Highly water repellent aerogels based on cellulose stearoyl esters

Herein we combine in a novel way the physical effect of porous structure of a cellulosic aerogel with the chemical effect of long alkyl tails by a well known homogeneous green esterification method, to achieve purely bio-based and highly water repellent cellulosic materials. As an alternative for a traditional fluoro derivatized hydrophobization, here long fatty acid tails are utilized to lower the surface energy. To minimize the process emission, ionic liquid (IL) 1-allyl-3-methylimidazolium chloride is used for the esterification, due to its non-volatility and recyclability. We have shown here that low degree of substitution (DS) of the fatty acid cellulose material enables the spontaneous formation of aerogels. Additionally, the very low content of the long stearoyl tails combined with the porous aerogel structure resulted in significant increase in hydrophobicity from an aqueous contact angle of 0° up to 124°. We foresee that this approach can allow sustainable and completely bio-based coatings and insulators paving the way for a new green application potential for cellulose based materials.