【作者】 廖伟；

【导师】 王兆梅；

【作者基本信息】 华南理工大学 ， 制糖工程， 2015， 硕士

【摘要】 纤维素硫酸酯(Cellulose Sulfates,CS)是纤维素经过硫酸酯化修饰而使其葡萄糖单元上的羟基部分或完全被取代而形成的衍生物。纤维素衍生物水凝胶因溶胀性好、力学强度大、透明度高而在医药、功能材料和食品工业等领域有广泛的应用。鉴于目前纤维素衍生物水凝胶主要局限于纤维素醚,本文首次开展了纤维素酯化物水凝胶的研究,主要内容包括:不同取代度CS的制备与表征、CS水溶液性质研究及特定取代度CS的溶胶-凝胶转化规律、CS水凝胶的性能及成胶机理。主要研究结果如下:1.以滤纸纤维素为原料、ClSO3H-DMF复合物为酯化剂制备了CS。并使用红外(FTIR)、核磁共振(13C-NMR)、X-衍射(XRD)、差示扫描量热(DSC)、扫描电镜(SEM)等方法分析其分子结构和粒子特性。FT-IR揭示产物中存在C-O-S和S=O等硫酸酯基的特征吸收峰,元素分析测知产物的取代度在0.27~0.99之间,分子量55000~18000 Da之间;13C-NMR显示产物CS中硫酸酯基的取代为C6位取代为主的C6、C2取代模式;XRD分析表明纤维素经过硫酸酯化后结晶度减小;DSC分析表明纤维素经过硫酸酯化后结合水分解温度升高、熔融温度降低,SEM显示CS为松散、粗糙的纤维结构。2.CS水混合体系为假塑性流体,可以在一定条件下发生溶液-凝胶的转化。各种取代度的CS在水中均能形成稳定的溶液,溶液特性粘度随硫酸酯基取代度的增大而降低;取代度低于0.5的CS在一定条件下均能形成凝胶,浓度、温度、存放时间对其溶胶-凝胶转化点有较大影响。采用旋转流变仪,在频率扫描范围为0.01~100 rad/s,发现6%(w/v)为溶胶状态(G?<G"),7%~8%分别在28 rad/s和12 rad/s出现溶胶-凝胶转化点(G?=G"),而9%为凝胶状态(G?>G");在温度扫描范围为25~80℃,发现6%为溶胶,7%~8%分别在60℃和40℃出现明显的溶胶-凝胶转化点,而9%在69℃从凝胶转化为溶胶;7%的CS在初始状态时出现溶胶-凝胶转化点,但24 h后和48 h后都为凝胶状态。3.CS的脱水收缩敏感性和持水力与其凝胶浓度有关,浓度、温度、pH、存放时间及添加物均对CS的凝胶性质有一定影响。随CS水凝胶的浓度升高,CS脱水收缩敏感性减小,持水性增强、硬度增大(浓度20%时其值分别为达到1.8±0.1%、98.3±0.9%、41.467±0.512 g);随CS水凝胶的温度对其强度存在极值,浓度15%的CS水凝胶在20℃时强度最大;存放一定时间,会增加其强度,一般来说,在7天内,时间越久凝胶强度越大;一定的酸性条件也会增强CS凝胶强度,降低溶液pH,CS的凝胶强度提高;添加甘油可改善凝胶强度,当甘油添加量为5%(w/v)时凝胶机械强度最大;添加Ca2+和HPO42-均使CS水凝胶性质改善,其硬度分别提高了67%和81%,胶粘性分别提高16倍和4.2倍,弹性分别提高4倍和7.74倍。CS的成胶机理宏观表现为粘度的急剧上升,微观表现为从单个分子独立分布在水中到分子间的聚合或交联,形成稳定的三维网络结构。更多还原

【Abstract】 Cellulose Sulfates(CS) are series of the cellulose derivatives, which were obtained by replacing the hydroxyl groups in the glucose units with sulfate ester partially or completely via sulfation modification. Hydrogel from cellulose derivatives are widely utilized in medicine, functional materials and food industry etc due to their excellent swelling, mechanical strength and transparency. Due to the fact that the wide spread cellulose-based hydrogel are only limited to the cellulose ethers, the aim of this study was to develop a novel hydrogel from cellulose ester----cellulose sulfate for the first time. In this thesis, the following research contents were included: preparation and characterization of CS with different degree of substitution(DS); Solution properties of CS and the sol-gel transformation; the properties of CS hydrogel and gelation mechanism. The main results are as follows:1. CS was prepared via sulfation modification with filter cellulose as raw material and ClSO3H-DMF complex as esterification agent. Fourier transform infrared spectroscopy(FTIR), nuclear magnetic resonance(13C-NMR), X-ray diffraction(XRD), differential scanning calorimetry(DSC) and scanning electron microscopy(SEM) were used to analyze its molecular structure and particles properties. FT-IR analysis witnessed the sulfation substitution by indicating the presence of C-O-S and S=O characteristic absorption peak. Element analyzer showed the Substitution Degree of sulfate group ranged between 0.27 and 0.99. The weightaverage molecular weight fell between 55,000 and 18,000 Da. 13C-NMR spectra showed that the sulfate group in CS was substituted by the pattern of all C6 and partial C2 substitution. XRD analyses showed that the cellulose crystallinity decreased after sulfation modification. DSC test demonstrated the decomposition temperature of combined water increased but the melting temperature decreased after sulfation. SEM image proved CS was a loose and rough fiber structure.2. CS/water mixtures behaved as a pseudoplastic fluid which could undergo sol-gel transition in a certain conditions. CS with various DS were able to form stable status in aqueous solution. The intrinsic viscosity of the CS solution decreased with the increasing of DS. CS with DS no more than 0.5 could form gel at certain conditions. The concentration, temperature and storing period had a great influence on the sol- gel transition point. According to rheology determination using rotational rheometer in the frequency scanning range from 0.01 to 100 rad/s, CS was in sol state at the concentration of 6%, the storage modulus(G’) being less than the loss modulus(G"). Sol-gel transition occurred at 7%~8% with G?=G" at 28 rad/s and 12 rad/s, respectively. CS with 9% was at gel state(G’>G"). When scanning in the temperature range from 25 to 80℃, CS at 6% was a sol, CS at 7%~8% showed significant sol-gel transition at 60℃ and 40℃, respectively. CS at 9% conversed from the gel to sol at 69℃. The CS concentration of 7% had the sol-gel transition points in the initial state, but stayed in gel state after storing for 24 h and 48 h.3. The susceptibility to sysneresis(STS) and water hold capacity(WHC) are influenced by the concentration of CS hydrogel. The concentration, temperature, p H, storing period and the addition of additives showed influence on properties of CS hydrogel. With the concentration of CS hydrogel increased, the dehydration contraction sensitivity of CS decreased, but its waterholding capacity and hardness improved,( for example theses parameters of 20% CS were 1.8±0.1%, 98.3±0.9% and 41.467±0.512 g respectively). The CS hydrogel at 15% showed the highest gel strength at 20℃. A prolonged storing time could enhance the strength of CS gel. In general, the longer of the storage time and the lower of the pH, the stronger CS gel was within 7 days. The addition of glycerol improved the gel strength. When the glycerol content was 5%(w/v), the gel was strongest. The addition of Ca2+ and HPO42- increased the rigidity of CS hydrogel by 67% and 81%, viscosity by 16 and 4.2 times and elasticity by 4 and 7.74 times respectively. In general, the gel formation mechanism of CS solution was due to the sharp increase of the viscosity at certain condition. Meanwhile from the viewpoint of molecular level, the gelation progress transferred from a single molecule independent distribution in the water to intermolecular polymerization or cross-linking, leading to a stable three-dimension network structure.更多还原