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Understanding the structural changes of lignin in poplar following steam explosion pretreatment

机译：了解蒸汽爆破预处理后杨木中木质素的结构变化

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摘要

To understand the modifications of lignin in the steam explosion process (209 degrees C, 7 min), lignin samples in native poplar (L-P), steam explosion solid residue (L-S) and steam explosion liquid (L-L) were separated and studied. The lignin samples (L-P, L-S and L-L) were characterized and analyzed by size exclusion chromatography (SEC), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance [carbon 13 numclear magnetic resonance (C-13-NMR) and heteronuclear single quantum coherence or heteronuclear single quantum correlation experiment NMR (HSQC) NMR] analysis. The results revealed that the pretreatment induced reductions in amounts of beta-O-4', beta-beta', and spirodienone structure, and increases in the syringyl/guaiacyl (S/G) ratio from 1.14 (L-P) to 1.70 (L-S) and 1.86 (L-L). The HSQC NMR spectra also gave more information about the predominance of G and S units, and only small amounts of p-hydroxyphenyl (H) units. Moreover, SEC demonstrated the depolymerization and repolymerization of lignin, which were the main reasons for the increase in the average molecular weight of L-S and the decrease in average molecular weight of L-L, respectively. In brief, after steam explosion treatment, the lignin structure changed, but the backbone structure was not noticeably modified.
机译：为了了解木质素在蒸汽爆炸过程（209摄氏度，7分钟）中的变化，我们对天然杨树（L-P），蒸汽爆炸固体残留物（L-S）和蒸汽爆炸液体（L-L）中的木质素样品进行了分离和研究。木质素样品（LP，LS和LL）通过尺寸排阻色谱（SEC），傅立叶变换红外光谱（FTIR）和核磁共振[碳13核磁共振（C-13-NMR）和异核单核]进行表征和分析量子相干或异核单量子相关实验NMR（HSQC）NMR]分析。结果表明，预处理可导致β-O-4'，β-β'和螺二烯酮结构的减少，并使丁香基/愈创木脂（S / G）的比例从1.14（LP）增加到1.70（LS）和1.86（LL​​）。 HSQC NMR光谱还提供了有关G和S单元占优势的信息，并且仅提供了少量的对羟基苯基（H）单元。而且，SEC证明了木质素的解聚和再聚合，这分别是L-S的平均分子量增加和L-L的平均分子量降低的主要原因。简而言之，经过蒸汽爆破处理后，木质素结构发生了变化，但主链结构没有明显改变。

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