Cellulosic aerogels
Aerogels, materials with extreme porosity and very low bulk density, can be made using the so called 'Critical Point Drying'- technique.
In a recent study aerogels were prepared from cellulose, xylan, lignin, their mixtures and from spruce wood. The procedure was:
- dissolution of the lignocellulose material in an ionic liquid
- creating a hydrogel by precipitating the dissolved polymeric material
with aqueous ethanol
- exchanging the aqueous precipitant to pure ethanol
- exchanging ethanol to liquid carbon dioxide
- increasing the temperature to above the Tc of carbon dioxide and
- releasing the pressure slowly to obtaing the aerogel material
Aerogel properties
The aerogels made from pure cellulose, cellulose-lignin or -xylane mixtures or from spruce wood had open pore structures and were brittle. The aerogels had bulk densities as low as 25 g / litre and BET areas up to 500 m2/ g
More:
Aaltonen, O., Jauhiainen O., The preparation of Lignocellulosic Aerogels from Ionic Liquid Solutions, Carbohydrate Polymers 75 (2009) 125-129.