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    A detailed investigation into the curing kinetics of zinc borate-epoxy composites
    (Elsevier, 2025) Kabakci, Gulden; Caner, Sumeyye; Yildirim, Cennet; Sakalli, Berdan; Yakisik, Zeliha Bengisu; Babur, Esra; Tezel, Guler Bengusu
    Epoxy resins (E) are widely used in composite applications due to their superior properties such as lightweight, manufacturing flexibility, and compatibility with numerous reinforcement elements. To enhance these properties and mitigate drawbacks like low toughness, curing agents that improve chain linkages and nanofillers are employed. Nano-sized zinc borates (ZB), commercially available materials, are frequently studied for improving the thermal stability, mechanical strength, and fire resistance of polymeric structures. ZB, with the formula 2ZnO.3B2O3.3.5H2O, is a white crystalline nanomaterial that possesses low toxicity, anti-corrosive properties, low density, and compatibility with various polymers. Although many studies focus on improving the thermal stability and mechanical properties of ZB-epoxy composites (ZB-E), research on curing processes remains limited. However, selecting parameters like temperature and curing duration under system transformations is crucial for composite production. Curing kinetic parameters are essential for accurately analyzing these processes. This study evaluates the curing process of epoxy systems containing different mass fractions of ZB (2-4-6-8-10 %) through dynamic differential scanning calorimetry (DSC) tests. DSC analyses were conducted at various heating rates (3-6-9 degrees C/min) with a final curing temperature of 120 degrees C. The obtained data were analyzed using different phenomenological kinetic equation models (Kissinger, Flynn-Wall-Ozawa, Boswell, and Moynihan) in Matlab-R2019b, and the curing kinetic parameters were calculated. At the same time, the reaction order was calculated using the Crane method. In the final stage, Arrhenius equations were applied to determine the activation energies of the systems. This study assesses the influence of ZB addition on epoxy curing kinetics and the activation energies of ZB-E structures. The activation energy (Ea) values calculated from different models (Kissinger, FWO, Moynihan, and Boswell) show some variation, but the overall trend is consistent: as the ZB content increases, the activation energy generally decreases. The Ea value calculated using the Kissinger, FWO, Moynihan, and Boswell methods decreases by approximately 35.48 %, 33.27 %, 33.27 %, and 34.63 % respectively, when the ZB content increases from 0 % to 10 %. It also provides a new perspective for pre-production optimization and characterization of composite curing systems, aiming to reduce manufacturing costs and production times.
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    Thermo-mechanical behaviours investigation of Nano-Sized Al2O3, TiO2, and Graphene Nanoplatelet Reinforced Epoxy Composites
    (Duzce University, 2024) Kabakçı, Gülden; Kılınçel, Mert; Tezel, Guler Bengusu
    Composite materials find extensive applications in various industries, thanks to their remarkable properties. These sectors include energy, maritime, motor sports, aviation, space and defense. The materials commonly used in these sectors are fiber reinforced plastic (FRP) composite materials. Epoxy materials are commonly used as matrix in the production of FRP materials. This study delves into the enhancement of epoxy-based nanocomposites by using graphene nanoplatelets (GNP-5nm), TiO2 (13nm), and Al2O3 (8nm) nanoparticles. These nanoparticles were added at varying mass ratios into a commercial epoxy to investigate their effects on some chemical, thermal and mechanical properties. Meticulous mixing methodologies were used to reduce clumping effects and ensure even distribution during the process. The curing process was carried out in a PLC (Programmable Logic Controller) controlled hot air oven under isothermal conditions under the influence of 100 °C for 30 minutes. Tensile strength, elongation at break, toughness, resilience modulus, elasticity modulus, hardness, FTIR analysis and thermal conductivity properties were characterized to assess the nanoparticle influence on the epoxy matrix. The results showed that there were remarkable improvements in mechanical properties with nanoparticle reinforcement. Especially, 1.25% Al2O3 inclusion exhibited a substantial increase of 140.32% in tensile strength and a 7% rise in shore D hardness compared to pure epoxy. This enhancement was attributed to enhanced O-H bonding between 'O' atoms in Al2O3 nanoparticles and epoxy polymer chains, enhancing matrix-filler interactions. Additionally, the effect of 1.0% TiO2 led to plasticity, displaying a 32% rise in elongation at break, signifying improved deformation energy absorption compared to neat epoxy. In thermal conductivity measurements, the highest thermal conductivity was observed in the sample with 1.25% GNP added and it increased by 123.5% compared to neat epoxy. In TiO2 and Al2O3 added samples, an increase of 69% and 47%, respectively, was observed at 1.25% additive rates compared to neat epoxy. According to the results, thanks to the nanoparticle reinforcement added into the epoxy matrix, composite structures can be given new and superior properties specific to the applications.