Enhancing thermal conductivities of hexagonal boron nitride/fluorinated polyimide composite materials using direct current electrical fields

•Composite sheets of hBN/fluorinated polyimide were prepared in the electric field.•The orientations of hBNs in the sheet were changed by the electric field treatment.•The aggregation structures of hBNs were also changed by the treatment.•One-way direct current treatment could enhance thermal conductivities of the sheets.•Electrical breakdown voltages of the sheets decreased by the treatment. The effect of the electrical field treatment using the direct current (DC) during preparation of the composite sheets on their effective thermal conductivity (TC) and electrical insulation property for the hexagonal boron nitride (hBN)/fluorinated polyimide was studied. By the electrical field treatment, the aggregation of hBNs was obviously observed in the cross-sections of the composite sheets, and the number of hBNs lying parallel to the in-plane direction of the sheets was decreased based on XRD study. Moreover, the effective TC in the out-of-plain direction of the composite sheets treated with a one-way electrical field was increased approximately 1.5-fold that of the corresponding sheets prepared without electrical field treatment at 14.2 vol%. On the other hand, electrical insulation properties were deteriorated by the electrical field treatment, and the values for breakdown voltage against DC roughly approximated that following electrical field treatments to high content of hBNs regardless of their size.