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Int J Mol Sci. 2010 Oct 20;11(10):4035-50. doi: 10.3390/ijms11104035.
Lignin, a polyphenolic molecule, is a major constituent of flax shives. This polyphenolic molecular structure renders lignin a potential source of a variety of commercially viable products such as fine chemicals. This work compares the performance of different lignin isolation methods. Lignin from flax shive was isolated using both conventional alkaline extraction method and a novel experimental pressurized low polarity water (PLPW) extraction process. The lignin yields and chemical composition of the lignin fractions were determined. The conventional alkali treatment with 1.25 M NaOH, heated at 80 °C for 5 h, extracted 92 g lignin per kg flax shives, while lignin yields from the PLPW extracts ranged from 27 to 241 g lignin per kg flax shives. The purity and monomeric composition of the lignins obtained from the different extraction conditions was assessed via UV spectroscopy and alkaline nitrobenzene oxidation. Lignin obtained from conventional alkali treatment with 1.25 M NaOH, heated at 80 °C for 5 h was of low purity and exhibited the lowest yields of nitrobenzene oxidation products. With respect to alkali assisted PLPW extractions, temperature created an opposing effect on lignin yield and nitrobenzene oxidation products. More lignin was extracted as temperature increased, yet the yield of nitrobenzene oxidation products decreased. The low yield of nitrobenzene oxidation products may be attributed to either the formation of condensed structures or the selective dissolution of condensed structures of lignin during the pressurized alkaline high temperature treatment. Analytical pyrolysis, using pyroprobe GC-MS, was used to investigate the molecular composition of the lignin samples. The total yield of pyrolysis lignin products was 13.3, 64.7, and 30.5% for the 1.25 M NaOH extracted lignin, alkaline assisted PLPW extracted lignin, and the unprocessed flax shives, respectively. Key lignin derived compounds such as guaiacol, 4-vinyl guaiacol, 4-methyl guaiacol, syringol, eugenol, isoeugenol, catechol, homocatechol, and vanillin were detected in all of the samples.
木质素是一种多酚分子，是亚麻屑的主要成分。这种多酚分子结构使木质素成为各种有商业价值的产品的潜在来源，如精细化学品。本工作比较了不同木质素分离方法的性能。采用常规碱性提取法和新型实验加压低极性水（PLPW）提取法从亚麻屑中分离木质素。测定了木质素级分的产率和化学组成。用 1.25 M NaOH 在 80°C 加热 5 h 的常规碱处理提取 92 g 木质素/每公斤亚麻屑，而 PLPW 提取物的木质素产率范围为 27-241 g 木质素/每公斤亚麻屑。通过紫外光谱法和碱性硝基苯氧化法评估了不同提取条件下获得的木质素的纯度和单体组成。用 1.25 M NaOH 在 80°C 加热 5 h 的常规碱处理得到的木质素纯度低，硝基苯氧化产物产率最低。对于碱辅助 PLPW 提取，温度对木质素产率和硝基苯氧化产物产生相反的影响。随着温度的升高，提取的木质素越多，但硝基苯氧化产物的产率却降低。硝基苯氧化产物产率低可能归因于木质素缩合结构的形成或加压高温碱性处理过程中缩合结构的选择性溶解。采用热探针 GC-MS 进行分析性热解，研究木质素样品的分子组成。1.25 M NaOH 提取的木质素、碱性辅助 PLPW 提取的木质素和未经处理的亚麻屑的热解木质素产物总产率分别为 13.3%、64.7%和 30.5%。在所有样品中都检测到关键木质素衍生化合物，如愈创木酚、4-乙烯基愈创木酚、4-甲基愈创木酚、丁香酚、丁香醛、异丁香醛、儿茶酚、邻苯二酚、香草醛。
