Study On MWNTs Surface Treatment And Mechanical Properties Of Modified PI Hybrid Films

Polyimide film, is a kind of Insulation material with superior properties. Inrecent years, with the development and application of high technology, the nanohybrid PI film is in urgent needed and become one of the hotspots in various field.Some research results show that zero dimensional inorganic nanoparticles （SiO₂,Al₂O₃, TiO₂, AlN） can improve the corona resistance of PI film in differentdegress, but with particle amount increasing, agglomeration would happen whichleading to decreasing of the hybrid membrane mechanic performance. Quasi one-dimensional carbon nanotube has many characteristics, such as high electricalconductivity, large length to diameter ratio. Using carbon nanotubes modifiedpolyimide film has the expectation which the corona resistance of hybridmembranes can be implemented under the small amount of doping carbonnanotubes. The PI film is mainly used in lapped insulation in electrical material,and certain requirements on the mechanical properties, while in the carbonnanotubes hybrid PI film the correlative research has been reported less.The PI film was modified by the MWNTs, and the mechanical and thermalproperties were studied in this article. The treatment process of the MWNTs wasidentified by the three-factor and three-level orthogonal design method L9（3）,and the different treatment process on mechanical properties of hybrid PI wasanalysed. The treatment process was confirmed as the following: the MWNTswere processed with mixed acid oxidation under6℃,6hours. A series ofMWNTs/PI hybrid film was prepared by in-situ polymerization and thermalimidization methods, the length to diameter ratio and doping amount of theMWNTs on the influence of mechanical properties and thermal stability ofMWNTs/PI hybrid film was analysised. The results indicated that the surface ofthe MWNTs has organic functional groups which are-OH and-COOH treated by mixed acid oxidation and Fenton/UV method. Those two methods can improvethe compatibility with organic pHase, and then increase the interfacial bondstrength of MWNTs and PI. When the content of MWNTs is less than1.1wt%,the L-MWNTs of large length to diameter ratio is more advantageous to enhancethe tensile strength of the hybrid film, up to118MPa,10.3%higher than that ofunmodified film; the S-MWNTs of less length to diameter ratio can provides awide range with0-1.72wt%of doping amount for the increase of the tensilestrength of the hybrid film. The elongation at break of the two kinds hybrid PIfilms will decrease when the MWNTs are added.When the MWNTs content ismore than1.8wt%, the elongation at break of hybrid film fells sharply, reducesthe toughness of hybrid films. The thermal stability of PI hybrid films wasimprove by introduction of the MWNTs, length to diameter ratio of MWNTshave little impact on improving thermal decomposition temperature of hybridfilm, the decomposition temperature of S film was625.86℃,6%higher thanthat of unmodified PI film.