Organophosphorus-Functionalized Zirconium-Based Metal–Organic Framework Nanostructures for Improved Mechanical and Flame Retardant Polymer Nanocomposites

Metal–organic framework (MOF) nanostructures provide unique opportunities in the fabrication of multifunctional polymer nanocomposites. However, achieving both enhanced mechanical properties and fire safety using labile metal–organic framework (MOF) reinforced epoxy composites is usually challenging, calling for post-synthetic modification (PSM) of MOFs. In this study, we have synthesized an organophosphorus functionalized zirconium-based MOF, P-UiO-66 NH2 (P-MOF). This as-synthesized modified MOF when reinforced with epoxy showcased improved mechanical and flame retardancy performance. Interestingly, the addition of 1 wt % of P-MOF in epoxy resin increases the tensile and flexural strength by 13.8 and 28.8% compared to the neat epoxy system. Similarly, in comparison with the pure epoxy nanocomposites, the tensile and flexural modulus of P-MOF reinforced nanocomposites was increased by 21.9 and 27.8%, respectively. Further, the flame retardancy properties of the P-MOF composites exhibited decreasing peak heat release rate (pHRR), smoke production rate (SPR), and carbon monoxide emission (CO) by 30, 42, and 43%, respectively, in parallel to the neat epoxy reinforced nanocomposites. This multifunctional property is primarily attributed to the enriched synergistic effects of the P-MOF with epoxy matrix, which promoted increased char layers on the epoxy surface, thus creating a carbonaceous layer to restrain the flame growth.