Mechanical Properties and Thermal Protection Performance of Fiber Reinforced Porous Phenolic Composite Prepared by an Impregnation and Polymerization Method

ABSTRACT Highly porous fiber reinforced phenolic resin has great practicality for thermal insulating and flame retardant. In this work, porous phenolic composite was prepared by an impregnation and polymerization method with quartz fiber felt as reinforcement, during which atmospheric pressure drying was applied without a time‐consuming solvent replacement process. As the solid content of the PR precursor increased, the average pore size of the composite decreased by one order of magnitude (101.1 to 9.06 μm), while the density (0.289–0.423 g/cm 3 ), cross‐linking degree, and thermal conductivity (0.078–0.101 W/m·K) increased. Multi‐point interfacial connection through an interface bonding layer was constructed, and the composite showed high strength (1.67–3.75 MPa) along the xy direction and high strain tolerance (up to 25%) along the z direction. The compressive damage evolution was studied through multiple loading and unloading experiments, showing that interfacial separation and fracture, cracking of the porous resin matrix and fiber debonding, interlaminar fracture and matrix collapse, and fiber breakage occurred successively with the increasing strain. The flame heating experiment for 400 s showed that the cold surface temperatures stabilized at around 500°C to 600°C and decreased with the increasing PR content in the composite, suggesting that ablation heat absorption is more dominant compared to heat insulation as the heat protection mechanisms.