纤维素硫酸酯水溶液性质的研究

Properties of Cellulose Sulfate Aqueous Solution

本文以α-纤维素为原料,ClSO_3H-DMF为酯化剂,采用多相硫酸酯化法制备纤维素硫酸酯(Cellulose Sulfate,CS)。通过元素分析确定了CS的硫酸酯基取代度为2.0左右,13C-NMR测试表明,CS的硫酸酯基取代模式是C-6完全硫酸酯基取代和C-2部分或完全取代。CS在去离子水中具有良好的溶解性。根据相近取代度的CS系列产物的分子量与特性粘度的关系,通过Mark-Houwink拟合,确定了CS的糖链在稀溶液中呈现一种较为紧密的构象。在浓溶液中,CS的动力粘度随浓度增加而增大;外加盐能够促进CS聚电解质的电荷排斥作用,导致其动力粘度增加;添加二价盐Ca^(2+)可产生CS糖链的络合,显著提高CS的动力粘度;溶液pH环境为影响CS动力粘度的主要因素之一,在中性条件下动力粘度最大,酸性或碱性环境都会使其动力粘度下降。

Cellulose sulfates （CS） were prepared by heterogeneous sulfation esterification of a-cellulose, using chlorosulfonic acid in dimethylformamide as the sulfation agent. The degree of substitution （DS） of sulfate groups in CS was approximately 2.0, as determined by elemental analysis. Carbon-13 nuclear magnetic resonance （13C-NMR） spectroscopy data suggested that the sulfation pattern of CS included complete C-6 substitution as well as complete or partial C-2 substitution. CS showed good solubility in deionized water. Upon using a series of CS solutions with similar DS and fitting with Mark-Houwink equation, the sugar chains of CS showed a relatively compact conformation in dilute solution, based on the relationship between molecular weight and intrinsic viscosity. At high concentration, the dynamic viscosity of CS increased with an increase in CS concentration. The addition of salt promoted charge repulsion within the polyelectrolyte in CS, resulting in an increase in dynamic viscosity of CS. The addition of Ca2＋ triggered complexation between CS and Ca〉 and significantly enhanced the dynamic viscosity of CS. The pH value of the solution was one of the main factors influencing the dynamic viscosity of CS, which was highest at neutral pH and decreased at acidic or alkaline pH values.