Investigation of the through-plane thermal conductivity of polymer composites with in-plane oriented hexagonal boron nitride

As a kind of analogy graphite materials, hexagonal boron nitride (hBN) has been widely used to improve the effective thermal conductivity of polymer composites. Due to their high aspect ratio, hBN platelets tend to orient along the in-plane direction of composites. While the through-plane thermal conductivity of polymer composites with in-plane oriented hBN platelets has been seldom systematically studied. In this work, hBN/PTFE composites are prepared via a cold pressing and sintering method. The orientation of hBN platelets is characterized by scanning electron microscopy and X-ray diffraction. The results indicate that hBN platelets are highly in-plane oriented in PTFE matrix. Theoretical models are successfully used to analyze and predict the effective thermal conductivity of the composites, which suggest that low effective thermal conductivity enhancement efficiency originates from the platelet-shaped filler's high in-plane orientation.