Growing metal–organic framework nanoparticles on short carbon fibers to improve flame retardancy, smoke suppression and mechanical properties of the flame retardant epoxy composites

The bimetallic metal–organic framework (CoZn-ZIF) particles of flower bulbs, were grown onto short carbon fibers (SCFs) through an in-situ growth method to prepare CoZn-ZIF@ SCFs. The flame retardant intumescent epoxy resin (EP) composites, were fabricated with CoZn-ZIF@SCFs and ammonium polyphosphate (APP). The limiting oxygen index value of 1wt%CoZn-ZIF@SCFs/4wt%APP/EP composite reached 28.9%, and V-0 rating in UL-94 was attained. Meanwhile, the peak of heat release rate and total heat release was reduced 57.6% and 30.4%, compared with pristine epoxy resin. The analysis of pyrolysis gases and residual char, showed that the improvement in flame retardancy and smoke suppression was due to the catalytic carbonization effect of CoZn-ZIF, along with the strengthening action of the residual layer by SCFs, which led to the generation of more residual char and made it more stable. The improvement in mechanical properties of the flame retardant composite, was due to the reinforcement effects of CoZn-ZIF@SCFs, and its action of interfacial adjustment. This research solved the contradiction between the flame retardancy and mechanical properties of epoxy resin, and proposed a new method to prepare flame-retardant epoxy resin with high performance. Graphical abstract