The Preparation And Characterization Of Microcellular Polyimide Composite Foams For EMI Shielding

Polyimide is a kind of high-performance polymer with high strength and modulus,excellent properties of high/low service temperature, excellent radiation and solvent resistance.The preparation of high-performance microcellular composite foams is meaningful and gains anincreased interest among in academic and industrial fields. In this study, two foaming methods,i.e., solid-state foaming and water vapor induced phase separation (WVIPS), were applied tofabricate microcellular PEI foams. The results indicated that PI foams prepared by WVIPSpresented better cell morphology, wider cell size (3.2-12.7μm) and higher expansion ratio(2.3-4.4). In addition, the WVIPS method was suitable for prepare microcellular PI foams withhigh filler loading. Based on the research, the WVIPS method was selected here to producemicrocellular PEI/graphene and PEI/nickel (PEI/Ni) foams and the results were shown asfollows:(1) The reorientation and enrichment of graphene platelets in cells wall during the phaseseparation decreased the electrical conductivity percolation threshold, however increased thespecific EMI shielding efficiency and elevated the microwave absorption properties.(2) The gradient distribution of nickel particles in the foams resulted from the naturallydeposit of nickel particles among the process of phase separation, on one hands, resulted thedifference of surface electrical conductivity on the upper and lower surfaces, on the other hands,the enrichment of nickel particles on the lower surface could endow the microcellularPEI/nickel composite foams excellent EMI shielding property.(3) The as prepared microcellular PEI/graphene and PEI/nickel composite foams allexhibit good mechanical properties, and the addition of fillers could enhance the Young’smodulus obviously.