Chitin Nanowhisker Aerogels.pdf

DOI: 10.1002/cssc.201200717 Chitin Nanowhisker Aerogels Lindy Heath,[a] Lifan Zhu,[b] and Wim Thielemans*[a, b] Introduction Aerogels are unique materials that display unusual and highly desirable properties such as low densities, high porosities, high internal surface areas, and low heat conductivity.[2] As a result, aerogels find application in areas such as catalysis,[3] thermal insulation,[4] drug delivery,[5] gas storage,[6] liquid absorption, and space and particle research.[4b,7] Organic aerogels, specifi- cally aerogels made from polysaccharides such as cellulose and chitin, are of particular importance because they utilize renew- able feedstocks. After cellulose, chitin is the second most abundant biopoly- mer in the world. Chitin is composed of b-(1,4)-linked chains of N-acetyl-d-glucosamine and acts as a structural polymer in living organisms such as shellfish, microorganisms, and insects. Crab and shrimp shells are the most common source of chitin.[8] Analogous to cellulose, chitin consists of both crystal- line and amorphous domains. The amorphous domains can be hydrolyzed to release the crystalline segments, so-called chitin nanowhiskers, by using an acid hydrolysis procedure.[9] The ex- cellent intrinsic properties of chitin, for example, bio- compatibility, non-toxicity, renewability, and biodegradability,[10] result in chitin finding application in a wide variety of areas, such as medicinal and pharmaceutical applications,[11] cosmet- ics,[12] and the treatment of industrial pollutants.[11a,13] Chitin also displays excellent wound-healing characteristics and has been used in applications such as wound dressing materials and tissue engineering.[11e,14] Previously, chitin aerogels have been prepared by using the dissolution of chitin followed by regeneration in solvent, typi- cally ethanol. Chitin dissolution systems include N,N-dimethyl- acetamide (DMAc)/lithium chloride (LiCl),[15] 1-butyl-3-imid- azolium acetate,[16] and NaOH–urea solutions.[17] Ch