| 摘要 | 静电纺丝技术是有效制备纳米纤维材料的主要途径之一，在生物医用材料、催化、能源、食品、化妆品等领域都有重要的应用价值。目前利用静电纺丝技术制备纳米纤维还面临着一些需要解决的问题，比如用于静电纺丝的材料种类还十分有限；材料复合受到相容性限制；纳米纤维性能有待改进；电纺丝单纤维的性能分析手段不完善等。本研究针对静电纺丝技术中的主要问题，进行了以下两方面的工作：鉴于癸二酸二（2-乙基己基）酯可作为增塑剂增加材料的柔软性，而甘油二酯（Diacylglycerol，DAG）可作为乳化剂增加复合溶液的稳定性，本研究利用固定化酶催化制备了癸二酸二（2-乙基己基）酯和甘油二酯，并对合成方法进行了优化；采用静电纺丝技术制备了明胶-壳聚糖复合纤维材料，并建立了原子力显微镜（AFM）联合扫描电子显微镜（SEM）测定电纺丝单纤维性能的方法。具体研究内容如下：1. 酶法制备二酯类助剂癸二酸二（2-乙基己基）酯是一种优良的低温增塑剂，可赋予材料良好的低温柔软性和耐光性。在有机溶剂中，分别采用固定化脂肪酶Lipozyme TL IM、Lipozyme RM IM和Novozym 435催化癸二酸和2-乙基己醇合成了癸二酸二（2-乙基己基）酯，考察了反应溶剂、反应温度、反应时间、酶量和底物比等对产率的影响。结果表明，在经优化的实验条件下反应，Lipozyme TL IM、Lipozyme RM IM和Novozym 435作为催化剂的产率依次为96.94%、96.23%和84.65%。在上述反应条件下，使用6次后，这3种固定化脂肪酶仍保持较高的催化活性。研究了这3种固定化脂肪酶催化癸二酸二（2-乙基己基）酯合成的有机溶剂效应，测试了在烷烃、醇、酮、醚等4类12种有机溶剂中的催化效率。结果表明3种固定化脂肪酶均偏好烷烃类溶剂，Novozym 435是溶剂适应性最强的酶。溶剂在辛醇和水中的分配系数（log P）对Novozym 435催化反应初始速率的影响与溶剂类别密切相关。另外还利用Novozym 435催化米糠油甘油解合成了可稳定复合材料溶液体系的乳化剂DAG，并利用响应面法对合成DAG的反应条件进行了优化。在单因素实验基础上选取反应温度、反应时间、酶添加量（酶和米糠油质量比）、底物质量比（米糠油：甘油）等4个因素作为自变量，以DAG的产率为响应值，进行5水平4因素中心组合设计优化，确定了影响DAG合成的关键因素以及最佳反应条件，在该条件下DAG产率是53.08%。2. 明胶-壳聚糖复合纤维的制备和表征明胶-壳聚糖复合材料是模拟人体组织器官的候选组合之一，具有较好的生物相容性。本研究采用静电纺丝技术制备了明胶-壳聚糖复合纤维材料，并优化了制备条件。傅里叶变换红外光谱（FTIR）和差示扫描量热（DSC）测定结果说明明胶-壳聚糖复合纤维中两种组分是相容的。建立了SEM联合HarmoniX模式的AFM的电纺丝单纤维性能表征方法，观察了明胶-壳聚糖复合纤维的形貌，测定了其弹性模量。SEM显示静电纺明胶-壳聚糖纤维比明胶纤维或壳聚糖纤维的形貌更规则。利用AFM在HarmoniX模式下定量测定了单纤维的Derjaguin-Müller-Toporov（DMT）模量，结果显示明胶-壳聚糖纤维比明胶纤维或壳聚糖纤维的DMT模量更高，并提出了可能的机理。本论文针对静电纺丝相关的材料和技术方法进行了研究，合成了可用于改善材料性能的癸二酸二（2-乙基己基）酯和甘油二酯，建立了电纺丝单纤维的力学性能表征方法。虽然研究还处于初期阶段，但为电纺纤维微结构的测量提供了新思路，更为进一步改进电纺纤维的性能提供了可供利用的材料和技术手段。这将有助于解决目前静电纺丝技术所面临的主要问题，促进静电纺丝技术的发展和应用。; Electrospinning is one of the main approaches for preparing nano-fibers, and has important applications in the fields of biomedical materials, catalysis, energy, food and cosmetics industries. However, there are still some unsolved problems in preparaing nano-fibers via electrospinning, including limited material categories, compatibility constraints for composite materials, limited technological options for improving the properties of nano-fibers and also for testing single fibers, etc. In order to resolve problems related to electrospinning, two works were conducted in this dissertation. As is well known, bis(2-ethylhexyl) sebacate is a plasticizer which can improve the flexibility of materials and diacylglycerol (DAG) is an emulsifier which might improve the stabilities of composite solution. In this study, bis(2-ethylhexyl) sebacate and diacylglycerol were synthesized by immobilized lipases respectively and the synthesis methods were optimized. Moreover, gelatin-chitosan fibers were prepared by electrospinning and a novel method of evaluating properties of electrospun fibers was established by combing scanning electron microscopy (SEM) and atomic force microscopy (AFM). The related experiments and results are summarized as follows:1. Enzymatic Preparation of Diester AdditivesBis(2-ethylhexyl) sebacate is a cold resisting plasticizer, which can provides excellent cold and light resistance to materials. Bis(2-ethylhexyl) sebacate was synthesized through the reaction of sebacic acid and 2-ethylhexanol catalyzed by different immobilized lipases Lipozyme TL IM, Lipozyme RM IM and Novozym 435, respectively, in organic solutions. The effects of reaction solvents, reaction temperature, reaction time, lipase dosage and substrate molar ratio on the product yield were investigated. The results showed that under the optimum synthesis conditions, the product yield was 96.94% with Lipozyme TL IM catalyst, 96.23% with Lipozyme RM IM catalyst, and 84.65% with Novozym 435 catalyst. Moreover, three kinds of immobilized lipases still maintained high catalytic activities after being used 6 times in those reaction conditions.The effects of organic solvents on bis(2-ethylhexyl) sebacate synthesis catalyzed by Lipozyme TL IM, Lipozyme RM IM and Novozym 435 were studied, respectively. Twelve solvents from four organic groups were investigated, including alkanes, alcohols, ketones and ethers. The results indicated that all of the three immobilized lipases had a predilection for alkanes. It was also found that Novozym 435 possessed the greatest solvent adaptability among these three immobilized lipases. The influence of organic solvents’ log P (logarithm of its partition coefficient between octanol and water) on the initial rate of Novozym 435-catalyzed reactions was closely correlated with organic groups. Besides, DAG, an emulsifier which can stabilize composite solution system, was synthesized by Novozym 435-catalyzed glycerolysis of rice bran oil in t-Butanol system. Response surface methodology was applied to optimize the product yield. Based on single-factor analysis, 5-level-4-factor central composite design was employed to evaluate and optimize the parameters of DAG synthesis, including reaction temperature, reaction time, and enzyme amount (mass ratio of lipase to rice bran oil) and substrate mass ratio (rice bran oil/glycerol). In the optimum DAG synthesis conditions, the yield of DAG was 53.08%. 2. Preparation and Characterization of Gelatin-chitosan Composite FibersGelatin-chitosan composite has good biocompatibility, and is one of the protential combinations for mimicking human tissues and organs. In this study, gelatin-chitosan composite fibers were prepared by electrospinning and the experimental parameters were optimized. The results of Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) demonstrated that the proportions of gelatin-chitosan composite fibers were compatible. SEM combined with AFM was utilized to evaluate the morphological and mechanical properties of the gelatin-chitosan fibers. The SEM images showed that the electrospun gelatin-chitosan fibers possessed more uniform morphologies than the pure gelatin or chitosan fibers. Moreover, AFM-HarmoniX mode was used to quantitatively assess the Derjaguin-Müller-Toporov (DMT) modulus of gelatin-chitosan fibers. The DMT modulus of gelatin-chitosan fibers showed higher values than the pure gelatin or chitosan fibers and the possible mechanism of this phenomenon was proposed. This dissertation focused on electrospinning related materials and methods, including synthesizing bis(2-ethylhexyl) sebacate and diacylglycerol for improving the performance of materials and establishing a novel method for determination mechanical properties of electrospun single fibers. While the research is still in its early stages, it provides a new route for measuring microstructure of electrospun fibers, and more importantly, it provides useful materials and methods for further improvements of electrospun fibers. The results will help to resolve some problems involved in electrospinning and promote the development and application of this technique. |
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