Aldehyde Approach to Hydrophobic Modification of Chitosan Aerogels

Biobased nanofiber aerogels are ones of the attractive emerging materials in the fields of biochemistry and materials chemistry, but their poor humidity stability due to high hydrophilicity has limited their practical uses. In this paper, a new series of hydrophobic nanofibrous aerogels made from regenerated chitosan and alkyl aldehydes were prepared via a simple one-pot reaction followed by supercritical drying. Hexanal-modified chitosan aerogel shows excellent hydrophobicity with a water contact angle of ∼136°, a low density of 0.04-0.07 g cm^-3, and structurally homogeneous three-dimensional nanofiber network at the nanoscale. Systematic investigations using various alkyl aldehydes revealed that pentanal-modified aerogel has similar high hydrophobicity and low density compared to the hexanal-modified material, while heptanal- and octanal-modified aerogels show drastic shrinkage during gelation. The aldehyde modification also suppresses permeation of water droplets into aerogel monoliths as well as reducing shrinkage under high humidity conditions.