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    Blast furnace slag or fly ash filled rigid polyurethane composite foams: A comprehensive investigation
    (Wiley, 2019) Akkoyun, Meral; Akkoyun, Serife
    Ground granulated blast furnace slag (BFS) and fly ash (FA) are iron-making industry and power plant byproducts, respectively. Although their use in concrete is quite common, investigation of the effects of these inorganic compounds on polymer properties is quite new, and their use as fillers in polymer foam composites has not yet been really explored. Their properties, such as high electrical resistivity, make them a good asset for use in rigid polyurethane foams that are widely used for insulation. In this study, a comprehensive investigation of the effect of BFS and FA on morphology, electrical and thermal conductivity, and rheological and mechanical properties of water-blown rigid polyurethane foams was performed. The relationship between these properties was examined. A relative enhancement of the properties is observed for filled foams, especially up to the percolation threshold. The results highlight a noticeable effect of the electrical percolation threshold on the different properties of foams. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47433.
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    Correlation Between Surface, Thermal, Mechanical and Morphological Properties of Polylactic Acid/Polypropylene and Polylactic Acid/Polyamide 6 Blends
    (Kırıkkale Üniversitesi, 2022) Tuna, Sibel; Akkoyun, Meral
    In the automotive sector, which is one of the sectors where polymers are mostly used, their behaviour and compatibility in secondary processes such as painting and coating applications are important in the preference of polymers according to their usage areas as well as mechanical and thermal properties. In this context, it is known that surface wettability of a polymer material is of great importance for different application areas and it can be stated that wetting and non-wetting behaviours play an important role in the selection of polymers and their industrial applications. In this study, the contact angle properties of polypropylene (PP) and polyamide 6 (PA6), which are the most used polymers in the automotive sector and their polymer blends prepared by using polylactic acid (PLA) were examined. When PLA/PP and PLA/PA6 mixtures were compared, it was observed that there were significant differences in contact angle measurements and these properties detected in water contact angle measurements were attributed to changes in chemical structures, functional groups and morphology of related polymers. Surface analysis were supported by thermal, mechanical and morphological analysis and differences in static contact angle measurement results were explained.
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    Demir (II, III) Oksit Katkılı Rijit Poliüretan Köpük Nanokompozitlerin Elektriksel ve Termal İletkenlikleri
    (Konya Teknik Üniversitesi, 2021) Akkoyun, Meral
    Demir (II, III) oksit partiküllerinin rijit poliüretan köpüklerin elektrik ve termal iletkenlikleri ile termal geçişlerine ve dolayısıyla bu gözenekli malzemelerin nihai yoğunluğu ve mikroyapısına etkisi araştırılmıştır. Demir (II, III) oksit eklenmiş rijit poliüretan köpük nanokompozitlerin mikroyapı çalışması, ortalama hücre boyutunun katkısız poliüretan için 294 µm değerinden ağırlıkça %50 katkılı köpük için 215 µm değerine kadar, %27 oranında bir düşüş ve katkı oranına bağlı olarak ortalama duvar kalınlığında bir artış olduğunu göstermiştir. Termal geçiş sonuçları, magnetit oranı arttıkça yumuşak segmentler için camsı geçiş sıcaklığında %32 oranında gözle görülür bir düşüşün ortaya çıktığını ve sert segmentleri temsil eden camsı geçiş sıcaklığının sabit kaldığını göstermiştir. Elektriksel iletkenlik ölçümlerinin sonuçları, katkısız poliüretan köpüğe kıyasla ağırlıkça %50 katkı oranına kadar %17 oranında önemli bir artış göstermiştir. Demir (II, III) oksit eklenmiş rijit poliüretan köpük nanokompozitlerin termal iletkenlik sonuçları, ağırlıkça %4 katkı oranı için 0.02431W/m.K değerinden 0.02648W/m.K değerine kadar gözlemlenen hafif bir artıştan sonra termal iletkenliğin azalması ve stabilizasyonu nedeniyle manyetit parçacıklarının ısıl yalıtım etkisini ortaya çıkarmıştır.
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    Improvement of thermal conductivity of rigid polyurethane foams with aluminum nitride filler
    (Sage Publications Ltd, 2021) Akkoyun, Serife; Akkoyun, Meral
    The aim of this work is the fabrication of electrically insulating composite rigid polyurethane foams with improved thermal conductivity. Therefore, this study is focused on the effect of aluminum nitride (AIN) on the thermal and electrical conductivities of rigid polyurethane foams. For this purpose, aluminum nitride/rigid polyurethane composite foams were prepared using a three-step procedure. The electrical and thermal conductivities of the foams were characterized. The thermal transitions, mechanical properties and morphology of the foams were also examined. The results reveal that AIN induces an increase of the thermal conductivity of rigid polyurethane foam of 24% which seems to be a relatively noticeable increase in polymeric foams. The low electrical conductivity of the foams is preserved.
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    Polyamide 12/Antimony Trioxide/Sepiolite or Boron Composites: Mechanical Properties and Flame Retardancy
    (2020) Öztürk, Ahmet Muşteba; Sarıbal, Fırat; Duman, Şeyma Duman; Akkoyun, Meral; Şen, İbrahim; Dondas, Dıdem Ovalı
    This study reports on the mechanical and flame-retardancy properties of polyamide 12 (PA 12) based composites reinforced with antimony trioxide, sepiolite, or boron powders. These composites were fabricated by the twin-screw extruder and hot-press techniques. The microstructural characteristics and flame-retardancy of the PA 12-based composite samples were obtained by using a scanning electron microscope, a vertical UL-94 burning, and limiting oxygen index tests. The Shore-D hardness, Charpy impact, and tensile tests were conducted to reveal the mechanical performance of composites. The PA 12/antimony trioxide/sepiolite sample presented the best mechanical performance. The additions of antimony trioxide/boron into the PA 12 matrix gave the best contribution to the flame-retardancy.
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    Polypropylene/Chemical Blowing Agent Foams: Effect of the Injection Speed and Core Back Distance on Microstructure and Mechanical Properties
    (Kırıkkale Üniversitesi, 2020) Akkoyun, Meral; Badem, İbrahim; Öztoksoy, Mert Emre; Aslan, Yeşim
    In recent years, many parts of the automotive industry, previously made of metal, has been passed to polymers due to their light weight, ie lower carbon emission and fuel consumption advantage. The aim of this work was to investigate the microstructure and mechanical properties of chemical foaming agent added polypropylene foam samples produced by injection molding. In particular, the effects of injection speed and core back distance on the evolution of cell diameter, compact outer layer thickness, cell density and mechanical properties were examined. In the first step the effect of various injection speeds (110; 125; 140 mm/s) was investigated. Then, various core back positions (0; 0.7 and 1.5 mm) were analyzed at a constant injection speed (110 mm/s). The results showed an increase of the cell diameter, the compact outer layer thickness and the elastic modulus as the injection speed increases. In addition, an important effect of the core back distance was observed with the presence of a critical core back distance. Below this critical value, the cell diameter and the elastic modulus drop due to a notable decrease of the skin layer thickness. Above this critical value, the cells started to collapse and lose their circularity.
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    SURFACE FREE ENERGY AND FLEXURAL PROPERTIES OF WOLLASTONITE FILLED POLYPROPYLENE COMPOSITES
    (Süleyman Demirel University, 2021) Soncu, Serkan; Akkoyun, Meral
    Nowadays, appearance is an important factor in vehicles. For this reason, paint application is widely used in plastic parts. Surface energy is a key parameter for the adhesion of paint on the surface of polymers. Among thermoplastic polymers, polycarbonate and acrylonitrile butadiene styrene are commonly used materials due to their higher surface energies. For low surface energy materials, surface energies can be increased using streamer, plasma, corona, mechanical etching and chemical etching methods. The aim of this work is to eliminate the pre-treatments applied to parts produced with polypropylene (PP) polymer using wollastonite (CaSiO3) additive. For this purpose, CaSiO3 filled PP composites containing 40 wt.% wollastonite with different sizes and coatings were produced by extrusion process. Afterwards, plate samples were prepared from granules using a hot pressing device. Flexural properties and surface free energy measurements were performed on these composites produced in plate form. From the results, an increased surface free energy was observed for small particle size and aminosilane coated wollastonite added PP composite with an increase by 23% of the total surface free energy. Flexural strengths were well correlated with the surface free energy results and showed an increase by 1.2% for the same additive.
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    Thermal and electrical properties of aluminum nitride/boron nitride filled polyamide 6 hybrid polymer composites
    (Wiley, 2021) Yildiz, Gorkem; Akkoyun, Meral
    The effects of boron nitride (BN) and aluminum nitride fillers on polyamide 6 (PA6) hybrid polymer composites were investigated. In particular, the thermal and electrical conductivity, thermal transition, thermal degradation, mechanical and morphological properties and chemical bonds characteristic of the materials with crystal structure of BN and aluminum nitride (AlN) filled PA6 prepared at different concentrations were characterized. Thermal conductivity of hybrid systems revealed a 1.6-fold gain compared to neat PA6. The highest thermal conductivity value was obtained for the composite containing 50 vol% additives (1.040 W/m K). A slight improvement in electrical conductive properties of composites appears and the highest value was obtained for the 50 vol% filled composite with only an increase by 3%. The microstructure of these composites revealed a homogeneous dispersion of AlN and BN additives in PA6 matrix. For all composites, one visible melting peak around 220 degrees C related to the alpha-form crystals of PA6 was detected in correlation with the X-ray diffraction results. An improved thermal stability was obtained for 10 vol% AlN/BN filled PA6 composite (from 405.41 degrees C to 409.68 degrees C). The tensile strength results of all composites were found to be approximately 22% lower than pure PA6.
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    Vollastonit ve Manyetit Katkılı Rijit Poliüretan Köpüklerin Isıl Geçiş ve Mekanik Özellikleri
    (Osman SAĞDIÇ, 2020) Altınel, Doğan Berkay; Akkoyun, Meral
    Poliüretan (PU) köpüklerin sahip olduğu düşük mekanik ve termal iletkenlik özelliklerine karşın işleme kolaylığı ve sert/esnek olarak üretilebildiklerinden dolayı otomotiv, yalıtım ve yapıştırıcı gibi uygulamalarda tercih edilen malzemelerdir. Sert poliüretan köpükler ise sahip oldukları düşük yoğunluk ve kapalı hücre yapısı özelliklerinden dolayı otomotiv, gemi ve inşaat sektörlerinde kullanılan malzemelerdir. Son yıllarda, farklı katkılarla takviye edilmiş olan poliüretan köpüklerin morfolojik, mekanik ve iletkenlik özellikleri gibi çeşitli özellikleri yoğun bir şekilde araştırılmaktadır. Ancak manyetit/vollastonit hibrit sistemlerin sert PU köpük kompozitlerin termal geçiş ve mekanik özellikleri üzerindeki etkisi henüz araştırılmamıştır. Bu çalışmanın amacı vollastonit (W) ve manyetit (M) takviyeli sert poliüretan köpüklerin termal geçiş sıcaklıkları ve mekanik özelliklerinin incelenmesidir. Köpüklerin mekanik ve termal geçiş özellikleri arasındaki ilişkiler ve özellikle manyetit/vollastonit (1:3, 1:1 ve 3:1) hibrit sistemlerin ağırlık oranlarının PU köpük özelliklerine etkisi incelenmiştir. Üretilen köpükler Fourier dönüşümlü kızılötesi spektrometre, diferansiyel taramalı kalorimetre ve çekme testi cihazı ile karakterize edilmiştir. Yapılan çalışmalar sonucunda, poliüretan köpüklerin kimyasal yapısının katkılardan (manyetit ve vollastonit) etkilenmediği tespit edilmiştir. Termal geçiş sonuçları iki ana davranışın varlığını ortaya çıkarmıştır. İlk durumda, sert segmentlerin camsı geçiş sıcaklığında genel bir artış gözlemlenmiştir ve bu davranış, polimer zincirleri arasında manyetit ve vollastonit partiküllerinin eklenmesinden dolayı poliüretan zincirlerinin hareketliliğinin azalması ile açıklanabilir. İkinci durumda, yumuşak segmentlerin camsı geçiş sıcaklığında gözlemlenen genel bir düşüş eğilimi, muhtemelen polimer matrisinde manyetit veya vollastonitin varlığından dolayı, polimer zincirleri arasında düğüm oluşumunun engellenmesinden kaynaklanmaktadır. Sert PU köpüklerde, vollastonitin manyetite göre çekme dayanımı özelliklerine daha belirgin bir olumsuz etkisinin olduğu görülmektedir.