Controllable Preparation And Performance Optimization Of Fiber-reinforced SiO₂Aerogel Composites For Thermal Insulation

Nanoporous SiO₂aerogels have broad application prospects in thermal insulationarea owning to their low thermal conductivity, supper hydrophobicity, low density andhigh temperature resistance. However, the SiO₂aerogels generally have poor mechanicalproperties owing to their nanoporous nature and high porosity, and need to be reinforcedto meet the practical requirements. Forming strengthened composites with fibers is agood strategy for SiO₂aerogel reinforcement. Researching on the relevant factors andoptimization methods of the fiber-reinforced SiO₂aerogel composites is significant forthe development of the SiO₂aerogel insulation materials.Aiming at improving the mechanical properties of SiO₂aerogel materials whilemaintaining low thermal conductivity, the ambient drying preparation process was firstlyresearched on. The nanoporous aerogels with porosity of94.89%, specific surface area of867.9g/m²and pore sizes of5¹0nm have been prepared with the optimization of thepreparation process. The thermal conductivity of the as-prepared aerogels was0.0221W/（m·K）, the compressive strength and bending strength of it were8.5MPa and0.07MPa, respectively. Moreover, the super-hydrophobic angle of the aerogels was159.8°.Three types of fibers （viz. glass fibers, polyester fibers and electrospun fibers） wereadded into SiO₂aerogels to formed fiber-reinforced aerogel composites. The effects offiber types and fiber contents and interfacial bonding on the properties of the compositeshave been studied. Results showed that, the composites with glass fiber-reinforced havebetter mechanical properties, thermal stability and fiber resistance, with thermalconductivity low as0.0252W/（m·K）. Oppositely, the composites reinforced by polyesterfiber and electrospun fibers exhibited great flexibility. When the specific energy of fibersis high and the scale of it is close to the one of the aerogels, the interfacial bondingbetween the SiO₂aerogel and the fibers was better. Moreover, when the contents of theglass fibers, polyester fibers and electrospun fibers were3wt%⁴wt%,1wt%²wt%and10wt%, respectively, the composites holds lower thermal conductivities and bettermechanical properties.4layers of aligned glass fibers were impregnated into the silica sol layer-by-layer tofabricate the aligned fiber-reinforced SiO₂aerogel composites with specific laminatedstructures （viz. LLLL, LTLL, LTTL, LTLT, LLTT, LTTT）. The experimental resultsindicated that, the compressive strength of the composites increased with the decreasing of the orthogonal number of the fiber layers. The bending modulus of the compositesincreased with the increasing of the fiber layers number laminated in the directionperpendicular to the stress. The thermal insulative property of the composites wasanisotropic during to the laminated structure of the fibers. The thermal conductivity of thecomposites on direction of L （viz. along the direction of fiber aligned） was up to0.057W/（m·K）. On the contrary, the thermal conductivity of the LLLL structure on Ndirection （viz. perpendicular to the fiber layers） was about0.026W/（m·K）, and keepconsistent when the laminated structure of the composites varied. Therefore, it’sconsiderable to design the structures of the aerogel composites with the laminatedmethods to control the preparation and optimize the thermal insulation and mechanicalproperties of the fiber-reinforced SiO₂aerogel composites.