Cellulose II aerogels: a review

Cellulose II aerogels are light-weight, open pores materials with high specific surface area. They are made in the same way as bio-aerogels based on other polysaccharides, via dissolution-(gelation)-solvent exchange-drying with supercritical CO₂. Gelation step is often omitted as cellulose allows keeping 3D shape during solvent exchange (which leads to cellulose coagulation) and drying. Drying in supercritical conditions preserves the porosity of “wet” (coagulated) cellulose. There are numerous ways to vary cellulose II aerogel morphology and properties by changing processing conditions and cellulose type. Together with chemical and physical modifications of cellulose and possibility of making hybrid and composite materials (organic–inorganic and organic–organic), it opens up a huge variety of aerogel properties and applications. On one hand, they are similar to those of classical aerogels, i.e. can be used for absorption and adsorption, as catalysts and catalysts support and in electro-chemistry when pyrolysed. On the other hand, because the preparation of cellulose aerogels may not involve any toxic compounds, they can be used in life science applications such as pharma, bio-medical, food and cosmetics. The review makes an overview of results reported in literature on the structure and properties of cellulose II aerogels and their applications. The reader may be surprised finding more questions than answers and clear trends. The review shows that several fundamental questions still remain to be answered and applications to be explored.