Metal-organic framework-derived bird's nest-like capsules for phosphorous small molecules towards flame retardant polyurea composites

The loading treatment of phosphorus flame retardants can mitigate their migration and plasticization effect. However, designing suitable carriers has remained a great challenge. Herein, two kinds of Co-based isomers, namely cobalt-cobalt layered double hydroxides (CoCo-LDH) and cobalt basic carbonate (CBC), were synthesized by employing ZIF-67 as a self-template, assemblied into two different nanostructures namely multi-yolk@shell CBC@CoCo-LDH (m-CBC@LDH) and solid CBC nanoparticles by facilely tuning the reaction time, which were employed as carriers, respectively. Subsequently, triphenyl phosphate (TPP)-loaded m-CBC@LDH (m-CBC-P@LDH) was prepared using TPP as the guest. The m-CBC@LDH with high specific surface area and hollow structure exhibited up to more than 30% of TPP loading. The peak of heat release rate and total heat release of polyurea composite blended with 5 wt% m-CBC-P@LDH reduced by 41.7% and 20.6% respectively, and the mechanical properties were less damaged. This work complements a feasible approach for preparation of metal -organic frameworks-derived flame retardant carriers.

Automated summary

The loading treatment of phosphorus flame retardants can be improved by designing suitable carriers. In this study, Co-based isomers (CoCo-LDH and CBC) were synthesized using ZIF-67 as a self-template and assembled into two different nanostructures (m-CBC@LDH and solid CBC nanoparticles). Triphenyl phosphate (TPP) was then loaded onto m-CBC@LDH, which exhibited a high TPP loading of over 30%. The polyurea composite blended with 5 wt% m-CBC-P@LDH showed a significant reduction in heat release rate and total heat release, indicating improved flame retardancy.