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·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 °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.