ABSTRACT
Aerogels are solids featuring very low density, high specific surface area, and a coherent open-porous network of loosely packed, bonded particles or fibers. Their particular architecture, low weight, and other fascinating properties render aerogels intriguing materials with promising applicability in catalysis, slowrelease of bioactive compounds, tissue engineering, high-performance acoustic and thermal insulation, liquid and gas sorption, gas separation, energy storage, kinetic energy absorption, or transportation, among others. Following the development of aerogels from inorganic and petrol-based organic precursors, research on aerogels from biopolymers, in particular from cellulose, has literally been booming since the turn of the millennium. This entry reviews current approaches toward aerogels from naturally occurring cellulose modifications (cellulose Iα and Iβ) and from the regenerated allomorph (cellulose II), also addressing challenges and measures to preserve the hierarchical network structure along the path from hydrogels via solvogels to the aerogels. The impact of various process parameters, such as dissolution, coagulation, and drying conditions on the properties of aerogels, is discussed. This includes also the pros and cons of direct solvents used in the manufacture of cellulose II aerogels, and the opportunities and limitations of reinforcing aerogels by chemical or physical means (cross-linking, interpenetrating networks, all-cellulose composites). The potential of cellulosic aerogels for commercial applications will be highlighted in the last part of this entry by some illustrative examples from the fast-developing and fascinating field of cellulosic aerogel research.
