Effect of Boron Nitride and Alumina of Different Sizes on Thermal Conductivity of Nylon 6/Polypropylene Composites

Introducing inorganic materials, such as boron nitride (BN), with good thermal conductivity and insulation properties into polymer materials can significantly enhance the thermal conductivity of the result composites. For thermoplastic composites, controlling the orderly distribution and connection of thermal conductivity fillers in the matrix during machining is key to improve thermal conductivity. In this study, the BN/Nano-Al₂O₃/Micro-Al₂O₃/PA6/PP composite with high thermal conductivity was prepared by introducing BN sheet and two sizes of alumina balls (Nano-Al₂O₃ and Micro-Al₂O₃) into nylon 6/polypropylene (PA6/PP) alloy by two-step method. By means of the shear force during the processing and the volume repulsion of PP phase, it was found that BN sheets and Al₂O₃ spheres were uniformly dispersed, oriented and connected in the PA6 phase. Nano-Al₂O₃ with small size was inserted into the gaps between BN sheets, while the addition of Micro-Al₂O₃ of large size changed the orientation of BN sheets. Nano-Al₂O₃ and Micro-Al₂O₃ common auxiliary BN can form the three-dimensional heat transfer filler network, reducing the anisotropy of thermal conductivity. Mixed with 25% mass fraction BN, when the mass fraction of Nano-Al₂O₃ and Micro-Al₂O₃ was 7.5%, the thermal conductivity of BN/Nano-Al₂O₃-7.5/Micro-Al₂O₃-7.5/PA6/PP composite reached the maximum, the in-plane thermal conductivity was 1.46 W(m·K), and the through-plane thermal conductivity was 1.39 W(m·K). Meanwhile, the introduction of the two kinds of Al₂O₃ greatly increased the tensile modulus of the composite. In addition, in the application of heat dissipation experiment, the composite reduced the temperature rise range of LED under working conditions.