Two-Dimensional Janus Supramolecular Nanocrystals for Simultaneously Flame-Retarding and Toughening of Epoxy Resin

Abstract

Obtaining maximum comprehensive performance enhancement at the least-cost has always been the core goal of additive modification to solve engineering application problems. Aiming at settling industrial practical application puzzles that it is difficult to simultaneously achieve efficient flame retardant, smoke suppression and toughening of epoxy resin (EP). Herein, unique Janus polyhedral oligomeric silsesquioxane/polyoxometalate (POM(Mo)-POSS(ibu-Li)) nanosheets was synthesized via simple one-pot method adopting laboratory-made lithium-containing hepta-isobutyl-POSS (ibu-Li-POSS) and low-cost industrial chromogenic agent H3PMo12O40 as raw materials. The incorporation of 2 wt% POM(Mo)-POSS(ibu-Li) nanoflakes into EP enormously enhanced the compatibility between nano-additives and EP matrix. Compared with EP, the flexural strength and impact strength increased by 36.2% and 78.2%, respectively. Toughness and strength have been synergistically improved. The dielectric constant and loss have been apparently reduced to meet the increasing requirements of EP-type electronic packaging materials and components. Notably, the synthesized POM(Mo)-POSS(ibu-Li) contained various flame retardant and smoke suppression elements such as P, Mo and Si. The ultralow loading (2 wt%) of POM(Mo)-POSS(ibu-Li)  distinctly reduced the peak of heat release rate, peak of smoke production rate and CO production rate by 43.9%, 40.6% and 65.8%, respectively. Meanwhile, the value of LOI increased directly from 24.0% of EP to 30.2% and pass the V-0 rating of UL-94 test. The dilemmas of poor dielectric properties, inherent flammability and brittleness of EP were completely penetrated. The successful application of POM(Mo)-POSS(ibu-Li) supramolecular nanosheets will inevitably lead to the frontier upsurge in the development of cost-effective POSS derivatives as superior nano-scale flame retardants and smoke suppressants.

Keywords: supramolecular nanosheets, Epoxy resin, mechanical properties, flame retardancy, Smoke suppression