Significant improvement of thermal conductivities for BNNS/PVA composite films via electrospinning followed by hot-pressing technology

Research and development on polymer composites with high thermal conductivities and ideal thermal stabilities have become one of the hot topics in functional composites. In this work, boron nitride nanosheets/polyvinyl alcohol (BNNS/PVA) thermally conductive composite films were respectively prepared from ball milling (BNNS/PVA-I), directional freeze-drying (BNNS/PVA-II) and electrospinning technology (BNNS/PVA-III), followed by hot-pressing method. BNNS/PVA-III thermally conductive composite films had better comprehensive properties than that of BNNS/PVA-(I-II) composite films. Thermal conductivity coefficient in vertical direction (λ⊥) of the BNNS/PVA-III composite films with 30 wt% BNNS was 1.031 W/mK, obviously higher than that of BNNS/PVA-I (λ⊥ of 0.573 W/mK) and BNNS/PVA-II (λ⊥ of 0.694 W/mK), respectively. And the λ in parallel direction (λ∥) was significantly enhanced to 18.630 W/mK, increased by 3101.0% and 1437.1% compared to that of BNNS/PVA-I (λ∥ of 0.582 W/mK) and BNNS/PVA-II (λ∥ of 1.212 W/mK), respectively. Meantime, the glass transition temperature (Tg) and heat-resistance index (THRI) of the BNNS/PVA-III thermally conductive composite films with 30 wt% BNNS was 42.7 °C and 144.5 °C, 7.0 °C and 1.9 °C higher than that of pure PVA matrix, respectively.