Effect of crosslinker molecular structure on mechanical and thermal properties of resorcinol formaldehyde aerogel

In this paper, three different crosslinking processes were performed on resorcinol formaldehyde (RF) aerogel using methylene diphenyl diisocyanate (MDI) (type 1), MDI and mono ethylene glycol (EG) (type 2), and MDI and glycerol (GL) (type 3) crosslinking agents. The crosslinking processes were done on the final dried gels, not the wet gels. The creation of cross linkage was proved using Fourier Transform Infrared Spectroscopy (FTIR). The changes of mechanical properties and thermal conductivity were attributed to the necks thickness. Atomic Force Microscopic (AFM) confirmed the thickening of the necks by quantitative and qualitative investigations. Compared to the unreinforced sample, the strength of type 3 crosslinked sample ascends by factors of 17.28 and 15.3, in compression and bending tests, respectively. The strain at break for type 2 crosslinked sample was increased 2.05 and 6 times, in compression and bending tests, respectively. Also, type 2 and 3 crosslinked aerogels showed the highest impact energies. The reduced compressive strength data verified that the mechanical strength improvement corresponded to the presence of urethane linkage, not the higher density. The thermal conductivity data revealed that the enhancement of neck size increases the thermal conductivity due to the increase of interparticle connections.