Preparation and characterization of graphitized polyimide film/epoxy resin composites with high thermal conductivities
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摘要: 将环氧树脂(EP)分别涂敷于聚酰亚胺石墨带(GPTs)和聚酰亚胺石墨膜(GPFs),通过真空热压成型与分别采用堆叠和叠层方法制备得到GPTs/EP复合材料和GPFs/EP复合材料。借助 XRD、SEM和PLM等手段对GPF及其环氧树脂基复合材料的晶体结构、形貌和光学织构进行表征,并研究GPF的体积分数和尺寸对其复合材料导热性能的影响。结果表明,相比于GPFs/EP复合材料,GPTs/EP复合材料的导热性能在不同方向显示出较大波动,其热导率和热扩散系数总体上随GPF体积分数的增加而增大,GPF体积分数为80%时热导率为453~615 W (m·K)−1。而对应的 80 % GPFs/EP复合材料热导率稳定可达894 W (m·K)−1,并具有高取向的“三明治”结构。但在平行于热压方向上两类复合材料热导率都很低,GPF体积分数为80%时,GPTs/EP复合材料和GPFs/EP复合材料的热导率分别为1.82 W (m·K)−1和1.15 W (m·K)−1。Abstract: Graphitized polyimide films (GPFs) and tapes (GPTs) were coated with epoxy resin (EP), and their EP composites were prepared by hot-pressing the laminated GPFs and stacked GPTs. The crystal structure, morphology and optical texture of the GPFs and GPTs as well as their EP composites were characterized by X-ray diffraction, scanning electron microscopy and polarized light microscopy. The effects of volume fraction and the dimensions of the GPFs and GPTs on the thermal conductivity of their composites were investigated. The thermal conductivity and thermal diffusion coefficient of GPT/EP composites increased with GPT volume fraction. The thermal conductivity in different locations perpendicular to the hot-pressing direction of a GPT/EP composite stacked with 80% GPTs varied between 453 W (m·K)−1 to 615 W (m·K)−1 due to the gap between the GPTs. The GPF/EP composite laminated with 80% GPF has a highly oriented sandwich structure, which has an in-plane thermal conductivity of 894 W (m·K)−1. However, the thermal conductivities of GPT/EP and GPF/EP composites with 80% GPTs or GPFs along the hot-pressing direction were 1.82 and 1.15 W (m·K)−1, respectively. The obvious difference in the thermal conductivities perpendicular and parallel to the hot-pressing direction confirms that the two composites are highly anisotropic.
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图 8 在垂直于热压方向不同体积含量(a)GPT/EP复合材料室温热扩散系数和(b)80 vol.%GPF/EP复合材料的室温热扩散系数随不同切割角度的变化
Figure 8. Thermal diffusivity perpendicular to the hot-pressing direction of (a) GPT/EP composites with different GPT volume fractions and (b) 80% GPF/EP composites at room temperature varying with sample cutting angles, respectively.
表 1 不同体积分数的GPT/EP复合材料与80% GPF/EP复合材料的密度和比热容
Table 1. Bulk density and specific heat capacity of GPT/EP composites with various volume fractions of GPT as well as GPF/EP composite with 80% GPF.
GPT/EP composites GPF/EP composites Vol.(%) 24 36 45 54 65 80 80 ρ(g cm−3) 1.15 1.25 1.30 1.35 1.41 1.49 1.49 C (J/(g·K)) 1.59 1.43 1.35 1.28 1.20 1.10 1.10 ρ×C(J (K·cm−3)) 1.83 1.79 1.76 1.73 1.69 1.64 1.64 -
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