Preparation And Characterization Of SiO₂ Composite Aerogels Enhanced With TDI/MDI

SiO₂ aerogels are widely used in the fields of building insulation,aerospace and other fields with low density,low thermal conductivity and light weight.However,their three-dimensional network structure leads to poor mechanical properties and easy cracking,which limit the practical application.In this paper,silica aerogels and organic enhanced SiO₂ composite aerogels were prepared by sol-gel process and atmospheric drying,and their structures and properties were characterized.Firstly,the preparation of bulk silica is based on tetraethyl orthosilicate?TEOS?as silicon source,trimethyl chlorosilane?TMCS?as surface modifier,and dried at atmospheric pressure.When the hydrolysis temperature is 50 ?,the molar ratio of TEOS to ethanol is 1/10,the pore size is uniform and the average pore size is about 20 nm.After the surface modification of TMCS,the hydrophilic-OH groups on the gel surface are converted into hydrophobic-CH3 groups,on the one hand increased the hydrophobicity of areogel,on the other hand,the gel pores are supported and the degree of shrinkage of the gel is reduced during the drying process.The density of the prepared bulk silica aerogels is0.135 g/cm3,the specific surface area is824.75cm2/g,the thermal conductivity is 0.02776 W/?m·K?and the compressive strength reaches 3.2 Mpa.Secondly,in order to improve the mechanical properties of aerogel,the organic reinforced composite silica airgel was prepared by sol-gel methodunder atmospheric pressure drying conditions,using3-aminopropyltriethoxysilane?APTES?as the silane coupling agent,and 2,4-toluene diisocyanate?TDI?and 4,4'-diphenyl Methane diisocyanate?MDI?as organic reinforcement.In the organic matter,a portion of the-NCO group is converted to-NH2 after action with water,the remaining-NCO groups combine with the-OH and-NH2 on the gel surface respectively,then form the urethane bond and the stabilized ureido group which adhere to the SiO₂ backbone.The results show that when the molar ratio of TEOS/APTES in the silicon source is 1:1,the composite aerogel density is 0.3755 g/cm3,the porosity is 82.93% and the pore size is about 30 nm,and the compressive strength reaches 13¹5 MPa.Finally,to investigate the relationship between aerosol nanoporous structure and properties,an airgel atomic model was established and molecular dynamics simulation and performance calculations were carried out.Through the calculation of mechanical properties and characterization,the kinetic model is amorphous,and the mechanical properties are consistent with the experimental preparation.Therefore the simulation results can be used to supplement the experimental data.