A Fourier-transform infrared and Raman study of biochemical and chemical treatments of Oak (Quercus rubra) and Barley (Hordeum vulgare) straw

FT-IR and Raman spectroscopies were used to investigate the changes in composition and structure of oak wood and barley straw that had been subject to chemical and biochemical treatments. The samples were also analyzed gravimetrically for rseidual neutral sugar composition and lignin and uronic acid content. The spectroscopic techniques provided complementary information. Changes in the relative proportions of crystalline and amorphous cellulose accompanying (bio)chemical treatment were best reflected in the Raman and DRIFT spectra, respectively. Delignification of both tissues produces bands in the Raman spectra consistent with the lignin oxidation. Treatment of both types of raw material with aqueous acid produced highly colored residues resulting in Raman spectra of limited use due to problems with fluorescence. However, the DRIFT spectra of these tissues did not suffer this problem and provided information on the behavior of lignin (hydrolysis and repolymerization) and the noncellulosic polysaccharides (hydrolysis) in acid conditions. The decreased fluorescence in the Raman spectra of barley straw after alkali extraction is suggested to be due to the removal of the covalently bound cinnamic acids.