一种接枝型性壳聚糖絮凝剂的制备

一种接枝型两性壳聚糖絮凝剂的制备
及分形理论在其絮凝性能研究中的应用*
杨朕，杨琥**，程镕时(
南京大学化学化工学院介观化学教育部重点实验室，高分子科学与工程系，南京
210093
关键词：接枝型两性壳聚糖絮凝剂 絮凝机理 絮凝动力学 分形理论
天然高分子絮凝剂，相比于传统的无机盐絮凝剂及合成高分子絮凝剂，具有用量少、环境友好、可再生、来源广泛等特点，其研究具有重要的现实意义[1,2]。

其中特别是两性型天然高分子，由于兼具阴、阳离子基团的双重特点，不仅使用性能得到提高，而且其适用范围也大为加宽。

[3]
因此，本文以天然高分子壳聚糖为基材，通过醚化和接枝共聚两步反应，制备了一种接枝型两性絮凝剂——羧甲基壳聚糖接枝聚丙烯酰胺共聚物（CMC-g -PAM ）。

FTIR 和1H NMR 波谱表征验证了产物的分子结构，且通过1H NMR 波谱，进一步计算出了不同原料配比的接枝共聚产物的接枝率。

溶解性测试发现，较原料壳聚糖和中间产物羧甲基壳聚糖（CMC ），CMC-g -PAM 在整个pH 范围内的的溶解性显著增强。

R e s i d u a l t u r b i d i t y (%)Dosage (mg/L)
Fig.1 Flocculation of Kaolin suspension by different kinds of CMC-g-PAM 絮凝试验中，以高岭土悬浊液为模拟水样，比较不同接枝率的CMC-g -PAM 的絮凝效果，发现具有较高接枝率（212%）且自身不存在交联的CMC-g -PAM15具
*国家自然科学基金（批准号：51073077）及中央高校基础科研业务费专项资金（批准号：1105020504）资助 **E-mail ：yanghu@
有最佳的絮凝性能（如Fig.1）。

进一步地采用分形理论[4]，通过光散射法[5]测定絮体分形结构参数——尺寸和分形维数（Fractal dimension ，D F ），结合传统的水体浊度和zeta 电位表征，分别在酸性、中性和碱性条件下，对CMC-g -PAM15的絮凝性能进行了系统考察。

结果表明:在酸性条件下，静电簇（patching ）为CMC-g-PAM15的主要絮凝机制；而在中性及碱性条件下，链接架桥（bridging ）则起到主导作用。

在此基础上，在不同pH 条件下，通过在线光散射技术，对絮凝过程中絮体分形结构参数进行了实时跟踪，结果如Fig.2所示。

F l o c s
i z e ( m )Time (min) D f Time (min)
(a) (b)
Fig.2 Variation of size (a) and D F (b) of floc as a function of flocculation time for
CMC-g -PAM15 at each optimal dosage at pH 4 (●), 7 (■) and 11 (▲).
由Fig.2进一步发现，三种不同pH 条件下，存在着截然不同的絮凝动力学过程：
1）酸性条件下，絮凝剂与悬浮颗粒间的异种电荷吸引作用使得高分子呈平坦状吸附在颗粒表面，因而絮凝初期絮体尺寸增长较慢；但由于吸附高分子后的颗粒表面电荷分布不均，静电簇作用使得絮体持续增长且结构紧密（D F 值大）。

2）中性条件下，絮凝剂分子呈中性，架桥作用的主导使得絮体在絮凝初期尺寸增长较快，但絮体结构较松散；随后，由于絮体中高分子链和初始颗粒的重排，使得絮体逐渐密实（D F 增大）。

3）碱性条件下，絮体在初始阶段的增长与中性条件下类似。

但由于此时絮凝剂高分子链上与颗粒表面都具有负电荷，同种电荷的排斥力阻碍了絮体结构的重排，因而碱性环境中絮体结构最松散和开放。

参考文献：
[1]Xiao J, Zhou Q, Natural Polymer Flocculants, Chemical Industry Press: Beijing,
2005.
[2]Lu Y B, Shang Y B, Huang X, Chen A M, Yang Z, Jiang Y X, Cai J, Gu W, Qian X
Z, Yang H, Cheng R S, Industrial & Engineering Chemistry Research, DOI:
10.1021/ie2000665.
[3]Yang H, Lu Y B, Cheng R S, Research progress on the preparation and application
of amphoteric chitosan, in Davis S P (Ed), Chitosan: Manufacture, Properties, and Usage, Nova Science Publishers: New York, 2011, Chapter 33.
[4]Zhou Y, Franks G V, Langmuir, 2006, 22(16): 6775.
[5]Yu J F, Wang D S, Ge X P, Yan M Q, Yang M, Colloids & Surfaces
A-Physicochemical & Engineering Aspects., 2006, 290(1-3): 288
Preparation of a Novel Amphoteric Grafted Chitosan Flocculants and Evaluation of Its Flocculation Performance by Fractal Theory*
Zhen Yang, Hu Yang**, Rongshi Cheng
Key Laboratory for Mesoscopic Chemistry of MOE, Department of Polymer Science & Technology, School of Chemistry & Chemical Engineering, Nanjing University,
Nanjing 210093
Abstract：Recently, extensive attention has been paid to research on natural polymer flocculants, since they have characteristics of low dose requirements, environmental-friendly, renewable and widely-sourced, in comparison with traditional inorganic and synthetic polymer flocculants. In this work, a novel kind of amphoteric grafted chitosan flocculants, carboxymethyl chitosan-graft-polyacrylamide (CMC-g-PAM) has been prepared. The flocculation properties of a series of CMC-g-PAM with different graft ratio were firstly investigated using kaolin suspension as synthetic wastewater. Among the flocculants, CMC-g-PAM15 with a high graft ratio of 212% and no crosslinking showed the best flocculation efficiency. Then, under acidic, neutral and alkaline condition, the flocculation performances of CMC-g-PAM15 were
systematically evaluated by light scattering and image analysis combing fractal theory, as well as traditional turbidity and zeta potential measurements. Different flocculation mechanisms were evident at various pHs: patching was dominant under acidic condition while bridging was mainly involved under neutral and alkaline solution. Furthermore, by in-situ fractal structure measurements of the floc, distinct dynamic processes of flocculation under the three pH conditions were also monitored and proposed.
Key Words：Amphoteric chemically bonded composite flocculants Flocculation kinetics Flocculation mechanism Fractal dimension Natural polymer。