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 higheffective 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 h BN 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 W m^(-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.