Supercritical methanol drying as a convenient route to phenolic–furfural aerogels

Organic aerogels are prepared by the acid catalyzed cross-linking of phenolic–furfural (PF) precursors in methanol solution, and the solvent is subsequently removed at high temperature as the supercritical fluid. The resulting aerogel is a brown opaque solid and has been prepared as 30 ml cylindrical monoliths exhibiting little or no shrinkage during formation. These solids, which are routinely available with a density as low as ca. 125 mg/cm3, have been characterized by chemical methods (infrared spectroscopy and CP-MAS 13C NMR spectrometry) and physical techniques (Brunauer–Emmet–Teller surface area, transmission and scanning electron microscopy). In addition, thermal conductivities have been determined, and show that the PF aerogels are excellent thermal insulators. These studies establish that the materials described herein exhibit chemical and physical properties very similar to those seen for organic aerogels prepared with low temperature processing techniques. The current method constitutes a convenient and rapid route to organic aerogels.