Co-Optimizing Insulative and Mechanical Properties of Quartz Fabric Reinforced Phenolic Composites by a Compromising Porous Structure for Thermal Insulation

Introducing porosity into structures is recognized as a practical strategy to achieve lightweightness and insulation for ablatives, but reduced matrix density leads to the weakening of mechanical and anti-ablation performances. Herein, a trade-off design of the porous structure is developed for integrating high-strength, insulation, and anti-ablation abilities into mid density nanoporous phenolic composites (NPC). Benefiting from a narrow nanopore size (20-62 nm) of the matrix, thermal conductivity of NPC can be effectively limited within 0.079-0.115 W/(m center dot K), while showing a mid-density of 0.89-1.04 g/cm3. Meanwhile, NPC shows a considerable axial tensile strength of 130.2-177.8 MPa and out-of-plane compressive strength of 300 MPa due to the compromising porosity (34-62%) and reinforcing of the 3D needle-punched quartz fiber preform. Besides, NPC exhibits excellent oxidation resistance in static radiation heating (1000 degrees C) and outstanding insulation and ablation resistance under an oxy-acetylene heat flux of 1.76 and 4.18 MW/m2 with the linear ablation rates of 0.102 and 0.185 mm/s, respectively. The results will further promote the development and application of phenolic ablatives in extreme re-entry environments.