Polimer Bilim ve Teknolojisi Lisansüstü Programı - Yüksek Lisans

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  • Öge
    Preparation and characterization of polylactide/poly (butylene adipate-co-terephthalate)/cellulose nanocrystal blend nanocomposites
    (Institute of Science And Technology, 2012-06-15) Sarul, Deniz Sema ; Nofar, Ü.M. Reza ; 515171012 ; Polymer Science and Technology ; Polimer Bilim ve Teknolojisi
    Biopolymers have been developed to replace petroleum-based polymers due to their environmental damage. Poly (lactic acid) or polylactide (PLA) is one of the most common biopolymers derived from sustainable sources such as corn starch and sugar cane with attractive properties such as renewability, high strength, modulus and transparency. Therefore, it stands out in the industry and is an alternative to petroleum-based polymers. PLA also suffers from a series of disadvantages, such as high brittleness, low toughness, low service temperature, slow crystallization and low melt strength, which limits its processability, formability and foamability. Many approaches have been reported in the literature to overcome these disadvantages, such as copolymerization, blending and composition with nanoparticles. Blending PLA with biodegradable polymers such as poly (butylene adipate-co-terephthalate) (PBAT), polycaprolactone (PCL) and poly [(butylene succinate)-co-adipate] (PBSA) is the most economical way to increase its toughness without compromising its biodegradability. In this thesis context, the second selected polymer is PBAT, which is 100% biodegradable synthetic random copolymer. Despite PLA, PBAT has remarkable properties such as ductility and flexibility, and it shows a very low tensile modulus and strength. The PLA/PBAT blend is an immiscible blend. Morphology of the immiscible blend varies depending on intrinsic properties of each polymer and blend ratio. The morphology greatly influences final blend performance; therefore, it must be checked to obtain the desired properties. According to literature, blending PLA with PBAT has been observed to significantly reduce the modulus and mechanical strength of PLA. A solid nanoparticle is added to the blend to increase compatibility between components and provide the stiffness/toughness balance. The selective localization of the nanoparticle is very important for the morphology design and for the blend to show the desired properties. The selective localization of nanoparticles depends on thermodynamic and kinetic parameters. While surface energy is a thermodynamic effect, viscosity is a kinetic effect. If the nanoparticle is localized in a low-viscous phase, it can reduce the viscoelastic difference between the two components or if it is found at the interface, it can prevent the coalescence of discrete domains. In this dissertation, cellulose nanocrystal (CNC) nanoparticles have been used to act as a filler. CNCs are rod-like particles that can be obtained by acid hydrolysis of cellulose, which has unique properties such as low cost, abundance in nature, renewability, biodegradability, high aspect ratio and high surface area. On the other hand, it is difficult to obtain a well dispersion of the CNC due to the presence of hydroxyl groups on the surface and strong interactions between the particles. In this thesis, the dispersion and selective localization of CNC in PLA/PBAT/CNC blend nanocomposites prepared by different ways are investigated. First, the thermodynamic equilibrium localization of the CNC was found in the PBAT phase with the Young's module, utilizing the surface energy values of PLA, PBAT and CNC given in the literature. In the literature, it is stated that the CNC is not well dispersed in the hydrophobic polymer when prepared directly by the melt mixing method. Therefore, samples were prepared using a combination of solution casting and melt mixing for a good dispersion of CNC. Firstly, blend nanocomposites containing 1, 3, 5, 7 and 10 wt.% CNCs were prepared by directly solution casting method using dimethylformamide (DMF) as the solvent. From scanning electron microscopy (SEM) images, the droplet size of PBAT increased in blend nanocomposites containing 1 wt.% CNC compared to neat blend indicating that the CNC is localized in PBAT. It was assumed that the CNC is migrated to the interface or PLA due to the decrease in PBAT droplet size with increasing CNC content. Rheological analysis showed that the CNC formed a strong network in the PLA phase, since the percolation threshold was formed above 1 wt.% CNC. The preference of CNC to be localized in low viscosity PLA indicates that kinetic factors could become more dominant than thermodynamic factors. The masterbatch containing 7 wt.% CNC prepared through solution casting was used and diluted by twin-screw extruder to produce PLA/PBAT/CNC blend nanocomposites with 1, 3, and 5 wt.% of CNC contents. In addition, the selective localization of CNC in PLA/PBAT/CNC blend nanocomposites was investigated using different processing method (twin-screw extruder and internal mixer) with three mixing strategies. It was observed that CNC migrated to PLA phase in each strategy since the internal mixer method took place over a long period of time. However, finer droplets of PBAT were obtained in PLA/PBAT/CNC blend nanocomposites prepared through twin-screw extruder due to higher shear force. In general, it was concluded that the viscoelastic properties of PLA/PBAT/CNC blend nanocomposites prepared with the combination of solution casting and melt mixing increased, but the desired results in mechanical properties could not be achieved.
  • Öge
    Controlled release of tetracycline hydrochloride from copolymer/gelatin nanofibers
    (Institute of Science And Technology, 2020-06-30) Metin, Ayşe ; Güvenilir, Fatoş Yüksel ; 515161027 ; Polymer Science and Technology ; Polimer Bilim ve Teknolojisi
    Use of nanofibers in biomedical applications have been rising significantly in recent years. Drug delivery systems are developed in order to enable the drug to perform with maximum therapeutically efficiency by preventing the degradation before the targeted spot and ensuring the protection of activation. Besides, drug delivery systems protect the body from the adverse effects of the active pharmaceutical ingredient. Conventionally, drug is given to the body by different methods such as injection, oral, implantation etc. When drug is used by these methods, it effects both the healthy and unhealthy organs. Also, conventional drug formulations cause quick release and quick removal from the body. Therefore, in most cases multiple dose is needed for healing. Multiple dose increases the toxic effects and may result in the occurrence of side effects. Recently, the importance of developing drug delivery systems with controlled release and controlled targeted spot release have risen significantly. Studies prove the success of polymeric drug delivery systems in controlled release. Electrospinning is the most frequently used method to obtain nanofiber. In this method, natural or synthetic polymer solutions are spinned under electric force in order to achieve nanofibers from 2nm up to a few micro-meters. Nanofibers presents great advantages for drug delivery systems due to their special properties such as high surface-volume ratio, pore structure, high permeability, easy penetrability and biocompatibility achieved by using natural polymers. Aliphatic polyesters synthesized with enzymatic ring opening polymerization do not generate a toxicity risk because of the method of synthesis without a catalyst and can be used in drug delivery systems. Enzymatically synthesized poly(ω-pentadecalactone-co-ɛ-caprolactone) has been chosen as the polymer in this study because of its biocompatibility, biodegradability and good mechanical strength properties. Due to the improvement of mechanical and degradation properties and hydrophobic structure, prevention of uncontrolled water release was expected from nanofibers synthesized from poly (ω-pentadecalactone-co-ε-caprolactone) copolymers by immobilizing lipase enzyme on rice husk ashes as the method found in literature. Besides, gelatin which is a natural polymer was used in order to achieve easier acceptance of drug release system by the body and increase the compatibility with human cell. Nanofiber membranes obtained with a lab scale electrospinning machine from various copolymer/gelatin concentrations and volume-wise several double mixture compositions were studied in two different solvent systems as the first step of the study. Chloroform and methanol (3:1 v, v) for copolymer, acetic acid and formic acid (1:1 v, v) for gelatin were chosen as the first solvent system. 15% and 30% by weight for copolymer and 8% and 15% by weight for gelatin were prepared in solution. Afterwards, obtained solutions were mixed with various volume ratios. The achieved mixtures were electrospinned using syringe for transfer. Phase separation was observed when the mixture was leaving the syringe during electrospinning process. Nanofibers obtained from the first solvent system were viewed by scanning electron microscope (SEM). Beaded and defected structure was observed on the membrane because of the phase separation. Increasing copolymer concentration in double mixtures resulted in increased beaded structure with a few nanofibers in between. Besides, an increase from %8 to 15% in weight of gelatin concentration increased the defects as well. A new solvent system has been researched in order to prevent the defects in the structure. As a result of this research, hexafluoroisopropanol; a solvent which can dissolve both the copolymer and gelatin, was chosen for the second solvent system. 15% copolymer and 8% gelatin solutions by weight were prepared and mixed with varios volume ratios (100:0, 70:30, 60:40, 50:50). As a result of SEM images, electrospinning of 50:50 volume ratio mixture of 15% copolymer and 8% gelatin solutions had the best fiber structure and the best fiber diameter distribution (average fiber diameter: 305.0±45.5nm). Membranes obtained with this ratio were used on the next steps of the study because of it having the most effective and the most proper structure. In order to increase the mechanical properties and the stability of the membranes, they were crosslinked for 2 and 24 hours in glutaraldehyde vapour. Then, in vitro degradation properties were examined in pH 7.4 phosphate buffer solution. 2 hours crosslinked membrane preserved its structure in phosphate buffer solution after 30 days. Degradation tests proved that 2 hours crosslinked membrane had high hydrolytic resistance against buffer solution. Even though 24 hours crosslinked membrane had better mechanical resistance, 2 hours crosslinked membranes were chosen because of the higher toxicity of 24 hour crosslinked membrane due to higher glutaraldehyde ratio. 2 hours crosslinked membrane was placed to shaking bath in buffer solution and mass loss was calculation in various time intervals (1, 3, 5, 7, 14, 21, 30 days). Membrane has lost the 20% of its initial mass after 10 days. Copolymer/gelatin nanofiber, 2 hours crosslinked copolymer/gelatin nanofiber and copolymer have been analysed by fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC) and contact angle measurement. As a result of contact angle measurement 2 hours crosslinked membrane was found suitable because it preserved its hydrophillic properties and improved its hydrolytic properties compared to non-crosslinked membrane. An increase in thermal resistance properties of the membrane was observed according to TGA results. As the second step of the study, calculated amount of Tetracycline Hydrochloride antibiotic was dissolved in HFIP. The amount of drug was arranged as 0.5%, 1%, 3% and 5% of the total polymer/gelatin concentration by weight. Drug loaded nanofiber membranes were obtained by electrospinning the mixture with 2ml/hour flow rate and under 25kV room temperature conditions. Afterwards, membrane was crosslinked for 2 hours in 25% glutaraldehyde solution vapour. Crosslinked nanofibers were dried for 2 hours in 80°C in order to remove remaining glutaraldehyde. After the crosslinking process, drug loaded copolymer/gelatin nanofiber membranes were cut in to 2 x 2 cm2 pieces and weighed. 3 samples were prepared as described for each drug loading ratio and these samples were sunk in 10 ml pH 7.4 phosphate buffer saline (PBS). Later on, samples were placed in 37°C shaking bath(120rpm). 1ml parts were taken of and changed with fresh PBS in determined time intervals. Removed mixtures were characterized by using UV spectrophotometer in 343nm. Amount of drug released was calculated by using calibration graph. Later on, cumulative drug release amount was reached. Initial drug amount in the membrane was calculated according to the drug ratio in polymer blend and the weight of the drug loaded membrane. SEM images of drug loaded nanofibers proved that, randomly aligned, even and beadless antibiotic loaded samples for each ratio were obtained. Fiber diameters showed normal distribution generally. A tendency in the decrease of diameter was observed after drug loading. Highest average nanofiber diameter (282.9 ± 64.6 nm) was measured in the lowest drug loading ratio (0.5% by weight). Other drug loading ratios ( 1%, 3% and 5% by weight) caused the formation of significantly thinner nanofibers (180-200 nm) (p <0.001). On the other hand, there was no meaningful diameter difference between 3 drug loaded samples (p> 0.05). EDS spectrum of 0.5% by weight drug loaded and crosslinked membrane was obtained in order to determine the presence of tetracycline hydrochloride in drug loaded copolymer/gelatin nanofiber structure. Cl spectrum has verified the presence of tetracycline hydrochloride because Chloride (Cl) is made up of the molecular structure of tetracycline hydrochloride. Additionally, nitrogen (N) and sulphur (S) peaks were detected in EDS spectrum. These peaks proved the presence of gelatin in nanofibers. Cumulative drug release graph showed that, instant release and 14th day release for each drug load were similar to each other. For each drug load ratio, instant release in 1 hour was less than 11%. On the other hand, 0.5% by weight drug loaded sample displayed relatively low instant release percentage (% 9.1 ± 0.1) and highest (p <0.001 or p <0.05) total drug release percentage (% 69.4 ± 0.2). 0.5% ratio drug having low instant release and highest gradual total drug release was determined as the most efficient antibiotic ratio for copolymer/gelatin ratio developed at this stage of the study. As the next stage of the study, antibacterial tests of the antibiotic loaded nanofibers were performed by using disk diffusion method; which is the measurement of the bacterial growth inhibition zones for the determination of antibacterial activity. Antibacterial activities were tested against Gram positive (S. aureus and B. subtilis) and Gram negative (E. coli) bacteria. Results showed that all samples with various loading ratios presented open inhibition zones against Gram positive bacteria (S. aureus and B. subtilis). Bigger inhibition zones were monitored in petri dishes with B. subtilis (~ 30-40 mm). This result proved that drug loaded membranes were extremely active and effective against B. subtilis. Meanwhile, samples showed limited activity against E. coli. No inhibition zone was detected for 0.5% by weight tetracycline hydrochloride and samples with higher concentrations showed very low antibacterial activity (~ 8-10 mm inhibition zone). It was found that; parallel with the literature, Gram negative bacteria E. coli was much more resistant to tetracycline hydrochloride antibiotic. Additionally; as expected, inhibition zones expanded as the antibiotic concentration increased. Optimal antibiotic ratio; obtained by release properties, was determined as 0.5%. 0.5% antibiotic ratio had enough efficacy for gram positive bacteria, however for broad spectrum antibiotic, antibiotic loading ratio has to be increased. In this study, increase of the mechanical properties by using enzymatically synthesized copolymer and increase of cell compatibility by using a natural polymer gelatin while obtaining nanofiber with electrospinning process were targeted. Nanofiber membrane with the optimal structure was successfully achieved by trying various copolymer/gelatin ratios and different solvents. Crosslinked samples were characterized without drug loading in order to increase the mechanical properties and degradation properties were examined. At the final step of the study, controlled release properties of antibiotic loaded membranes with various ratios has been examined and their activity against bacteria was measured.
  • Öge
    Poli(akrilamid)’in Çapraz Bağlı Poli(hema-co-mma) Reçineye Aşılanması Ve Fenol İle Bisfenol A ‘nın Giderilmesinde Kullanılması
    (Fen Bilimleri Enstitüsü, 2017-01-19) Usta, Handan ; Şenkal, Bahire Filiz ; 10135686 ; Polimer Bilim ve Teknolojisi ; Polymer Science and Technology
    Fenollerin eldesi on dokuzuncu yüzyılın sonlarından itibaren kömür katranından sağlanmıştır. 1898 yılında Felix Hoffmann tarafından asetilsalisilik asitten fenol sentezi gerçekleştirilmiştir. Fenol ve türevlerine pestisit, sentetik kauçuk, farmasötik ürünler, petrokimya yada diğer sanayilerden kaynaklı atık sularda yaygın olarak rastlanmaktadır. Fenol kaprolaktam ve bisfenol A üretiminde de kullanılmaktadır.Bu ürünler naylon ve epoksi reçinelerinin üretiminde de o kullanılmaktadır. Fenol aynı zamanda otomativ, inşaat ve alet endüstrisinde ihtiyaç duyulan fenolik reçinelerin başlangıç maddesi olarak kullanılmaktadır.Fenolün diğer önemli kullanım alanları dezenfektan ve tıbbi ürünleridir. Boya ve vernik sökücüler, lake, kauçuk, mürekkep, aydınlatıcı gazlar, tabaklama boyaları, parfümler, sabunlar ve oyuncak gibi materyallerin üretiminde fenol kısmi olarak rol oynamaktadır. Bu tezde bir fenol türevi olan bisfenol A için de incelemeler yapılmıştır.İlk bisfenol A sentezi Thomas Zincke tarafından gerçekleştirilmiştir.1905 yılında fenol ve asetonun sentezi sonucunda bisfenol A elde edilmiştir. 1953 yılında yeni bir plastik olan polikarbonatın başlangıç materyali olarak bisfenol A kullanılmıştır 1957 yılında Amerika Birleşik Devletlerinde ve 1958 yılında Avrupa da ticari olarak üretimi yapılmıştır. Aynı zamanda epoksi reçinelerinin üretiminde bisfenol A kullanılmaya başlanmıştır. Bunun yanı sıra bisfenol A doymamış polyester, polisülfon, polieterimid ve poliarilat reçineleri üretiminde başlangıç materyali olarakda kullanılmaktadır Fenol ve fenol türevleri çevreye zararlı en önemli organik bileşiklerdendir ve içme suyunda hoş olmayan tat ve kokuya sebep olurlar. Fenol su varlığında çok düşük konsantrasyonlarda bile, balık dahil olmak üzere su içerisinde ki canlılar için istenmeyen özelliklere sahiptir ve toksiktir. Özellikle, klorlanmış fenoller sudaki yaşam için daha da tehlikelidir. Fenoller insan sağlığı üzerinde zararlı etkilere sahiptir. Özellikle beyin, sindirim sistemi, kalp, göz, karaciğer, böbrek, akciğer, periferik sinir, deri ve doğmamış çocuklar üzerinde olumsuz etkilere neden olurlar. 0.002 mg L-1, Dünya Sağlık Örgütü tarafından yapılan düzenlemelere göre içme sularında fenol konsantrasyonunun izin verilen sınırdır. Sulu çözeltilerde fenol ve türevlerinin giderilmesinde kullanılan yöntemler üç ana kategoriye ayrılabilir. Bu yöntemler fiziksel, kimyasal ve biyolojik yöntemler olarak adlandırılabilir. Atık sulardan fenolün kaldırılmasında çeşitli yöntemler kullanılmaktadır. Membran filtrasyon, oksidasyon, biyolojik yada fotokatalitik bozunma ve adsorpsiyon yöntemleri fenolün giderilmesinde kullanılan yöntemler arasında gösterilebilmektedir. Adsorpsiyon organik ve inorganik kirleticileri gidermek için kullanılan önemli bir yöntemdir. Atık sulardan fenol ve fenolik kirleticilerin giderilmesindeı için zeolitler, karbon nanotüpleri, polimerik sorbentler ve kil gibi farklı adsorbanlar kullanılmaktadır. Fenolik bileşiklerin adsorpsiyonunun üç mekanizması π-π etkileşimleri, electron alışverişi ile kompleks oluşumu ve Hidrojen bağ oluşumudur. Bu deneyimler fenollerin giderimi için yeni polimerik sorbentlerin hazırlanmasında kullanılmıştır. Bu tezde iki farklı sorbent hazırlanmış ve sulu çözeltilerden fenol ve Bisfenol A giderilmesi için kullanılmıştır. İlk olarak poli(HEMA-MMA-EGDMA) terpolimeri sentezi gerçekleştirilmiştir. Bu sentez işlemi için başlatıcı olarak AIBN, çapraz bağlayıcı olarak etilen glikol dimetakrilat (EGDMA) (%10), monomer olarak da hidroksietil metakrilat (HEMA) (%50) ile metil metakrilatın (%40) ve porojen olarak da toluen varlığında süspansiyon polimerizasyon yöntemi gerçekleştirilmiştir (reçine 1). Elde edilen bileşiklerin spektroskopik karakterizasyonu için FT-IR kullanılmıştır. Reçine1'in FT-IR spektrumuna göre, 3300-3500 cm-1 aralığındaki geniş aralık -OH gerilim titreşimleri ve 1722 cm-1'deki keskin pik, terpolimer içindeki karbonil gruplarına karşılık gelmektedir. Diğer polimerik reçine redoks polimerizasyonu metoduyla reçine 1 üzerine poli(akrilamid)’in aşılanmasıyla elde edilmiştir. Redoks polimerizasyonu sırasında başlatıcı olarak seryum amonyum nitrat kullanılmıştır.Aşı polimerizasyonu HEMA birimleri üzerindeki hidroksil grupları aracılığıyla gerçekleştirilmiştir. Reçne 2 içerisinde bulunan toplam azot içeriğini belirlemek amaçi ile Kjeldahl azot analizi yöntemi kullanılmıştır. Analiz sonucuna göre 7 mmol/g azot içeriği reçine 2 içerisinde saptanmıştır. Reçine 2 nin amaçlanan bileşik olduğunu ispatlamak amaçı ile tekrar reçine 2 için FT-IR analizi yapılmış ve istenilen sonucun elde edilmiş olduğu görülmüştür.Reçinenin FT-IR spekturumuna göre 3300-3500 cm-1 arasında gözlemlenen -NH grubuna ait pikler ve 1655 cm1 deki pik, reçine'deki amid grubunun -C = O gerilme titreşimine karşılık gelmektedir Poli (akrilamid) aşılanmış reçinenin (reçine2)'nin toplam azot içeriği 7,0 mmol/g olarak bulunmuştur. Fenol ve Bisfenol A reçine 1 ve reçine2 üzerinde ki tutma kapasiteleri pH ve konsantrasyona bağlı olarak bulunmuştur. Aynı zamanda reçinelerin fenol ve Bisfenol A tutma kinetikleri incelenmiştir. Reçine 1 ve reçine 2 için kinetik modelleri uygulanmıştır. Kinetik incelemeler için yalancı birinci dereceden kinetik denklem ve yalancı ikinci dereceden kinetik denklemler deneysel sonuçlara uygulanmıştır.Yapılan incelemeler sonucunda fenol ve bisfenol A nın adsorpsiyonunun yalancı ikinci dereceden kinetik modele uygun olduğu görülmüştür. Bu sonuçların yanı sıra fenol ve bisfenol A nın tutma kapasiteleri arasında ki farklar deneysel sonuçlar üzerinden de açıklanmıştır.
  • Öge
    Stiren-akrilik Kopolimerlerin Sentezi Ve Boyada Kullanımları
    (Fen Bilimleri Enstitüsü, 2017-01-17) Özdamar, Buğra ; Serhatlı, İbrahim Ersin ; 10134990 ; Polimer Bilim ve Teknolojisi ; Polymer Science and Technology
    Bu çalışmada, farklı yapılara sahip farklı silan türleri doğrudan stiren-akrilik kopolimerlere eklenmiştir. Bu kopolimerler yüksek PVC boya formülasyonunda formüle edilmiştir. Bu boyalar, ovalama direnci, sertlik ve esneklik özelliklerine göre test edilmektedir.
  • Öge
    Halloysitlerin Endüstriyel Boya Uygulamaları
    (Fen Bilimleri Enstitüsü, 2017-01-16) Kamhi, Melih ; Uyanık, Nurseli ; 10132684 ; Polimer Bilim ve Teknolojisi ; Polymer Science and Technology
    Bu çalışmada halloysitin farklı oranlarda iki farklı kürlenmeye ve formülasyona sahip endüstriyel boyaya eklenerek, kapsamlı boya testlerinin yapılması amaçlanmıştır. Yapılan bu boya testleri sonuçlarına göre, halloysitin boyaların termal dirençlerini ve parlaklıklarını önemli ölçüde arttırdığı, diğer testler için ise herhangi bir olumsuz yaratmadığı tespit edilmiştir.