Monday, April 30, 2012
Napoleon Ballroom C-D, 3rd fl (Sheraton New Orleans)
The crystalline structure of cellulose has been evaluated by several techniques including x-ray diffraction, solid-state 13C NMR, and Raman spectroscopy to understand the changes in structure that can occur during conversion processes. However, the characterization of cellulose crystalline structure in lignocellulosic biomass is complicated by contributions from non-crystalline components, particularly hemicellulose and lignin. Isolation of cellulose from biomass is difficult and often causes unknown modification. We recently discovered that the non-centrosymmetric crystalline structures of cellulose give unique non-linear optical responses using sum-frequency-generation (SFG) vibration spectroscopy. SFG allows selective detection of crystalline cellulose in lignocellulosic biomass without interferences from hemicellulose, lignin, and other cell wall components. To demonstrate a correlation between the amount of crystalline cellulose in biomass and SFG signal intensity, model biomass samples were prepared by mixing commercially-available cellulose, xylan, and lignin in defined concentrations. The SFG signal intensity was sensitive to a wide range of crystallinity, but varied non-linearly with the mass fraction of cellulose in the samples as well as with cellulose type. In summary, SFG will be a new complementary analytical tool that can reveal cellulose structural information in lignocellulosic biomass that has been inaccessible in the past with conventional analytical tools such as XRD, NMR, IR, and Raman spectroscopies. This presentation will discuss SFG vibration spectra and changes in cellulose crystalline structure that occur during pretreatment and enzymatic hydrolysis of lignocellulosic biomass. In addition, the SFG signal of different cellulose polymorphs (Iα, Iβ, II, III) will be presented to demonstrate the uniqueness of SFG spectroscopy.