Tuesday, May 3, 2011
The cellulose crystalline structure has been evaluated by several different techniques including x-ray diffraction and solid-state 13C NMR to understand the digestibility of biomass. However, the measurement of cellulose crystallinity in lignocellulosic biomass samples is complicated by contributions from the non-crystalline components in biomass, particularly the hemicellulose and lignin. The content of amorphous cellulose has been shown to be a strong determinant for the digestibility of a cellulose sample and consequently, it has become increasingly important that the crystallinity of the cellulose in biomass samples is measured with a minimum of sample modification. Isolation of the cellulose from biomass samples is difficult and often causes cellulose modification in an unknown way. We recently discovered that the non-centrosymmetric crystal structures of cellulose give unique non-linear optical responses using sum-frequency-generation (SFG) vibration spectroscopy, which allows selective detection of the crystalline cellulose in lignocellulosic biomass without interferences from hemicellulose, lignin, and other cell wall components. Hence 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 during pretreatment and enzymatic hydrolysis for lignocellulosic biomass.