Co-based metal-organic framework with phosphonate and triazole structures for enhancing fire retardancy of epoxy resin

A phosphonate and triazole containing binary carboxylic acid ligand was synthesized via azide-alkyne "click" reaction, which was further coordinated with cobalt nodes to form metal-organic framework (MOF) containing two important fire retardant elements, phosphorus and nitrogen (PN-MOF). With the loading of 6 wt% PN-MOF in epoxy resin (EP), the peak heat release rate, average heat release rate, total heat release, and total smoke production of EP/PN-MOF composites dramatically decreased by 44.6%, 52.9%, 44.0% and 36.2%, respectively. Meanwhile, the limiting oxygen index increased from 24.3% to 29.8%. Thanks to the excellent catalytic activity of PN-MOF in carbonation and oxidation, the release of toxic gasses from the composites was significantly reduced, particularly, the production of CO was decreased by 48% in comparison with neat EP. In addition, the glass transition temperature and modulus of EP/PN-MOF composites were increased, suggesting a strong interfacial interaction between PN-MOF and EP matrix. Overall, this research provides an efficient strategy for the preparation of MOF-type flame retardant to simultaneously enhance the flame retardancy and physical properties of polymeric materials.