Due to its low strength, brittleness and difficulty in forming, aerogel usually needs mechanical modification to obtain practical application value. The mechanical reinforcement of aerogel can be divided into inorganic reinforcement, polymer reinforcement and organic inorganic hybrid reinforcement.
Inorganic Enhancement
Using ethyl orthosilicate, dimethyl diethoxysilane and mullite fiber as raw materials, the aerogel thermal insulation composite was prepared by sol-gel, supercritical drying and high temperature cracking at 1200℃. The obtained aerogel composite has good formability. Using aluminum silicate fiber and glass fiber as skeleton materials, fiber composite Si02 aerogels were prepared by atmospheric drying. The two fiber composite Si02 aerogel materials are resistant to high temperature, have high fire and heat insulation properties, and the combustion performance reaches class A.
Polymer Reinforced
Polymer reinforcement is to introduce polymer into the skeleton or pore of aerogel material, and form organic cross-linked network with Si02 particles to enhance the effect. This method can significantly improve the integrity and mechanical properties of aerogel, and is an ideal reinforcement method. The properties of the aerogel are mainly determined by its internal pore structure. The mechanics and formability of crosslinked Si02 aerogel can be effectively controlled by selecting suitable polymer type and content. By combining hydrophilic PVA with superhydrophobic Si02 aerogel, a heat-insulating aerogel composite was prepared, which maintained the microporous structure of the aerogel well by using the special interfacial interaction. Alginic acid was introduced to the surface of Si02 particles, which effectively inhibited the collapse of Si02 aerogel due to surface tension during drying, and the composite aerogel was prepared with high surface area and porosity. The combustible organic polymer and Si02 strengthen the skeleton of the aerogel, greatly improve the toughness and formability of the material, but at the same time reduce the flame retardant property of the composite aerogel.
Organic and Inorganic Hybrid Enhancement
The mechanical properties of aerogel can be enhanced by forming the supporting skeleton of organic material and inorganic aerogel and using organic material with high mechanical strength as the carrier of brittle aerogel structure. The silica gel was enhanced by forming a nanoscale interpenetrating network containing silica gel skeleton and cellulose nanofiber network. The bacterial cellulose formed by Acetobacter xylosa growing on solid AGAR was then dried by gel and supercritical fluid to form an enhanced Si02 aerogel with low density, high specific surface area, high porosity and low thermal conductivity, and excellent bending and tensile properties. By adding clay material to the polyimide reinforced Si02 aerogel structure, the results show that the hydroxyl group on the clay surface can significantly enhance the modulus of the material and slightly reduce the specific surface area of the material through covalent and hydrogen bonding interactions with the gel network.