【作者】 李杰；

【导师】 潘志娟；

【作者基本信息】 苏州大学 ， 纺织材料与纺织品设计， 2014， 博士

【摘要】 近年来，随着纳米科学与技术的发展，纳米纤维成为了纺织服装、材料科学等领域的研究热点之一。目前，基于不同的原理，制造纳米纤维的方法主要有拉伸、模板聚合、相分离、自组织和静电纺等。对比上述几种方法，静电纺最容易获得连续的纳米纤维，装置简单、成本低廉，通过改进常规静电纺接收装置，还可以制备出具有良好取向和高度规则排列的纳米纤维束。目前，尽管在静电纺丝成形机理、产品结构调控、聚合物功能化应用等领域已有较大发展，制备连续纳米纤维束的方法也有较大突破，但纺丝连续性、纳米纤维束的基本性能等都还有待提升。本文先通过酸化的方法去除SWNTs制备过程中的杂质，然后酰胺化使其表面带上酰胺键。将功能化处理后的SWNTs添加到聚酰胺6（PA6)纺丝液中，通过独特的静电纺工艺稳定、连续地制备出PA6/SWNTs复合纳米纤维束，进而研究纺丝工艺参数对泰勒锥形态及射流轨迹的影响，分析稳定、连续纺丝的条件，形成静电纺纳米纤维束的成形理论。通过优化纺丝工艺参数，制备填充不同含量、长径比SWNTs的PA6/SWNTs复合纳米纤维束，研究SWNTs在纳米纤维内部的形态、分布及导电增强效果，同时探索复合纳米纤维束内部电荷的传递机制及其微应变传感机理。研究表明酰胺化处理后SWNTs长度减小，相互纠缠现象减弱，其表面接枝上酰胺键，能够较好地分散在PA6/甲酸溶液体系中。以该纺丝液制备纳米纤维束的最佳工艺参数为：纺丝电压20kV，纺丝流量0.09ml/h，卷绕速度为5.4m/min。力学测试结果表明：添加酰胺化处理SWNTs的纳米纤维束的拉伸断裂应力比添加酸化处理SWNTs的提高了很多，从43.42MPa增加到了79.75MPa，同时初始模量增大了超过一倍。从PA6/SWNTs纳米纤维束拉伸曲线可以看出，纤维束有较明显的屈服点，而屈服平台后的强化区很难看出，纤维束几乎没有不同时断裂性。通过傅里叶变换分析，拉伸曲线上出现的锯齿状波动为测试过程中的噪音所致，并非通常认为的纤维断裂不同时性引起。利用高速摄像机记录并研究了静电纺制备纳米纤维束形成过程中，泰勒锥及射流轨迹的动态变化规律，利用SEM和AFM测定与分析了纺丝不同阶段纤维的形态结构与粘弹性，结合不同卷绕速度下纳米纤维、纳米纤维束直径与卷绕速度间关系的研究，探讨了静电纺纳米纤维束的成形机理。研究结果表明：纺丝液出喷丝口后，在电场作用下细化形成射流，进而沉积在浴液表面，纤维呈无规毡状分布，此时，虽然纤维表面已经固化，但其内部高聚物并未完全固化，呈高浓度的粘弹状；在浴液表面被集束作用后，纤维开始沿牵引方向定向排列，初步形成纳米纤维束；在烘干装置的作用下去除纤维中残留的溶剂及水分，并因卷绕速度大于纺丝速度而被进一步拉伸，纤维沿轴向定向排列的程度提高。粘弹性的测定结果表明：射流飞行过程中直接接收的纳米纤维表面力学性能最差，浴液表面收集的次之，而烘干成形后的纳米纤维力学性能最好。通过控制卷绕速度可以提高纳米纤维的定向度，制备出方便退绕的纳米纤维束。卷绕速度小于7.2m/min时，卷绕过程主要是使浴液表面无规纳米纤维重新排列，较少涉及单根纳米纤维的拉伸；卷绕速度超过7.2m/min后，因为牵伸倍数较大，不仅使无规纳米纤维趋于沿轴向定向排列，形成稳定的纤维束结构，而且纳米纤维自身也受到一定程度的拉伸，力学性能显著提高。静电纺丝在较小空间及时间内形成的纳米纤维分子链取向差、结构不完善、物理机械性能较差。利用本文的静电纺丝方法制备纳米纤维束时，纤维在受热条件下被快速卷绕，从而获得程度较大的拉伸作用，能够提高其物理机械性能。利用3D MAXWELL电场模拟软件，模拟了纳米纤维束形成过程中的电场强度及分布。模拟结果表明，随着纺丝高度的增大，针头处电场强度减弱，电场分布更分散，正负极间电场梯度趋于平缓，负极处电场从浴盘左侧逐渐向中间偏移。实验及理论分析的结果表明，负极收集材料的导电性会以微弱电流的方式对电场起到分压作用，负极收集浴液电导率减小，泰勒锥体积增大、泰勒锥角增大，而稳定直线段长度先是基本没有较大变化，然后在浴液电导率为0时突然减小。SWNTs对聚合物纤维具有良好的电学增强效应，本文研究了填充不同质量分数和尺寸的SWNTs后，PA6/SWNTs复合纳米纤维束电学性能的变化。研究结果表明，随着SWNTs质量分数的增加，PA6/SWNTs复合纳米纤维束的导电性能增强，其电导率最大可提高9个数量级，SWNTs质量分数的阈值约为0.8wt%；不同SWNTs含量下，添加长径比为10000~15000的SWNTs的PA6/SWNTs纳米纤维束的电导率均大于添加长径比为1000~1500的纳米纤维束，且添加高长径比SWNTs后，PA6/SWNTs纳米纤维束较早出现电导率阈值；在测试长度分别为2mm~2cm时，试样的测量长度对其电导率的影响不大，最大差异为7.8%。用自行设计的一套安捷伦4339B高阻仪适用的夹具，研究了PA6/SWNTs复合纳米纤维束的应变传感性。当纤维束发生10%~60%范围内的应变时，纤维的电阻变化量与应变之间呈线性正相关性，应变传感的线性度均较好；随着纤维中SWNTs质量分数的增加，电阻的变化量减小；相同SWNTs含量下，随着SWNTs长径比增大，电阻变化率减小，也就是灵敏度降低；试样长度对纳米纤维束的应变传感特性没有显著影响。更多还原

【Abstract】 Recently, with the rapid development in nanoscience and nanotechnology, nanofibersbecome a hot topic in the fields of textile and material science.Based on different principles, lots of methods can produce fibers in nano-scale, suchas stretching, template polymerization, phase separation, self-organization andelectrospinning. Compared them, electrospinning has been recognized as the most feasibletechnique for the fabrication of continuous polymeric nanofibre, besides that, it also canproduce nanofiber bundles and nanofiber yarns by changing the negative pole. Althoughthe shaping mechanism of electrospinning, product structure control and its functionalapplication from various polymeric materials have developed well, the basic performanceof nanofiber bundles and the continuity still need to be intensively studied.Single wall nanotubes(SWNTs) were acidized to purify the inclusions and thenamidated to graft amide group. Add the functionalized SWNTs into PA6/formic acidsolution, and consecutively produce PA6/SWNTs nanofiber bundles by uniqueelectrospinning. After that, study the nanofiber bundles shaping mechanism by discussingthe morphology of the Taylor cone and the trajectory of the jet flow, also by studying thespinning conditions of producing nanofiber bundles steadily and continuously. Finally,PA6/SWNTs composite nanofiber bundles with different length-diameter ratios anddifferent contents of SWNTs were made by the optimized parameters. Study thedistributions, status and the electrical properties enhancement effects of SWNTs inside ofnanofibers, meanwhile, discuss the transfer mechanism of the charge and the strain sensingmechanism.The results show that the length of SWNTs decreased and dispersed well in thePA6/formic acid solution after amidating. The optimized parameters to produce nanofiberbundles were20kV,0.09ml/h and5.4m/min. Mechanical properties results show that compared to the filaments with acided SWNTs, the breaking stress of PA6/SWNTsnanofiber filaments with amide functionalized SWNTs increased obviously, up to79.75MPa from43.42MPa, furthermore, the initial module was also increased about100%.The stretching curve indicated that all the nanofibers in the bundle breakdown in thesame time and the yield point without intensifying area after that exist in the curve. TheFast Fourier Transform (FFT) results show that the serrated waves in the curve are noisewhich generated from the stretching process, really not from the asynchronous fracture.The Taylor cone and the trajectory of the flow jet were recorded by a high speedcamera and the shaping mechanism was investigated by studying the relationships betweenthe winding speeds and the diameters of the nanofibers and bundles. The stream of liquiderupting from the spinneret firstly, and then deposited onto the surface of the negativecollector forming randomly-oriented nonwoven fiber mats, at this point, the surface of thenanofiber is solidified, but the inner of it is still viscoelastic state, the solvent wouldevaporate in the follow-up drying and winding process. After that, under the bundlingeffect of the bath, nanofiber filaments were converted into bundls and wound onto apackage. The morphological structure and viscoelasticity of the nanofiber in differentstages were tested by scanning electron microscope (SEM) and Atomic ForceMicroscope(AFM). The AFM results show that the mechanical property of the nanofiberafter drying is the best, and after that are the bath stage and the flying stage, respectively.At last, the easy backing-off bundles comprised with high alignment and orientationdegree of nanofibers were obtained by controlling the winding speed. When the windingspeed is lower than7.2m/min, the main role of the winding process is rearrange therandomly-oriented nanofibers without stretching it. However, when the winding speed isfaster than7.2m/min, the quantities of the nanofibers in the bundle is already fixed and thehook can no longer unbend. So the winding process can be regarded as hot-stretching, themolecular chain would be rearranged and the mechanical property of it would beimproved.The intensity and distribution of the electric fields in the electrospinning process have be simulated by using the3D Maxwell software, the results show that with the increase ofthe spinning space, the electrical intensity close to the spinneret tip weakened anddistributed more separately, the electrical field of the negative pole move to the central partfrom left. The conductivity of the negative pole can relieve the electrical voltage by theweak current way, when the conductivity of the bath decreased, the volume and the angleof the Taylor cone increased, while the straight segment change little firstly, but decreasedsuddenly when the bath conductivity down to0S/cm.The conductivity of the as-spun nanofiber bundles with different length-diameter ratioand contents of SWNTs were studied and there is almost109order of magnitudeimprovement by adding SWNTs. The percolation threshold of it is about0.8wt%and theelectrical conductivity increased directly with adding SWNTs up to that threshold and.The conductivity of the PA6/SWNTs nanofiber bundles with length-diameter of10000~15000SWNTs were larger than with length-diameter of1000~1500under the samecontents, and the percolation threshold came out earlier. The testing length has little effecton its conductivity and the biggest difference was7.8%when changing the testing lengthfrom2mm~2cm.A custom-made test fixture was used to extend the as-spun bundles and measure thestrain sensitivity of the PA6/SWNTs nanofiber bundles. The results show that there is apositive relationship between△R/R and△L/L when the strain varied between10%and60%. Also, higher CNT concentration and length-diameter yield lower△R/R, and hencehigher sensitivity, while the sensitivity varied little when changing the initial testing length.更多还原