Biomacromolecules, Vol.12, No.4, 933-941, 2011
Transition of Cellulose Crystalline Structure and Surface Morphology of Biomass as a Function of Ionic Liquid Pretreatment and Its Relation to Enzymatic Hydrolysis
Cellulose is inherently resistant to breakdown, and:the native crystalline structure (cellulose I) of cellulose is considered to be one of the major factors limiting its potential in terms of cost-competitive lignocellulosic biofuel production. Here we report the impact of ionic liquid pretreatment on the cellulose crystalline structure in different feedstocks including microcrystalline cellulose (Avicel), switchgrass (Panicum virgatum), pine (Pinus radiata); and eucalyptus (Eucalyptus globulus), and its influence on cellulose. hydrolysis kinetics of the resultant biomass. These feedstocks were pretreated using 1-ethyl-3-methyl imidazolium acetate ([C2mim][OAc) at 120 and 160 degrees C for 1,3,6, and 12 h. The influence of the pretreatment. conditions on the cellulose crystalline structure was analyzed by X-ray diffraction (XRD). On a. larger length scale, the impact of ionic liquid pretreatment on the surface roughness of the biomass was determined by small-angle neutron scattering (SANS). Pretreatment resulted in a loss of native cellulose crystalline structure. However, the transformation processes were distinctly different for Avicel and for the biomass samples. For Avicel, a transformation to cellulose II occurred Oral! processing conditions For the biomass samples, the data suggest that pretreatment for most conditions resulted in an expanded cellulose I lattice. For switchgrass, first evidence of cellulase II only Occurred after 12 h of pretreatment at 120 degrees C. For eucalyptus, first evidence of cellulose II required, more intense pretreatment (3 hat 160 degrees C). For pine, no-clear evidence of cellulose II content was detected for the most intense pretreatment conditions of this:study (12 h at 160 degrees C). Interestingly, the rate of enzymatic hydrolysis of Avicel was slightly lower for pretreatment at 160 degrees C compared with pretreatment at 120 degrees C. For the biomass samples, the hydrolysis rate was much greater for pretreatment at 160 degrees C compared with pretreatment at 120 degrees C. The result for Avicel can be explained by more complete conversion to cellulose II upon precipitation after pretreatment at 160 degrees C. By comparison, the result for the biomass samples suggests that another factor, likely lignin carbohydrate complexes, also impacts the rate of cellulose hydrolysis in addition to cellulose Crystallinity.