"静电纺丝-固态热拉伸"法制备高导热聚合物基纳米复合材料及机理研究

Researches and development on thermal conductivity polymeric composites have become one of the hot topics on functional composites. It is a scientific problem with importance to take account of highly thermal conductivity, low dielectric and high strength/toughness of thermal conductivity polymeric composites by structure/function integration design, and to further develop and improve the thermal conductive mechanism of the composites. In our present work, the novel method of "electrospun combining with solid hot stretch" is firstly proposed to fabricate the poly (p-phenylene-2,6-benzobisoxazole)/boron nitride nanotubes/polyimide (HMPBO/BNNTs/PI) nanocomposites with highly thermal conductivity, low dielectric and high strength/toughness. Herein, branched PI powder is employed as polymer matrix, BNNTs as base thermal conductive fillers and HMPBO short fibers as the reinforcements. Meanwhile, based on the random unit packaging models, classic Y. Agari Equation and finite element parameter modeling method, the corresponding thermal conductive model and empirical equation of the nanocomposites would be built, and the interrelation on "thermal conductive network structure-polymer matrix molecular chain movement-thermal conductivity" are systematically investigated by changing constant thermal field temperatures, and the corresponding thermal conductive mechanism of the HMPBO/BNNTs/PI nanocomposites would be further improved and developed. Researches above and the obtained results will provide a new method and theoretical foundation for designing and developing the novel thermal conductivity polymeric composites with highly thermal conductivity, low dielectric and high strength/toughness, and will guide the production and application of these thermal conductivity polymeric composites in the highly thermal conductive systems such as microelectronics, electronic information and electromagnetic shielding, etc.

聚合物基导热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。如何通过结构/功能一体化设计，研制兼具高导热、低介电且高强韧的聚合物基导热复合材料，完善和发展导热机理已成为目前亟需解决的技术难点和科学问题。本项目提出采用静电纺丝和固态热拉伸相结合的新方法，以支化聚酰亚胺(PI)为树脂基体，以氮化硼纳米管(BNNTs)为导热填料，以聚对苯撑苯并双噁唑(HMPBO)短纤维为增强体，制备兼具高导热、低介电且高强韧的HMPBO/BNNTs/PI纳米复合材料；基于随机单元堆积模型、经典Y. Agari方程和有限元参数建模法，建立复合材料的导热模型和经验方程；分析研究“导热网络结构-聚合物基体分子链运动-导热性能”的相互关系，完善和发展其导热机理，拟为高导热、低介电且高强韧聚合物基导热复合材料的设计和开发提供一种新方法和理论依据，并指导该类材料在微电子、电子信息和电子屏蔽等高导热系统中的生产和应用。

聚合物基导热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。设计制备兼具高导热、低介电且高强韧的聚合物基导热复合材料，完善和发展导热机理已成为目前亟需解决的技术难点和科学问题。本项目采用静电纺丝和固态热拉伸相结合的方法，以聚酰亚胺（PI）为树脂基体，氮化硼（BN）为导热填料，聚对苯撑苯并双噁唑（PBO）纤维为增强体，制备出了兼具高导热、低介电和高强韧的PI复合材料，研究“导热网络结构-基体聚合物分子链运动-导热性能”的相互关系，完善和发展了复合材料的导热机理。XPS、FTIR和TG等分析表明，POSS分子已成功接枝在BN和PBO纤维表面，POSS-g-BN的表面疏水性显著改善，POSS-g-PBO纤维表面亲水性提高，其PBO纤维表面变得更加粗糙，直径也有所增加；静电纺丝可以实现PAA纤维的定向排列，PAA纤维表面随着BN的引入出现有序排列的白色物，且随BN用量的增加而增多；PI复合材料的导热系数（λ）随BN用量的增加而增加。当BN用量为30 wt%时，导热系数为0.696 W/mK，约为纯PI（0.1741W/mK）的4倍多。复合材料的介电常数（ε）和介电损耗正切值（tanδ）均随BN用量的增加而增大。同等BN用量下，ε和tanδ随频率的增加呈下降趋势。当BN用量为30 wt%时，1MHz下PI复合材料的ε和tanδ分别为3.77和0.007。复合材料具有较好的热稳定性，且随BN用量的增加而升高。当BN用量为30 wt%时，PI复合材料的耐热指数为279oC，远高于纯PI的253oC；复合材料的λ实验值远小于并联模型和Maxwell模型上限值，但大于串联模型，Maxwell模型下限值和EMT模型理论值。本项目的研究可以为高导热、低介电且高强韧聚合物基导热复合材料的设计和开发提供一种新方法和理论依据，并指导该类材料在微电子、电子信息和电子屏蔽等高导热系统中的生产和应用。