Acetylation of Cellulose Nanowhiskers with Vinyl Acetate under Moderate Conditions Nihat Sami C ¸etin, Philippe Tingaut,* Nilgu ¨l O ¨ zmen, Nathan Henry, David Harper, Mark Dadmun, Gilles Se `be* Introduction Cellulose is the main constituent of wood and plants and is one of the most abundant renewable resources on earth. Cellulose is composed of 1,4-b-glucopyranose units asso- ciated by hydrogen bonding, which forms a semicrystalline structure where highly ordered regions (crystallites) are distributed among disordered domains (the amorphous phase). [1] The crystallites (also called whiskers or nano- whiskers) are nanometer-sized and can be recovered by various methods and used as reinforcing agent in polymer- based composite materials. [2–4] Because of their high specific strength, modulus, and aspect ratio, cellulose nanowhiskers can significantly improve the mechanical properties of the composites at nanofiber loading levels as low as 6%. [5] Transparent composites with improved mechanical and thermal characteristics can also be prepared, even at high nanofiber loading. [6–8] The other advantages of these nanowhiskers stem from their low density, renewable nature, biodegradability, and relatively low cost. To realize property improvements, the cellulose nano- whiskers must be homogeneously dispersed in the poly- meric matrix, which is a non-trivial task. Because of their high surface area and hydrophilic nature, the nanowhiskers tend to flocculate by hydrogen bonding. Stable suspensions of cellulose nanowhiskers can, however, be prepared in water by acid hydrolysis of the biomass. The cellulose nanowhiskers do not flocculate as they are stabilized by Full Paper N. S. C ¸etin, N. O ¨ zmen Faculty of Forestry, Kahramanmaras ¸ Su ¨tc ¸u ¨I ˙ mam University, Kahramanmaras ¸, Turkey D. Harper Tennessee Forest Products Center, The University of Tennessee, 2506 Jacob Drive, Agriculture Campus, Knoxville, Tennessee 37996-4570, USA N. Henry, M. Dadmun Chemistry Department, The University of Tennessee, Knoxville, Tennessee 37996-1600, USA G. Se `be Unite ´ Sciences du Bois et des Biopolyme `res, Universite ´ Bordeaux 1, INRA, CNRS, UMR US2B, 351 Cours de la Libe ´ration, Talence F-33405, France Fax: þ33 5 4000 6439; E-mail: g.sebe@us2b.u-bordeaux1.fr P. Tingaut Swiss Federal Laboratories for Materials Testing and Research (EMPA), Uberlandstrasse. 129, CH-8600 Du ¨bendorf, Switzerland Fax: þ41 44 823 4007; E-mail: philippe.tingaut@empa.ch A novel and straightforward method for the surface acetylation of cellulose nanowhiskers by transesterification of vinyl acetate is proposed. The reaction of vinyl acetate with the hydroxyl groups of cellulose nanowhiskers obtained from cotton linters was examined with potassium carbonate as catalyst. Results indicate that during the first stage of the reaction, only the surface of the nanowhiskers was modified, while their dimensions and crystallinity remained unchanged. With increasing reaction time, diffu- sion mechanisms controlled the rate, leading to nanowhiskers with higher levels of acetylation, smaller dimensions, and lower crystallinity. In THF, a solvent of low polarity, the suspensions from modified nanowhiskers showed improved stability with increased acetylation. Macromol. Biosci. 2009, 9, 997–1003 ß 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/mabi.200900073 997