Comparative study of ligno-cellulosic material from wheat straw and of pure and mixed standard compounds via solid state 13C NMR spectroscopy, conventional pyrolysis and TMAH thermochemolysis

Abstract

The ligno-cellulosic material (LCS) isolated from wheat straw, via successive acid and base treatments, exhibits high complexing capacities, mostly related to the lignin fraction, and may have important applications for metal completion. In the present study LCS was examined via a combination of spectroscopic and pyrolytic methods: solid slate cross polarization/magic angle spinning 13C nuclear magnetic resonance (CP/MAS 13C NMR), conventional Curie point pyrolysis–gas chromatography–mass spectrometry (CuPy–GC–MS) and tetramethylammonium hydroxide (TMAH) thermochemolysis–GC–MS). Parallel experiments were also performed on cellulose and tignin standards and 50:50 cellulose:lignin mixture. These studies afforded information on lignin:cellulose relative abundances in LCS (ca. 15:85) and on the composition of the lignin fraction, including the presence of substantial amounts of carboxylic groups which should be important for metal complexation. Examination of standards and mixture also illustrated (i) the usefulness of TMAH thermochemolysis for the detection of cellulose and of carboxylic groups compared with conventional pyrolysis and (ii) the conspicuous limitations of some of the above methods when applied to ligno-cellulosic materials and resulting biases.