碳纳米纤维增强聚酰亚胺复合气凝胶的合成与性能

Synthesis and properties of carbon nanofiber reinforced polyimide composite aerogels

以4,4′-二氨基二苯醚(ODA)、均苯四甲酸二酐(PMDA)为单体,酸化碳纳米纤维(a-CNF)为增强材料,采用溶胶-凝胶方式成型,运用冷冻干燥技术制备PI复合气凝胶。对复合气凝胶的形貌、隔热、吸波以及压缩性能等进行表征分析。研究结果表明:随着a-CNF含量的增加,PI复合气凝胶的收缩率从45.52%降至35.32%,密度也随之从0.084 g/cm^(3)降至0.069 g/cm^(3),气凝胶孔洞分布呈增大增宽趋势。a-CNF的引入有效抑制了PI复合气凝胶的收缩率,热导率降低;整个体系的导电损耗增加,同时由于气凝胶的多孔结构提供了较好的阻抗匹配,使得PI复合气凝胶的反射损耗(RL)在8.3 GHz达到-9.7 dB。加入质量分数为15%的CNF/PI复合气凝胶压缩强度和压缩模量分别是纯PI气凝胶的近1.5倍和2倍。

4,4′-diaminodiphenyl ether(ODA)and pyromellitic dianhydride(PMDA)were used as monomers.Carbon nanofiber(CNF)was used as the reinforcing agent.CNF reinforced polyimide(PI)composite aerogels were prepared with acidified CNF(a-CNF)via sol-gel process followed by freeze-drying technology.The morphologies,thermal insulation,microwave absorption as well as compression properties of PI composite aerogels were characterized.The results show that the volume of PI composite aerogels is shrunk from 45.52%to 35.32%,and the density is decreased from 0.084 g/cm^(3) to 0.069 g/cm^(3) with the increase of a-CNF content.The composite aerogels exhibit bigger pore sizes and wider pore size distribution after the introduction of a-CNF as well.CNF in PI matrix play roles for reducing the shrinkage of PI composite aerogels,thereby the thermal conductivity is reduced.Additionally,the reflection loss(RL)of PI composite aerogel with 15%(mass fraction)of a-CNF(15%CNF/PI)reaches-9.7 dB at 8.3 GHz.This is due to the fact that the introduction of CNF induced the conduction loss and the porous structure of aerogels provides better impedance matching.The compressive strength and modulus of PI composite aerogels with 15%of a-CNF content are increased by approximately 1.5 times and 2 times compared with pure PI aerogel,respectively.