Simple and Consecutive Melt Extrusion Method to Fabricate Thermally Conductive Composites with Highly Oriented Boron Nitrides.

In the region of thermally conductive polymer composites, forcing anisotropic fillers into the highly oriented structure is the most effective method to improve thermal conductivity and mechanical properties simultaneously. However, up to now, such highly oriented structure was mainly achieved in low viscosity polymer matrix or solutions. For the purpose of expanding the range of applications, in the present work, a new strategy, the consecutive and powerful shear flow field, was applied to introduce highly oriented boron nitride (BN) into high viscosity polymer matrix. Results indicated that BN was almost totally oriented along the extrusion plane; as a result, the anisotropic index and thermal conductivity of the composite filled with 40 wt % BN reached as high as 480% and 3.57 W/(m K), respectively. Furthermore, compared with the samples with randomly oriented BN, elongations at break were improved more than 50-fold at the same filler content. Finite element analysis was also applied to systematically investigate the effect of the orientation direction of BN on heat dissipation property of the composites, and results indicated that orienting the longitudinal direction of BN parallel to the heat source is the best way to reduce the heat source temperature to a low level. Therefore, the simple, consecutive, and environmentally friendly melt extrusion with powerful shear flow field is an outstanding method to fabricate high efficiency thermally conductive composites, and the simulative results also have important significance on designing such composites for different applications.