FRACTIONAL CHARACTERIZATION OF WHEAT-STRAW LIGNIN COMPONENTS BY ALKALINE NITROBENZENE OXIDATION AND FT-IR SPECTROSCOPY

A method was developed for the isolation and fractional characterizati on of phenolic monomers in wheat straw lignin using (a) methanol/tolue ne, ethanol/toluene, or chloroform extraction for isolation of free ph enolic monomers; (b) treatments with various alkalis and hydrogen pero xide for different lengths of time to extract loosely bound phenolic a cids and aldehydes; and (c) alkaline nitrobenzene oxidation of lignin in the residue of alkali-treated wheat straw, extracted hemicellulose, and cellulose for determination of tightly bound phenolics. The yield of free phenolic monomers ranged from 0.007 to 0.031% of dry straw. T he predominant components of the alkali-labile free monomers were foun d to be ferulic and p-coumaric acid, which together comprised 65-82% o f the total. The results of alkaline nitrobenzene oxidation indicated a high guaiacyl content in the original wheat straw and a high relativ e syringyl content in treated wheat straw. A comparison of FT-IR spect roscopic data of untreated and treated wheat straw illustrated that th e most obvious features in the spectra of alkaline treated wheat straw were the disappearance of the ester linkage absorption and reduced li gnin content in treated wheat straw.