Preparation And Properties Of Graphene Modified Polyimide Nanocomposites

As one of the most excellent polymer materials,polyimide is widely used in aerospace,microelectronics and other fields due to its high thermal stability and outstanding mechanical properties.With the rapid development of science and technology,electronic devices tend to be lighter and smaller and the traditional polyimide can not meet the needs of modern society due to the lower dielectric constant.Therefore,the modification of polyimide to improve its dielectric properties has attracted the attention of many researchers.Graphene is an emerging carbon nanomaterial formed by sp2 hybridization of carbon atoms and has received extensive attention since its discovery.Its special and stable crystal structure gives graphene many unique properties,such as electrical properties,thermal properties,mechanical properties,etc.Thus,the graphene is often used as fillers to add to polymers to improve its comprehensive performance.In this paper,graphene is used as a modified component to prepare polyimide composite materials with high dielectric.The primary problem in the preparation of graphene/polyimide films is to solve the problem of dispersion of graphene in organic solvents and polyimide matrices.Therefore,a novel reducing agent with surface active function,hydroxypropyl hydrazine,was used to reduce graphene and the graphene/polyimide composite films were prepared by in-situ polymerization.The main contents of this paper can be sum-marized as follows:(1)A new reducing agent,hydroxypropyl hydrazine,was prepared and used to reduce graphene oxide for comparison with hydrazine hydrate as a reducing agent.We characterized by infrared spectroscopy(FT-IR),thermal stability(Tg),scanning electron microscopy(SEM)and X-ray diffraction(XRD),etc.The results showed that hydroxypropyl hydrazine was an effective reducing agent,the wrinkles of the prepared graphene were obvious,and the solubility in some organic solvents was improved.(2)Different content of graphene/polyimide composite films were prepared.During the preparation,0.5 wt%to 2 wt%of graphene oxide was added,and then reduced with hydroxypropyl hydrazine and hydrazine hydrate to finally obtain graphene/polyimide composite films(HPH-rGO/PI、HH-rGO/PI).The results showed that the dielectric constant of the obtained HPH-rGO/PI and HHrGO/PI composites at 50 Hz were about 30 and 13.5,and the dielectric loss was only about 0.38 and 0.14,respectively.The tensile strength was also significantly increased to 161MPa and 152 MPa.The SEM and TEM images also showed that graphene was well dispersed in the polyimide matrix and no significant agglomeration was observed.(3)The same content of graphene/polyimide composite films were compared to observe the regularity of the change.The results showed that hydroxypropyl group could effectively inhibit the π-π agglomeration of graphene during the reduction of graphene which contributes to the uniform dispersion of graphene in the polyamic acid under the same content.Therefore,the orientation polarization of graphene was enhanced,so that the dielectric constant of HPHrGO/PI composites was improved to different degrees compared with other composite materials and as the content of graphene increased,it gradually increased.A high dielectric constant of 30 was obtained,which was 10 times that of the pure PI film,4.5 times that of the 2.0GO/PI and 2.2 times that of the 2.0HH-rGO/PI.Moreover,the addition of graphene had no obvious influence on the thermal stability of the three composites.Thermal decomposition temperature of the composites remained at around 560℃ and the residual carbon rate at high temperature was maintained above 60%.