Freeze-drying method as a new approach to the synthesis of polyurea aerogels from isocyanate and water

摘要

Polyurea (PUA) aerogels were prepared as the polycondensation product of triisocyanate and water. PUA aerogels were formed through supercritical drying (SC) and, for comparison, by freeze-drying (FD). The effect of isocyanate concentration, catalyst concentration, and drying method on properties like density, specific surface area, pore volume, compressive strength, and morphology was investigated. The properties of aerogels strongly depend on the concentration of the isocyanate in the parent solution and, to a lesser extent, on catalyst concentration. For example, aerogels with higher isocyanate concentration exhibited a higher surface area and modulus. Depending on the formulation, the materials had a density between 0.128 and 0.220?g/cm_(3), surface area between 140 and 210?m_(2)/g, pore volume between 0.593 and 1.500?cm_(3)/g, compressive modulus between 6.5 and 25?MPa, and thermal conductivity between about 0.028 and 0.033?W/m?K. Most importantly, the drying method did not strongly affect the properties of the materials. These were within ~15% for SC and FD. The results indicate that freeze-drying can be successfully used to fabricate aerogels in a cost-effective way. Polyurea aerogels had been successfully synthesized via a sol–gel process followed by supercritical and freeze-drying methods. The effect of isocyanate concentration, catalyst concentration, and drying method on properties like density, specific surface area, pore volume, compressive strength, and morphology was investigated. Highlights Polyurea aerogels can be successfully synthesized via a sol–gel process followed by an eco-friendly freeze-drying method. The resulting aerogels have excellent thermal, mechanical properties, and great processability for application in various industries. Freeze-drying method can be used as a cheaper method to obtain aerogels with properties comparable to materials obtained via a supercritical drying method.