Polyurethane foam scaffold for silica aerogels: effect of cell size on the mechanical properties and thermal insulation

Silica-based aerogels have been successfully reinforced by means of reticulated polymeric polyurethane (PU) foams with different cell sizes. The resultant silica aerogel-PU foam composites (Sil-PU composites) were fully characterized (density, shrinkage, aerogel percentage, and porous structure), and the mechanical properties and thermal conductivities were analyzed. Moreover, the effect of the application of a surface modification was assessed. A clear influence of the foam pore size on the final properties was found, and the mechanical properties of the aerogels have been notably improved reaching higher elastic modulus (from 130 to 307 kPa), excellent recovery ratios (above 95%), and significant deformations (more than 70%) without breaking. Therefore, the synthesized composites showed a great elasticity (high recovery ratios), tenacity, resilience, and stiffness in comparison with the non-reinforced aerogels. The obtained samples also showed excellent insulating capacities, reaching values between 14.0 and 12.3 mW/(m·K) for the surface-modified composites that were dried under supercritical conditions. Thus, using reticulated PU foams as a skeleton for aerogels is a promising strategy for a broad spectrum of applications in which silica aerogels are suitable candidates.