Characterization of kenaf (Hibiscus cannabinus) lignin by pyrolysis-gas chromatography-mass spectrometry in the presence of tetramethylammonium hydroxide

Pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) in the presence of tetramethylammonium hydroxide (TMAH) was applied to kenaf (Hibiscus cannabinus) fibers in order to clarify the chemical composition of in situ lignin. The core and bast samples obtained from the middle position of variety Chinpi-3 were pyrolyzed at 500 degreesC for 4 s with TMAH. The core pyrogram revealed peaks retaining the structural attributes of guaiacyl and syringyl P-aryl ether subunits. and the bast pyrogram was dominated by peaks retaining the structural attributes of syringyl beta-aryl ether subunit. Both pyrograms lacked products derived from p-hydroxyphenyl beta-aryl ether subunit, Product distribution showed that: (1) the core in situ lignin comprises 1.5 parts of syringyl-, I part of guaiacyl beta-aryl ether subunits, and (2) in the bast in situ lignin the syringyl beta-aryl ether subunits are present in greater quantities than the guaiacyl P-aryl ether subunits. The syringyl to guaiacyl lignin unit (S/G) ratios determined by conventional pyrolysis and alkaline CuO oxidation also supported the TMAH/Py results, 4-Methoxy and 3,4-dimethoxycinnamic acid methyl esters were present in the core pyrolyzate and absent in the bast pyrolyzate. 4-Methoxycinnamic acid methyl ester was present in greater quantities than 3,4-dimethoxycinnamic acid methyl esters. (C) 2002 Elsevier Science B.V. All rights reserved.