The high integration of electronic components especially requires materials with good heat dissipation, very dazzling polymer thermal conductivity additives, and boron nitride is considered the most ideal one. However, improving the thermal conductivity of polymer and boron nitride filled composites encounters two obstacles. One is the obstacle between the filler and the matrix and the interface between the filler and the filler; the second is that the filler cannot be well dispersed in the matrix, which not only cannot effectively improve the thermal conductivity but also reduces the mechanical properties of the matrix. The Shenzhen Institute of Technology of the Chinese Academy of Sciences and the Chinese University of Hong Kong jointly signed an article published in Composites Communications 24 (2021) 100650. The article proposes a research plan for "building a three-dimensional network structure to improve the thermal conductivity of polymers/boron nitride".

① Heat conduction mechanism.

In the two forms of heat conduction (phonon heat conduction and electronic heat conduction), the polymer mainly exhibits phonon heat conduction. Two theories to explain the thermal conductivity of polymer/boron nitride filled composites: one is the thermal conduction path theory "The thermally conductive pathway theory"; the other is the percolation theory "The thermal percolation theory".

② Factors affecting the thermal conductivity of polymer composites.

The polymer matrix, filler and the interface between them. The matrix includes crystallinity, molecular chain orientation, intermolecular forces, polymer processing parameters, etc.; filler body thermal conductivity, added amount, particle size, dispersibility, orientation; etc.; chemical polarity between interfaces and Intermolecular forces.

③Processing of polymer/boron nitride thermally conductive composite materials.

The author proposes that the processing method of constructing a three-dimensional network is very effective in improving the thermal conductivity of composite materials. These methods are:

A. Hot pressing. 

The thermal conductivity of the polystyrene/polypropylene/boron nitride ternary composite prepared by hot pressing reaches 5.57 W/(m∙K) when the boron nitride content is 50 wt %.

The thermal conductivity of the polymer/boron nitride/aluminum nitride ternary composite material prepared by hot pressing of boron nitride modified by coupling agent reaches 2.60 W/( when the content of boron nitride and aluminum nitride is 40 wt% m∙K).

B. Really fast auxiliary filtering.

The thermal conductivity of the lignin polymer/boron nitride/natural rubber ternary composite prepared by vacuum assisted filtration reaches 1.17 W/(m∙K) when the boron nitride content is 25 wt %.

According to the morphology of the pearl, the thermal conductivity of the polyvinyl alcohol/boron nitride composite prepared by vacuum-assisted filtration reaches 6.90 W/(m∙K) when the boron nitride content is 6 wt %.

C. Template self-assembly.

The thermal conductivity of the lignin polymer/boron nitride composite prepared by template self-assembly reaches 2.85 W/(m∙K) when the content of boron nitride nanosheets is 9.29 wt %.

The thermal conductivity of epoxy resin polymer/boron nitride composite prepared by template self-assembly reaches 4.42 W/(m∙K) when the content of boron nitride nanosheets is 34 wt %.

The thermal conductivity of epoxy resin/polyvinylidene fluoride/boron nitride composite prepared by template self-assembly reaches 1.47 W/(m∙K) when the content of boron nitride nanosheets is 21 wt %.

D. 3D printing.

A polymer/boron nitride composite material with higher thermal conductivity is obtained by 3D printing. The thermal conductivity of the prepared polymer boron nitride composite material reaches 9.0 W/(m∙K) when the content of boron nitride nanosheets is 60 wt %.