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.

中文翻译：

---

农作物秸秆和针叶木木质素的化学结构与热降解关系

摘要 利用酶解/弱酸水解法（EMAL）制备的农作物秸秆（小麦秸秆，WS）木质素和针叶木（松木，PW）木质素的结构特征通过FTIR（傅里叶变换红外）、13C-1H 2D进行了深入阐明。 -NMR（核磁共振）和定量 31P-NMR 结合 DFRC（衍生化后还原裂解）。然后，通过TG-FTIR-MS（热重-FTIR-质谱）和Py-GC/MS（热解-气相色谱/质谱）评估化学结构和热降解的关联。结果表明，WS-EMAL 的官能团和芳香单元组成与 PW-EMAL 不同，前者为 HGS-木质素，后者为典型的 G-木质素。WS-EMAL 和 PW-EMAL 主要通过 β-O-4 键交联，但含量不同。WS-EMAL 中未缩合的 β-O-4 键为 1168 μmol/g，低于 PW-EMAL（1297 μmol/g）。这些结构上的差异导致两种木质素之间在热稳定性、典型挥发物的演化行为和 G-、S-、H-、C-酚的选择性方面存在很大差异。深入讨论了结构特征对热解行为的机理影响，并获得了两种木质素之间的相关性。两种木质素之间的 C-酚。深入讨论了结构特征对热解行为的机理影响，并获得了两种木质素之间的相关性。两种木质素之间的 C-酚。深入讨论了结构特征对热解行为的机理影响，并获得了两种木质素之间的相关性。