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Öğe 3D-Printed Biocomposites from Hemp Fibers Reinforced Polylactic Acid: Thermal, Morphology, and Mechanical Performance(North Carolina State Univ Dept Wood & Paper Sci, 2025) Celik, Esra; Uysal, Mesut; Gumus, Omer Yunus; Tasdemir, CagatayThermal, morphological, and mechanical properties were studied for 3D- printed biocomposites prepared from polylactic acid (PLA) and hemp fibers. For this purpose, the neat PLA, PLA/Hemp fiber (3 wt%), PLA/Hemp fiber/Maleic anhydride (3 wt% and 0.6 wt%), and PLA/Hemp fiber/Maleic anhydride/Glycerol (3 wt% and 0.6 wt% + Glycerol added in 10% of PLA) biocomposites were extruded to obtain filaments for fused filament fabrication (FFF). Thermogravimetric analysis (TGA) provided temperatures corresponding to 5%, 10%, and 90% mass losses for materials before and after 3D printing. During 3D printing, filaments were extruded with a nozzle temperature of 220 degrees C; consequently, their thermal properties worsened after 3D printing. In thermal analysis, T g increased by adding hemp fiber and maleic anhydride but was decreased with glycerol addition. The tensile and flexural strengths of neat PLA and biocomposites were not statically different, but flexural strength was slightly increased by adding ingredients one by one. Regarding modulus of elasticity (MOE) of materials, the sample group of the PLA/hemp fiber/maleic anhydride had the highest value. However, glycerol addition decreased MOE by 17%. These results showed that material performance of the PLA could be improved or remain statistically identical by adding hemp fiber, maleic anhydride, and glycerol.Öğe 4-(Benzimidazolisonitrosoacetyl)biphenyl modified chitosan and its copper complex: Synthesis and electrorheological properties(Elsevier Sci Ltd, 2025) Kayapa, Faruk; Karipcin, Fatma; Ozen, Muruvvet Begum; Gumus, Omer Yunus; Unal, Halil IbrahimA novel chitosan Schiff base derivative (CsB) was synthesized for the first time by a condensation reaction of chitosan with 4-(benzimidazolisonitrosoacetyl)biphenyl. As a result of the coordination reaction of copper ions, its copper(II) complex (CsBCu) was constructed. Then, the structures were confirmed by ICP-OES, ATR-FTIR, TG/ DTA, and SEM analysis. Furthermore, electrorheological (ER) properties of the synthesized compounds, as a new dry-based ER fluid, were extensively studied in silicone oil (SO). CsBCu/SO exhibited a higher shear stress value of 78 Pa at a 2.5 kV mm-1 applied electrical field than Cs/SO and CsB/SO, which is attributed to the contribution of the paramagnetic nature of the Cu element. The shear and oscillation tests revealed ER and viscoelastic behavior of the suspensions upon applying an external electric field (E).Öğe A comparative study of coal fly and bottom ashes as sustainable electroactive vibration damping materials(Korean Soc Environmental Engineers - Ksee, 2024) Begen, Deniz; Calis-Ismetoglu, Gokce; Gumus, Omer Yunus; Unal, Halil IbrahimCoal is used in most of the power and chemical plants to meet energy needs which produce various waste ashes. Reuse of these ashes as electroactive materials has great importance for sustainable development. In this study, it was detected that the main components of coal fly (CFA) and bottom ashes (CBA) were oxides of silica (SiO2), 2 ), iron (Fe2O3), 2 O 3 ), aluminium (Al2O3), 2 O 3 ), and magnesium (MgO), besides carbon. These are well-known electrorheological (ER) active materials. The aim of this study is to reveal dielectric and electroactive vibration damping capabilities of CFA and CBA. According to the dielectric and ER flow tests carried out in insulating silicone oil (SO), the optimum concentration of particles was determined to be 35 wt.% for both ashes. Higher ER yield stress (tau y tau y = 135 Pa), higher ER efficiency (32.8), and better viscoelastic properties (tau c= tau c = 128 Pa, G' = 680 kPa) under 3.0 kV mm-1 applied electric field were obtained for 35CFA/SO suspension system compared to 35CBA/SO (tau y tau y = 125 Pa, ER eff = 24.0, tau c = 55 Pa, G' = 260 kPa). Although it was concluded that both ashes can be upcycled to sustainable and smart vibration damping alternative materials, better performance was observed for CFA particles.Öğe Biodegradable Nanocomposite Filament Based on PLA/PCL/CNCs for FDM 3D Printing: Production, Characterization and Printability(Wiley, 2025) Ilhan, Recep; Gumus, Omer Yunus; Lekesiz, HuseyinAdditive manufacturing (AM) is a widening technique for the processing of polymers that is not only used by personal users but also by some industries. The development of biodegradable and bio-based composites for AM attracts great interest with respect to various aspects such as environmental issues, user health, and biomedical applications. Polylactic acid (PLA) is a good candidate for bio-based materials. However, its brittleness needs to be improved. In this study, PLA-based filaments with improved toughness by adding polycaprolactone (PCL) (10% and 20% by weight) and cellulose nanocrystals (CNCs) (5% by weight) were produced for the fused deposition modeling (FDM) technique. The physical, thermal, morphological, and mechanical properties of the produced filaments were comprehensively characterized. All filament diameters were found to be within the suitable range for FDM applications (1.75 +/- 0.05 mm). TGA analyses showed that the filaments could maintain their thermal stability up to approximately 256 degrees C and that the CNCs enhanced their thermal stability. The addition of PCL and CNCs did not cause significant changes in T g and T m of the neat PLA (T g = 58.14 degrees C and T m = 175.93 degrees C). The tensile test results indicated that the PCL and CNCs reinforcement increased the elongation at break from 6.76% to 40.25% and the toughness from 2.94 to 14.48 MJ/m3. In the last part, the three-dimensional (3D) printability was demonstrated by producing auxetic sheets with optimized printing parameters based on MFI, TGA, and DSC data, and good dimensional stability was obtained.Öğe Effect of Carbon Nanotube Reinforcement on Creep and Recovery Behavior of Additively Manufactured Polymers: An Experimental and Prediction Study(Springer Heidelberg, 2024) Feratoglu, Kamil; Istif, Ilyas; Gumus, Omer Yunus; Turkes, ErolIn this study, one of the most frequently used polymeric materials in fused deposition modeling (FDM) acrylonitrile butadiene styrene (ABS) is reinforced with different amount of carbon nanotubes (CNTs). Thermogravimetric analysis and differential scanning calorimetry analysis are applied to examine thermal degradation behavior of produced nanocomposite filaments. Specimens are manufactured by fused deposition modeling by using produced nanocomposite filaments. Tensile, creep and viscoelastic-viscoplastic behaviors of FDM-printed nanocomposite samples are investigated by conducting tensile, creep and loading-unloading tests under different strain rates and strain levels. Morphology of 3D printed samples is examined through scanning electron microscopy. Void densities which plays important role in mechanical behavior of additively manufactured samples are determined via ImageJ and CNT reinforcement on void densities are investigated. Data obtained from tests are used in system identification process, and multi-input-single-output model structures are proposed for the prediction of tensile, creep and recovery behaviors of 3D printed nanocomposite materials.Öğe Electrochemical characterization of poly(thiophene-3-boronic acid) for aqueous environments(Elsevier, 2024) Eken, Taha Yasin; Gumus, Omer Yunus; Uzunsoy, DenizPoly(thiophene-3-boronic acid) (PTBA) was studied as a promising active material for aqueous environments in this paper. Using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), the solubility and electrochemical behavior of it was studied in a range of aqueous solutions. Fourier Transform Infrared Spectrometry (FTIR) results verify the successful synthesis. PTBA shows promising solubility qualities in certain pH ranges, especially in alkaline solutions. However, among alkaline, neutral, and acidic environments the best environment for redox properties of aqueous 1 mM PTBA is the neutral one. The peak current (ip) of 1 mM PTBA for 100 mV/s in the neutral environment is 0.01 mA and half peak potential (Ep/2) is _ 0.1 V (vs Ag/AgCl). Diffusion coefficient of PTBA is found as 4.97 x 10_8 cm2/s. The impedance tests also confirm that the neutral solvent decreases the charge transfer resistance.Öğe Menthol and organic acid-based hydrophobic deep eutectic solvents as plasticizers in biodegradable poly (lactic acid) films(Elsevier, 2025) Uzun, Sukran Asgin; Dagdelen, Adnan Fatih; Gumus, Omer Yunus; Dundar, Ayse Neslihan; Saricaoglu, Furkan TurkerThis study examined hydrophobic deep eutectic solvents (DESs) as plasticizers for poly (lactic acid) (PLA) films, comparing their performance to plasticizers like epoxidized soybean oil (ESBO) and di(2-ethylhexyl) phthalate (DEHP). DESs were produced by mixing DL-menthol (hydrogen bond acceptor, HBA) with pyruvic acid (Pyr) and levulinic acid (Lev) (hydrogen bond donors, HBD). The densities of DESs were similar to ESBO and DEHP and exhibited low viscosity and shear-thinning behavior. Chemical and thermal analysis revealed successful production of DESs, indicated by lower melting points and hydrogen bond interactions between HBA and HBD. PLA films plasticized with DESs showed varied properties depending on plasticizer concentration. M-Pyr plasticized films had the lowest water uptake and solubility at a 5 % concentration. DESs imparted a yellowish tint to PLA films, with M-Lev showing higher b* values. Light transmission decreased with increasing plasticizer concentration, enhancing UV barrier properties. Adding 20 % M-Pyr and M-Lev to DES plasticized films enhanced their tensile strength by 21.73-80.60 % while reducing elongation at break by 45.94 % and 39.10 %, respectively. DESs also influenced puncture force, deformation, and heat seal ability. Water vapor and oxygen permeabilities of DES-plasticized PLA films were reduced by 50 % and 38.35 % at 20 % plasticizer concentration. FT-IR analysis verified DESs' compatibility with PLA, indicating negligible shifts in characteristic peaks. DESs exhibited low volatility and migration with high antioxidant capacity, making them suitable plasticizers. Menthol-based hydrophobic DESs demonstrated effectiveness as plasticizers for PLA films, improving mechanical and barrier properties while ensuring stability and low volatility.Öğe Redox Properties of Poly (aniline boronic acid) in Aqueous Environment with Glucose and Table Sugar Addition(2024) Eken, Taha Yasın; Gumus, Omer Yunus; Uzunsoy, DenizPolyaniline boronic acid, a conducting polymer with unique properties, has gained attention for its potential applications in batteries, sensors, drug delivery systems, and electrochemical devices. Understanding the redox behavior of this polymer in the presence of sugars is of particular interest due to the potential implications for its functionality in various applications. Cyclic voltammetry is employed to analyze the redox behavior of the polymer in aqueous solutions with glucose and table sugar. Preliminary results suggest that the presence of glucose improves, and table sugar declines the peak values. The diffusion coefficient of the polymer is found as 2.6x10-9 cm2/s. The choice of supporting electrolyte, exemplified by potassium carbonate and potassium chloride, also exhibited an influence on redox behavior of polyaniline boronic acid, and peak potential and peak values are higher in potassium chloride solutions.
