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.