Green and mild approach for carbon fibers recycling from honeycomb sandwich thermoset composite wastes

Abstract Cross‐linked bismaleimide (BMI) resin is a high‐performance thermoset resin that cannot be remelted and reshaped. Therefore, carbon‐fiber‐reinforced BMI resin (CF/BMI) composites are difficult to recycle. In this study, a green chemical method was employed to recycle aerospace honeycomb sandwich CF/BMI composite structure wastes under mild conditions. The material was first cut into a specific shape, followed by treatment in dichloromethane to separate out the CF/BMI composite laminate, and finally, the laminate was degraded in diethylenetriamine. The BMI polymer was removed from the carbon fiber surface. The degradation degree of the BMI was nearly 100 wt%, and clean carbon fibers with good mechanical properties were recovered. A possible degradation mechanism for the CF/BMI composites was proposed. Moreover, the degradation liquid products were used directly as curing agents for epoxy resin to fabricate new resin materials. Thus, the recyclability of complex structure composite wastes was maximized to achieve minimum waste generation. Highlights A mild method was developed for recycling sandwich‐structured composites. The composite was completely degraded (~100 wt%), recycling high‐value CF. A degradation mechanism of the thermoset composite was proposed. Degradation liquid was reused directly with EP to fabricate new materials. A green recycling process for the composites was established.