LAUSR

Abstract The structural characteristics of crop straw (wheat straw, WS) lignin and softwood (pine wood, PW) lignin prepared using the enzymatic/mild acid hydrolysis method (EMAL) were deeply elucidated by FTIR (Fourier transform infrared), 13C–1H 2D-NMR (nuclear magnetic resonance), and quantitative 31P-NMR combined with DFRC (derivatization followed by reductive cleavage). Then, the association of chemical structure and thermal degradation was evaluated by means of TG-FTIR-MS (thermo-gravimetric-FTIR-mass spectrometry) and Py-GC/MS (pyrolysis-gas chromatography/mass spectrometry). The results showed that the functional groups and aromatic unit compositions of WS-EMAL were distinct from those of PW-EMAL, identifying the former as a HGS-lignin and the latter as a typical G-lignin. Both WS-EMAL and PW-EMAL were mainly cross-linked by β-O-4 linkages but had different contents. The amount of uncondensed β-O-4 linkages in WS-EMAL was 1168 μmol/g, which was lower than that in PW-EMAL (1297 μmol/g). These distinctions in structure caused a large difference in thermal stability, evolution behavior of typical volatiles and selectivities of G-, S-, H-, C-phenols between the two lignins. The mechanistic influence of structural features on pyrolysis behavior was intensively discussed, and a correlation between the two lignins was obtained.