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    Characterization of Natural Reinforcements and their Composites
    (Savvy Science Publisher, 2021) Karahan, Mehmet; Karahan, Nevin; Ozkan, Fatma; Yildirim, Kenan
    In this study, the mechanical properties of flax, jute and jute/carbon woven fabrics, and their composites were investigated and compared with 3K carbon fabric composites. Mechanical properties of yarn, fabric and composites were separately investigated and compared for each scales. In addition, yarn and fabric structures were characterized. It was found that, fabric structure, yarn physical properties and fiber cross-section and fiber molecular structure parameters of reinforcement have seriously effect on the composite mechanical properties. It can be concluded that fabric tensile strength attribute to composite tensile strength, but there was not a direct relation between fabric tensile strength and composite tensile strength. The tensile strength of natural fiber fabrics were determined to be significantly reduced depending on the temperature increasing. This condition should be considered as a important limitation for composite applications of natural fibers. Mechanical test results are proved that natural fiber composites not to be an important alternative to conventional composites. © 2021 Karahan et al.; Licensee Savvy Science Publisher.
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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.
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    TWIST SETTING TEMPERATURE AND TIME EFFECTS ON MORPHOLOGY OF POLYETHYLENE TEREPHTHALATE YARN
    (Ege Univ, 2014) Yildirim, Kenan; Kostem, A. Melek; Aydin, Nurcan; Tuna, Huseyin; Cenan, Ayhan
    The twist on the yarn should be fixed by heat to remove twist liveliness. This procedure changes the properties of polyethylene terephthalate (PET) yarn in aspect to both fiber morphology and yarn mechanical behavior. The yarn properties are affected by heat setting process factors which mainly are heat-setting method, temperature and time. This study investigates the effect of temperature and time of the heat setting processes on the yarn properties. The change of the morphology of the yarn was determined by tensile test, differential scanning calorimetric (DSC) analysis, boiling water shrinkage test, bobbin hardness and twist amount per unit length test. The study demonstrates that the time of the heat setting does not have a considerable effect on the PET yarn properties. The temperature of the heat setting has dominant influence onto the properties of the PET yarn, especially on the boiling water shrinkage and tensile behavior. The tensile strain and bobbin hardness increase, and shrinkage decrease with increasing heat setting temperature. The force-strain curve shape is changed by altering twist setting parameters. These results show us that heat setting temperature related to stress relaxation arise from twist insertion, rearrangement of the macromolecules and molecular orientation in the amorphous region.