粘度法研究壳聚糖对外加盐的敏感性

SENSIBILITY OF THE CHITOSAN TO THE ADDITION OF SALT BY VISCOMETRY

聚电解质的特性粘度对外加盐的响应是反映聚电解质对外加盐敏感性的一个重要特征，通过分别测定壳聚糖在不同小分子强电解质（ＮａＣｌ、ＫＣｌ、ＣａＣｌ２、ＢａＣｌ２）和相同小分子强电解质（ＮａＣｌ）但不同离子强度的稀溶液粘度，得到：（１）壳聚糖特性粘度与外加盐的离子强度的平方根的倒数成正比；（２）不同小分子强电解质中阳离子对壳聚糖特性粘度的影响次序是Ｎａ＋＞Ｋ＋＞Ｂａ２＋＞Ｃａ２＋．同时，测算了壳聚糖在不同外加盐浓度中的ＭａｒｋＨｏｕｗｉｎｋ方程参数α，发现其值皆大于０５，得到了壳聚糖分子链的僵硬性参数Ｂ的值为００７４，揭示了壳聚糖具有较大的分子链刚性和抗盐性能．

Chitosan is one kind of important nature polymer.There are amino groups (—NH 2) in the chitosan chains.It can be dissolved in acid aqueous solution,which lead to —NH + 3 groups formation,and displays the anionic polyelectrolyte property.The macromolecule chains are stretched caused by electrostatic repulsion of the groups —NH + 3 on the chains.The stretched chains will tend to be coiled with addition of salt because of the charge screening effect of added salt.Since the determination of the intrinsic viscosity of polyelectrolyte is an effective method to study the sensibility of polyelectrolyte to the addition of salt,the dilute solution viscosity of three chitosan samples with molecular weight ( M V=2 6×10 5,5 6×10 5 and 1 06×10 6) was measured both in solutions of NaCl with different ionic strengths (0 01,0 03,0 06 and 0 10mol/L) and in those of NaCl,KCl,CaCl 2 and BaCl 2 with the same ionic strength (0 06mol/L) respectively.All the viscosity measurement is proceeded by a dilute type Ubbelohde viscometer at 308 15K.The intrinsic viscosity of chitosan is found to be a linear function of 1/ I(I is the ionic strength).It is also found that the response of the intrinsic viscosity of chitosan to the added salts proceeds in the order of anion Na +>K +>Ba 2+ >Ca 2+ .Accroding to the comparison of the ionic radius and hydrate number among the four anions,it displays that the influence of intrinsic viscosity of chitosan on the added salt is due to both the anion radius and anion solvent power.Meanwhile the parameter α of Mark Houwink equation is estimated to be 0 78, 0 70, 0 67 and 0 62 in corresponding added salt ionic strength (0 01,0 03,0 06 and 0 10mol/L). They are all larger than 0 5,the value common to Gaussian coils in θ solvent.According to all hydrodynamic theories,the high α value must indicate that the chitosan chain is very extended in aqueous solution.On basis of Smidsrod equation,the value of empirical parameter B ,which is a measure of relative stiffness of different polymer chains,is found to be 0 074.Parameter B can also be used as a measure of the sensibility of polymer to the added salt.Compared with the data of other polymers in literature,in can be concluded that the chitosan has a higher chain stiffness and a better resistance ability to the added salt.