【作者】 金媛；

【导师】 邵惠丽；

【作者基本信息】 东华大学 ， 材料学， 2014， 博士

【摘要】 蜘蛛和蚕都能在环保的条件下,即以水为溶剂,在常温、常压下,通过干法纺高效纺制出强韧的纤维。目前,对蜘蛛和蚕的仿生纺丝技术的研究,正成为众多领域尤其是高分子材料领域研究的热点之一。但是,鉴于蜘蛛丝蛋白尚无法大量获取,而蚕的成丝过程与蜘蛛的成丝过程比较相似,蚕丝丝素蛋白的主要氨基酸组份与蜘蛛丝蛋白也比较接近,且蚕丝来源丰富、便于提纯,在一定的成丝条件下,其机械性能甚至可与蜘蛛丝媲美,因此,以蚕丝丝素蛋白为模型来进行仿生纺丝研究越来越引起研究者的重视。在开展蚕丝的仿生纺丝过程中,有必要在了解蚕体内的纺丝系统和丝素蛋白(SF)水溶液结构与性质的基础上,模拟制备合适的纺丝液,探索采用干法纺丝和环保的工艺,开发出高性能的再生丝素蛋白纤维。鉴于迄今为止对蚕体内溶液流变性能及SF聚集体结构尺寸变化规律的研究鲜有报道,并且,人类对蚕的成丝机理也尚未达成共识,因此,本论文在开展蚕丝的仿生纺丝研究之际,将先对蚕体内各部位纺丝液的结构与性质进行分析研究,并进一步模拟蚕体内纺丝液的变化过程,探讨众多因素对再生丝素蛋白水溶液结构与性质的影响,从中了解蚕丝蛋白的纤维化机理。在此基础上,进一步探索开发较常规干纺工艺更为简单环保的工艺制备出性能优良的再生丝素蛋白纤维。为了对蚕体内纤维化过程有更深入地了解,本论文首先采用偏光显微镜、旋转流变仪、红外光谱仪、拉曼光谱仪和动态光散射仪对蚕吐丝过程中丝腺不同部位的SF水溶液的结构与性能进行了研究。研究发现,只有前部丝腺和中部丝腺前区的溶液具有偏光现象。随着SF水溶液从中部后区向前区流动,溶液的粘度和弹性均逐渐变小,SF分子构象也逐渐向p-折叠构象转变。同时,SF发生了聚集,在中部丝腺前区形成了尺寸较大且较为均匀的聚集体。这些结果表明,蚕体内SF溶液在从后部丝腺向前部丝腺流动的过程中,溶液中的SF分子逐渐由原先的无序状态转变成有序态结构。并且,在蚕体内中部丝腺前区的SF溶液很可能已经形成了液晶态结构。为了模拟蚕体内纺丝液的变化过程,本论文进一步采用自制的平板剪切装置,以较高浓度的再生丝素蛋白(RSF)水溶液为研究对象,研究了不同剪切速率下,溶液浓度、pH值和Ca2+含量等因素对RSF水溶液性质与结构的影响。研究表明,RSF水溶液经过一定的剪切作用后将呈现出各向异性的性质。并且,在本论文研究范围内,RSF浓度的提高、pH值的降低、Ca2+的添加均有助于剪切作用下RSF水溶液由各向同性转变为各向异性。为了进一步探讨剪切时间对高浓度RSF水溶液体系的影响,本论文还将光学剪切台与同步辐射小角X射线散射设备联用并结合流变性能分析,在线研究了恒定剪切速率下,剪切不同时间的RSF水溶液结构与性质的变化。研究发现,适当延长剪切时间与提高剪切速率(应力)等效,均有利于RSF分子的聚集及有序排列并促进向β-折叠构象的转变；随着剪切时间的延长,RSF水溶液的粘度逐渐增加至出现峰值,此时溶液中足够多的RSF分子已由无序状态沿剪切方向聚集形成了类棒状结构聚集体,对应溶液开始呈现各向异性(偏光现象)。继续延长剪切时间,体系粘度下降,溶液中RSF聚集体长径比增大,棒状结构和偏光现象更为明显。综合这些研究结果,我们推测,在本论文研究条件下,当高浓度RSF水溶液在一定剪切速率下剪切至开始呈现各向异性时,溶液中的丝素蛋白分子很可能开始形成了一种棒状液晶态有序结构。并且,本论文在对由常规非简化方法制备(即同时调节了pH值和Ca2+含量)的高浓度RSF水溶液与简化工艺法制备(即仅调节Ca2+含量)的高浓度RSF水溶液的相关研究中均获得了上述类似的结果。由此表明,pH值的调整对于RSF水溶液中液晶态结构的形成并无明显影响。为此,结合剪切实验结果,本论文提出了更为环保的以仅添加适量Ca2+的RSF水溶液为纺丝液来制备RSF纤维的简化干法纺丝工艺,并采用毛细管纺丝装置实施了干法纺丝。研究发现,所得初生纤维由于尚未达到天然蚕丝的高倍拉伸状态,因此二级结构和力学性能与天然脱胶丝相比尚有差距。因此,本论文进一步对纺丝工艺及后拉伸等条件进行了探讨。结果表明,适当提高卷绕速率、纺丝液浓度和毛细管长径比有利于促使纤维中丝素蛋白分子发生向β-折叠构象的转变并提高纤维的力学性能,本论文实验条件下较合适的卷绕速率为3cm/s,纺丝液浓度为53wt%,毛细管长径比为80。为了进一步改善纤维结构,提高纤维性能,本论文选择乙醇-水混合溶液作为后处理剂,对简化工艺法RSF初生纤维进行拉伸浸泡后处理。研究结果表明,和常规非简化法RSF纤维相比,简化工艺法RSF纤维表现出了更完善的二级结构、结晶结构、取向结构和更好的力学性能。经后处理的简化工艺法RSF纤维的结晶度约为48%,和天然脱胶丝相近。同时,纤维的取向度也有大幅度提高,力学性能明显改善,其断裂强度、初始模量和断裂能分别达到了357.3MPa、10.3GPa和52.7kJ/kg,大大优于天然脱胶丝。此外,本论文还采用微流体芯片纺丝装置进行了简化工艺法RSF水溶液的干纺初探,发现通过该技术,RSF纤维的结构与性能有望进一步改善。这些结果表明,通过简化RSF纺丝液的制备工艺,即无需调节溶液的pH值,仅加入适量Ca2+并利用干法纺丝及适当的后处理手段,可以更为简单环保地制备高性能RSF纤维。在上述研究的基础上,为进一步探明Ca2+在简化工艺法RSF纤维形成过程中的作用,本论文采用简化工艺法制备了不同Ca2+含量的RSF水溶液并进行了干法纺丝和拉伸后处理,分析了Ca2+含量对RSF水溶液及所得纤维结构和性能的影响。研究表明,Ca2+含量对RSF水溶液的流变性能和可纺性影响较大。随着Ca2+含量的增加,高浓度RSF水溶液的粘度逐渐下降。在本论文条件下,Ca2+含量在1.25-2.50mmol/g范围内,高浓度RSF水溶液干纺可纺性相对较好。并且,Ca2+的加入促进了RSF水溶液中p-折叠构象和大尺寸RSF聚集体的形成,也进一步促使所纺制的RSF初生和后处理纤维中p-折叠构象含量和结晶度的提高,同时也有利于纤维内部大分子链和晶区的取向排列,由此使纤维的力学性能也相对较好。对Ca2+作用机理的研究发现,Ca2+的加入会与RSF分子链的亲水区形成类似COO--Ca2+--OOC的螯合结构,从而促进分子链间氢键以利于p-折叠构象的形成。并且,这种紧密的分子结构在经过喷丝头的剪切和后处理过程中的拉伸作用后,更易于沿外力方向上进行有序排列,从而形成结构完善、性能较好的RSF纤维。更多还原

【Abstract】 Both silkworm and spider can efficiently dry spin outstanding fibers under environmentally friendly conditions using water as solvent at atmospheric pressure and room temperature. Recently, the studies on biomimicking the spinning processes of spider and silkworm have been carried out with great attentions by researchers in many fields, especially in the field of polymer materials. However, the poor protein amount produced by spider has set a restriction to the further research on animal silk. In contrast, silkworm silk has similar amino acid composition and formation mechanism as spider silk. Meanwhile, silkworm silk can be obtained easily and shows excellent mechanical properties as spider silk under certain spinning conditions. Therefore, silkworm silk has been selected as a model to perform the biomimetic spinning of silk by many researchers.When studying the biomimetic spinning of silk, it is necessary to understand the spinning system of silkworm and the structures and properties of the silk fibroin (SF) aqueous solution in vivo, then a suitable spinning dope can be prepared by mimicking the SF state and an environmentally friendly dry spinning technology can be explored to produce high performance regenerated silk fibroin (RSF) fibers. However, the investigations on the rheological properties of the natural SF solutions and the structural change of SF aggregates along the silk gland are rarely reported. Meanwhile, the formation mechanism of silk is still incompletely known. Therefore, before studying the biomimetic spinning of silk, the structures and properties of the natural spinning dopes in different divisions of silk gland were firstly investigated in this thesis. Then the changing process of natural dope was mimicked in vitro and the effects of various factors on the structures and properties of RSF aqueous solution were discussed to better understand the formation mechanism of silk. Based on these works, an environmentally friendly and simple dry spinning technology was further explored to prepare high performance RSF fibers. To understand the formation process of silk in vivo, in this thesis, the structures and properties of the SF aqueous solutions from different divisions of silk gland were investigated using polarized microscope, rotational rheometer, FT-IR spectrometer, Raman spectrometer and dynamic laser light scattering instrument. It was found that only the anterior division and the anterior part of middle silk gland showed birefringence. With flowing from the posterior part to the anterior part in the middle silk gland, the viscosity and elasticity of the SF aqueous solution decreased, and its conformation was also gradually transformed into P-sheet. Meantime, the aggregation of SF gradually occurred and the larger aggregates with more uniform size were eventually formed in the anterior part of middle silk gland. These results indicated that as the SF solution flowed from the posterior division to the anterior division in the silk gland, it was gradually changed from isotropy to anisotropy and the liquid crystal structure might be initially formed in the anterior part of middle silk gland.In order to biomimic the SF dope in silk gland, the condensed RSF aqueous solution was prepared.Then, the effects of solution concentration, pH value and Ca2+content on the structures and properties of the RSF solution under different shear rates were studied using plate shear device. It was found that the RSF aqueous solution was changed to anisotropy after being applied sufficient shear. Meanwhile, it was also found that the increase of concentration, decrease of pH value and the addition of Ca2+promoted the solutions’structural transition from isotropy to anisotropy. Furthermore, the effect of shear time on the structures and properties of condensed RSF aqueous solution system was investigated online by using optical shearing instrument, synchrotron radiation small angle X-ray scattering and rotational rheometer. It was found that the extension of shear time and the increase of shear rate (stress) were equivalent, and both could lead the aggregation of RSF molecules and the conformational transition to β-sheet. As the shear time increased, the viscosity of the RSF aqueous solution gradually increased to a maximum. Meantime, rod like structures were formed due to the aggregation of enough RSF molecules along the shear direction, and the corresponding solution showed birefringence. As the shear time was further extended, the solution viscosity decreased and the length/diameter ratio of RSF aggregates increased. The rod like structures and the birefringence of the solution became more obviously. These results indicated that the RSF molecules might gradually form a rod-like liquid crystalline structure in the solution when the condensed RSF aqueous solution was optically anisotropic after being applied sufficient shear.In addition, both the conventionally prepared RSF aqueous solution (with the adjustment of pH value and Ca2+concentration) and the simply prepared RSF aqueous solution (with solely adjusting the Ca2+concentration) showed similar results. This indicated that the adjustment of pH value had little effect on the formation of liquid crystal structure in the RSF aqueous solution.In view of the shear experiments’ results, a new and more environmentally friendly dry spinning technology with solely adding Ca2+was proposed to prepare RSF dry-spun fiber using capillary spinning equipment. The resultant RSF fiber exhibited poorer structures and mechanical properties compared with the natural degummed silk, which was due to the deficient drawing of the artificial silk in air. In order to improve its mechanical properties, the parameters for the spinning and post-treatment were further adjusted. It was found that a proper increase of the take-up rate, spinning dope concentration and the length/diameter ratio of capillary promoted the formation of β-sheet conformation and hence improved the mechanical properties of the fibers. In this thesis, the suitable take-up rate, spinning dope concentration and the length/diameter ratio of capillary were about3cm/s,53wt%and80, respectively. Moreover, the ethanol aqueous solution was chosen as the post-treatment agent, and then the RSF fiber was drawn and immersed in the solution to improve its properties and structures. It was found that compared with the conventionally prepared RSF post-treated fiber, the simply prepared RSF post-treated (Sim-Post) fiber showed better secondary structure, crystalline structure and orientation, as well as better mechanical properties. After post-treatment, the crystallinity of the Sim-Post fiber was about48%, which was similar to that of the natural degummed silk. Meanwhile, the mechanical properties of the Sim-Post fiber were also greatly enhanced, with an average breaking strength of357.3Mpa, an initial modulus of10.3GPa and a breaking energy of52.7kJ/kg, which were even better than those of the natural degummed silk. In addition, the microfluidic chip was tried to dry spin RSF fibers from the simply prepared RSF aqueous solution. It was found that the structures and properties of the resultant RSF fiber could be improved by using this technology. The above results indicated that high performance RSF fibers could be obtained more simply and environmentally friendly by simplifying the preparation process of RSF spinning dope, which was without the adjustment of pH value and with solely adding Ca2+,using a dry spinning technology and a proper post-treatment.Based on the above work and in order to understand the role of Ca2+on the formation of RSF fibers, the RSF aqueous solutions with different concentrations of Ca2+were prepared for dry spinning and post-treatment. Meanwhile, the effects of Ca2+on the structures and properties of RSF aqueous solutions and the resultant fibers were investigated. Results showed that the concentration of Ca2+greatly affected the rheological properties and spinnability of RSF aqueous solutions. As the concentration of Ca2+increased, the viscosity of the solution decreased. In this thesis, when the concentrations of Ca2+were1.25～2.50mmol/g, the RSF aqueous solutions showed good spinnability. Meanwhile, the addition of Ca2+prompted the formation of β-sheet and the aggregation of RSF, which further caused the increase of β-sheet content and crystallinity in the resultant as-spun and post-treated RSF fibers. Moreover, Ca2+was favorable for the orientation of macromolecular chains and crystalline regions in the fibers, which resulted in better mechanical properties. Studies on the role of Ca2+on RSF fiber formation showed that the Ca2+could form a COO--Ca2+--OOC bond between two negatively charged hydrophilic spacers of RSF chains, which promoted the formation of intermolecular hydrogen bond and led to the β-sheet conformation. Moreover, this packed structure could be assembled orderly after physical shearing and drawing during spinning and post-treatment, which resulted in forming high performance RSF fibers.更多还原