Using Raman Spectroscopy to Analyze Wood, Cellulose-Nanomaterials, and Their Composites
Raman spectroscopy is an important analytical method for investigating wood and cellulose nanomaterials because it provides molecular level information on composition and structure. Over the last several years, a number of capabilities developed at the Forest Service’s Forest Product Laboratory in Madison, Wisc., include: (1) information on molecular structure, (2) organization and distribution of cell wall components, (3) quantitation of lignin, (4) information on chemical modifications of components during processing, (5) the composition of lignin, (6) polymorphy of cellulose, (7) cellulose crystallinity, (8) the ultrastructure of cellulose, and (9) the accessibility of cellulose to chemicals. The information obtained using these methods is proving to be useful in making progress in understanding processes for biorefinery and cellulose nanomaterials.
A major advancement was the development of a new method to estimate cellulose crystallinity based on Raman spectroscopy. A major advantage of this method is that it works on moist samples and the crystallinity need not be corrected for the presence of amorphous cellulose.
This finding leads to the more recent understanding that cellulose in green wood does not have crystalline regions. This is a critical discovery because the crystalline regions impede saccharification to produce sugars for a biorefinery, but are necessary to provide fibrils and crystals for cellulose nanomaterials. A revised model of wood cell wall was proposed to accommodate the new information. The new model and new methods should help to improve processes methods in these two areas of biomass utilization.