Acid chlorite delignification is frequently used to obtain a mixture of cellulose and hemicellulose known as holocellulose from biomass. While a majority of lignin is removed after holocellulose pulping, there appears to be a minor fraction of lignin that is more resistant to acid chlorite treatment and remains in the holocellulose even after repeated delignification treatment. This type of lignin, defined as hololignin, has not been characterized, is likely to contribute to biomass recalcitrance and is clearly of fundamental interest to understand its structural characteristics. In this study, hololignin isolated from poplar holocellulose was characterized with a wide array of techniques including GPC, quantitative ¹³C, DEPT-135, HSQC, and ³¹P NMR. The results were compared to those from milled wood lignin (MWL), the representative native lignin isolated from poplar. NMR analysis demonstrated a depletion of cinnamyl aldehyde, acetyl group, and decrease of p-hydroxybenzoate structural units in hololignin. An enrichment of condensed structures in hololignin was observed. Hololignin also had a significantly lower molecular weight than MWL. Finally, hololignin is relatively enriched in guaiacyl units and has a lower S/G ratio, lower β-O-4 ether linkages, fewer aliphatic and phenolic hydroxyl groups, and more carboxylic acid groups than MWL.

中文翻译：

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香木素的性质

酸性亚氯酸盐脱木素经常用于从生物质中获得纤维素和半纤维素的混合物，称为全纤维素。尽管在木质纤维素制浆后除去了大部分木质素，但似乎有一小部分木质素对酸性亚氯酸盐处理更具抵抗力，即使经过反复的脱木质素处理后，木质素仍保留在木质纤维素中。尚未定义这种类型的木质素（定义为完整木质素），它可能有助于生物量的顽固性，并且显然对于了解其结构特征具有根本的兴趣。在这项研究中，从杨木全纤维素中分离出的木质素具有多种技术，包括GPC，定量¹³ C，DEPT-135，HSQC和³¹1 H NMR。将结果与碾磨的木质素（MWL）（从白杨中分离出的代表性天然木质素）的结果进行了比较。NMR分析表明，在木质素中肉桂醛，乙酰基的消耗和对羟基苯甲酸酯结构单元的减少。观察到全息素中的浓缩结构富集。hololignin的分子量也明显低于MWL。最后，全木质素在愈创木脂单元中相对富集，并且比MWL具有更低的S / G比，更低的β-O-4醚键，更少的脂族和酚羟基以及更多的羧酸基。