Preparation And Properties Of Carbon Nanofibers/Polyimide Composite Film

As a new type of nano-carbon material,carbon nanofibers(CNFs)not only have the size between conventional carbon fibers and carbon nanotubes,but also possess the characteristics of higher modulus,higher strength,higher conductivity,higher specific surface area,and better radiation shielding performance.However,fibrous materials usually exit some problems,which are easily agglomerated,difficult to disperse in solution,and it is difficult for the inorganic surface to combine with polymer materials.When CNFs is directly doped,the performance of composite materials can be ofen affected.Therefore,it is necessary to modify the surface of CNFs to produce etched grooves on the surface,increase surface roughness and functional groups,and refine the surface crystallites,which is conducive to enhance the degree of binding between CNFs and the polymer matrix.For this reason,the adverse effects on the properties of composite materials can be solved,which are casuse by the direct doping of CNFs.Polyimide(PI)is superior to general polymer merterials in the following aspects,such as mechanical property,thermal property,electrical property,chemical stability and anti-radiation performance.Based on its better comprehensive properties,PI is often used as an anti-radiation material in the aerospace field.However,the complex space environment has put forward higher requirements on the performance of traditional PI materials.In this paper,after being acidified the surface,CNFs is introduced into the polyamic acid by using the solution mixing method,and then the composite film of PI/CNFs-COOH is prepared,and CNFs can be mixed uniformly and well dispersed in the PI matrix,which has better mechanical property,electrical property,thermal property and anti-electron radiation performance.The main research contents are as follows:After the surface of CNFs was functionally modified by a simple and easy method,a series of benzene-type PI/CNFs-COOH composite films were prepared successfully.Firstly,the carboxylated carbon nanofibers were prepared by the treatment methods of purification and acidification,and then the structural changes of CNFs after surface modification was studied by using a variety of test methods,such as Fourier infrared spectrometer,X-ray element analyzer,transmission electron microscope,scanning electron microscope,etc.Secondly,After comparing the properties of benzene-type PI/CNFs-COOH composite films prepared by three different methods,and the solution mixing method was determined to be the relatively optimal method to prepare composite films.It showed that after acidification,the number of functional groups and the roughness of the surface of CNFs could increase,and the surface crystallites could be refined,which was conducive to the combination CNFs with PI matrix.The surface of PI/CNFs-COOH composite film was smooth,uniformly dispersed,and had the better performance.By changing the content of CNFs-COOH,a series of benzene-type PI/CNFs-COOH-(???)composite films were successfully prepared by using solution mixing method.The main properties of the composite film were studied by using a variety of test methods,such as Fourier infrared spectrometer,ultraviolet visible spectrometer,thermogravimetric analyzer,scanning electron microscopes,dielectric constant meters and high-resistance meters test.Before and after electron irradiation,the changes about the mechanical properties of the composite film were tested by using X-ray element analyzer and microcomputer electronic universal testing machine.It showed that some properties of PI/CNFs-COOH-?(with the CNFs-COOH content of 0.5%)and PI/CNFs-COOH-?(with the CNFs-COOH content of 0.7%)composite films were more excellent than those of benzene type PI film,such as the thermal stability,the flexibility property,the mechanical property and resistance to electron irradiation.By changing the content of CNFs-COOH,the electrical property of PI/CNFs-COOH composite film can be adjusted.By changing the content of CNFs-COOH,a series of biphenyl type PI /CNFs-COOH-n(n=1?6)composite films were successfully prepared by using solution mixing method.The main properties of the composite film were studied by using a variety of test methods,such as Fourier infrared spectrometer,ultraviolet visible spectrometer,thermogravimetric analyzer and dielectric constant meters.It showed that When the content of CNFs-COOH was 0.5% or 0.7%,some properties of PI/CNFs-COOH-3(with the CNFs-COOH content of 0.5%)and PI/CNFs-COOH-4(with the CNFs-COOH content of 0.7%)composite films were more excellent than those of biphenyl type PI film,such as the thermal stability,the flexibility property and the mechanical property.