The Synthesis And Performance Of Silica Aerogel/Polymer Composites

Silica aerogel is a porous material with high porosity,low density,high specific surface area,low thermal conductivity,ultra-low dielectric constant and low refractive index.As a new type of high effective thermal insulation material,it has been widely used in aerospace,military,construction and other fields.However,aerogel is brittle and fragile,which limits its development space.Silica aerogel nanoparticle network frame structure is introduced into the polymer matrix,on the one hand,can fundamentally solve the problem of aerogel poor mechanical properties;on the other hand,add the graphene by choosing different matrix and strengthen the body in order to obtain aerogel/polymer composites with better performance in thermal insulation,mechanical properties and flexibility.To expand the application field of aerogel,and promote the development of aerogel industry.In this paper,silica aerogel powder was used as additive,epoxy resin and polyimide were selected as matrix respectively,to prepare composite materials with excellent comprehensive properties via in-situ in-situ compositing.The effects of silica aerogel powder on the microstructure,mechanical properties,thennal insulation and heat stability of polymers were study.The enhancement mechanism of nano skeleton structure aerogel and graphene on mechanical properties and thermal insulation properties of polymers was discussed.The main contents include the following three aspects:(1)The low density silica aerogel powder was prepared by adjusting sol-gel process,supercritical drying and ball milling process using tetraethyl orthosilicate as silica source,oxalic acid and ammonia as catalyst.The silica aerogel powder was obtained with a tap density of 0.0739 g/cm3,a thennal conductivity of 0.0256 W·m-1·K-1,a specific surface area of 796.06 m2/g,and a uniform particle size.(2)Flexible thermal insulation film was prepared by two-step method,using silica aerogel powder as thermal insulation filler and polyimide as matrix.The effects of composite ways and aerogel addition on mechanical properties and thennal properties of polyimide composites were compared and analyzed,the heat conduction mechanism of composites was deduced.It is found that the silica aerogel powder dispersed evenly in the polyimide matrix and remained the original pore structure.Silica aerogel significantly improved the thermal insulation and heat resistance of polyimide.When the silica aerogel contents is 20 wt.%,the initial weight loss temperature of the silica aerogel/polyimide composite films increase from 400 to 543℃.And the thermal conductivity is decreased from 0.371 W/(m K)to 0.071 decreased to 0.071 W/(m.K).(3)Silica aerogel/epoxy composites and silica aerogel/graphene/epoxy composites were fabricated by in-situ polymerization with silica aerogel as thermal insulation filler and graphene as reinforcing phase.The effects of silica aerogel and graphene addition on the microstructure,mechanical properties and thermal insulation properties of epoxy resin were investigated.When the silica aerogel addition is 8 wt.%,the graphene addition is 0.1 wt.%,the thermal conductivity of silica aerogel/graphene/epoxy composites is 0.063 W/(m K),what decreases by about 68%compared with pure epoxy.The tensile strength of the ternary composites is 50.05 MPa,and the elongation at break is 13.30%,elastic modulus of 1825 MPa,which increased by 21.39%,6.70%,4.41%respectively compared with silica aerogel/epoxy composites.