Synergetic\nImprovement in Thermal Conductivity and\nFlame Retardancy of Epoxy/Silver Nanowires Composites by Incorporating\n“Branch-Like” Flame-Retardant Functionalized Graphene

Abstract

The\nsignificant fire hazards on the polymer-based thermal interface\nmaterials (TIM) used in electronic devices are but often neglected.\nAlso, high filler loading with the incident deterioration of mechanical,\nthermal, and processing properties limits the further application\nof the traditional polymer-based TIMs. In this work, a ternary TIMs\nwith epoxy resin (EP) matrix, silver nanowires (AgNWs), and a small\namount of flame-retardant functionalized graphene (GP-DOPO) were proposed\nto address the above questions. Briefly, a facile “branch-like”\nstrategy with a polymer as the backbone and flame-retardant molecule\nas the branch was first used to functionalize reduced graphene oxide\n(RGO) toward increasing the flame-retardant grafting ratio and RGO’s\ncompatibility in matrix, and the resulted GP-DOPO was then in situ\nintroduced into the EP/AgNW composites. As expected, the incorporation\nof GP-DOPO (2 wt %) can increase the thermal conductivity to 1.413\nW/(m K) at a very low AgNW loading (4 vol %), which is 545 and 56%\nincrements compared to pure EP and EP/AgNW, respectively. The prominent\nimprovement in thermal conductivity was put down to the synergetic\neffect of AgNW and GP-DOPO, i.e., the improving dispersion and bridging\neffect for AgNWs by adding GP-DOPO. Moreover, the high flame-retardant\ngrafting amount and the excellent compatibility of GP-DOPO resulted\nin a strong catalytic charring effect on EP matrix, which further\nformed a robust protective char layer by combining the AgNW and graphene\nnetwork. Therefore, the flame retardancy of EP/AgNW was significantly\nimproved by introducing GP-DOPO, i.e., the peak heat release rate,\ntotal heat release and total smoke production reduced by 27.0, 32.4,\nand 30.9% reduction compared to EP/AgNW, respectively.