Influence of molecular orientation direction on the in‐plane thermal conductivity of polymer/hexagonal boron nitride composites

The effect of the molecular orientation direction of a polymer matrix on the in‐plane thermal conductivity (TC) of injection‐molded polymer/hexagonal boron nitride (h‐BN) composites is investigated. In this system, the h‐BN platelets align in the in‐plane direction owing to injection shear flow. Three molecular orientations (perpendicular, random, and parallel to the h‐BN plane) are achieved using liquid crystalline polyesters and the in‐plane TCs are compared. Although a parallel orientation of the polymer chains provides the highest TC of the matrix in the injection direction, the TC of the composites is the lowest of the three systems for this orientation. The highest in‐plane TC is found in the perpendicularly oriented system, irrespective of the in‐plane direction. These results reveal that perpendicularly oriented molecular chains serve as effective heat paths between h‐BN platelets that are arranged one above the other, and consequently, a continuous thermal network is created in the in‐plane direction. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39768.