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    Development and characterization of polypropylene or polyamide 6 hybrid composites filled with magnetite and silicon carbide
    (Springer, 2025) Kurtlu, Meral Akkoyun; Tuncay, Beril; Tuna, Sibel
    Polymers, which are becoming widespread day by day and find use in almost every domestic and industrial sectors, have many advantageous properties, on the other hand, their use in areas where thermal conductivity needed is limited due to their low thermal conductivity. To overcome this problem, the requirement for composite materials with high thermal conductivity is increasing and studies on this subject are becoming widespread. In this context, it is known that the thermal conductivity values of the polymer composite structure can be improved by adding fillers to the polymer structures that will augment the thermal conductivity. In this study, to improve the thermal conductivity of polypropylene (PP) and polyamide 6 (PA6), hybrid composites of PP or PA6, separately, filled with silicon carbide (SiC) and magnetite (Fe3O4) were prepared. For this purpose, PP/SiC/Fe3O4 and PA6/SiC/Fe3O4 composites were produced in 1:1 filler ratio with different filler contents (5, 10 and 20% by wts) by extrusion method and shaped by compression molding to determine the optimum amount of additives. Afterward, thermal conductivity, electrical conductivity, mechanical, molecular spectroscopic, and microstructure analyses were carried out for the characterization of all composites. When the study results were examined, it was seen that the PP/SiC/Fe3O4 composite structure containing the highest filler ratio of 20% (by wt) improved by 26% and a thermal conductivity value with a higher enhancement of 38% was obtained for PA6/SiC/Fe3O4 composite prepared at the same filler content compared to neat polymers.
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    Effect of Barium Titanate on the Mechanical and Piezoelectric Performance of Natural Rubber-Based Composites
    (Wiley-V C H Verlag Gmbh, 2025) Yildiz, Gorkem; Ozdemiryurek, Ege; Kurtlu, Meral Akkoyun
    The effects of barium titanate (BaTiO3) filler on the rheology, mechanical, and piezoelectric properties of natural rubber (NR) based industrial rubber mixture were investigated. The results revealed lower time to reach 90% curing (tc90) and lower tensile strength and elongation at break values for BaTiO3-filled rubber composites compared to the pure rubber mixture. The piezoelectric charge constant (d(33)) and the generated voltage of BaTiO3-filled rubber composites increased up to 3 pC/N and 120 mV, respectively, for a total filler content of 40 vol.% with the increase of the filler content.
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    Evaluation of the use and performance of natural filler based polypropylene/leonardite composites
    (Elsevier Sci Ltd, 2024) Sen, Ibrahim; Tuna, Sibel; Kurtlu, Meral Akkoyun
    The use of polypropylene (PP), which has reached a considerably high level in the last century and is one of the polymers whose properties have been investigated and studied in much more detail with the use of various additives, can be obtained as composite structures with the use of both inorganic and organic additives, and the desired properties can be modified according to the desired purpose. In this study, it was aimed to evaluate the behavior of leonardite, a rich source of humic acid, with PP composite structures, whose performance with thermoplastic materials has never been investigated before, although there are studies on its use in different sectors. To evaluate the effects of different ratios of leonardite additives on PP polymer, the composites were prepared with a twin screw extruder, and the test specimens were produced using an injection molding device. Spectroscopic, density, microscopic, mechanical (tensile, impact, flexural), thermal and color analyses of composites containing leonardite at 0, 0.5, 1, 3, 5, and 10 wt% were carried out. As the amount of leonardite in the composite increased, a slight increase was observed in the density values of the composites, with a maximum of 4.7%. In microstructure analysis, a homogeneous distribution of the filler was observed in composites reinforced up to 1 wt%, while agglomeration occurred at higher rates. While the highest tensile strength and flexural strength values were found for the 5 wt% leonardite filled composite, it was observed that these values increased from 31.8 MPa to 32.7 MPa and from 32.84 MPa to 37.84 MPa compared to the pure PP, respectively. The highest Izod impact strength value was determined for the 10 wt% leonardite filled composite and an increase in this value was obtained from 2.47 kJ/m2 to 2.85 kJ/m2. The nucleation effect explains the decrease in supercooling temperature observed in the thermal analysis results. Furthermore, an increase of the thermal stability of PP/leonardite composite structures was demonstrated. When the color analysis results were examined, it was seen that the leonardite additive caused the color of the composite to darken, as expected.
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    Impact of production methods on properties of natural rosin added polylactic acid/sodium pentaborate and polylactic acid/calcium carbonate films
    (Elsevier, 2024) Kocak, Esin; Kurtlu, Meral Akkoyun
    Nowadays biopolymers play an important role in packaging materials due to their protection properties against physical and chemical degradation or mechanical resistance. In this study, sodium pentaborate anhydride (B 5 NaO 8 ), eggshell (CaCO 3 ) nanoparticles, and natural rosin additives were introduced to pure PLA to produce a biofilm protecting from UV rays. The impact of the preparation method of hybrid biocomposite films was carried out based on the polymer casting method and using in the first case only magnetic mixing whereas magnetic mixing coupled with ultrasonic homogenizer was used in the second case. All biocomposite films were obtained for a nanoparticle content fixed at 7.5 wt% and various rosin rates (1, 5, 10, and 40 wt%). This study aims to expand the UV protection zone in PLA films. The thermal and mechanical properties, transmittance of UV - visible rays, microstructure analysis, and contact angle values were evaluated to detect the effect of the preparation method on the final properties. The results showed that the homogeneous distribution of the particles was more effective using an ultrasonic homogenizer. The increase of the rosin amount exhibited a reduction of the UV - visible light transmittance and the wettability was observed, demonstrating a potential use of these films in packaging.
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    Impact of titanate coated magnetite nanoparticles on the properties of rigid polyurethane foams
    (2025) Yılmaz, Buse Fem; Kurtlu, Meral Akkoyun; Tuna, Sibel
    Closed cell polyurethane-based materials represent more than 23% of all polyurethane manufacturing. Unlike to the use of closed cell polyurethane foams in a large variety of applications, these materials exhibit some drawbacks. Their limited mechanical strength and their limited thermal constancy hindering their usage in some areas can be given as examples. In the purpose to overcome and enhance the weaknesses of rigid polyurethane foams and at the same time enlarge the utilization areas of these materials, numerous studies were realized in the literature. The utilization of Fe?O? nanoparticles in various fields, including magnetic resonance, has gained significant attention in recent years. These additives can improve at the same time the thermal and mechanical properties of polyurethane foams. Nevertheless, the development of new methods concerning the surface modification of the nanoparticles is important. The improvement of the interfacial interactions at the polyurethane-filler interface was largely investigated with various agents such as silica, surfactants and precursor metals in the literature. However, the use of a titanate-based coupling agent was not yet researched. In this work, a surface coating of Fe3O4 nanoparticles with a titanate-based coupling agent (Ti-Fe3O4) was realized to produce Fe3O4 filled rigid polyurethane foam nanocomposites at different filler ratios. Microstructural, mechanical, thermal and electrical conductivity properties of all foam nanocomposites were characterized. The FTIR spectra exhibited only the presence of physical interactions. In addition, an increase of the crystallinity ratio with the increase of the filler content was observed. Concerning the electrical and thermal conductivity results, a noticeable improvement was detected from the pure rigid polyurethane foam to the 50 wt.% Ti-Fe3O4 filled nanocomposite. From the mechanical test results, a higher performance was observed for the rigid polyurethane foam nanocomposite produced at 12.5 wt.%.
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    Manufacturing and Characterization of Three Modified Vegetable Oil-Added Polylactic Acid Composites
    (Wiley, 2024) Sen, Ibrahim; Atagur, Metehan; Tuna, Sibel; Eroglu, Murat; Kurtlu, Meral Akkoyun; Sever, Kutlay
    Polylactic acid (PLA) was modified with three types of modified vegetable oils (MVOs), which are the epoxidized soybean oil (ESBO), maleinized sunflower oil (MSO), and maleinized olive oil (MOO), at different weight fractions. A corotating twin screw extruder was used to produce composite materials by the melt-mixing process. The effect of MVO content, from 2.5% to 10%, on the morphology, mechanical properties, density, and water absorption was investigated in detail. The addition of ESBO and maleinized vegetable oils leads to a slight decrease in the density of PLA from 1.252 to 1.231 g/cm3. As the concentration of MVO in PLA increases, the amount of water absorption also increases, and the highest water absorption value was observed in P10MSO. The FTIR spectra of all concentrations of the MOO and MSO have two peaks at 1781 and 1861 cm-1, attributed to the C=O stretching which is related to maleic acid copolymerization. In general, the elastic modulus (EM) was slightly changed by the addition of MVOs to PLA, while the tensile strength (TS) decreased. Due to the plasticizing effect of MVOs, an increase in the Izod impact strength was obtained.
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    On the use of olive leaf powder to improve the performance of water-blown rigid polyurethane foam composites
    (Sage Publications Ltd, 2025) Tuna, Sibel; Kurtlu, Meral Akkoyun
    Nowadays, polyurethane (PU) foams were preferred in a broad extent of applications particularly due to their lowest thermal conductivity values satisfying the demand for energy efficiency while their use as natural filler added foam composites can reduce the polymer content allowing a more environmentally friendly production. The purpose of this work was to research the impact of olive leaf powder of various particle sizes and weight ratios on the microstructure, thermal, and mechanical properties of rigid polyurethane foam composites. All results exhibited optimum mechanical, thermal, and microstructure properties for the finest particle sized and 3 wt% added foam composites. This foam composite demonstrated an enhancement by 54%, 41%, and 61% for the tensile strength, elongation at break, and compression strength values, respectively. The thermal degradation temperature of the foam composites was also improved in correlation with the reduction of the glass transition temperature of the soft segments while the glass transition of the hard segments increased. Concerning the thermal conductivity results, the highest reduction by 11% was observed for the finest particles filled at 5 wt%, compared to the pure rigid PU foam, in correlation with the cell size showing a maximum reduction by 18% for the same composite.