Preparation And Properties Of Polyimide Nanocomposites

The birth and development of nano-materials provide exciting opportunities andexpansive potential application for polymer nanocomposites. However, because of the largespecific surface area and high specific surface energy, nanoparticles are generallythermodynamic instable and readily aggregate to reach the level of the particles in micronwhich leads to losing of their special features and seriously limits its wide application.Polyimide(PI),as one of the most important high-performance polymer family,has beenwidely used in microelectronic and aerospace industries because of their good dielectricproperties, excellent mechanical properties, high glass transition temperature and outstandingthermal stability. In order to extensively improve the mechnical and thermal properties of PI,their modification with nanomaterials has become one of the focuses in recent years. And CNT,as one of the 1-D nanomaterials, are one of important candidates.In order to improve the dispersion and interaction between nanomaterials (CNT, ND) andmatrix, CNT were modified using concentrated HNO3. Fourier transform infrared spectroscope(FTIR), Scanning electronic microscope (SEM), X-ray diffraction (XRD), and thermalgravimetric analysis (TGA) were employed to charaeterize the functionalized CNT. The resultsindicated that–COOH groups were successfully introduced onto the surface of the CNT. Wehave functionalized nanodiamonds with epoxy groups by ring-opening reaction of epoxygroups with the carboxylic groups on ND surface. The rusults of FTIR, elemental analysis(EA), TGA and other characterizations proved that the epoxy groups were grafted onto thenanodiamond surface, and the ratio of grafted EP monomers is 19.25 wt%.In the processing of preparation of polyimide/carbon nanotubes (PI/CNT) composite films, wetake a novel method, namely, solid-state shear pulverization (S3P) processing. Firstly wesynthesized poly (amic acid) (PAA) by ODA (4,4′-oxydianiline) and PMDA (pyromelliticdianhydride), and precipitated it in water to obtain PAA powder. Then CNT were pulverized withPAA powder, ODA and BTDA (3,3',4,4'-benzophenonetetracarboxylic dianhydride) inhigh-shear processing, and the mixtures were stirred for 15 hours in solvent. Finally, PAA/CNTsolutions were cast and subsequently heated to 300oC for imidization to form PI/CNT nanocomposite films. The mechanical properties of the nanocomposites were determined, andthe films were examined by SEM, XRD, TGA, DMA. CNT were well dispersed as proved by themicrophotographs of SEM, and the tensile strength of the nanocomposites increased from82.20MPa (0 wt %) to 143.20MPa (5.0 wt %).The adding of CNT into polyimide matrix led toobvious improvement in the thermo stability and Tg of PI/CNT nanocomposites(increased to341oC from 303oC).