Mechanical properties of polymer-modified silica aerogels dried under ambient pressure

Silica gels prepared by copolymerizing tetraethylorthosilicate with 3-aminopropyltriethoxy-silane were modified using polymer derived from toluene diisocyanate and dried under ambient pressure. The successful preparation of silica aerogels depended on the effective control of shrinkage during drying. The resulting material, polymer-modified silica aerogel, was then characterized by thermogravimetric analysis and uniaxial compression tests. Results indicated that the apparent elastic modulus and compressive strength of the polymer-modified silica aerogels decreased with increasing amounts of incorporated polymer because of decreasing shrinkage and density, while the strains at the surface cracking point and the final failure point increased significantly during compression tests. The strength and modulus of the silica skeleton could be calculated from the apparent strength and modulus of the silica aerogels respectively. It was interestingly shown that the elastic modulus of the silica skeleton of the silica aerogels increased because of the incorporated polymers, while the polymers had no effects on the compressive strength of the silica skeleton. In addition, the relationships between the apparent elastic modulus or the apparent compressive strength of the polymer-modified silica aerogels and their shrinkage were quantitatively expressed.