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BOZTOPRAK, YALÇIN

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YALÇIN

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    Synthesis and characterization of UV-curable cellulose acetate butyrate-based oligomers and their cotton fabric coatings
    (SPRINGER, 2021) BOZTOPRAK, YALÇIN; Dehmen, Ozan Gazi; Onen, Hacer Aysen; Yildiz, Zehra; Gungor, Atilla; Boztoprak, Yalcin
    In order to improve the thermal stability and flexibility, cellulose acetate butyrate (CAB) was modified with toluene diisocyanate-hydroxyethyl methacrylate (TDI-HEMA) adduct in various molar ratios. The obtained oligomer was characterized by proton nuclear magnetic resonance (H-1 NMR) and Fourier transform infrared (FTIR) spectroscopies. Gloss, cross-hatch, contact angle, and Taber abrasion tests were all used to investigate the film forming performance of the modified CAB oligomers on glass plates. The UV-cured free films of the synthesized oligomers were examined in terms of the mechanical tests. By using the synthesized CAB oligomers, coating formulations were prepared and applied onto cotton fabrics in order to make the cotton fabrics more durable in outdoor environments. The existence of the coating layer on the fabric surfaces was investigated by scanning electron microscopy (SEM). The coated UV-cured fabrics were evaluated separately in terms of abrasion, thermal conductivity, and air and water vapor permeability properties. Results proved that the oligomer (50%-CAB) in which 50% of the hydroxyl groups of CAB were reacted with TDI-HEMA adduct showed the best mechanical properties with the highest tensile strength and modulus values. Considering the coated fabrics, the least deformation against abrasion, the highest air/water vapor permeability, and the best thermal conductivity were all recorded in 50%-CAB coated sample.
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    Mechanical properties of double and triple fibre-reinforced epoxy hybrid composites
    (ICE PUBLISHING, 2020) BOZTOPRAK, YALÇIN; Boztoprak, Yalcin
    A composite material can be defined as a combination of two or more materials that provide better properties than the material used alone. Composite materials can be preferred because of their many advantages - for example, they are stronger and lighter compared with conventional materials. Usage of fibre-reinforced composite structures has increased in industries such as automotive, marine transportation, civil engineering, sporting goods, medical equipment and prosthetic devices.
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    Graphene oxide-containing isocyanate-based polyimide foams: Enhanced thermal stability and flame retardancy
    (WILEY, 2021) ÇAKIR, MUSTAFA; Cakir, Mustafa; Kilic, Volkan; Boztoprak, Yalcin; Ozmen, Fadime Karaer
    Isocyanate-based graphene oxide-containing polyimide foams were synthesized by a semi-prepolymer method. In this method, while the first solution containing pre-polymer was derived from pyromellitic dianhydride and excess polymethylene polyphenylene isocyanate (PM200), the second solution contains dianhydride derivatives, water, catalysts, surfactants, and graphene oxide. PIFs were prepared with 0%, 0.25%, 0.50%, 0.75%, and 1% graphene oxide by weight, respectively. PIFs exhibited a minimum side reaction and urea generation was not seen for all PIFs instead of imide bonding. The addition of graphene oxide (GO) leads to a more close-packed structure. Therefore, crosslinking density and thermal stability of graphene oxide-containing polyimide foams increased. Upon the addition of 1% GO, almost seven times higher compression strength was obtained compared to neat PIFs. Also, LOI values supported the theory that thermally stable and flame retardant PIFs can be synthesized via the isocyanate-based process with GO.
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    Investigation of crack detection properties of elastomer-based nanocomposites under cyclic strain loading with graphene and carbon black interaction filler
    (2022-01-01) BOZTOPRAK, YALÇIN; Kasim H., BOZTOPRAK Y., YAZICI M.
    In this study, the synergistic effect created by adding Graphene (GE) nanoplatelets and carbon black (CB) fillers to the rubber matrix was used to determine the high stretchable sensor properties. GE and CB-filled rubber nanocomposite (HcN) strain sensors have been shown to detect and trace crack initiation and crack propagation of different sizes under cyclic loading. Tests were performed with four different crack sizes (0, 2.5, 5, and 10 mm) at five different strain levels (0%, 5%, 10%, 15%, and 20%) to determine the strain sensing performance of the specimens. The electrical response of HcNs under loading was measured with the four-point probe technique and recorded with a high-performance data acquisition system. The progression of external cracks created by scalpel on HcNs was examined by measuring electrical resistance changes caused by cyclic strain loading between 0% and 20%. The electrical response of 4 phr and 8 phr filled HcNs behaved qualitatively similar to each other, while 1 phr filled HcNs showed a significantly different response in terms of quality and quantity. In 4 phr GE-filled specimens, the resistance increase was changed steadily depending on the crack length, and unstable conditions occurred at 5 and 10 mm crack lengths at 1 and 8 phr GE filler ratios. The flexible and stretchable elastomer-based conductive strain sensing sensors, developed with the synergistic interaction of well-dispersed carbon-based fillers in the matrix, can detect and record damaged conditions caused by cyclic loading in many application areas.