Supramolecular Nanoshell Encapsulated Lithium POSS Microparticles: An Integrated Flame-Retarding and Smoke-Suppressing Agent for Epoxy Systems

In order to solve practical application challenges in achieving balanced performance for flame-retardant epoxy resins with suppressed smoke and maintained mechanical integrity. Here, Li-Ph-POSS and cost-effective H3PMo12O40 were used as the starting materials. A submicrometer sphere with core–shell structure (POSS(Li)-POM(Mo)@POSS(Li)) was synthesized by using the electrostatic interaction between them. The POSS(Li)-POM(Mo) supramolecular nanolayer is used as the shell, and the Li-Ph-POSS aggregates are used as the core. Relative to pure EP, the composite with 2 wt % additive showed 10% lower bending strength but 49.2% higher char residue at 800 °C. More importantly, the flame-retardant efficacy was markedly enhanced. The composite achieved a UL-94 V-0 rating with its limiting oxygen index (LOI) rising from 23.5 to 28.0%, while the peak heat release rate (p-HRR) and peak smoke production rate (p-SPR) decreased by 60.6 and 68.9%, respectively This work solves the fatal disadvantage of poor flame retardancy of EP, achieves a balance between high-efficiency flame retardant and performance maintenance. Further, it opens up ideas for the subsequent research of low-cost and high-efficiency POSS-based flame retardant derivatives.