高导热CNT/PVA纳米纤维膜制备与研究

PREPARATION AND RESEARCH OF HIGHLY THERMAL CONDUCTIVE CNT/PVA NANOFIBROUS FILM

蒋文龙

11849251

硕士

材料工程领域工程

祝渊

2020-05-28

2020-07-20

哈尔滨工业大学

深圳

随着微电子工业的不断发展，电路板热流密度不断上升，现有的导热、散热材料已跟不上电子行业的发展脚步，电子元器件的热管理成为研究热点。由于金属基、陶瓷基、碳基导热材料存在着耐蚀性能差、绝缘性能差、抗冲击能力较差等缺陷，所以具有体积小、质量轻、可变形能力强、绝缘性能好以及高耐蚀性的聚合物基导热材料成为研究的重点。但聚合物材料本征热导率较低，目前主要通过添加高导热填料来提高其导热率。制备出具有优异性能的聚合物基导热材料是解决高集成电子元器件散热问题的关键。本文选择使用静电纺丝技术制备碳纳米管（CNT）/聚乙烯醇（PVA）纳米纤维薄膜，并通过实现PVA高分子链、高导热填料CNT及薄膜内纤维三个尺度的结构取向排列来制备具有高导热率的CNT/PVA纳米纤维膜。针对PVA高分子链解缠取向，本文研究了超声处理、机械搅拌处理及剪切挤出处理等前处理方式对于纤维内PVA大分子链缠结解缠结的效果。分析二维广角X射线衍射仪（Two-dimensional Wide-angle X-ray Diffdiffraction，2D WAXD）的表征结果发现超声前处理可以有效地使PVA大分子链解缠结，便于其在后续制备过程中被拉伸伸直、取向。针对复合纤维内导热填料CNT的取向，本文首先通过既添加碳纳米管水分散剂又进行超声辅助处理的方式改善了CNT在水中的分散稳定性，制得CNT均匀分散的CNT/PVA复合纺丝液。观察CNT在复合纤维内的排列情况发现，经过有效的分散处理，CNT在PVA纤维内部沿纤维轴向具有很好的取向。在研究不同长径比的CNT在复合纤维内部排列情况时发现长径比更小的纤维能够更好的在纤维内部取向。进一步比较CNT浓度对于复合纤维薄膜热导率的影响时发现在CNT浓度为8 wt.%时，复合纤维薄膜热导率最优达2.59 W/(m·K)，而未添加CNT的纯PVA静电纺丝薄膜的热导率仅为0.7 W/(m·K)。针对薄膜内复合纤维的取向，本文改进了纤维的接收装置。最终通过笼状转子制得具有高取向度的纤维薄膜。随着纤维取向度增加，纤维薄膜热导率随之增至3.17 W/(m·K)，较滚筒收集纤维薄膜的热导率高出23%。为进一步提高复合纤维薄膜的热导率，本文通过热拉伸处理进一步提高复合纤维薄膜内大分子链、填料、纤维的排列取向性。在比较同一CNT浓度不同热拉伸倍数对复合纤维薄膜热导率的影响时发现热拉伸能有效提高薄膜热导率。在热拉伸倍数为8倍时，纤维薄膜热导率可达7.79 W/(m·K)，较未热拉伸时高出约150%。在比较不同CNT浓度样品在同一热拉伸倍数（8倍）下的热导率变化时发现，各个浓度样品受热拉伸增益效果与其未拉伸时的状态有关，但普遍表现为热导率的上升。原始排列较好，导热填料添加适中的样品受到热拉伸的增益效果更为明显。

With the continuous development of microelectronics industry, the heat flux of circuit board is rising continuously. The existing thermal conductive and diffusive materials are unable to keep pace with the development of the electronic industry. The thermal management of electronic components has become a research hotspot. The traditional metal-based, ceramic-based and carbon-based thermal conductive materials have the disadvantages of poor corrosion resistance, poor insulation performance and poor impact resistance. Therefore, the polymer-based thermal conductive materials with small size, light weight, strong deformability, good insulation performance and high corrosion resistance have become the focus of research. However, the intrinsic thermal conductivity of polymer materials is low, and the thermal conductivity is mainly enhanced by adding highly thermal conductive fillers. The preparation of polymer-based thermal conductive materials with excellent performance is the key to solving the heat diffusion problem of highly integrated electronic components. In this paper, we used electrospinning technology to prepare carbon nanotube (CNT)/polyvinyl alcohol (PVA) nanofibrous film. We achieved the multi-level ordered structure including aligning PVA polymer chains, highly thermal conductive fillers (CNT) and nanofibers to prepare CNT/PVA nanofibrous film with high thermal conductivity.For PVA polymer chain’s disentanglement and orientation, we researched the effects of the ultrasonic treatment, the mechanical stirring treatment and the shear extrusion treatment on the disentangling of PVA macromolecular chains in fiber. By analyzing the characterization results of the two-dimensional wide-angle X-ray diffraction (2D WAXD), we found that the PVA macromolecular chains could be effectively disentangled by the ultrasonic treatment. So the PVA macromolecular chains could be stretched to be straight and orient in the subsequent preparation process.For the orientation degree of CNT as a thermal conductive filler in the composite fiber, we firstly improved its dispersion stability in water by adding water dispersing agent of carbon nanotubes and ultrasound-assisted treatment. We finally obtained CNT/PVA composite spinning solution with uniform dispersion of CNT. When observing the arrangement of CNT in the composite fiber, it was found that after effective dispersion treatment, CNT had a high orientation degree in the axial direction within the PVA fiber. When studying the arrangement of CNT with different length-diameter ratio in the composite fiber, it was found that the CNT with smaller length-diameter ratio had higher orientation degree in the fiber. Further, comparing the thermal conductivity of composite films with different CNT contents, we found that when the CNT content was 8 wt.%, the thermal conductivity of CNT/PVA composite films reached the optimal value of 2.59 W/(m·K), while the thermal conductivity of pure PVA electrospun films without CNT was only 0.7 W/(m·K).For the orientation of the composite fiber in the film, we improved the fiber collecting device. We finally prepared the film with highly oriented fibers by using the cage rotor. With the increase of the fiber’s orientation degree, the thermal conductivity of the film increased to 3.17 W/(m·K), which was 23% higher than that of film collected by the drum. Further, in order to enhance the thermal conductivity of the CNT/PVA composite film, we improved the orientation degree of the macromolecular chains, fillers and fibers in the film by hot stretch treatment. When comparing the effects of the same CNT concentration and different hot stretch ratios on the thermal conductivity of the CNT/PVA composite film, it was found that hot stretch could effectively improve the thermal conductivity of the film. When the hot stretch ratio was 8 times, the thermal conductivity of the film could reach 7.79 W/(m·K), which was about 150% higher than that of the non-hot stretch ratio. When comparing the thermal conductivity of samples with different CNT contents under the same hot stretch ratio (8 times), it was found that the thermal conductivity generally increased. We thought the effect of hot stretch on the samples with various CNT contents was related to the state when they were not stretched. The sample with good original arrangement and moderate thermal conductive fillers got more benefits when subjected to the hot stretch.

静电纺丝 CNT/PVA纳米纤维薄膜 高导热率 多尺度取向

electrostatic spinning CNT/PVA nanofibrous film high thermal conductivity multi-level orderness

中文

联合培养

南方科技大学

蒋文龙. 高导热CNT/PVA纳米纤维膜制备与研究[D]. 深圳. 哈尔滨工业大学,2020.