Preparation And Properties Of High Temperature Conductive Shape Memory Polyimide Materials

Shape memory polyimide(SMPI)combines shape memory properties with polyimide's advantages of extreme high and low temperature resistance,high mechanical strength and space irradiation resistance.The material endows an abroad prospect,being involved in intelligent application domain of expandable structures,intelligent jet engine,variable satellite ailerons and so on.Nevertheless,the driving method of SMPI gives priority to the direct thermally driven,having brought many inconveniences in remote driver or practical applications being incapable of providing a direct heat source,making for that electrically driven SMPI has become one of the solutions.Furthermore,SMPI equips itself with electromagnetic shielding efficiency as shielding material.And this SMPI is suitable for high temperature and other harsh environment keeping abreast of intelligence field to reduce or eliminate electromagnetic radiation damage,gaining great commercial value in the area of engineering application.First,basing on the connection between structure and high temperature property of polyimide,a two-step method is used to obtain a polyimide matrix by dehydrate and condensation of anhydride and amine monomers containing aromatic structure and a fluorine-containing functional group.A high-temperature conductive shape memory polyimide composite on account of the characteristics of relatively simple film formation technology and controllability is successfully produced with that.The material is expected to implement electro-activated shape memory effect(EASME)as well as be identified as an electromagnetic shielding material.A kind of SMPI prepared with 6-FODA and BPDA as substrate and carbon fiber as functional materials are determined by taking morphology,glass transition temperature(T_g),HASME,EASME and film formation properties of SMPI/C composite materials as evidence.The electrically driven shape memory polyimide composites(EASMPI)is prepared by regulating the ratio of grinding carbon fiber(GCF)and SMPI matrix.And detailed performance characterization of EASMPI is carried out.The results show that EASMPI with a T_g higher than 300~oC have good electrical conductivity and efficient energy transfer efficiency,making for successful accomplishment of EASME at 15.87 V supply.The measured value of the recovery stress that are critical to the output efficiency of the shape memory material is 40.1 MPa,being obviously superior than those of other SMPs.The critical factor to the achievement of EASME consists in the continuous conductive path formed by GCF in the matrix and the good compatibility between fillers and the matrix.Electromagnetic shielding shape memory polyimide composites(EMSMPI)is prepared by mixing different ratios of carbon black and carbon fiber into SMPI matrix,the properties of which are characterized in detail.The results indicate that the shielding performance of EMSMPI material can reach 24.44 dB,satisfying the commercial shielding requirement(20 dB)at the lower concentration of conductive filler.Meanwhile,EMSMPI can be used as a shielding material with reusability in high temperature of330°C,with excellent shape memory effect and thermomechanical properties.The results of dynamic mechanical analysis manifest that the doping amount of carbon material is proportional to the T_g of SMPI/C material,but it could damage the structure of material and adversely affects its shape memory performance.The conductivity of SMPI/C material increases with the carbon content,being positively correlated with their electromagnetic shielding properties in consort with the thickness of material.The shielding mechanism of the material is mainly absorption attenuation based.So,the regulation of carbon filler concentration is the crucial factor determining the performance of SMPI/C.