| In this thesis, graphene and polyimide composite film were chosen as the research object, the graphene impacting polyimide film in thermal, mechanical, electrical performance was analyzed specifically. Besides, during carbonization of polyimide composite film, the induction of graphene was also investigated.Firstly, Polypyromellitimide, Biphenyl polyimide, Ketone-anhydride polyimide were selected, to research factors including charging sequence, monomer ratio, reaction time, reaction temperature affecting their viscosity and curing temperature. On this basis,performance of the three kinds of polyimide film was studied. It is found that their thermal stability can reach 560 ℃ basically the same, but ketone-anhydride polyimide has higher carbonation ratio than the other two, and its tenacity is the best. At the same time, its optical properties and electrical insulativity are as well as mechanical property.Transmittance in visible light area is greater than 80%, the volume resistivity reaches to2.45×1014 Ω· m.Secondly, the graphite oxide was prepared by a modified Hummers method.Further ultrasound dispersed, freeze dried and high-temperature reduced, and the graphene was prepared. By Thermal Gravity Analysis, thermal decomposition of graphene oxide and graphene were studied before 800℃ to illustrate the rationality of high-temperature reduction. According to SEM, TEM and XRD analysis of graphene before and after reduction, it is proved that graphene keeps a good space fold structure after reduction, and the characteristic diffraction peak appears, above showed the degree of graphene reduction is higher.Then, the Graphene/Polyimide was synthesized by in-situ polymerization of BTDA and ODA. Using test methods such as XRD, FTIR and SEM, how the graphene dispersed in polyimide was studied. The results demonstrate that 1.0% of the graphene has the best dispersion; it can effectively prompt the production of polyimide grain formation and nucleation effect. Studies on Heat Tolerance find the heat-resistant temperature have an increase of 40 ℃, from pure polyimide’s 525 ℃ to 565 ℃ of0.5wt% RGO/PI. When the content of graphene reaches to 1.0%, the tensile strength has an enhancement of 92.7% rising to 501.3±3MPa, and the elongation has been increased by 175%. The transmission of light analysis reveals that the transmittance of composite film decreases significantly with the content of graphene adding. Conductive performance study shows that the composite film resistivity gradually reduces with increase of the graphene, and the resistance rate reaches to 4.0×107Ω·m(graphene content is 2.0wt%), it meets the anti-static requirement.Finally, the composite film was carbonized under different temperatures, and their morphology, structure and electrical, thermal performance were studied respectively. It is found that carbon membrane has more defects for pyrolytic reaction before 800 ℃,after 800 ℃, the structure of carbon film tends to be smooth. When the content of graphene is 1.0wt%, the inducing carbonization effect is significant. And, graphene makes the carbonization process accelerated. On the other hand, there are strong π-πoverlapping action between polyimide carbon film and graphene, because of graphene inducing polyimide carbon molecule orientation restructuring along the graphene surface, it easing carbonized shrinkage problem for internal stress. At the same time,the graphene/carbon film shows ductile fracture characteristics certain degree. The electrical resistivity of carbon film decreased with carbonization temperature and the content of graphene rising, and it can be up to 1.2×10-4Ω·m, the in-plane thermal conductivity also increases from the pure carbon film’ 0.81w/m· K to 10.51w/m· K. |
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