Strengthen flame retardancy of epoxy thermoset by montmorillonite particles adhering phosphorus‐containing fragments

Bio-Inspired Iron-Loaded Polydopamine Functionalized Montmorillonite as an Environmentally Friendly Flame Retardant for Epoxy Resin

As an important thermosetting material, flame-retardant epoxy resin has various applications in the aerospace, chemical, and electronics industry, and other fields. However, the flame retardancy of epoxy resins is often improved at the expense of mechanical performance. The contradiction between flame retardancy and mechanical properties seriously impedes the practical applications of epoxy resin (EP). Herein, iron-loaded polydopamine functionalized montmorillonite (D-Mt-Fe³⁺), which was prepared by dopamine, iron chloride and montmorillonite in an aqueous solution, was introduced to prepare iron-loaded polydopamine functionalized montmorillonite/epoxy resin composites (D-Mt-Fe³⁺/EP). As expected, D-Mt-Fe³⁺/EP-10 with 10 phr of D-Mt-Fe³⁺ passed the UL-94 V-0 rating, achieved a limiting oxygen index (LOI) value of 31.0% and reduced the smoke production rate (SPR) and total smoke production (TSP), indicating that the introduction of D-Mt-Fe³⁺ could endow EP with satisfactory flame retardancy through the radical scavenging function of dopamine in the gas phase and the catalytic charring effect of iron ions, respectively. Encouragingly, the mechanical property was also enhanced with the flexural strength increased by 25.5%. This work provided an attractive strategy for improving both the mechanical properties and fire resistance of EP, which greatly broadened their applications in the chemical industry and electronics field, etc.

Efficient Adsorption of Dyes Using Polyethyleneimine-Modified NH2-MIL-101(Al) and its Sustainable Application as a Flame Retardant for an Epoxy Resin

Metal-organic frameworks (MOFs) exhibit highly designable properties and have been used in wide applications. To further improve their performance, the modification of MOFs is an effective method. However, the modification process is usually complicated. Besides, the sustainable use of MOFs is difficult to achieve due to the complicated recycling treatment. Herein, we designed a polyethyleneimine (PEI)-modified NH₂-MIL-101(Al) composite (PEI@NH₂-MIL-101(Al)). This composite showed excellent dye removal performance of methyl orange (MO, 89.4%) and Direct Red 80 (DR80, 99.8%). Remarkably, the dye removal application of PEI@NH₂-MIL-101(Al) also acted as a modification process toward flame retardant application. Thus, the dye-adsorbed PEI@NH₂-MIL-101(Al) composite (MO-PEI@NH₂-MIL-101(Al) and DR80-PEI@NH₂-MIL-101(Al)) was sustainably used as an effective flame retardant for an epoxy resin (EP) at low additions (4.0 wt %). The limiting oxygen values of EP/MO-PEI@NH₂-MIL-101(Al) and EP/DR80-PEI@NH₂-MIL-101(Al) increased to 26.5 and 26.7%, respectively. The heat release and the smoke production of dyes-PEI@NH₂-MIL-101(Al)/EP were greatly reduced compared with those of EP. This strategy provides a simple and effective modification method for MOFs. Meanwhile, the modified MOF composite can achieve sustainable application, giving full play to the advantages of MOFs.

Novel Phosphorus-Nitrogen-Containing Ionic Liquid Modified Metal-Organic Framework as an Effective Flame Retardant for Epoxy Resin

Metal-organic frameworks (MOFs) have shown great potential in flame retardant applications; however, strategies for fully exploiting the advantages of MOFs in order to further enhance the flame retardant performance are still in high demand. Herein, a novel MOF composite was designed through the generated cooperative role of MOF (NH₂-MIL-101(Al)) and a phosphorus-nitrogen-containing ionic liquid ([DPP-NC₃bim][PMO]). The ionic liquid (IL) was composed of imidazole cation modified with diphenylphosphinic group (DPP) and phosphomolybdic acid (PMoA) anions, which can trap the degrading polymer radicals and reduce the smoke emission. The MOF acts as a porous host and can avoid the agglomeration of ionic liquid. Meanwhile, the -NH₂ groups of NH₂-MIL-101(Al) can increase the compatibility with epoxy resin (EP). The framework is expected to act as an efficient insulating barrier to suppress the flame spread. It was demonstrated that the MOF composite (IL@NH₂-MIL-101(Al)) is able to effectively improve the fire safety of EP at low additions (3 wt. %). The LOI value of EP/IL@NH₂-MIL-101(Al) increased to 29.8%. The cone calorimeter results showed a decreased heat release rate (51.2%), smoke production rate (37.8%), and CO release rate (44.8%) of EP/IL@NH₂-MIL-101(Al) with respect to those of neat EP. This strategy can be extended to design other advanced materials for flame retardant.