Synergistic Flame Retardant Effect between Ionic Liquid Functionalized Imogolite Nanotubes and Ammonium Polyphosphate in Epoxy Resin

Abstract

Ionic liquid functionalized imogolite nanotubes (INTs-PF6-ILs) were introduced into the epoxy resin (EP)/ammonium polyphosphate (APP) system to investigate the flame retardant performance and thermal properties using the limiting oxygen index (LOI) test, the UL-94 test, and the cone calorimeter test (CCT). The results suggested that a synergistic effect exists between INTs-PF6-ILs and APP on the char formation and anti-dripping behavior of EP composites. For the EP/APP, an UL-94 V-1 rating was obtained for the loading of 4 wt% APP. However, the composites containing 3.7 wt% APP and 0.3 wt% INTs-PF6-ILs could pass the UL-94 V-0 rating without dripping behavior. In addition, compared with the EP/APP composite, the fire performance index (FPI) value and fire spread index (FSI) value of EP/APP/INTs-PF6-ILs composites were remarkably reduced by 11.4% and 21.1%, respectively. Moreover, the char formed by EP/APP composites was intumescent, but of poor quality. In contrast, the char for EP/APP/INTs-PF6-ILs was strong and compact. Therefore, it can resist the erosion due to heat and gas formation and protect the inside of the matrix. This was the main reason for the good flame retardant property of EP/APP/INTs-PF6-ILs composites.

Methods and Mechanical Properties of Polymer Hybrid Composites and Hybrid Polymer Composites: Influence of Ionic Liquid Addition

“…Table 7 also indicates the mixing methods that are commonly employed in the fabrication of polymer hybrid composites. Mechanical and magnetic stirring are prevalent methods for thermoset hybrid composites [15,18], while melt blending and melt extrusion are generally applied in fabricating thermoplastic hybrid composites [13,20]. In natural polymer hybrid composites, there are two distinctive fabrication methods: thermomechanical kneading [1] and two-roll milling [28].…”

“…It can be seen that there is a predominance of synthetic polymers as preferred polymer matrices over natural polymers. The usage of synthetic polymers is evident through examples like bismaleimide resin [15], epoxy resin [2,8,[16][17][18][19], high-density polyethylene [20], polyamide-6 [13], poly(methyl methacrylate) [21], polyurethane [6,9,11,22,23], poly(vinyl alcohol) [24,25], and unsaturated polyester resin [26,27]. These polymers, prized for their versatility and tailored properties, seem to dominate composite fabrication.…”

“…Ammonium polyphosphate is a flame-retardant filler used to enhance the fire resistance of polymer composites. It releases non-flammable gases when exposed to high temperatures, thereby reducing the flammability of the composite [9,15,18,26,27]. Expandable graphite flakes are used to improve the thermal and flame-retardant properties of composites.…”

“…When these specific properties are needed, researchers are more likely to choose imidazolium-based ionic liquids over phosphonium-based ones. In addition, 1-butyl-3-methylimidazolium hexafluorophosphate has been used in multiple studies [9,15,[17][18][19]26,27,29], indicating its prevalence in research related to polymer hybrid composites. This ionic liquid likely contributes specific attributes such as hydrophobicity or thermal stability, suggesting its versatility and unique roles in enhancing polymer hybrid composite properties.…”

Multifunctional Modifying Systems Based on Ionic Liquids for Epoxy Resin Systems and Composites

“…Restrictive requirements for flame retardants and their effectiveness and properties (especially in terms of environmental and health impacts) are forcing the search for halogen-free solutions. Organophosphorus compounds used in composites to increase their thermal stability can be described as reactive (such as 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, DOPO [9,11]) or non-reactive (such as triphenyl phosphate, TPP [12][13][14][15]). Their flame-retardant effect is directly related to the form in which phosphorus is present in them and can sometimes consist, for example, of generating large amounts of foam during combustion, which prevents further ignition (swelling when exposed to fire).…”