Performance evaluation of glass and rock wool fibers to improve thermal stability and mechanical strength of monolithic phenol-formaldehyde based carbon aerogels

Rock and glass wool fiber reinforced phenol-formaldehyde monolithic composite aerogels (PF/RWF and PF/GWF, respectively) were prepared using solvent saturated sol-gel and impregnation of fibers by initial PF sol. The composite wet gels were dried by using ambient-pressure drying technique. After it, synthesized polymeric aerogels were transformed to rock and glass wool fiber reinforced monolithic carbon composite aerogels (C/RWF and C/GWF) through carbonization at 850 °C. The effect of fiber concentration on the physical and morphological properties of both types of composite aerogels was evaluated. The SEM analysis was also conducted to understand the microstructural changes during the carbonization step. Compressive stress-strain behavior of polymeric and carbon composite aerogels changed drastically by addition of fibers. The Young's modulus of polymeric and carbon composite aerogels increased by increasing of fibers concentration in the aerogel structure and showed a yield stress. The compressive strength of carbon composite aerogels was decreased with respect to the formation of voids and cracks around the fibers through the pyrolysis step. The degradation kinetic parameters of polymeric composite aerogels were evaluated using characteristic kinetic temperature-characteristic kinetic temperature range model (CKT-CKTR). The results showed the higher performance of rock wool fibers to thermal stability enhancement of PF aerogels. By 2.5 wt% wool fibers content, the maximum oxidation rate temperature increased from 594 °C for carbon aerogel to about 620 and 643 °C for C/RWF and C/GWF composite aerogels, respectively. The effect of rock wool fibers on the improvement of thermal oxidation resistance of samples was stronger than glass wool fibers.