To further enhance the reinforcing effect of polyimide (PI) fibers on carbon nanotube polymer composites, in this work, networks of long chains of phosphate monoester (PMOEs) were grown on the surface of PI fibers, and silanized multiwalled carbon nanotubes (Si-MWCNTs) were dispersed into the phenolic resin (PR) matrix. Subsequently, these two interpenetrating networks were entangled tightly at the PI-PMOEs fiber paper/PR matrix by vacuum-assisted wet papermaking technology and impregnation and vacuum curing technology. A novel type of PI-PMOEs fiber-reinforced carbon nanotube polymer composite was prepared. Structural observation and analysis revealed that the fiber surface activity and roughness were improved, resulting in enhanced interfacial adhesion. The Si-MWCNTs at the interface play an anchoring role, which leads to a strong mechanical interlock between the PI-PMOEs fibers and the matrix. Therefore, the generation and propagation of cracks encountered greater resistance, and the mechanical properties of the composites were improved. Compared with the Si-MWCNTs/PR composite with tensile strength of 20.29 MPa and elongation at break of 0.1%, the tensile strength and elongation at break of 80PI-PMOEs/Si-MWCNTs/PR (the basis weight of paper is 40 wt.%) composite are increased to 91.22 MPa and 2.0%, respectively. In addition, a tightly connected fiber "large skeleton" was provided by the PI-PMOEs fiber paper with a uniform pore size distribution. The Si-MWCNTs network and the thermally degraded carbides of the matrix formed a "small skeleton" based on the "large skeleton", resulting in a complete and dense protective barrier layer. The volatilization of pyrolysis products (CO, small-molecule hydrocarbons, aromatic compounds, etc.) was restricted, and heat and mass transfer were suppressed. Finally, the composites exhibited excellent flame retardancy.

Graphical abstract

中文翻译：

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具有磷酸单酯网络的聚酰亚胺纤维的绿色制造，以增强碳纳米管聚合物复合材料：同时改善机械性能和阻燃性

为了进一步增强聚酰亚胺（PI）纤维对碳纳米管聚合物复合材料的增强效果，在这项工作中，在PI纤维的表面上生长了磷酸单酯（PMOEs）长链网络，并硅烷化了多壁碳纳米管（Si-MWCNTs） ）分散到酚醛树脂（PR）基质中。随后，通过真空辅助湿法造纸技术以及浸渍和真空固化技术，将这两个互穿网络紧密缠绕在PI-PMOEs纤维纸/ PR基质上。制备了新型的PI-PMOEs纤维增强碳纳米管聚合物复合材料。结构观察和分析表明，纤维的表面活性和粗糙度得到改善，导致界面粘合性增强。界面处的Si-MWCNT起到锚固作用，从而导致PI-PMOEs纤维与基质之间的牢固机械互锁。因此，裂纹的产生和传播遇到更大的阻力，并且复合材料的机械性能得到改善。与拉伸强度为20.29 MPa，断裂伸长率为0.1％的Si-MWCNTs / PR复合材料相比，80PI-PMOEs / Si-MWCNTs / PR的拉伸强度和断裂伸长率为40重量％。 ％）复合材料分别增加到91.22 MPa和2.0％。另外，PI-PMOEs纤维纸提供了紧密连接的纤维“大骨架”，且孔径分布均匀。Si-MWCNTs网络和基体的热降解碳化物在“大骨架”的基础上形成了“小骨架”，形成完整且致密的保护性隔离层。限制了热解产物（CO，小分子烃，芳族化合物等）的挥发，并抑制了传热和传质。最后，该复合材料表现出优异的阻燃性。

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