Preparation And Performance Optimization Of Low Density Fiber Reinforced Silicone Modified Phenolic Nanofoam

Lightweight Fiber reinforced silicone-modified phenolic nanofoam composite is anovel char ablation materials with integrated anti-ablation and insulation properties,have been used in the thermal environment re-entry modules of deep space and planetary entry probes with ultra-high temperature,high heat flux,long reentry time.In this paper,silicone-modified phenolic nanofoam was prepared by sol-gel polymerization using phenolic resin,ethyl orthosilicate and polydimethylsiloxane as precursors.Low density fiber reinforced silicone-modified phenolic nanofoam composite was produced by vacuum impregnation and evaluated for ablation performance.Silicon-modified phenolic nanofoam was synthesized by sol-gel polymerization from a mixture of phenolic resin ethyl orthosilicate ester hydrolyzate or polydimethylsiloxane with hexamethylenetetramine as the catalyst and ethylene glycol as the porogen and solvent,accompanied by solvent exchange and drying The silicon-modified phenolic nanofoam exhibits a phenolic nanofoam encapsulated SiO₂ microsphere structure.The FTIR analysis indicated that the phenolic nanofoam and SiO₂ microsphere are connected by the Si-O-C and Si-C chemical bond,and the thermal stability of silane modified phenolic resin nanofoam was significantly improved,the residual weight at 1000°C charcoal is 65wt%.Nitrogen adsorption-desorption of silicone-modified phenolic nanofoams exhibit typical Type IV isotherms and H3 hysteresis loops means the presence of mesopores,the material maintained the original nano-pore structure after the introduction of organic silicone.In this paper,low-density fiber-reinforced silica-modified phenolic nanofoam composites were prepared by vacuum-assisted impregnation with carbon fiber needled fabric as preform.The composite particles were coated with SiO₂ microspheres in the fiber voids.The phenolic particles uniformly encapsulated the fibers.The results of nitrogen adsorption and desorption showed that the specific surface area,pore size and pore volume of the modified phenolic nanometer foam composites increased with the increase of the amount of ethyl silicate,but still the mesoporous materials.The results show that the addition of ethyl orthosilicate to improve the mechanical properties of the composites increases the compressive strength and Young's modulus in the XY and Z directions,and the compressive strength in the XY and Z directions increases from 2.2MPa to 8.1MPa,1.2MPa to 4.4MPa.The Young's modulus in the XY and Z directions increased from 47.2MPa to 346.8MPa,16.0MPa to 140.2MPa.Oxygen-acetylene ablation test results show that the low density fiber reinforced silicon modified phenolic nanofoam composites show better ablation resistance and thermal insulation properties than the original materials under the three heat fluxes of 1.2MW/m2,2.5MW/m2 and 3.6MW/m2.The surface temperature,mass ablation rate and line ablation rate of the material reduced from 1764? to 1728?,0.02616g/s to 0.02196g/s and 0.0432mm/s,to 0.0268mm/s,respectively which means the effect of ethyl orthosilicate on the modification of phenolic resin nanofibers was remarkable,and the composite properties prepared by adding 3% wt of ethyl ortho-silicate modified phenolic nanofoam were the most superb especially among conditions of high thermal flux and long term ablation.