Mechanical and thermal insulation properties of isocyanate crosslinked resorcinol formaldehyde aerogel: Effect of isocyanate structure

In this article, the mechanical and thermal properties of resorcinol formaldehyde (RF) aerogels were improved using two different crosslinkers including hexamethylene diisocyanate (HDI) and methylene diphenyl diisocyanate (MDI). The crosslinking was performed after the aerogel drying process, with two concentrations of crosslinking agent. The formation of urethane linkages was investigated by Fourier transform infrared spectroscopy. The effect of crosslinking process and crosslinking agent type on the mechanical properties was analyzed by compression, bending, and impact tests. The improvement of mechanical strength was attributed to the neck thickness, which was studied by atomic force microscopic test. The results revealed that a higher improvement was obtained by increasing the crosslinking agent value. HDI crosslinked aerogel represented the highest strain-at-break and MDI-reinforced sample showed the highest strength. By crosslinking, the samples density was increased <59% and the reduced compressive strength was enhanced upto eight times. The effect of crosslinking on the thermal conductivity was explored. The increment of neck size and density enhanced the solid conductivity and, consequently, raised the thermal conductivity. (c) 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48196.