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    Microstructural, thermal and ablative properties of TiB2 modified carbon fiber reinforced resorcinol formaldehyde composites for thermal protection of aerospace vehicle
    (Wiley, 2025) Aras, Sefa; Cavusoglu, Ferda Civan; Yilmaz, Nevin Gamze Karsli; Unlu, Derya
    Ablative polymeric composites were fabricated using vacuum impregnation and hot press molding techniques. The composites consisted of needled carbon fiber felt as the reinforcing material and resorcinol-formaldehyde (RR) or boron-modified resorcinol-formaldehyde resin (RRB) as the matrix. Different weight percentages of titanium diboride (TiB2) were incorporated as a filler. The ablation mechanisms of the composites were derived from SEM-EDS, XPS, and XRD analysis of char layers formed after exposure to an oxyacetylene flame. The composites displayed excellent thermal insulation properties during the oxyacetylene test. The back surface temperatures ranged from 24.8 to 26.8 degrees C, indicating minimal heat penetration through the composites. This composite demonstrated a linear ablation rate (LAR) of 0.0053 mm/sec, a mass ablation rate (MAR) of 0.0195 g/sec, and a charring rate (CR) of 0.0543 mm/sec. During ablation, the low LAR, MAR, and CR values of C-RRB-T composites confirm that these composites are promising for thermal protection system applications in aerospace.Highlights Resorcinol formaldehyde matrix was modified with boron and filler TiB2. Composites were fabricated using vacuum impregnation and hot press molding. The thermal stability and char yields of the composites increased with TiB2. The addition of TiB2 to the C-RRB composite improved the ablation properties.
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    Synthesis, Characterization, and Thermal Pyrolysis Mechanism of Resorcinol-Formaldehyde Resin-Containing Phenylboronic Acid
    (Wiley-V C H Verlag Gmbh, 2024) Aras, Sefa; Cavusoglu, Ferda Civan; Unlu, Derya
    In the present study, a resin is synthesized from resorcinol and formaldehyde in the presence of phenylboronic acid. Properties of resins such as free formaldehyde content, total solid content, density, gelation time, viscosity are determined. The chemical structure of the resorcinol-formaldehyde resin and the resorcinol-formaldehyde resin containing phenylboronic acid is confirmed by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The thermal stability and curing behaviors of the polymers are investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry, respectively. Modification of the resorcinol-formaldehyde resin with a boron source, phenylboronic acid results in a certain increase in thermal stability with a higher residual weight. The 6% PBA loaded polymer has the highest thermal efficiency, so the thermal behavior of it is investigated by curing at different temperatures. The 80 degrees C/4 h curing method is the most reasonable for energy savings. In differential scanning calorimetry (DSC) analysis, a 6 wt% PBA loading ratio was determined as the optimum value according to the energy requirements. In this study, a resin is synthesized from resorcinol and formaldehyde in the presence of phenylboronic acid. The 80 degrees C/4 h curing method is the most reasonable for energy savings. While the char residue yield of pure RR resin was 47.9%, the char residue yield of RRB6 resin increased to 54.9%.image (c) 2024 WILEY-VCH GmbH