Flexible BNOH@ polyurethane composites with high in-plane thermal conductivity for efficient thermal management

Developing flexible thermal management materials is quite urgent for emerging flexible electronics and wearable devices. Here, a novel strategy is used to prepare hydroxyl-functionalized boron nitride@polyurethane (BNOH@PU) composites with desired BN orientation in the in-plane direction through the foaming process of PU and hot-pressing. BNOH flakes can react with isocyanates to form amido linkages, which is beneficial for reducing interfacial thermal resistance (ITR) between BNOH and PU. In addition, BNOH flakes will be rearranged along the direction of PU backbones through the volume compression of the foaming process and trend to be oriented in the in-plane direction after hot-pressing. The out-of-plane or in-plane thermal conductivities of the composites are 1.69 and 3.19 W m⁻¹ K⁻¹ at 30 wt% BNOH content, and the corresponding thermal conductivity enhancement (TCE) is 1986% and 3838%, respectively. Meanwhile, BNOH@PU exhibited low ITR between BNOH flakes (1.252 × 10⁻⁷ K m²/W), good flexibility and stretchability, which was a promising thermal management material for wearable devices.

The interfacial thermal resistance (ITR) and the phonon scattering between fillers and polymer matrix could be reduced significantly via the hydroxyl functionalization of BN. In-plane thermal conductivity enhanced BNOH@PU composites with desired BN orientation in the in-plane direction through the foaming process of PU and hot-pressing.