Fabrication And Characterization Of Short Silicon Carbide Fiber-reinforced PMR Polyimide Composites

In situ polymerization of monomer reactants(PMR) polyimides are recognized as the state-of-the-art high temperature polymer matrix resins of polymer composites for servicing temperatures above 300℃.It was developed by NASA at 1960's.PMR based composite possess excellent mechanical properties at 300～320℃.However, continuous filament reinforced polyimide composite has some defect.Its high cost, short precision and not suitable for small but precise part are big blocks for industrial applications.Silicon carbide is ceramic material with good heat-conducting property, thermal shock resistance and chemical stability.Silicon carbide fiber is one of the new type fiber reinforce material.It has excellent performances,good tensile strength,high modulus and good thermostability(1200℃),the same as silicon carbide ceramic.The compressive property and impact resistance of silicon carbide fiber reinforced polymer composite are better than carbon fiber reinforced composite.Short fiber reinforced polyimide composites are easy to be processed for manufacturing of small and complicated high-temperature components or parts.In this study,a new method which used to fabricate a new type composite has been explored.Short silicon carbide fiber reinforced PMR type polyimide composites were prepared from short silicon carbide fiber and PMR type polyimide matrix resin,which derived from 4,4'-methylenediamine(MDA),diethyl ester of 3,3',4,4'-oxydiphthalic acid(ODPE),monoethyl ester of cis-5-norbornene-endo-2,3-dicarboxylic acid(NE). The rheological property of the PMR polyimide matrix resins was investigated.The composites were prepared from the fiber/B-stage PMR polyimide dry prepreg by thermolforming process molding.Different technique parameters had been tried,for example,the initial hot pressing temperature had tried 250～270℃and the maximal pressure had tried 2～4MPa.Then an optimized molding cycle was designed for the fabricating of SSCF/PI composites according to the rheological properties of the B-stage polyimide matrix resin,the optimal technique processing parameters was: preheat the flat-panel vulcanizing machine to 230℃,apply pressure gradually at 260～270℃,the maximum pressure was 3MPa.The final SSCF/PI composite with 2～3 mm width was obtained.An optimal control method temperature and pressure in the thermoforming process had been developed.Both mechanical and chemical properties of the composite fabricated by this proved technical process exhibited ideal performance.The morphology of the composite was observed by a microscope.The composites exhibited good thermal stability and mechanical properties.The decomposition temperature of the polyimide matrix resin and the composite were 440℃and 457℃, respectively.The glass transition temperature of PMR polyimide was 366℃as determined by DMA.The photomicrographs and SEM photos indicated a uniform dispersion of short silicon carbide fibers into both the B-stage dry prepreg and the composite.The mechanical properties with flexural strength and tensile strength of 81.355MPa and 116.280 MPa were obtained,increased by 18.2%and 19.1%, respectively.The short silicon carbide fiber-reinforced polyimide composites also exhibited high thermal stability and good mechanical properties.