Phenolic Modified SiO₂ Aerogel as a Hybrid Thermal Insulation Systems

SiO₂ aerogel is a good thermal insulation material, but its porous nanostructure makes it brittle and has a poor mechanical property. SiO₂ aerogel with a good elastic property was prepared by combining methyltrimethoxysilane (MTMS) and hexadecyltrimethoxysilane to form a composite organic silane precursor. However, its mechanical properties were not significantly improved. SiO₂/phenolic-modified aerogel was prepared by modifying SiO₂ aerogel with thermosetting phenolic resin, which effectively improved the mechanical properties of SiO₂ aerogel. The results show that when the molar ratio of hexadecyltrimethoxysilane to MTMS is in the range of 0-0.05, the elastic properties of the aerogel continue to improve with the increase of the introduction of hexadecyltrimethoxysilane. The maximum compressive strength can reach 0.03 MPa, and the strain tolerance range is 10-18%. When the mass ratio of MTMS to phenolic resin is within the range of 0-5.5, the modified aerogel presents a nanoscale gel network structure. The maximum compressive strength can reach 0.048 MPa, which is nearly 60% higher than the maximum compressive strength of the aerogel before modification. The allowable strain range is 14.7-17.5%. After 20 stress-strain tests, the maximum compressive strength only decreases by 4%, indicating good stability. It simultaneously possessing low density (0.176 g/cm³), volume shrinkage rate, and low thermal conductivity. The thermal conductivity in an air atmosphere at 28 °C is 0.057 W/(m·K). The modified aerogel prepared by the sol-gel reaction and atmospheric drying process has broad application prospects.