乙酰化处理对碱木质素在四氢呋喃中微结构的影响

摘要

The effect of acetylation on the microstructure of alkali lignin (AL) in tetrahydrofuran (THF) was studied. The physicochemical properties of AL and acetylated alkali lignin (ACAL) were compared. Dynamic light scattering, gel penetration chromatography (GPC), transmission electron microscopy (TEM), intrinsic viscosity, fluorescence spectrophotometry, quartz crystal microbalance with dissipation (QCM-D) measurements, and layer-by-layer (LbL) self-assembly were used to investigate the aggregation and adsorption of AL and ACAL. Intermolecular and intramolecular associations in AL decreased fol owing acetylation. AL in THF existed mainly as mono-molecules and intermolecular associations and had a more compact conformation. ACAL existed mainly as mono-molecules with a more stretched conformation. ACAL had a larger hydrodynamic radius than AL (of the same absolute molecular mass), because of its stretched conformation. QCM-D and LbL self-assembly measurements suggested that AL aggregates have a strong tendency to adsorb at the liquid-solid interface, but ACAL hardly adsorb at this interface because of its stronger interaction with THF. The compact conformation and strong adsorption property of AL resulted in inaccurate molecular weights of non-acetylated AL, as measured by GPC with a THF mobile phase. In order to get more reliable molecular weights from GPC measurements, acetylation for AL should be used in the sample pretreatment.%通过对比碱木质素(AL)和乙酰化碱木质素(ACAL)在四氢呋喃(THF)中溶液行为和物理化学性质的差异，揭示了乙酰化处理对碱木质素在THF中微结构的影响。分别采用动态光散射、凝胶渗透色谱(GPC)、透射电子显微镜(TEM)、特性粘度、荧光光谱仪、耗散型石英晶体微天平(QCM-D)和自组装技术等研究了AL和ACAL在聚集形态、聚集机理以及吸附特性等方面的特征。研究发现，乙酰化处理会降低碱木质素在THF中的分子间和分子内聚集程度。 AL在THF中以单分子和聚集体的形式共同存在，分子较为蜷曲； ACAL在THF中则更多地是以单分子形式存在而几乎不存在大聚集体，分子较为伸展，其流体力学半径要比相同绝对分子量的AL更大。 THF中的AL聚集体会在液固界面上发生强烈的吸附，但ACAL由于与溶剂间的相互作用较强而几乎不会吸附在液固界面上。由于AL 分子在THF中较为蜷曲且吸附能力较强，因此利用以THF为流动相的GPC直接测量AL的分子量时所得结果并不准确，为保证GPC的测量结果更加全面可靠，需要在测量前对碱木质素进行乙酰化处理。