Lignin–phenol–formaldehyde aerogels and cryogels

Highly porous organic aerogels have been prepared for the first time from a mixed lignin–phenol–formaldehyde (LPF) resin. Six different P/L weight ratios and two (L + P)/F weight ratios have been tested, leading most of times to nice and reproducible hydrogels which were subsequently either supercritically of freeze-dried. A broad family of aerogels and cryogels, respectively, was thus obtained. These materials were thoroughly investigated in terms of porous structure, based on pycnometry, adsorption and electron microscopy studies. The pore-size distributions were found to depend strongly on the initial composition, but not on the method of drying. The thermal conductivity of aerogels and cryogels has been measured and found to be minimal in materials combining both high mesopore volume and ideal pore sizes.

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► Lignin–phenol organic aerogels and cryogels are reported here for the first time.
► Most compositions tested, including lignin contents as high as 80%, were suitably gelled.
► Aerogels and aerogels had very similar pore-size distributions, which is very unusual.
► Optima of surface areas, micro- and mesopore volumes were evidenced and explained.
► Insulating properties as high as those of polystyrene foam were measured.