes in the crystallite. Moreover, loading more amount CNC in the nanocomposites leads to an enhancement of the intensity of crystalline peaks. The addition of CNC to the PLA matrix making a positive effect on the crystallite size and the ordering of the material is better in the nanocomposites that are produced from the MB preparation technique. Additionally, the thermogravimetric test of the neat PLA after extrusion, PEG, PLA/PEG blend, and its nanocomposites were performed to understand the thermal degradation behavior of materials. It was observed that neat PLA, PEG, and nanocomposites have shown one step degradation process. However, the PLA-PEG blend showed a two-step degradation process. The initial thermal degradation temperature of each nanocomposite ranges from about 260°C to 290°C. Maximum degradation temperature observed in neat PEG as 412 °C. These TGA curves demonstrate that the thermal stability of PLA decreases with the addition of PEG. The reduction of the thermal degradation temperature of PLA with the addition of the PEG can be related to some impurities after the chemical reaction between the OH- groups of PEG and ester groups of PLA. With the addition of the 1, 2, and 4 % (wt) CNC on the PLA/PEG, the decomposition temperature shifted to the higher temperatures of 261, 268, and 287°C, respectively. Additionally, the materials which were obtained by the MB preparation technique resulted in a thermal degradation temperature of 284 °C for both materials. Whereas PLA has better thermal degradation temperature in comparison to nanocomposites. Moreover, complex viscosity and storage modulus were considered for the rheological behavior of the materials. The results evidenced that neat PLA and its blend and nanocomposites show a Newtonian plateau at low frequencies, and it was observed that shear thinning behavior at high frequencies. Existence of PEG can be triggered transesterification reactions with PLA in the extrusion process, and these reactions were resulted in the degradation of the PLA matrix meanwhile reduction of polymer molecular weight. This reduction resulted in the reduction of PLA's complex viscosity and even addition of CNC could not enhance the complex viscosity. Considering the storage modulus, the addition of PEG made a negative effect on the moduli of PLA in the low and high-frequency range whereas some enhancements were observed in the storage modulus at the low frequencies with the addition of CNC. This improvement could not be obtained for the MB preparation technique due to the agglomerates. Changing of rigid and brittle nature of PLA with the addition of additives was analyzed with the tensile test. Tensile strength and Young's Modulus of neat PLA before extrusion are 50 MPa and 3500 MPa, respectively. However, after extrusion, it has been seen that a significant decrease in these values as about 42 MPa and 1720 MPa, respectively. PEG was selected as not only a processing aid to improve PLA-CNC interaction but also as a plasticizer. Hence, the addition of PEG into the PLA matrix results in an increment for elongation at the break. Besides, Young's modulus as well as the tensile strength of the blend slightly decreased. With the CNC loading, tensile strength and modulus are slightly enhanced. Whereas elongation at break is reduced due to the addition of CNC which is a stiffer phase. The masterbatch preparation aggregates might result in stress concentration points, so tensile properties cannot enhance. Consequently, it needs to be noted that in the twin screw extrusion process, materials were exposed to high shear. Thus, materials can be easily degraded. Even though PEG used as a well dispersing agent, these results were demonstrated that melt mixing is an inappropriate route to produce PLA-CNC nanocomposites. There is no surface treatment of CNC and that can promote the agglomeration of nanoparticles dramatically.
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.

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