ARTICLE Cellulose Solvent-Based Biomass Pretreatment Breaks Highly Ordered Hydrogen Bonds in Cellulose Fibers of Switchgrass Noppadon Sathitsuksanoh, 1,2 Zhiguang Zhu, 1 Sungsool Wi, 3 Y.-H. Percival Zhang 1,2,4 1 Biological Systems Engineering Department, Virginia Polytechnic Institute and State University (Virginia Tech), 210-A Seitz Hall, Blacksburg, Virginia 24061; telephone: 540-231-7414, fax: 540-231-3199; e-mail: ypzhang@vt.edu 2 Institute for Critical Technology and Applied Science (ICTAS), Virginia Polytechnic Institute and State University, Blacksburg, Virginia 3 Chemistry Department, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 4 DOE BioEnergy Science Center (BESC), Oak Ridge, Tennessee Received 25 June 2010; revision received 23 August 2010; accepted 4 October 2010 Published online 21 October 2010 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/bit.22964 ABSTRACT: The switchgrass (SG) samples pretreated by cellulose solvent- and organic solvent-based lignocellulose fractionation were characterized by enzymatic hydrolysis, substrate accessibility assay, scanning electron microscopy, X-ray diffraction (XRD), cross polarization/magic angle spinning (CP/MAS) 13 C nuclear magnetic resonance (NMR), and Fourier transform infrared spectroscopy (FTIR). Glucan digestibility of the pretreated SG was 89% at hour 36 at one filter paper unit of cellulase per gram of glucan. Crystallinity index (CrI) of pure cellulosic materials and SG before and after cellulose solvent-based pretreatment were determined by XRD and NMR. CrI values varied greatly depending on measurement techniques, calculation approaches, and sample drying conditions, suggesting that the effects of CrI data obtained from dried samples on enzymatic hydrolysis of hydrated cellulosic materials should be interpreted with caution. Fast hydrolysis rates and high glucan digestibilities for pretreated SG were mainly attrib- uted to a 16.3-fold increase in cellulose accessibility to cellulase from 0.49 to 8.0 m 2 /g biomass, because the highly ordered hydrogen-bonding networks in cellulose fibers of biomass were broken through cellulose dissolution in a cellulose solvent, as evidenced by CP/MAS 13 C-NMR and FTIR. Biotechnol. Bioeng. 2011;108: 521–529. ß 2010 Wiley Periodicals, Inc. KEYWORDS: biomass; biofuels; cellulose accessibility; cellulose solvent-based pretreatment; crystallinity index; drying of cellulose; switchgrass Introduction The production of biofuels and biobased products from renewable cellulosic biomass would promote rural econ- omy, decrease greenhouse gas emissions, and enhance national energy security (Lynd et al., 2002; Zhang, 2009). The current production of second generation biofuels, cellulosic ethanol, cannot compete with that made from corn and sugarcane, because of high processing costs, the requirement for huge capital investment, and relatively low revenues from low-value ethanol (Zhang, 2008). Biomass saccharification usually involves two sequential steps: lignocellulose pretreatment/fractionation and enzymatic hydrolysis. The root causes of biomass recalcitrance have been attributed to several factors: low substrate accessibility to enzymes, high crystallinity of cellulose, presence of hemicellulose, lignin, and other components, and high degree polymerization of cellulose chains (Zhang and Lynd, 2004; Himmel et al., 2007; Rollin et al., 2010). Highly ordered hydrogen bonds and van der Waals forces among sugar chains in crystalline fibers result in high crystallinity index (CrI) values and very low substrate accessibility (Lynd et al., 2002; Hong et al., 2007). Switchgrass (SG) (Panicum virgatum L.) is a native, warm-seasoned, perennial, C 4 grass in North America and is distributed in more than half of the United States. It has several valuable features, such as modest/high productivities, adaptation to many types of soil and climate, Correspondence to: Y.-H. Percival Zhang Contract grant sponsor: DOE BioEnergy Science Center (BESC) Contract grant sponsor: USDA Biodesign and Bioprocessing Research Center (BBRC) Contract grant sponsor: ICTAS Scholar Program ß 2010 Wiley Periodicals, Inc. Biotechnology and Bioengineering, Vol. 108, No. 3, March, 2011 521