By Prof Arthur Ragauskas
Cellulose was first discovered by the French scientist Anselme Payen in 1838, when he noticed a resistant fibrous solid that remained behind after treating plant tissue with acids and ammonia. Cellulose is a polydispersed linear polymer of β-(1,4)-D-glucose and a cellulose fiber is composed of bundles of microfibrils where the cellulose chains are stabilized by hydrogen bonding. Microfibrils are comprised of elementary fibrils where monocrystalline domains are linked by amorphous sections. Although studied extensively, only recently have the nanoscale benefits of cellulose become apparent. In general, there are three broad categories of nanocellulose structures including:
Cellulose whiskers which are rod-like nanoparticles obtained by controlled acid hydrolysis of native cellulose typically with length ranges from 100 to 300 nm and diameter between 5 and 20 nm.[i]
Microfibrillated cellulose consists of bundles of elementary fibrils separated by less ordered regions which depending on the plant species the lateral dimensions of fibrils are of the order of 10–100 nm with a length in the mm scale.[ii]
Nanocellulose balls are spherical structures prepared by a controlled acid hydrolysis procedure.[iii]
Nanocellulose under a microscope. Image Credit http://www.nist.gov
Each of these structural variations of cellulose are being actively pursued for various applications from health care to cosmetics, to advanced nanocomposites for the transportation, packaging, and construction industries, to innovative foams, fillers, and films. A quick inspection of the scientific and patent literature indicates that nanocellulose research has entered an exponential growth phase. Given society’s demand for high performance materials, that are benign, green and sustainable this is driving nanocellulose research and development which has undoubtedly entered a golden age.
The pace of innovation in this field will undoubtedly accelerate since (i) several commercial ventures have begun to manufacture nanocellulose materials on a large-scale (ii) the past two decades of investment in nanotechnology make available a significant infrastructure to characterize nanocellulose structures and (iii) the research accomplishments of nanocellulose over the past decade clearly document a host of promising physical properties. In summary, just as conventional pulp and paper became an integrated component of modern society, nanocellulose is rapidly making many of the products we depend on today ‘better!’
[i] Cellulose nanowhiskers: promising materials for advanced applications. By Eichhorn, Stephen J., Soft Matter (2011), 7(2), 303-315.
[ii] Nanocelluloses: A New Family of Nature-Based Materials. By Klemm, Dieter; Kramer, Friederike; Moritz, Sebastian; Lindstroem, Tom; Ankerfors, Mikael; Gray, Derek; Dorris, Annie. Angewandte Chemie, International Edition (2011), 50(24), 5438-5466.
[iii] Facile synthesis of spherical cellulose nanoparticles. By Zhang, Jianguo; Elder, Thomas J.; Pu, Yunqiao; Ragauskas, Arthur J., Carbohydrate Polymers (2007), 69(3), 607-611