Controlling degradation and recycling of carbon fiber reinforced bismaleimide resin composites via selective cleavage of imide bonds

Carbon fiber reinforced bismaleimide resin (CF/BMI) composites are widely used in aerospace field due to their high thermal stability, chemical resistance and excellent mechanical properties. With the large-scale application of CF/BMI composites, it is inevitable to produce a lot of solid wastes, which have a serious impact on the environment, so people have to recycle waste CF/BMI composites. In view of the physical and chemical properties of BMI resin, we developed a green and friendly chemical recovery method of CF/BMI composites by selectively breaking imide bonds for controlled chemical degradation of BMI resin. In 5 wt% NaOH/H2O reaction system, the controlled chemical degradation of CF/BMI composites can be realized by selective cleavage of imide bonds, and the 4,4'-Diaminodiphenyl methane (DDM) and 2,2',2 '',2'''-((methylenebis(4,1-phenylene))bis(azanetriyl))tetrasuccinic acid (MBTA) can be recovered, and the carbon fiber (CF) can be recycled at the same time. Under the optimal reaction conditions, the yields of DDM and MBTA reached 6.7 wt% and 27.9 wt% at 180 degrees C for 8 h, respectively. Meanwhile, CF in CF/BMI composites can be completely recovered, and the tensile strength of recovered carbon fiber (rCF) is about 97.6% of that of virgin carbon fiber (vCF). This work provides a very promising strategy for the recycling of CF/BMI composites. The high value-added CF and chemicals (DDM and MBTA) can be recovered by controlled degradation of CF/BMI composites via selective cleavage of imide bonds.