Synthesis and characterization of novel phenolic resin/silicone hybrid aerogel composites with enhanced thermal, mechanical and ablative properties

A novel lightweight phenolic resin/silicone (PR-Si) hybrid aerogel composite was fabricated through vacuum impregnation using PR-Si hybrid aerogels as matrix and low density (0.184 g/cm3) carbon-bonded carbon fibre as 3-dimensional reinforcement. The PR-Si hybrid aerogels was synthesized through a facile sol-gel polymerization, accompanied by solvent exchange and ambient pressure drying from a mixture of PR and methyltrimethoxysilane (MTMS) with ethylene glycol as the porogen and hexamethylenetetramine as the catalyst. The hybrid aerogels possess hierarchically micro-meso-macroporous structure and higher thermal stability than that of the pristine PR aerogels. The obtained aerogel composites exhibit low density (0.312–0.356 g/cm3), high compressive strength (0.76–4.08 MPa), low thermal conductivity (0.098–0.240 W/(mK)), and good thermal ablative and insulative properties in oxyacetylene flame simulated high temperature environment (linear ablation rates as low as 0.073 mm/s and internal temperature peaks below 200 °C at 38 mm in-depth position as the surface temperature approximately 1800 °C).