Preparation of silica aerogel/polyurethane composites for the application of thermal insulation

In this study, polyurethane was blended with silica aerogel to improve its thermal insulation property. The silica aerogel/polyurethane composite with a suitable composition 35/65 (v/v) has low thermal conductivity (0.13 W/m K) and a hydrophobic property (water contact angle of 95.6°). The pore size, pore distribution, and structure of silica aerogel (tetraethoxysilane-based) were studied to select the suitable silica aerogel for blending. The co-precursor method and the solvent exchange method were used to prepare the silica aerogel for comparison. Fourier Transform Infrared spectra confirmed that the co-precursor method created more Si-CH₃ groups on the silica surface than solvent exchange method. The silica aerogel prepared by the co-precursor method had a thermal conductivity of 0.032 W/m K with a porosity of 97 %, and a water contact angle of 130°. This silica aerogel prepared was then used to blend with the polyurethane prepared by diisocyanate and poly (tetramethylene oxide), with 1,4-butanediol (1,4-BD) as the chain extender. Silica aerogel/polyurethane composites were formed as films of various compositions by the solvent casting method. Scanning electron microscopic (SEM) photographs revealed that the composites were uniform. The optimal composition of silica aerogel/polyurethane is 35/65 (v/v) with the water contact angle of 95.6° and the thermal conductivity 0.13 W/m K. The silica aerogel/polyurethane composites have no disadvantages of brittleness and hygroscopic property, and possess a low thermal conductivity property.