Following our previous works on hydro- and aerogels from different lignins cross-linked with oligo(alkylene glycol)-α,ω-diglycidyl ethers and on the preparation of phenol-formaldehyde (PF) adhesives of high lignin content, this paper reports the preparation of mechanically stable, monolithic aerogels from ligneous precursor materials that have been brought to gelation by either step-reaction or chain reaction polymerization. Dialysis and subsequent thermo-induced gelation of ligneous resole resin pre-condensates (LPF, 40% replacement of phenol by lignin, ν = 1000 mPa s) in ethylene glycol afforded freestanding, homogeneous gels. Incremental replacement of ethylene glycol by ethanol and scCO2 drying produced aerogels that suffered from comparatively little shrinkage and perfectly maintained the initial cylindrical shape even at bulk densities as low as 25 mg cm-3. Scanning electron microscopy, nitrogen sorption at 77 K and thermoporosimetry using o-xylene as probe solvent revealed a largely homogenous internal mesoporous morphology featuring accessible specific surface areas as high as 527 m2 g-1. Chain reaction polymerization of consecutively Fenton-oxidized and per-methacrylated lignin in toluene using a suitable radical source turned out to be an efficient means to produce entirely lignin-based aerogels (apparent density 32-222 mg cm-3) that had an internal surface of up to 370 m2 g-1. Carbonization at 1300°C maintained the shape of the respective aerogels and interconnectivity of pores, however at significant shrinkage.

Synthesis, properties and carbonization of different types of ligneous aerogels

253rd National Meeting (2017)

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