【作者】 凌芬；

【导师】 李光；

【作者基本信息】 东华大学 ， 材料学， 2007， 硕士

【摘要】 近年来纳米碳纤维以其独特的物理化学特性引起了人们对它的极大的兴趣。本文选用一种新颖的纳米碳纤维的制备方法——聚合物共混纺丝法，成功地制备出了直径小于200nm的纳米碳纤维，探讨了共混聚合物的相容性、纺丝工艺条件、碳化温度对产物形态、结构和性能的影响。并将本实验制备得到的纳米碳纤维添加到环氧树脂中制备环氧树脂／纳米碳纤维复合材料，对纳米碳纤维的加入对复合材料的结构与性能影响做了简单的探讨。本课题的实验内容主要包括以下三个方面：(一)以聚丙烯(PP)为热解高聚物、酚醛树脂(PF)为碳纤维前躯体进行共混，采用熔融纺丝法将共混体系纺丝，对得到的纤维拉伸，之后碳化纤维除去聚丙烯，得到酚醛基纳米碳纤维。采用扫描电镜等对PP／PF共混体系的相容性及微观结构进行分析，研究了纺丝牵伸比、降温母粒含量对纳米碳纤维形态的影响；用拉曼光谱、X-射线衍射技术对纳米碳纤维的微晶结构进行研究，揭示了其中的演变规律与形成特点。结果表明：随着降温母粒加入量的增加，酚醛树脂的分散尺寸增大；随着牵伸比的增加，纳米碳纤维的直径减小，综合考虑各种因素，认为制备纳米碳纤维的最佳共混比为60／20／20(PP／PF／降温母粒)，最终制得了具有良好的电性能的直径小于200nm的纳米碳纤维。XRD和拉曼光谱测试分析发现PP／PF共混纤维600℃碳化处理后已经开始产生一些石墨微晶，在900℃的条件下进行碳化所得的纳米碳纤维石墨化程度还较低，仍属于无定形碳范围。(二)选用聚丙烯腈(PAN)为纤维前驱体，以聚甲基丙烯酸甲酯(PMMA)，为热解聚合物，采用溶液共混法制备PAN／PMMA共混溶液，通过湿法成型将上述共混溶液制成共混纤维。采用红外光谱、扫描电镜等分析研究共混物的相容性，发现PAN／PMMA的相态结构为PAN以微纤形式分散在PMMA中，具有适用于制备纳米碳纤维的相态结构。将PAN／PMMA共混纤维经预氧化，高温碳化后，获得了纳米碳材料。当体系中PAN质量分数为30％时，碳化后获得了直径为200～500nm的纳米碳纤维，且原丝拉伸倍数的提高有利于纳米碳纤维直径的减小；而当PAN质量分数为70％时，则获得了多孔状活性碳纤维。本实验制得的纳米碳纤维具有良好的电性能并且也属于无定形碳范围。(三)选用本实验制备的纳米碳纤维，采用超声波分散的方法制备了纳米碳纤维／环氧树脂复合材料，对其力学性能、电学性能、热稳定性进行了测量，并借助SEM对其断口形貌进行了表征。实验结果表明，随着纳米碳纤维的加入量的增加，复合材料的拉伸强度呈现一个先增加后减小的趋势，由此可见，纳米碳纤维的加入起到了一定的增强效果。复合材料的电阻率随着CNF含量的增加而减小，当CNF％=5％时，电阻率达到了10~4Ω·cm。更多还原

【Abstract】 Carbon nanofibers (CNFs) have been the focal point of numerousresearch programs in the past ten years because of their unique physicaland chemical properties. Recently polymer blend technique has beendeveloped as a novel method to prepare carbon nano materials, includingcarbon nanotubes and carbon nanofibers. In this paper, CNFs with thediameter less than 200nm were prepared by blend spinning process. Theinfluence of the compatibility, spinning condition, carbonizationtemperature on the morphology and structure of the CNFs was discussed.The CNFs were dispersed throughout epoxy resin matrices by sonicationto fabricate the composites. The effects of loading and dispersion ofcarbon nanofibers on the structures and properties of composites wereinvestigated. The whole research work contains three parts.Firstly, the phenol-formaldehyde (PF) and polypropylene (PP) blendfibers were prepared by melt-spinning technique and carbonized at high temperature under a nitrogen atmosphere. After carbonization of theblend fibers, the PP component was removed and the PF component leftin the form of thin carbon fibers. The compatibility of PP/PF blend andthe effects of experimental parameters, such as the content of chemicaldegradation agent and the draw ratio, on the morphology of the thincarbon fibers were investigated via FTIR and SEM. Craphite structures ofthe thin fibers under different carbonization conditions were investigatedvia XRD and Raman spectra. Results showed that the diameter of theproduced carbon fiber was decreased with the increasing of draw-ratioand increased with the increasing of chemical degradation agent content.PP/PF/chemical degradation agent =60/20/20 was selected as the optimalblend ratio and CNFs prepared at optimal condition were smaller thantwo hundred nanometers. XRD and Raman spectra showed that the PP/PFblend treated at 600℃produced some graphite crystallite. But thegraphitization degree of CNFs treated at 900℃was still lower, and itbelonged to the range of amorphous carbon.Secondly, polymethyl methacrylate (PMMA) was used as thermallydecomposable polymer(TDP); and Polyacrylonitrile (PAN) as carbonprecursor polymer (CPP). CPP and TDP polymer blends were preparedthrough solution mixing. The blend fibers were obtained afterwet-spinning. Oxidization and carbonization were made to remove TDP.Effectes of spinning condition, draw ratio and carbonization condition on properties and structure of the resulted carbon nanofibers were discussedby means of SEM, TGA, FTIR, electrical conductivity test, Ramanspectra, etc. The results showed that porous carbon fibers obtained whenthe blending ratio of PAN/PMMA was 7/3 and superfine carbon fibersobtained when the blending ratio of PAN/PMMA was 3/7. The carbonnanofibers obtained in this work had good conductivity and it alsobelonged to the range of amorphous carbon.Finally, CNFs /epoxy resin composites were fabricated by usingultra-sonication method. Electrical conductivity, tensile strength, andthermal stability of the composites were studyed. The electrical resistivitywas decreased as the increase of carbon content. The composite showedan electrical resistivity of 10~4Ω·cm when the CNFs loading was 5 wt%.The tensile strength of them first increased and then decreased with theincreasing of CNFs content, and the composite with 2 wt% CNFs contentshowed higher tensile strength than others.更多还原