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    Applications of polyimide coatings: a review
    (Springer International Publishing Ag, 2021) Hicyilmaz, Ayse Sezer; Bedeloğlu, Ayşe
    Polyimides, high-performance polymers with superior properties such as high temperature stability, resistance to solvents and high strength, can be used in high-tech applications of the aerospace and aviation, medical or electronics industry in different forms (film, fiber, nanofiber, membrane, foam, adhesive or coating). Among these applications, coating has a special place and is used to develop advanced structures having high temperature resistance, flame retardancy and etc. for high tech industries via an economical and feasible way. Therefore, in this review, we aimed to report the broad application status of polyimide coatings by reviewing publications, patents and commercial products. Thus, this study can assist in selecting suitable polyimide types and production methods for polyimide coating applications and in understanding their applicability for future products.
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    Polyimide-coated fabrics with multifunctional properties: Flame retardant, UV protective, and water proof
    (Wiley, 2019) Hicyilmaz, Ayse Sezer; Altin, Yasin; Bedeloğlu, Ayşe
    Multifunctional technical textiles are of great interest both by industry and academia and these products are considered as high value-added products that contribute to the economies of countries. In this study, polyamic acid (PAA) was synthesized through polycondensation of pyromellitic dianhydride (PMDA) and 4,4 '-oxydianiline (ODA) in dimethyl acetamide (DMAc) at low temperature. Then, PAA was coated onto woven cotton and polyester fabric by padding technique. Finally, polyimide (PI)-coated multifunctional cotton and polyester fabrics were obtained by an easy coating technique and low-temperature imidization. Thus, low cost, easily accessible and widely used cotton and polyester fabrics were converted to high-performance textile products, which are flame retardant, UV protective, acid resistant, and waterproof. The chemical, thermal, morphological, optical, mechanical, wettability, chemical resistance, and flame retardancy properties of developed fabrics were investigated. Optical results showed that both PI-coated cotton and polyester fabrics are UV-A protective compared to noncoated fabrics. Moreover, PI-coated samples have high contact angles which are 111.43 degrees and 113.40 degrees for PI-coated cotton (PI-c-C) and PI-coated polyester (PI-c-PET), respectively. Young's modulus of PI-c-PET fabrics increased four times more than noncoated polyester fabric. PI coating changed the burning behavior of both cotton and polyester fabrics in a positive way. All the test results showed that these developed multifunctional textile products might find an application in different industrial areas such as automotive, aerospace, protective clothing, and so on due to easy and inexpensive production techniques and also superior properties. (c) 2019 Wiley Periodicals, Inc.
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    Silver nanowire loaded self-healing EVA films
    (Sage Publications Ltd, 2022) Hicyilmaz, Ayse Sezer; Bedeloğlu, Ayşe
    In this study, ethylene vinyl acetate (EVA) transparent nanocomposite films, which heal easily with the inclusion of a low amount of silver nanowire (AgNw), were produced. For this purpose, first AgNw was homogeneously dispersed in the polymer solution and then, nanocomposite films were produced from the solutions by casting method. The thermal, mechanical and optical properties of the produced films were characterized. Self-healing properties of nanocomposite films were confirmed by optical microscopy and mechanical tests. Optical microscope results showed that the optimum recovery temperature was 130 degrees C and the addition of a small amount (5% w/w) of AgNw reduced the recovery time of the scratch on EVA film reducing the healing time by 66.66% (from 15 minutes to 5 minutes). In addition, tensile test results supported the optical microscope results. DSC results showed that the regular crystal regions were formed in composite films due to the high thermal conductivity and nucleating agent effect of AgNw. On the other hand, DSC curves proved that the healing process was occurred via re-entanglement of the polymer chains by heat effect, while silver nanowire addition did not affect the mechanical strength and transparency of the films, significantly. AgNw-loaded-EVA-based self-healing transparent films can be used for applications such as tempered glass laminates, electrical cables, coatings, packages, especially to protect the product and reduce the cost of repair.
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    The effects of the weathering methods on the properties of the ABS, ASA and PMMA polymers
    (Elsevier Sci Ltd, 2022) Yildirim, Fatma Filiz; Hicyilmaz, Ayse Sezer; Yildirim, Kenan
    In this study, the effects of natural and accelerated weathering methods on the mechanical and color properties of three commercially available thermoplastic polymers used in the automotive industry were investigated. The polymers are poly (methyl methacrylate) (PMMA), acrylonitrile butadiene styrene (ABS) and acrylonitrile styrene acrylate (ASA). All the samples were exposed to natural weathering conditions directly during one year (between November 11th, 2019 and November 11th, 2020) in Bursa, Turkey. This pioneering research was carried out for the first time in Turkey. The chosen accelerated weathering methods against the natural weathering are by Xenon-arc lamp and UV lamps, respectively. Statistical evaluation of data obtained from the tensile stress and the tensile strain curves was performed by Student-Newman-Keuls (SNK) test. The determination of color change values was carried out either visually by the grey scale assessment or spectrophotometrically. The correlation coefficients amongst weathering methods were investigated for visual and instrumental assessment methods with the Kendall's correlations method. PMMA samples showed the best performance for all three different weathering methods. While the fastest degradation occurred in ABS and ASA samples, which contained butadiene monomer, no remarkable change was observed in the tensile stress of all samples. However, the tensile strain values of weathered samples decreased. This shows that the polymers harden when exposed to either natural or accelerated weathering by photo-oxidation reaction. The correlation coefficients of the assessments of the color change by the spectrophotometer are lower than the ones by the grey scale. Therefore, the correlation coefficient of the assessments of the color change by the grey scale was taken into account. There was a high correlation between natural weathering and the accelerated weathering by Xenon-arc lamp. The correlation coefficient was 0.755. On the other hand, the correlation coefficient between natural weathering and the accelerated weathering by UV fluorescent lamps was 0.591.