Inspired by the tessellation of strawberry achenes on skin: Preparation of ZIF-67 derived multifunctional flame retardant through supramolecular assembly of cobalt alginate biopolymer in melamine-containing polyphosphazene skeleton

The preparation of derivatives using metal–organic framework (MOF) as template is often accompanied by the loss of pore structure. Inspired by the distribution of strawberry achenes on skin, restriction sites based on biopolymers were introduced to reduce the loss of mesoporous structure. Hexachlorocyclotriphosphazene (HCCP) and melamine (MEL) are used as monomers to synthesize dodecahedral polyphosphazene (PZS) on ZIF-67 (named as ZIF@PZM). The micropore structure of PZM allows hydrogen ions of alginic acid (AA) to pass through, thus etching the internal ZIF-67. The released cobalt ions are complexed to form cobalt alginate (CoA) biopolymer. At the same time, hydrogen-bonded supramolecular assembly of CoA with N-H of MEL occurs in PZM skeleton. Tessellation of CoA in PZM as a limiting site reduces the loss of mesoporous structure. As a result, a novel hollow dodecahedron flame retardant composed of two polymers is obtained (CoA/PZM). With the addition of 2.0 wt%, the total heat release (THR) and total smoke production (TSP) of EP/CoA/PZM composites decreased by 55.3% and 50.8%, respectively. The component of PZM significantly improved the UV resistance with a 98.3 % reduction in UV transmittance. CoA improved the compatibility between filler and EP matrix, enhancing mechanical properties. This work takes MOF as sacrificial templates, constructing multifunctional flame retardants with multiple elements and special nanostructures through the supramolecular assembly of biopolymers and PZM.