Preparation of a Cobalt-Based Metal–Organic Framework and Its Application as a Synergistic Flame Retardant in Epoxy Resins

A cobalt-based organic framework (PNCo-MOF) was prepared using a phosphonate and triazole containing binary carboxylic acid ligand as an organic ligand, which coordinated with Co(NO3)2·6H2O. The potential of PNCo-MOF as a synergistic flame retardant was examined, and EP@APP/PNCo-MOF composites were formed by combining PNCo-MOF with ammonium polyphosphate (APP) into the epoxy (EP) matrix. The findings revealed that the EP composite with 2 wt % PNCo-MOF and 8 wt % APP (EP@8APP/2PNCo-MOF sample) displayed superior flame retardant, mechanical, and dielectric properties. In comparison to the neat EP, the peak heat release rate (PHRR), total heat release (THR), and total smoke production (TSP) of the EP@8APP/2PNCo-MOF sample decreased by 78.7%, 60.8%, and 49.0%, respectively. Furthermore, it achieved a V-0 rating in the UL-94 tests. Because of the synergistic effect of APP and PNCo-MOF, EP@8APP/2PNCo-MOF exhibited a higher LOI value and lower PHHR, THR, and TSP values than the EP composite containing 10 wt % APP (EP@10APP sample). Additionally, the addition of PNCo-MOF improved the dispersion of APP into the EP matrix, leading to enhanced mechanical properties of the EP composites. Overall, this study provided an effective approach for developing MOF-type synergistic flame retardants to improve the flame retardancy and physical properties of polymeric materials.