液晶聚合物/氮化硼复合材料有序取向调控及其导热行为研究

The development of high thermal conductive polymer composites provides an effective route to solve the problem of heat accumulation faced by modern industry. However, due to the low thermal conductivity of the matrix, and lack of effective controllable dispersion method of the fillers, thermal conductivity of thermoplastic polymer composites is far from satisfactory. Therefore, this project intends to prepare high thermal conductive polymer composite with excellent mechanical property based on thermoplastic liquid crystal polyester (LCP) and hexagonal boron nitride, via fused deposition modeling 3D printing. Through regulating printing process, aligned liquid crystal oriented domains and ordered hexagonal boron nitride arrangement is expected to be obtained in the composite induced by the shear and extensional flow fields, which contribute to the construction of high efficient liquid crystal oriented thermal conduction chain and boron nitride thermal conduction path. The synergistic orientation behavior and internal interaction mechanism of the LCP molecules / boron nitride flakes controlled by 3D printing is devoted to be investigated. The effect of synergistic orientation behavior of the composites on the thermal conductivity will be explained. The thermal conduction mechanism model of composites will be established on the basis of the bi-continuous effectively thermal conducive path formed from oriented LCP molecules and boron nitride flakes. This research is expected to provide a theoretical basis for the preparation of high thermal conductive polymer composites.

聚合物基高导热复合材料的研究和发展为现代工业界面临的热堆积问题提供了有效的解决方案。然而，目前热塑性聚合物基导热复合材料，由于存在本征导热性能差、对填充粒子缺乏有效的可控分散手段等问题，其导热能力无法满足产业发展需求。基于此，本项目拟以热塑性液晶聚酯(LCP)为基材，以六方氮化硼为填料，利用熔融沉积3D打印技术，调控成型过程因素，实现对复合材料中液晶分子的诱导取向和氮化硼的定向控制，协同构建高效液晶有序取向导热链和片状氮化硼导热通路，获得具有优异力学性能的高导热LCP复合材料。分别研究熔融沉积过程对液晶分子的诱导取向机制和对氮化硼的定向控制机理，揭示液晶分子与氮化硼在剪切牵引作用下的协同取向行为及其内在关联；阐明复合材料体系中基材和填料双有序导热链路结构对导热性能的影响规律；构建液晶分子/氮化硼协同取向-导热链路结构-导热行为的逐级对应关系模型。为制备聚合物基导热复合材料提供理论基础。

聚合物基导热复合材料广泛应用于化工传热、新能源散热以及LED照明等领域。目前热塑性聚合物基导热复合材料，由于存在本征导热性能差、对填充粒子缺乏有效的可控分散手段等问题，其导热能力无法满足产业发展需求。本项目以液晶聚酯（LCP）为基体材料，不同片径的氮化硼（BN）为导热填料，通过双螺杆挤出进行熔融共混，制备了适合3D打印熔融沉积的线型材料，并通过3D打印方法制备LCP导热复合材料，研究了传统螺杆挤出注塑与3D打印熔融沉积成型制备LCP复合材料的导热性能和取向行为差异。通过偏光显微镜、扫描电镜以及二维广角X射线衍射方法对LCP及其复合材料在不同加工流程阶段的取向行为，比较和分析了不同粒径和添加量BN在LCP基材中的取向状态。大片径BN通过熔融沉积呈现出较高的取向度，然而BN的加入尤其是小片径BN的加入一定程度上影响了LCP本体液晶分子的有序取向。纯LCP基材通过3D打印熔融挤出后可以获取较高的取向度，在3D打印的块体材料中，其取向方向上的导热系数可达到0.74 W m-1 K-1, 在填充20%片径为50um的BN时，3D打印的块体复合材料导热系数可达到1.77 W m-1 K-1。