In-situ synthesis of silica aerogel/polyurethane inorganic-organic hybrid nanocomposite foams: Characterization, cell microstructure and mechanical properties

Abstract

Silica aerogel nanoparticles have various applications due to their unique properties such as low thermal conductivity, high specific surface area as well as low density. However, due to low mechanical properties of pure silica aerogel, its composite with other materials is used as thermal insulators. In this work, hydrophobic silica aerogel was synthesized using sol-gel as well as solvent substitution methods, and calcined at 200, 300, 400 and 500 °C. In order to improve the mechanical properties, nanocomposites of hydrophobic silica aerogel and polyurethane with 0.5, 1, 3 and 5 wt% of nanoparticle content were prepared. Nanocomposite foams of polyurethane/silica aerogel were prepared with two separate methods: mixing silica aerogel in polyol and mixing those in diisocyanate. Cyclopentane was used as foaming agent. Results of FESEM, BET and water contact angle analysis showed that silica aerogel nanoparticles possess high specific surface area. Furthermore, the calcined particles at 500 °C showed hydrophilic properties. Optical microscopy Images showed that the sample containing 1 wt% of nanoparticles has the lowest cell diameter, highest cell density and narrower cell size distribution due to higher cell nucleation and homogeneity. Moreover, with the increase in nanoparticle content, the cell size distribution was broadened and cell density decreased. Results of scanning electron microscopy (SEM) analysis confirmed that lower contents of hydrophilic nanoparticles in both mixing media leads to more homogeneous and uniform cell microstructure. Results of compression tests showed that in samples with lower cell size and homogenous cell microstructure, the resistance against compression increased and the mechanical properties improved, this was clearly evident in nanocomposite foam containing 1 wt% of silica aerogel.