One-step exfoliation and deprotonation of ANF/BNNS suspension for constructing 3D vertically aligned skeleton in epoxy-based thermal management composites

Two-dimensional (2D) boron nitride nanosheet (BNNS) is promising in polymer-based thermal management materials (TMMs) by pre-constructing three-dimensional (3D) thermally conductive skeleton, but it yet suffers from the challenges of high-effective exfoliation and affinitive compatibility with matrix. In this work, we developed a one-step exfoliation and deprotonation approach by the high-effective ball milling technique to prepare aramid nanofiber (ANF)/BNNS suspension. Under the strong collision/shear effect of ball-milling, micron-level hBN sheets were exfoliated into smaller and thinner BNNS with edge functional groups, meanwhile, poly-p-phenylene terephthalamide (PPTA) fibers were split into ANF by dissociating the intermolecular hydrogen bonds. More importantly, both the exfoliation and deprotonation could be accelerated by each other to achieve a 100% yield of ANF/BNNS suspension with strong hydrogen/covalent bonding interactions between them. Subsequently, the prepared ANF/BNNS suspension was used to construct 3D vertically aligned ANF/BNNS skeleton by the unidirectional freezing method. The obtained epoxy-based composite (EP/ANF/BNNS) revealed excellent thermal conductivity of 2.41 Wm−1 K−1 at 14.9 vol% BNNS loading due to the vertically oriented heat conduction paths and low interfacial thermal resistance in the skeleton. Moreover, EP/ANF/BNNS composite showed high thermal stability and extraordinary fire retardancy with dramatically decreased heat release rate (265 W g−1) and total heat release (20.6 kJ g−1). Therefore, this work demonstrates a high-efficient one-step ball-milling exfoliation and deprotonation technique for preparing ANF/BNNS suspension, which reveals an enormous potential in preparing advanced TMMs by constructing 3D thermally conductive skeletons.