Short carbon fiber-reinforced PMR polyimide composites with improved thermo-oxidative and hygrothermal stabilities

A series of short carbon fiber-reinforced polyimide composites (SCF/PI) with different SCF loadings was prepared by thermal curing of B-staged molding powders, which were obtained by impregnating short carbon fibers with PMR monomer solution in ethyl alcohol, followed by thermally baking up to 220 degrees C. The B-staged molding powders possess good melt-flowing characteristics and processing properties. Experimental results demonstrated that the fully-cured SCF/PI composites exhibited high thermal stability with the glass transition temperatures determined by dynamic mechanical analysis (DMA) of 412-432 degrees C and the decomposition temperatures at 5% of weight loss in the range 497-512 degrees C. The SCF/PI composites also had good mechanical properties, which were affected by the SCF loading. The tensile strength and the flexural strength of SCF/PI composites increased as the SCF loadings increased and then decreased gradually. SCF-20/PI has the highest tensile strength of 101 MPa and SCF-10/PI gave the highest flexural strength of 154 MPa. The SCF/PI composites exhibited a great improvement in impact toughness in comparison with PMR-15. Despite the impact strength of SCF/PI being slightly decreased as the SCF loading was increased, it was still within the range of 15-23 J cm(-2). Furthermore, SCF/PI composites exhibited excellent thermal-oxidative and hygrothermal stabilities. The SCF/PI composites showed a weight loss of less than 6% after isothermal aging for 500 h at 320 degrees C in air. There was no significant difference in thermogravimetric analysis (TGA) and DMA curves for SCF-20/PI after hygrothermal treatment at 120 degrees C under 2 atm for 50 h.