Short communication Facile synthesis of spherical cellulose nanoparticles Jianguo Zhang a , Thomas J. Elder b , Yunqiao Pu c , Arthur J. Ragauskas a, * a School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332, USA b USDA-Forest Service, South Research Station, Pinceville, LA 71360, USA c Institute of Paper Science and Technology, Georgia Institute of Technology, Atlanta, GA 30 332, USA Received 17 October 2006; received in revised form 19 January 2007; accepted 26 January 2007 Available online 7 February 2007 Abstract A practical procedure for synthesizing cellulose nanospheres with sizes ranging from 60 to over 570 nm was developed. This meth- odology provides a near linear relationship between cellulose nanoparticle size and treatment time. The hydrolyzed nanocelluloses are predominantly cellulose II polymorphic crystalline structure and relatively uniform in particle size. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Acid sonication; Cellulose II; Cellulose electron microscopy; Cellulose AFM; Crystallinity index; Nanosphere 1. Introduction Cellulose is the most ubiquitous and abundant biopoly- mer in nature and its biosynthesis, chemistry, and ultra structure remains an active field of study (Klemm, Schmau- der, & Heinze, 2002; Klem, Heublein, Fink, & Bohn, 2005). Over the past decades, interest in sustainability and green chemistry has lead to a renewed interest in novel cellulosic materials (Ragauskas et al., 2006) and composites (Gra- dwell et al., 2004) derived from a variety of cellulosics including cellulose whiskers (Samir, Alloin, & Dufresne, 2005). These latter structures typically have fiber lengths ranging 100 to several hundred nanometer and diameters of 3–20 nm and are usually prepared by acid hydrolysis of cellulosic fibers. The exact size, dimensions, and crystal- linity of these whiskers is dependent upon the acid hydro- lysis conditions and source of cellulose employed. Typically, the use of tunicate and bacterial cellulose yield larger nanocrystalline cellulose whiskers, while cellulose from wood yields smaller structures (Beck-Candanedo, Roman, & Gray, 2005; Bondeson, Mathew, & Oksman, 2006). Recently, Li, Ding, and Li (2001) reported the potential of preparing nanospherical cellulose structures with diameters of several hundred nanometers from short-staple cotton by pre-swelling the fibers prior to acid hydrolysis. This note provides a high-yielding, size-predict- able methodology for the synthesis of cellulose nanoparticles. 2. Experimental 2.1. Pretreatment Cellulose fibers (30.00 g, Buckeye cellulose, 100% cellu- lose) were processed through a Wiley mill (Arthur H. Tho- mas Co.) equipped with a 20 mesh screen. The obtained cellulose was transferred into 5.00 M NaOH solution (250.00 ml) warmed to 80 °C for 3 h. The slurry was then filtered and thoroughly washed with DI water until the wash water was neutral pH. The resulting cellulosic fibers were air-dried, and then added to DMSO (250 ml) in a 80 °C water bath for 3 h. The fibers were then filtered and washed with DI water (3 · 250 ml). 2.2. Synthesis and purification The pretreated fibers were transferred into an acidic aqueous solution consisting of 1000.00 ml mixed acid 0144-8617/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbpol.2007.01.019 * Corresponding author. Tel.: +1 404 894 9701; fax: +1 404 894 4778. E-mail address: arthur.ragauskas@chemistry.gatech.edu (A.J. Ragauskas). www.elsevier.com/locate/carbpol Carbohydrate Polymers 69 (2007) 607–611