超声-弱碱协同作用下巨龙竹木质素的分离及表征

Isolation and structural characterization of lignin isolated from Dendrocalamus sinicus by ultrasonic-alkaline treatment

巨龙竹是一种具有极高研究和开发价值的大型经济用材竹种,其基础理化性质有待进一步解析研究。为表征巨龙竹木质素的化学结构,在超声-弱碱协同作用下处理竹材原料,脱蜡竹粉在2%NaOH溶液中分别经超声处理5,20,40,60和90 min,并设置仅在2%NaOH溶液中抽提90 min的对照组,最后得到6个木质素样品L_1~L_6。采用红外光谱(FTIR)、核磁共振碳谱(^(13)C NMR)和二维核磁共振(2D HSQC)分别对分离得到的巨龙竹木质素进行结构分析。结果表明:超声-弱碱协同处理对竹材木质素具有良好的促溶效果,随着超声作用时间的增加,木质素得率从6.6%提高到22.9%;巨龙竹木质素大分子主要由愈创木基(G)、紫丁香基(S)和对羟基苯基(H)结构单元构成,属于禾草类木质素(GSH型);巨龙竹木质素大分子的主要联接键为β-O-4'醚键,其次是β-β'和β-5'结构;但随着超声处理时间的增加,巨龙竹木质素中一定量的β-O-4'联接键会被打断。

In response to the severe challenges of resource scarcity and energy shortage, the preparation of biobased materials, energy and chemicals has attracted increasing attention. Fractionation of lignocelluloses based on the concept of biorefinery is of vital importance for their effective utilization. Dendrocalamus sinicus, belonging to Bambusoideae of Gramineae, has strong and woody stems （maximum diameter of 30 cm, maximum height of 33 m）. It is the largest bamboo species in the world and widely distribute in the southwest of China. According to whether the bottom of D. sinicus bends or not, it can be divided into two subspecies, straight-bar D. sinicus and askew D. sinicus. Due to its easy propagation, fast growth and high productivity, the bamboo species is considered as a potential renewable non- woody forestry feedstock for the production of biofuel and biomaterials. However, the detailed physicochemical properties of the largest bamboo species have not been clarified so far. In this study, five soluble lignin fractions （L1, L2, L3, L4 and L5 ） were isolated under the ultrasonic-alkaline （2% NaOH） combined treatment for 20, 40, 60 and 90 min, respectively. In addition, another bamboo lignin fraction （L6 ） was isolated by 2% NaOH without ultrasonic treatment as control. Isolated lignin samples were characterized by FTIR, ^13C NMR and 2D HSQC NMR. The results showed that the ultrasonic-alkaline combined treatment could promote bamboo lignin dissolution. The obtained bamboo lignin belongs to GSH-type lignin, consisting syringl （S）, gualacyl （G） and p-hydroxylphengl （H） units. The major inter-unit linkages presented in the obtained bamboo lignin were β-O-4＇ aryl ether linkages, β-β＇, and β-5＇ linkages. With the increased of ultrasonic treatment time, the yield of lignin increased from 6.6% to 22.9%, and a certain amount of β-O-4＇ linkages were degraded. The results of present study provided useful information for the selection and evaluation to superior germplasm resources.