Preparation and properties of phenolic foam modified with boric acid and organosiloxane by supercritical CO₂ technology

In this study, a silica boron modified phenolic resin foam (SiBPF) is prepared in a reactor under specific pressure and temperature and using supercritical CO₂ (scCO₂) as a physical foaming agent, to improve phenolic foam (PF) brittle and friable properties and avoid environmental pollution caused by conventional physical foaming. To determine the partially curing degree for foaming, the influence of partially curing time at partially curing degrees between 39.88% and 53.17% was studied. Further, through an orthogonal experimental method, the optimized foaming process parameters—partially curing time of 6 h, adsorption time of 9 h, foaming pressure of 1 MPa, and foaming temperature of 130°C—were determined. The SiBPF, thus prepared under the optimized conditions, exhibited a density of 0.2356 g/cm³, an average cell size of 86.66 μm, and a cell density of 7.10 × 10⁶ cells/cm³. Its compressive strength was found to be 7.28 MPa, with a specific compressive strength of 30.90 MPa/g·cm⁻³. At 800°C, the carbon residue rate, thermal decomposition temperature T_5%, and T_max reached 77.61%, 355.21, and 702.70°C, respectively. The thermal conductivity of SiBPF was measured to be 0.0644 W/mK, with the rear temperature stabilizing at 60°C on a hot platform of 100°C.