Fiber finishes for improving galvanic resistance of imide-based composites

Galvanic corrosion resistant carbon/bismaleimide (BMI) composites have been demonstrated through the use of reactive finishes to form coatings that isolate the carbon fibers from the BMI matrix. A family of novel reactive coupling agents was formulated into phenolic-based finishes that react with carbon fibers and the matrix resin during processing to form chemical bonds at the interface and in the interphase. Each fiber is coated uniformly with the phenolic finish before the BMI prepregging process. The finish serves to isolate the carbon fibers from the BMI matrix and interrupts the galvanic cell. Both static measurements on galvanic corrosion couples and dynamic electrochemical impedance spectroscopy measurements show that the finishes dramatically improve composite corrosion resistance. Flexural and short beam shear strengths show that BMI matrix composites with finished fibers are equivalent to those with unsized fibers. The mechanical data is supported by voltage contrast x-ray photoelectron spectroscopy (VC-XPS) measurements and SEM failure surface analyses which show that interfacial adhesion is superior in the finished composites. This approach has the potential to substantially improve galvanic corrosion resistance of the interface in BMI matrix composites by preventing the interfacial debonding thought to be responsible for the observed reaction acceleration. The reactive finish approach provides a cost-efficient means of improving galvanic corrosion resistance in composites with any BMI formulation.