基于多尺度结构设计的本征型高导热环氧树脂及其复合材料的制备和导热机理

Research and development on polymer matrix composites with high thermal conductivity and electrical insulation have become one of the hot topics in functional composites. It is a technologically difficult and scientific challenging to fabricate the corresponding polymeric composites with combined functionalities including high thermal conductivity, electrical insulation and excellent mechanical properties. In this project, the integration of intrinsically high thermal conductivity resin and continuous filler network was proposed to fabricate the above composites. Based on the multi-scale structure design, the intrinsic high thermal conductivity liquid crystal epoxy resin would be obtained by introducing ordered structure into the epoxy monomer and curing agent molecules, also supplemented by designing and regulating topological structure of cross-linked network for synthesized epoxy. Furthermore, the surface functionalized continuous phase boron nitride nanosheets-boron nitride (fBNNS-BN, which would be fabricated via the combining method of electrospinning and crystal self-assembly) thermally conductive fillers were synthesized and used to modify the liquid crystal epoxy resin, to realize the high thermal conductivity and high performance of epoxy matrix by adding relatively lower loading of fBNNS-BN fillers. In addition, the relationship of“thermally conductive channels-cross-linked network(ordered structure)-thermal conductivity” in the intrinsic high thermal conductivity liquid crystal epoxy resins will be revealed and the structure-performance relationship in the corresponding composites will be studied as well. Thermally conductive model and empirical equation would be proposed to further improve and develope the corresponding thermal conduction mechanism. Researches above and the obtained results would provide a new fabricating method and theoretical foundation for designing and developing the intrinsic high thermal conductivity epoxy resins and their composites. This would guide the production and application of such materials in thehighly thermally conductive fields such as utlra high voltage electrical apparatus and semiconductor components, etc.

高导热聚合物基复合材料的研究和开发已成为功能复合材料的研究热点之一。如何制备兼具高导热、高绝缘且力学性能优异的聚合物基复合材料已成为目前亟需解决的技术难点和科学问题。本项目提出采用本征型和填充型工艺相结合的方法，从多尺度结构设计出发，通过环氧单体和固化剂的分子设计引入有序结构，加以交联网络的拓扑结构设计调控制备本征型高导热液晶环氧树脂；采用表面改性氮化硼纳米片-氮化硼（fBNNS-BN，静电纺丝和晶体自组装相结合的方法制得）为导热填料对其进行掺杂改性，实现在较低fBNNS-BN填料用量下环氧的高导热和高性能化。研究本征型高导热液晶环氧及其复合材料“导热通路-交联网络（有序结构）-导热性能”的相互关系，建立导热模型和经验方程，完善和发展导热机理，为本征型高导热液晶环氧树脂及其复合材料的研发提供一种新方法和理论依据，并指导该类材料在特高压电气设备和半导体元器件等高导热系统中的生产和应用。

本项目通过环氧分子设计引入液晶有序结构，加以固化网络优化调控和导热填料掺杂制备本征高导热液晶环氧及其复合材料。主链型液晶环氧树脂（M-LCER）及氮化硼（BN）/M-LCER导热复合材料实现了M-LCER本征高导热及较低BN用量下BN/M-LCER导热复合材料的高导热性能。M-LCER保持向列相液晶特性，表现出优异的本体导热性能，导热系数（λ）和热扩散系数（α）分别为0.51 W/(m·K)和0.27 mm2/s，较通用双酚A环氧树脂（E-51）的本体λ（0.19 W/(m·K)）和α（0.12 mm2/s）分别提升了168.4%和125.0%。当BN用量为30 wt%时，BN/M-LCER导热复合材料的λ为1.02 W/(m·K)，为纯M-LCER基体λ的2倍，增幅和大小均远高于相同用量BN/E-51导热复合材料的λ（0.52 W/(m·K)）。BN液晶功能化改性（gBN）进一步提升相同填料用量下gBN/M-LCER导热复合材料的导热性能。当gBN用量为30 wt%时，gBN/M-LCER导热复合材料的λ和α分别达到1.12 W/(m·K)和0.90 mm2/s，为纯M-LCER基体λ和α的2.2和3.3倍，明显高于相同用量BN/M-LCER导热复合材料的λ和α（0.80 mm2/s）。侧链型液晶环氧树脂膜（S-LCEF）的垂直方向和平行方向的导热系数（λ⊥和λ∥）分别为0.33 W/(m·K)和1.25 W/(m·K)，远高于E-51的λ⊥（0.19 W/(m·K)）和λ∥（0.65 W/(m·K)）。S-LCEF的拉伸强度为10.6 MPa，经1次和4次修复后的拉伸强度分别保持在90.6%和61.3%。盘状液晶环氧树脂（D-LCER（DOPO-POSS））的λ⊥、λ∥、α⊥和α∥分别为0.35 W/(m·K)、1.37 W/(m·K)、0.21 mm2/s和0.83 mm2/s，远高于E-51。当DOPO-POSS的用量为10.0 wt%时，D-LCER（DOPO-POSS10.0）的阻燃性能最优，LOI提高至31.1、阻燃等级达到V-0级，远优于E-51和D-LCER。本项目研究可为本征型高导热液晶环氧及其复合材料的研发提供一种新方法和理论依据，并指导该类材料在特高压电气设备和半导体元器件等高导热系统中的生产和应用。