Flame-retardant, thermally conductive, and mechanically strong epoxy composites with phenylphosphonic acid-functionalized boron nitride nanosheets

Abstract

Epoxy resin (EP)-based thermally conductive composites have become strong candidate materials for heat dissipation of electronic devices. However, the inherent low thermal conductivity (TC) and combustible nature of traditional EPs have markedly limited their application. In this work, we developed an EP-composite containing phenylphosphonic acid (PPA)-functionalized boron nitride nanosheets (BNNS), i.e., PPA@BNNS, via ball milling exfoliation of hexagonal boron nitride with PPA, which served as an interfacial modifier and a flame retardant. The PPA attached on the BNNS surface through π-π interactions enhanced the interfacial compatibility between filler and EP, minimized BNNS agglomeration, and improved the mechanical strength of EP/PPA@BNNS composite. In particular, the EP/PPA@BNNS composite with 30 wt% filler exhibited a 4.5-fold increase in TC relative to neat EP, manifesting the well-connected thermal conductive pathways formed by the uniformly dispersed PPA@BNNS and the reduced interfacial thermal resistance. Moreover, the EP/PPA@BNNS composite with 5 wt% filler displayed superior flame retardancy; the peak heat release rate and total heat release were reduced to half those of neat EP owing to the physical barrier action and catalytic carbonization effect of PPA@BNNS.