Study On Preparation And Properties Of Polyimide/Graphite Anti-static Composite Film

Polyimide(PI)is a new type of special engineering plastics with good heat resistance,dielectric properties,corrosion resistance.It is one of the modified materials which the scientists are interested in.Polyimide has good insulation performance whose resistivity can reach 1015 orders of magnitude,the electron motion in the material is difficult,and the charge accumulation is easy.During the usage of space materials,the charge accumulation is very dangerous for equipment and will greatly affect the measurement precision of equipments.So the antistatic process on polyimide materials can widely broadened the application areas of polyimide materials.In this paper,graphite microchip was first prepared by ultrasounding and agitating expanded graphite,then PI/Graphite microchip composite films with 1-8wt% of inorganic content were prepared by in situ synthesized.4,4'-diaminodiphenyl ether(ODA)and pyromellitic dianhydride(PMDA)were used as raw materials,N,N-dimethylacetamide(DMAc)was used as solvent.Singlelayer and three-layer PI/graphite composite films were prepared using different methods of laying,And the films were analysised by a series of tests and characterizations.The Section morphology of PI composite films were characterized by scanning electron microscopy.Results show that the size of graphite is micro-scale,the thickness is nano-scale,which was agree with the requirements of the nano graphite microchip.When the content of graphite microchip is less,graphite microchip dispersed more evenly in the composite film,the distribution of graphite microchip is directional,the structure of three-layer composite film is clear.When the graphite microchip content is more,the disorder of the graphite microchip distribution increased with agglomeration,the pure film layer in themiddle of composite film was cut.FT-IR shows the absorption spectrum of the composite film is the same as the pure polyimide film,the characteristic peak is obvious.Amide carbonyl peak at 1650 cm-1 disappeared completely,showing that the introduction of graphite microchip and the ways of laying has no effect on imidization process.For the performance test of single-layer composite film,the mechanical properties of composite film decreased,and the thermal stability increased with the initial decomposition temperature,which reaching up to 600 oC.When the doping amount of the graphite microchip was 4 wt%,the percolation threshold was reached,the volume resistivity and surface resistivity can decrease to 108 orders of magnitude,which achieves the requirement of the semi-conductive composite film.As the mechanical strength of single layer composite film is smaller,and volume resistivity decrease with the introduction of the tiny pieces of graphite microchip,the film is easy to breakdown,which limits the possibility of practical application of composite film,three-layer composite film with pure film layer in the middle was prepared.For the three-layer composite films,the content of 4wt% is also the Percolation threshold,the surface resistivity was reduced to 108 orders of magnitude and the volume resistivity was 1011 orders of magnitude,this ensured the antistatic and also prevented the film to breakdown.The tensile strength of three-layer composite film in the percolation threshold was greater than single-layer composite films,the tensile strength was more than 90 MPa and the thermal stability was maintained with the initial decomposition temperature of 600 ?.